nickel_lang_core/error/

mod.rs

//! Error types and error reporting.
//!
//! Define error types for different phases of the execution, together with functions to generate a
//! [codespan](https://crates.io/crates/codespan-reporting) diagnostic from them.
pub use codespan_reporting::diagnostic::{Diagnostic, Label, LabelStyle};

use codespan_reporting::term::termcolor::{ColorChoice, StandardStream, WriteColor};
use malachite::base::num::conversion::traits::ToSci;

use ouroboros::self_referencing;

use crate::{
    ast::{
        Ast, MergeKind,
        alloc::{AstAlloc, CloneTo},
        compat::ToMainline as _,
        typ::{EnumRow, RecordRow, Type},
    },
    cache::InputFormat,
    eval::{
        callstack::CallStack,
        value::{EnumVariantData, NickelValue},
    },
    files::{FileId, Files},
    identifier::{Ident, LocIdent},
    label::{
        self, MergeLabel,
        ty_path::{self, PathSpan},
    },
    position::{PosIdx, PosTable, RawSpan, TermPos},
    repl,
    serialize::{ExportFormat, NickelPointer, NickelPointerElem},
    term::{Number, record::FieldMetadata},
    typ::{TypeF, VarKindDiscriminant},
    typecheck::error::RowKind,
};

pub use nickel_lang_parser::error::{ParseError, ParseErrors};

pub mod report;
pub mod suggest;
pub mod warning;

pub use warning::Warning;

/// A `Reporter` is basically a callback function for reporting errors and/or warnings.
///
/// The error type `E` is a generic parameter, so the same object can be a `Reporter`
/// of various different things.
pub trait Reporter<E> {
    /// Called when there is something (`e`) for the reporter to report.
    fn report(&mut self, e: E);

    /// A utility function for reporting error variants.
    ///
    /// When this is called with an `Ok(_)` it does nothing; when called with an `Err(e)`
    /// it reports `e`.
    fn report_result<T, E2>(&mut self, result: Result<T, E2>)
    where
        Self: Sized,
        E2: Into<E>,
    {
        if let Err(e) = result {
            self.report(e.into());
        }
    }
}

impl<E, R: Reporter<E>> Reporter<E> for &mut R {
    fn report(&mut self, e: E) {
        R::report(*self, e)
    }
}

/// A [`Reporter`] that just collects errors.
pub struct Sink<E> {
    pub errors: Vec<E>,
}

impl<E> Default for Sink<E> {
    fn default() -> Self {
        Sink { errors: Vec::new() }
    }
}

impl<E> Reporter<E> for Sink<E> {
    fn report(&mut self, e: E) {
        self.errors.push(e);
    }
}

/// A [`Reporter`] that throws away all its errors.
pub struct NullReporter {}

impl<E> Reporter<E> for NullReporter {
    fn report(&mut self, _e: E) {}
}

/// A general error occurring during either parsing or evaluation.
#[derive(Debug, PartialEq, Clone)]
pub enum Error {
    EvalError(EvalError),
    TypecheckError(TypecheckError),
    ParseErrors(ParseErrors),
    ImportError(ImportError),
    ExportError(ExportError),
    IOError(IOError),
    ReplError(ReplError),
}

pub type EvalError = Box<EvalErrorData>;
pub type TypecheckError = Box<TypecheckErrorData>;
pub type ImportError = Box<ImportErrorKind>;
pub type ExportError = Box<ExportErrorData>;
pub type ReplError = Box<ReplErrorKind>;

impl Error {
    pub fn eval_error(ctxt: EvalCtxt, error: EvalErrorKind) -> Self {
        Error::EvalError(Box::new(EvalErrorData { ctxt, error }))
    }

    pub fn export_error(pos_table: PosTable, data: impl Into<PointedExportErrorData>) -> Self {
        Error::ExportError(Box::new(ExportErrorData {
            pos_table,
            data: data.into(),
        }))
    }

    pub fn import_error(kind: ImportErrorKind) -> Self {
        Error::ImportError(Box::new(kind))
    }
}

/// Runtime errors might need additional context to be properly reported. The most important one is
/// the position table, which is need to map position indices stored inside a [NickelValue] back to
/// a [TermPos]. Additional data is useful, such as the callstack.
#[derive(Default, PartialEq, Clone)]
pub struct EvalCtxt {
    pub pos_table: PosTable,
    pub call_stack: CallStack,
}

// Skip the pos table, because it's likely to be huge and uninformative.
impl std::fmt::Debug for EvalCtxt {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        f.debug_struct("EvalCtxt")
            .field("call_stack", &self.call_stack)
            .finish()
    }
}

/// An error occurring during evaluation with additional [context][EvalCtxt].
#[derive(Debug, PartialEq, Clone)]
pub struct EvalErrorData {
    pub ctxt: EvalCtxt,
    pub error: EvalErrorKind,
}

/// An error occurring during evaluation.
#[derive(Debug, PartialEq, Clone)]
pub enum EvalErrorKind {
    /// A blame occurred: a contract has been broken somewhere.
    BlameError {
        /// The argument failing the contract. If the argument has been forced by the contract,
        /// `evaluated_arg` provides the final value.
        evaluated_arg: Option<NickelValue>,
        /// The label of the corresponding contract.
        label: label::Label,
    },
    /// A field required by a record contract is missing a definition.
    MissingFieldDef {
        id: LocIdent,
        metadata: FieldMetadata,
        pos_record: PosIdx,
        pos_access: PosIdx,
    },
    /// Mismatch between the expected type and the actual type of an expression.
    TypeError {
        /// The expected type.
        expected: String,
        /// A freeform message.
        message: String,
        /// Position index of the original unevaluated expression.
        orig_pos: PosIdx,
        /// The evaluated expression.
        term: NickelValue,
    },
    /// `TypeError` when evaluating a unary primop
    UnaryPrimopTypeError {
        primop: String,
        expected: String,
        pos_arg: PosIdx,
        arg_evaluated: NickelValue,
    },
    /// `TypeError` when evaluating a binary primop
    NAryPrimopTypeError {
        primop: String,
        expected: String,
        arg_number: usize,
        pos_arg: PosIdx,
        arg_evaluated: NickelValue,
        pos_op: PosIdx,
    },
    /// Tried to evaluate a term which wasn't parsed correctly.
    ParseError(ParseError),
    /// A term which is not a function has been applied to an argument.
    NotAFunc(
        /* term */ NickelValue,
        /* arg */ NickelValue,
        /* app position */ PosIdx,
    ),
    /// A field access, or another record operation requiring the existence of a specific field,
    /// has been performed on a record missing that field.
    FieldMissing {
        // The name of the missing field.
        id: LocIdent,
        // The actual fields of the record used to suggest similar fields.
        field_names: Vec<LocIdent>,
        // The primitive operation that required the field to exist.
        operator: String,
        // The position of the record value which is missing the field.
        pos_record: PosIdx,
        // The position of the primitive operation application.
        pos_op: PosIdx,
    },
    /// Too few arguments were provided to a builtin function.
    NotEnoughArgs(
        /* required arg count */ usize,
        /* primitive */ String,
        PosIdx,
    ),
    /// Attempted to merge incompatible values: for example, tried to merge two distinct default
    /// values into one record field.
    MergeIncompatibleArgs {
        /// The left operand of the merge.
        left_arg: NickelValue,
        /// The right operand of the merge.
        right_arg: NickelValue,
        /// Additional error-reporting data.
        merge_label: MergeLabel,
    },
    /// An unbound identifier was referenced.
    UnboundIdentifier(LocIdent, TermPos),
    /// An element in the evaluation Cache was entered during its own update.
    InfiniteRecursion(CallStack, PosIdx),
    /// A serialization error occurred during a call to the builtin `serialize`.
    SerializationError(PointedExportErrorData),
    /// A parse error occurred during a call to the builtin `deserialize`.
    DeserializationError(
        String, /* format */
        String, /* error message */
        PosIdx, /* position of the call to deserialize */
    ),
    /// A parse error occurred during a call to the builtin `deserialize`.
    ///
    /// This differs from `DeserializationError` in that the inner error
    /// isn't just a string: it can refer to positions.
    DeserializationErrorWithInner {
        format: InputFormat,
        inner: ParseError,
        /// Position of the call to deserialize.
        pos: PosIdx,
    },
    /// A polymorphic record contract was broken somewhere.
    IllegalPolymorphicTailAccess {
        action: IllegalPolymorphicTailAction,
        evaluated_arg: Option<NickelValue>,
        label: label::Label,
    },
    /// Two non-equatable terms of the same type (e.g. functions) were compared for equality.
    IncomparableValues {
        eq_pos: PosIdx,
        left: NickelValue,
        right: NickelValue,
    },
    /// A value didn't match any branch of a `match` expression at runtime. This is a specialized
    /// version of [Self::NonExhaustiveMatch] when all branches are enum patterns. In this case,
    /// the error message is more informative than the generic one.
    NonExhaustiveEnumMatch {
        /// The list of expected patterns. Currently, those are just enum tags.
        expected: Vec<LocIdent>,
        /// The original term matched
        found: NickelValue,
        /// The position of the `match` expression
        pos: PosIdx,
    },
    NonExhaustiveMatch {
        /// The original term matched.
        value: NickelValue,
        /// The position of the `match` expression
        pos: PosIdx,
    },
    FailedDestructuring {
        /// The original term matched.
        value: NickelValue,
        /// The position of the pattern that failed to match.
        pattern_pos: PosIdx,
    },
    /// Tried to query a field of something that wasn't a record.
    QueryNonRecord {
        /// Position of the original unevaluated expression.
        pos: PosIdx,
        /// The identifier that we tried to query.
        id: LocIdent,
        /// Evaluated expression
        value: NickelValue,
    },
    /// An unexpected internal error.
    InternalError(String, PosIdx),
    /// Errors occurring rarely enough to not deserve a dedicated variant.
    Other(String, PosIdx),
}

#[derive(Clone, Debug, Eq, PartialEq)]
pub enum IllegalPolymorphicTailAction {
    FieldAccess { field: String },
    Map,
    Merge,
    FieldRemove { field: String },
    Freeze,
}

impl IllegalPolymorphicTailAction {
    fn message(&self) -> String {
        use IllegalPolymorphicTailAction::*;

        match self {
            FieldAccess { field } => {
                format!("cannot access field `{field}` sealed by a polymorphic contract")
            }
            Map => "cannot map over a record sealed by a polymorphic contract".to_owned(),
            Merge => "cannot merge a record sealed by a polymorphic contract".to_owned(),
            FieldRemove { field } => {
                format!("cannot remove field `{field}` sealed by a polymorphic contract")
            }
            Freeze => "cannot freeze a record sealed by a polymorphic contract".to_owned(),
        }
    }
}

pub const UNKNOWN_SOURCE_NAME: &str = "<unknown> (generated by evaluation)";

/// An error occurring during the static typechecking phase.
#[self_referencing(pub_extras)]
#[derive(Debug)]
pub struct TypecheckErrorData {
    /// The allocator hosting the types and AST nodes.
    alloc: AstAlloc,
    /// The actual error data.
    #[borrows(alloc)]
    #[covariant]
    pub error: TypecheckErrorKind<'this>,
}

impl Clone for TypecheckErrorData {
    fn clone(&self) -> Self {
        TypecheckErrorData::new(AstAlloc::new(), |alloc| {
            // We must clone the "shallow" layer of the error data to satisfy the `CloneTo`
            // interface
            TypecheckErrorKind::clone_to(self.borrow_error().clone(), alloc)
        })
    }
}

impl PartialEq for TypecheckErrorData {
    fn eq(&self, other: &Self) -> bool {
        self.borrow_error() == other.borrow_error()
    }
}

/// The various kinds of typechecking errors.
#[derive(Debug, PartialEq, Clone)]
pub enum TypecheckErrorKind<'ast> {
    /// An unbound identifier was referenced.
    UnboundIdentifier(LocIdent),
    /// A specific row was expected to be in the type of an expression, but was not.
    MissingRow {
        id: LocIdent,
        kind: RowKind,
        expected: Type<'ast>,
        inferred: Type<'ast>,
        pos: TermPos,
    },
    /// A dynamic tail was expected to be in the type of an expression, but was not.
    MissingDynTail {
        expected: Type<'ast>,
        inferred: Type<'ast>,
        pos: TermPos,
    },
    /// A specific row was not expected to be in the type of an expression.
    ExtraRow {
        id: LocIdent,
        expected: Type<'ast>,
        inferred: Type<'ast>,
        pos: TermPos,
    },
    /// A additional dynamic tail was not expected to be in the type of an expression.
    ExtraDynTail {
        expected: Type<'ast>,
        inferred: Type<'ast>,
        pos: TermPos,
    },
    /// A parametricity violation involving a row-kinded type variable.
    ///
    /// For example, in a function like this:
    ///
    /// ```nickel
    /// let f : forall a. { x: String, y: String } -> { x: String; a } =
    ///   fun r => r
    /// in ...
    /// ```
    ///
    /// this error would be raised with `{ ; a }` as the `tail` type and
    /// `{ y : String }` as the `violating_type`.
    ForallParametricityViolation {
        kind: VarKindDiscriminant,
        tail: Type<'ast>,
        violating_type: Type<'ast>,
        pos: TermPos,
    },
    /// An unbound type variable was referenced.
    UnboundTypeVariable(LocIdent),
    /// The actual (inferred or annotated) type of an expression is incompatible with its expected
    /// type.
    TypeMismatch {
        expected: Type<'ast>,
        inferred: Type<'ast>,
        pos: TermPos,
    },
    /// The actual (inferred or annotated) record row type of an expression is incompatible with
    /// its expected record row type. Specialized version of [Self::TypeMismatch] with additional
    /// row-specific information.
    RecordRowMismatch {
        id: LocIdent,
        expected: Type<'ast>,
        inferred: Type<'ast>,
        cause: Box<TypecheckErrorKind<'ast>>,
        pos: TermPos,
    },
    /// Same as [Self::RecordRowMismatch] but for enum types.
    EnumRowMismatch {
        id: LocIdent,
        expected: Type<'ast>,
        inferred: Type<'ast>,
        cause: Option<Box<TypecheckErrorKind<'ast>>>,
        pos: TermPos,
    },
    /// Two incompatible types have been deduced for the same identifier of a row type.
    ///
    /// This is similar to [Self::RecordRowMismatch] but occurs in a slightly different situation.
    /// Consider a unification variable `t`, which is a placeholder to be filled by a concrete type
    /// later in the typechecking phase.  If `t` appears as the tail of a row type, i.e. the type
    /// of some expression is inferred to be `{ field: Type; t}`, then `t` must not be unified
    /// later with a type including a different declaration for field, such as `field: Type2`.
    ///
    /// A [constraint][crate::typecheck::unif::RowConstrs] is added accordingly, and if this
    /// constraint is violated (that is if `t` does end up being unified with a type of the form `{
    /// .., field: Type2, .. }`), [Self::RecordRowConflict] is raised.  We do not necessarily have
    /// access to the original `field: Type` declaration, as opposed to [Self::RecordRowMismatch],
    /// which corresponds to the direct failure to unify `{ .. , x: T1, .. }` and `{ .., x: T2, ..
    /// }`.
    RecordRowConflict {
        /// The row that couldn't be added to the record type, because it already existed with a
        /// different type assignement.
        row: RecordRow<'ast>,
        expected: Type<'ast>,
        inferred: Type<'ast>,
        pos: TermPos,
    },
    /// Same as [Self::RecordRowConflict] but for enum types.
    EnumRowConflict {
        /// The row that couldn't be added to the record type, because it already existed with a
        /// different type assignement.
        row: EnumRow<'ast>,
        expected: Type<'ast>,
        inferred: Type<'ast>,
        pos: TermPos,
    },
    /// Type mismatch on a subtype of an an arrow type.
    ///
    /// The unification of two arrow types requires the unification of the domain and the codomain
    /// (and recursively so, if they are themselves arrow types). When the unification of a subtype
    /// fails, we want to report which part of the arrow types is problematic, and why, rather than
    /// a generic `TypeMismatch`. Indeed, failing to unify two arrow types is a common type error
    /// which deserves a good reporting, that can be caused e.g. by applying a function to an
    /// argument of a wrong type in some cases:
    ///
    /// ```text
    /// let id_mono = fun x => x in let _ign = id_mono true in id_mono 0 : Number
    /// ```
    ///
    /// This specific error stores additionally the [type path][crate::label::ty_path] that
    /// identifies the subtype where unification failed and the corresponding error.
    ArrowTypeMismatch {
        expected: Type<'ast>,
        inferred: Type<'ast>,
        /// The path to the incompatible type components
        type_path: ty_path::Path,
        cause: Box<TypecheckErrorKind<'ast>>,
        pos: TermPos,
    },
    /// Within statically typed code, the typechecker must reject terms containing nonsensical
    /// contracts such as `let C = { foo : (4 + 1) } in ({ foo = 5 } | C)`, which will fail at
    /// runtime.
    ///
    /// The typechecker is currently quite conservative and simply forbids to store any custom
    /// contract in a type that appears in term position. Note that this restriction
    /// doesn't apply to annotations, which aren't considered part of the statically typed block.
    /// For example, `{foo = 5} | {foo : (4 + 1)}` is accepted by the typechecker.
    CtrTypeInTermPos {
        /// The term that was in a flat type (the `(4 + 1)` in the example above).
        contract: Ast<'ast>,
        /// The position of the entire type (the `{foo : 5}` in the example above).
        pos_type: TermPos,
    },
    /// Unsound generalization.
    ///
    /// When typechecking polymorphic expressions, polymorphic variables introduced by a `forall`
    /// are substituted with rigid type variables, which can only unify with a free unification
    /// variable. However, the condition that the unification variable is free isn't enough.
    ///
    /// Consider the following example:
    ///
    /// ```nickel
    /// (fun x => let y : forall a. a = x in (y : Number)) : _
    /// ```
    ///
    /// This example must be rejected, as it is an identity function that casts any value to
    /// something of type `Number`. It will typically fail with a contract error if applied to a
    /// string, for example.
    ///
    /// But when `let y : forall a. a = x` is typechecked, `x` is affected to a free unification
    /// variable `_a`, which isn't determined yet. The unsoundess comes from the fact that `_a` was
    /// introduced **before** the block with the `forall a. a` annotation, and thus shouldn't be
    /// allowed to be generalized (unified with a rigid type variable) at this point.
    ///
    /// Nickel uses an algorithm coming from the OCaml implementation, recognizing that the
    /// discipline needed to reject those case is similar to region-based memory management. See
    /// [crate::typecheck] for more details. This error indicates that a case similar to the above
    /// example happened.
    VarLevelMismatch {
        /// The user-defined type variable (the rigid type variable during unification) that
        /// couldn't be unified.
        type_var: LocIdent,
        /// The position of the expression that was being typechecked as `type_var`.
        pos: TermPos,
    },
    /// Record-dict subtyping failed because the record was inhomogeneous.
    InhomogeneousRecord {
        /// One row of the record had this type.
        row_a: Type<'ast>,
        /// Another row of the record had this type.
        row_b: Type<'ast>,
        /// The position of the expression of record type.
        pos: TermPos,
    },
    /// Invalid or-pattern.
    ///
    /// This error is raised when the patterns composing an or-pattern don't have the precise
    /// same set of free variables. For example, `'Foo x or 'Bar y`.
    OrPatternVarsMismatch {
        /// A variable which isn't present in all the other patterns (there might be more of them,
        /// this is just a sample).
        var: LocIdent,
        /// The position of the whole or-pattern.
        pos: TermPos,
    },
    /// An error occured during the resolution of an import.
    ///
    /// Since RFC007, imports aren't pre-processed anymore, and import resolution can happen
    /// interleaved with typechecking. In particular, in order to typecheck expressions of the form
    /// `import "file.ncl"`, the typechecker might ask to resolve the import, which can lead to any
    /// import error.
    ImportError(ImportErrorKind),
}

impl IntoDiagnostics for ParseErrors {
    fn into_diagnostics(self, files: &mut Files) -> Vec<Diagnostic<FileId>> {
        self.errors
            .into_iter()
            .flat_map(|e| e.into_diagnostics(files))
            .collect()
    }
}

/// An error occurring during the resolution of an import.
#[derive(Debug, PartialEq, Eq, Clone)]
pub enum ImportErrorKind {
    /// An IO error occurred during an import.
    IOError(
        /* imported file */ String,
        /* error message */ String,
        /* import position */ TermPos,
    ),
    /// A parse error occurred during an import.
    ParseErrors(
        /* error */ ParseErrors,
        /* import position */ TermPos,
    ),
    /// A package dependency was not found.
    MissingDependency {
        /// The package that tried to import the missing dependency, if there was one.
        /// This will be `None` if the missing dependency was from the top-level
        parent: Option<std::path::PathBuf>,
        /// The name of the package that could not be resolved.
        missing: Ident,
        pos: TermPos,
    },
    /// They tried to import a file from a package, but no package manifest was supplied.
    NoPackageMap { pos: TermPos },
}

/// An error occurring during serialization.
#[derive(Debug, Clone, PartialEq)]
pub struct ExportErrorData {
    /// The position table, mapping position indices to spans.
    pub pos_table: PosTable,
    /// The cause of the error.
    pub data: PointedExportErrorData,
}

/// The type of an error occurring during serialization, together with  a path to the field that
/// contains a non-serializable value.
#[derive(Debug, Clone, PartialEq)]
pub struct PointedExportErrorData {
    /// The path to the field that contains a non-serializable value. This might be empty if the
    /// error occurred before entering any record.
    pub path: NickelPointer,
    /// The cause of the error.
    pub error: ExportErrorKind,
}

impl PointedExportErrorData {
    /// Pushes a [NickelPointerElem] to the end of the path of this export error.
    pub fn with_elem(mut self, elem: NickelPointerElem) -> PointedExportErrorData {
        self.path.0.push(elem);
        self
    }

    /// Attaches a position table to this error, producing a [ExportError].
    pub fn with_pos_table(self, pos_table: PosTable) -> ExportErrorData {
        ExportErrorData {
            data: self,
            pos_table,
        }
    }
}

impl From<ExportErrorKind> for PointedExportErrorData {
    fn from(error: ExportErrorKind) -> Self {
        PointedExportErrorData {
            error,
            path: NickelPointer::new(),
        }
    }
}

/// The type of error occurring during serialization.
#[derive(Debug, PartialEq, Clone)]
pub enum ExportErrorKind {
    /// Encountered a null value for a format that doesn't support them.
    UnsupportedNull(ExportFormat, NickelValue),
    /// Tried exporting something else than a `String` to raw format.
    NotAString(NickelValue),
    /// A term contains constructs that cannot be serialized.
    NonSerializable(NickelValue),
    /// No exportable documentation was found when requested.
    NoDocumentation(NickelValue),
    /// A number was too large (in absolute value) to be serialized as `f64`
    NumberOutOfRange {
        term: NickelValue,
        value: Number,
    },
    /// The YAML documents export format expects the value to be an array.
    ExpectedArray {
        value: NickelValue,
    },
    Other(String),
}

/// A general I/O error, occurring when reading a source file or writing an export.
#[derive(Debug, PartialEq, Eq, Clone)]
pub struct IOError(pub String);

/// An error occurring during an REPL session.
#[derive(Debug, PartialEq, Eq, Clone)]
pub enum ReplErrorKind {
    UnknownCommand(String),
    MissingArg {
        cmd: repl::command::CommandType,
        msg_opt: Option<String>,
    },
    InvalidQueryPath(ParseError),
}

impl From<EvalErrorData> for Error {
    fn from(error: EvalErrorData) -> Error {
        Error::EvalError(Box::new(error))
    }
}

impl From<EvalError> for Error {
    fn from(error: EvalError) -> Error {
        Error::EvalError(error)
    }
}

impl From<ParseError> for Error {
    fn from(error: ParseError) -> Error {
        Error::ParseErrors(ParseErrors {
            errors: vec![error],
        })
    }
}

impl From<ParseErrors> for Error {
    fn from(errors: ParseErrors) -> Error {
        Error::ParseErrors(errors)
    }
}

impl From<TypecheckErrorData> for Error {
    fn from(error: TypecheckErrorData) -> Error {
        Error::TypecheckError(Box::new(error))
    }
}

impl From<TypecheckError> for Error {
    fn from(error: TypecheckError) -> Self {
        Error::TypecheckError(error)
    }
}

impl From<ImportErrorKind> for Error {
    fn from(error: ImportErrorKind) -> Error {
        Error::ImportError(Box::new(error))
    }
}

impl From<ImportError> for Error {
    fn from(error: ImportError) -> Error {
        Error::ImportError(error)
    }
}

impl From<ExportErrorData> for Error {
    fn from(error: ExportErrorData) -> Error {
        Error::ExportError(Box::new(error))
    }
}

impl From<ExportError> for Error {
    fn from(error: ExportError) -> Error {
        Error::ExportError(error)
    }
}

impl From<IOError> for Error {
    fn from(error: IOError) -> Error {
        Error::IOError(error)
    }
}

impl From<std::io::Error> for IOError {
    fn from(error: std::io::Error) -> IOError {
        IOError(error.to_string())
    }
}

impl From<PointedExportErrorData> for EvalErrorKind {
    fn from(error: PointedExportErrorData) -> EvalErrorKind {
        EvalErrorKind::SerializationError(error)
    }
}

impl From<ImportErrorKind> for TypecheckError {
    fn from(error: ImportErrorKind) -> Self {
        Box::new(TypecheckErrorData::new(AstAlloc::new(), |_alloc| {
            TypecheckErrorKind::ImportError(error)
        }))
    }
}

/// Return an escaped version of a string. Used to sanitize strings before inclusion in error
/// messages, which can contain ASCII code sequences, and in particular ANSI escape codes, that
/// could alter Nickel's error messages.
pub fn escape(s: &str) -> String {
    String::from_utf8(strip_ansi_escapes::strip(s))
        .expect("escape(): converting from a string should give back a valid UTF8 string")
}

impl From<ReplErrorKind> for Error {
    fn from(error: ReplErrorKind) -> Error {
        Error::ReplError(Box::new(error))
    }
}

pub const INTERNAL_ERROR_MSG: &str = "This error should not happen. This is likely a bug in the Nickel interpreter. Please consider \
 reporting it at https://github.com/tweag/nickel/issues with the above error message.";

/// A trait for converting an error to a diagnostic.
pub trait IntoDiagnostics {
    /// Convert an error to a list of printable formatted diagnostic.
    ///
    /// # Arguments
    ///
    /// - `pos_table`: the position table, mapping position indices stored in Nickel values to
    /// - `files`: this is a mutable reference to allow insertion of temporary snippets. Note that
    ///   `Files` is cheaply clonable and copy-on-write, so you can easily get a mutable `Files` from
    ///   a non-mutable one, but bear in mind that the returned diagnostics may contains file ids that
    ///   refer to your mutated files.
    ///
    /// # Return
    ///
    /// Return a list of diagnostics. Most errors generate only one, but showing the callstack
    /// ordered requires to sidestep a limitation of codespan. The current solution is to generate
    /// one diagnostic per callstack element. See issue
    /// [#285](https://github.com/brendanzab/codespan/issues/285).
    fn into_diagnostics(self, files: &mut Files) -> Vec<Diagnostic<FileId>>;
}

// Allow the use of a single `Diagnostic` directly as an error that can be reported by Nickel.
impl IntoDiagnostics for Diagnostic<FileId> {
    fn into_diagnostics(self, _files: &mut Files) -> Vec<Diagnostic<FileId>> {
        vec![self]
    }
}

// Helpers for the creation of codespan `Label`s

/// Create a primary label from a span.
fn primary(span: &RawSpan) -> Label<FileId> {
    Label::primary(span.src_id, span.start.to_usize()..span.end.to_usize())
}

/// Create a secondary label from a span.
fn secondary(span: &RawSpan) -> Label<FileId> {
    Label::secondary(span.src_id, span.start.to_usize()..span.end.to_usize())
}

/// Create a label from an optional span, or fallback to annotating the alternative snippet
/// `alt_term` if the span is `None`.
///
/// When `span_opt` is `None`, the code snippet `alt_term` is added to `files` under a special name
/// and is referred to instead.
///
/// This is useful because during evaluation, some terms are the results of computations. They
/// correspond to nothing in the original source, and thus have a position set to `None`(e.g. the
/// result of `let x = 1 + 1 in x`).  In such cases it may still be valuable to print the term (or a
/// terse representation) in the error diagnostic rather than nothing, because if you have let `x =
/// 1 + 1 in` and then 100 lines later, `x arg` - causing a `NotAFunc` error - it may be helpful to
/// know that `x` holds the value `2`.
///
/// For example, if one wants to report an error on a record, `alt_term` may be defined as
/// `{ ... }`. Then, if this record has no position (`span_opt` is `None`), the error will be
/// reported as:
///
/// ```text
/// error: some error
///   -- <unknown> (generated by evaluation):1:2
///   |
/// 1 | { ... }
///     ^^^^^^^ some annotation
/// ```
///
/// The reason for the mutable reference to `files` is that codespan do no let you annotate
/// something that is not in `files`: you can't provide a raw snippet, you need to provide a
/// `FileId` referring to a file. This leaves the following possibilities:
///
/// 1. Do nothing: just elude annotations which refer to the term
/// 2. Print the term and the annotation as a note together with the diagnostic. Notes are
///    additional text placed at the end of diagnostic. What you lose:
///     - pretty formatting of annotations for such snippets
///     - style consistency: the style of the error now depends on the term being from the source or
///       a byproduct of evaluation
/// 3. Add the term to files, take 1: pass a reference to files so that the code building the
///    diagnostic can itself add arbitrary snippets if necessary, and get back their `FileId`. This
///    is what is done here.
/// 4. Add the term to files, take 2: make a wrapper around the `Files` and `FileId` structures of
///    codespan which handle source mapping. `FileId` could be something like
///    `Either<codespan::FileId, CustomId = u32>` so that `to_diagnostic` could construct and use
///    these separate ids, and return the corresponding snippets to be added together with the
///    diagnostic without modifying external state. Or even have `FileId = Either<codespan::FileId`,
///    `LoneCode = String or (Id, String)>` so we don't have to return the additional list of
///    snippets. This adds some boilerplate, that we wanted to avoid, but this stays on the
///    reasonable side of being an alternative.
fn label_alt(
    span_opt: Option<RawSpan>,
    alt_term: String,
    style: LabelStyle,
    files: &mut Files,
) -> Label<FileId> {
    match span_opt {
        Some(span) => Label::new(
            style,
            span.src_id,
            span.start.to_usize()..span.end.to_usize(),
        ),
        None => {
            let range = 0..alt_term.len();
            Label::new(style, files.add(UNKNOWN_SOURCE_NAME, alt_term), range)
        }
    }
}

/// Create a secondary label from an optional span, or fallback to annotating the alternative
/// snippet `alt_term` if the span is `None`.
///
/// See [`label_alt`].
fn primary_alt(span_opt: Option<RawSpan>, alt_term: String, files: &mut Files) -> Label<FileId> {
    label_alt(span_opt, alt_term, LabelStyle::Primary, files)
}

/// Create a primary label from a term, or fallback to annotating the shallow representation of this
/// term if its span is `None`.
///
/// See [`label_alt`].
fn primary_term(pos_table: &PosTable, term: &NickelValue, files: &mut Files) -> Label<FileId> {
    primary_alt(
        pos_table.get(term.pos_idx()).into_opt(),
        term.to_string(),
        files,
    )
}

/// Create a secondary label from an optional span, or fallback to annotating the alternative
/// snippet `alt_term` if the span is `None`.
///
/// See [`label_alt`].
fn secondary_alt(span_opt: TermPos, alt_term: String, files: &mut Files) -> Label<FileId> {
    label_alt(span_opt.into_opt(), alt_term, LabelStyle::Secondary, files)
}

/// Create a secondary label from a term, or fallback to annotating the shallow representation of
/// this term if its span is `None`.
///
/// See [`label_alt`].
fn secondary_term(pos_table: &PosTable, term: &NickelValue, files: &mut Files) -> Label<FileId> {
    secondary_alt(pos_table.get(term.pos_idx()), term.to_string(), files)
}

fn cardinal(number: usize) -> String {
    let suffix = if number % 10 == 1 {
        "st"
    } else if number % 10 == 2 {
        "nd"
    } else if number % 10 == 3 {
        "rd"
    } else {
        "th"
    };
    format!("{number}{suffix}")
}

impl<T: IntoDiagnostics> IntoDiagnostics for Box<T> {
    fn into_diagnostics(self, files: &mut Files) -> Vec<Diagnostic<FileId>> {
        (*self).into_diagnostics(files)
    }
}

impl IntoDiagnostics for Error {
    fn into_diagnostics(self, files: &mut Files) -> Vec<Diagnostic<FileId>> {
        match self {
            Error::ParseErrors(errs) => errs
                .errors
                .into_iter()
                .flat_map(|e| e.into_diagnostics(files))
                .collect(),
            Error::TypecheckError(err) => err.into_diagnostics(files),
            Error::EvalError(err) => err.into_diagnostics(files),
            Error::ImportError(err) => err.into_diagnostics(files),
            Error::ExportError(err) => err.into_diagnostics(files),
            Error::IOError(err) => err.into_diagnostics(files),
            Error::ReplError(err) => err.into_diagnostics(files),
        }
    }
}

impl IntoDiagnostics for EvalErrorData {
    fn into_diagnostics(self, files: &mut Files) -> Vec<Diagnostic<FileId>> {
        let mut pos_table = self.ctxt.pos_table;

        match self.error {
            EvalErrorKind::BlameError {
                evaluated_arg,
                label,
            } => blame_error::blame_diagnostics(
                &mut pos_table,
                files,
                label,
                evaluated_arg,
                &self.ctxt.call_stack,
                "",
            ),
            EvalErrorKind::MissingFieldDef {
                id,
                metadata,
                pos_record,
                pos_access,
            } => {
                let mut labels = vec![];

                // If there's a contract attached to the missing field, point the error message
                // at the contract instead of the access. This seems like a more useful error,
                // because if someone hands you a `x | { fld | String }` and you call `x.fld`,
                // then the `x.fld` shouldn't be blamed if `fld` is missing: we should point
                // at the original `x` and at the `fld` in the record contract.
                if let Some(label) = metadata
                    .annotation
                    .first()
                    .map(|labeled_ty| labeled_ty.label.clone())
                {
                    if let Some(span) = label.field_name.and_then(|id| id.pos.into_opt()) {
                        labels.push(primary(&span).with_message("required here"));
                    }

                    if let Some(span) = pos_table.get(pos_record).into_opt() {
                        labels.push(secondary(&span).with_message("in this record"));
                    }

                    // In this branch, we don't point at the access location because it
                    // isn't to blame.
                } else {
                    if let Some(span) = id.pos.into_opt() {
                        labels.push(primary(&span).with_message("required here"));
                    }

                    if let Some(span) = pos_table.get(pos_record).into_opt() {
                        labels.push(secondary(&span).with_message("in this record"));
                    }

                    if let Some(span) = pos_table.get(pos_access).into_opt() {
                        labels.push(secondary(&span).with_message("accessed here"));
                    }
                }

                let diags = vec![
                    Diagnostic::error()
                        .with_message(format!("missing definition for `{id}`",))
                        .with_labels(labels),
                ];

                diags
            }
            EvalErrorKind::TypeError {
                expected,
                message,
                orig_pos,
                term: t,
            } => {
                let label = format!(
                    "this expression has type {}, but {} was expected",
                    t.type_of().unwrap_or("<unevaluated>").to_owned(),
                    expected,
                );

                let labels = match (
                    pos_table.get(orig_pos).into_opt(),
                    pos_table.get(t.pos_idx()).into_opt(),
                ) {
                    (Some(span_orig), Some(span_t)) if span_orig == span_t => {
                        vec![primary(&span_orig).with_message(label)]
                    }
                    (Some(span_orig), Some(t_pos)) if !files.is_stdlib(t_pos.src_id) => {
                        vec![
                            primary(&span_orig).with_message(label),
                            secondary_term(&pos_table, &t, files).with_message("evaluated to this"),
                        ]
                    }
                    (Some(span), _) => {
                        vec![primary(&span).with_message(label)]
                    }
                    (None, Some(span)) => {
                        vec![primary(&span).with_message(label)]
                    }
                    (None, None) => {
                        vec![primary_term(&pos_table, &t, files).with_message(label)]
                    }
                };

                vec![
                    Diagnostic::error()
                        .with_message("dynamic type error")
                        .with_labels(labels)
                        .with_notes(vec![message]),
                ]
            }
            EvalErrorKind::ParseError(parse_error) => parse_error.into_diagnostics(files),
            EvalErrorKind::NotAFunc(t, arg, pos_opt) => vec![
                Diagnostic::error()
                    .with_message("not a function")
                    .with_labels(vec![
                        primary_term(&pos_table, &t, files)
                            .with_message("this term is applied, but it is not a function"),
                        secondary_alt(pos_table.get(pos_opt), format!("({t}) ({arg})"), files)
                            .with_message("applied here"),
                    ]),
            ],
            EvalErrorKind::FieldMissing {
                id: name,
                field_names,
                operator,
                pos_record,
                pos_op,
            } => {
                let mut labels = Vec::new();
                let mut notes = Vec::new();
                let field = escape(name.as_ref());

                if let Some(span) = pos_table.get(pos_op).into_opt() {
                    labels.push(
                        Label::primary(span.src_id, span.start.to_usize()..span.end.to_usize())
                            .with_message(format!("this requires the field `{field}` to exist")),
                    );
                } else {
                    notes.push(format!(
                        "The field `{field}` was required by the operator {operator}"
                    ));
                }

                if let Some(span) = pos_table.get(pos_record).as_opt_ref() {
                    labels.push(
                        secondary(span)
                            .with_message(format!("this record lacks the field `{field}`")),
                    );
                }

                suggest::add_suggestion(&mut notes, &field_names, &name);

                vec![
                    Diagnostic::error()
                        .with_message(format!("missing field `{field}`"))
                        .with_labels(labels)
                        .with_notes(notes),
                ]
            }
            EvalErrorKind::NotEnoughArgs(count, op, span_opt) => {
                let mut labels = Vec::new();
                let mut notes = Vec::new();
                let msg = format!("{op} expects {count} arguments, but not enough were provided");

                if let Some(span) = pos_table.get(span_opt).into_opt() {
                    labels.push(
                        Label::primary(span.src_id, span.start.to_usize()..span.end.to_usize())
                            .with_message(msg),
                    );
                } else {
                    notes.push(msg);
                }

                vec![
                    Diagnostic::error()
                        .with_message("not enough arguments")
                        .with_labels(labels)
                        .with_notes(notes),
                ]
            }
            EvalErrorKind::MergeIncompatibleArgs {
                left_arg,
                right_arg,
                merge_label,
            } => {
                let mut labels = vec![
                    primary_term(&pos_table, &left_arg, files)
                        .with_message("cannot merge this expression"),
                    primary_term(&pos_table, &right_arg, files)
                        .with_message("with this expression"),
                ];

                let span_label = match merge_label.kind {
                    // For a standard merge, the span of the label indicates the position of the
                    // original merge expression
                    MergeKind::Standard => "originally merged here",
                    // For a piecewise definition, there isn't such merge expression (the merge has
                    // been generated by the parser). The spans thus point to the corresponding
                    // field identifier
                    MergeKind::PiecewiseDef => "when combining the definitions of this field",
                };

                if let Some(merge_label_span) = pos_table.get(merge_label.span).into_opt() {
                    labels.push(secondary(&merge_label_span).with_message(span_label));
                }

                fn push_merge_note(notes: &mut Vec<String>, typ: &str) {
                    notes.push(format!(
                        "Both values are of type {typ} but they aren't equal."
                    ));
                    notes.push(format!("{typ} values can only be merged if they are equal"));
                }

                let mut notes = vec![
                    "Merge operands have the same merge priority but they can't \
                    be combined."
                        .to_owned(),
                ];

                if let (Some(left_ty), Some(right_ty)) = (right_arg.type_of(), left_arg.type_of()) {
                    match left_ty {
                        _ if left_ty != right_ty => {
                            notes.push(format!(
                                "One value is of type {left_ty} \
                                while the other is of type {right_ty}"
                            ));
                            notes.push("Values of different types can't be merged".to_owned());
                        }
                        "String" | "Number" | "Bool" | "Array" | "EnumTag" => {
                            push_merge_note(&mut notes, left_ty);
                        }
                        "Function" | "MatchExpression" => {
                            notes.push(
                                "Both values are functions (or match expressions)".to_owned(),
                            );
                            notes.push(
                                "Functions can never be merged with anything else, \
                                even another function."
                                    .to_owned(),
                            );
                        }
                        "EnumVariant" => {
                            if let (
                                Some(EnumVariantData { tag: tag1, .. }),
                                Some(EnumVariantData { tag: tag2, .. }),
                            ) = (right_arg.as_enum_variant(), left_arg.as_enum_variant())
                            {
                                // The only possible cause of failure of merging two enum variants is a
                                // different tag (the arguments could fail to merge as well, but then
                                // the error would have them as the operands, not the enclosing enums).
                                notes.push(format!(
                                    "Both values are enum variants, \
                                    but their tags differ (`'{tag1}` vs `'{tag2}`)"
                                ));
                                notes.push(
                                    "Enum variants can only be \
                                    merged if they have the same tag"
                                        .to_owned(),
                                );
                            } else {
                                // This should not happen, but it's recoverable, so let's not fail
                                // in release mode.
                                debug_assert!(false);

                                notes.push(
                                    "Primitive values (Number, String, EnumTag and Bool) \
                                    and arrays can only be merged if they are equal"
                                        .to_owned(),
                                );
                                notes.push("Enum variants must have the same tag.".to_owned());
                                notes.push("Functions can never be merged.".to_owned());
                            }
                        }
                        _ => {
                            // In other cases, we print a generic message
                            notes.push(
                                "Primitive values (Number, String, EnumTag and Bool) \
                                    and arrays can only be merged if they are equal"
                                    .to_owned(),
                            );
                            notes.push("Enum variants must have the same tag.".to_owned());
                            notes.push("Functions can never be merged.".to_owned());
                        }
                    }
                }

                vec![
                    Diagnostic::error()
                        .with_message("non mergeable terms")
                        .with_labels(labels)
                        .with_notes(notes),
                ]
            }
            EvalErrorKind::UnboundIdentifier(ident, span_opt) => vec![
                Diagnostic::error()
                    .with_message(format!("unbound identifier `{ident}`"))
                    .with_labels(vec![
                        primary_alt(span_opt.into_opt(), ident.to_string(), files)
                            .with_message("this identifier is unbound"),
                    ]),
            ],
            EvalErrorKind::InfiniteRecursion(_call_stack, pos_idx) => {
                let labels = pos_table
                    .get(pos_idx)
                    .as_opt_ref()
                    .map(|span| vec![primary(span).with_message("recursive reference")])
                    .unwrap_or_default();

                vec![
                    Diagnostic::error()
                        .with_message("infinite recursion")
                        .with_labels(labels),
                ]
            }
            EvalErrorKind::Other(msg, span_opt) => {
                let labels = pos_table
                    .get(span_opt)
                    .as_opt_ref()
                    .map(|span| vec![primary(span).with_message("here")])
                    .unwrap_or_default();

                vec![Diagnostic::error().with_message(msg).with_labels(labels)]
            }
            EvalErrorKind::InternalError(msg, span_opt) => {
                let labels = pos_table
                    .get(span_opt)
                    .as_opt_ref()
                    .map(|span| vec![primary(span).with_message("here")])
                    .unwrap_or_default();

                vec![
                    Diagnostic::error()
                        .with_message(format!("internal error: {msg}"))
                        .with_labels(labels)
                        .with_notes(vec![String::from(INTERNAL_ERROR_MSG)]),
                ]
            }
            EvalErrorKind::SerializationError(err) => {
                err.with_pos_table(pos_table).into_diagnostics(files)
            }
            EvalErrorKind::DeserializationError(format, msg, span_opt) => {
                let labels = pos_table
                    .get(span_opt)
                    .as_opt_ref()
                    .map(|span| vec![primary(span).with_message("here")])
                    .unwrap_or_default();

                vec![
                    Diagnostic::error()
                        .with_message(format!("{format} parse error: {msg}"))
                        .with_labels(labels),
                ]
            }
            EvalErrorKind::DeserializationErrorWithInner { format, inner, pos } => {
                let mut diags = inner.into_diagnostics(files);
                if let Some(diag) = diags.first_mut() {
                    // TODO: should we really use a pos_idx here, or are those fresh TermPos coming
                    // out from the YAML parser?
                    if let Some(span) = pos_table.get(pos).as_opt_ref() {
                        diag.labels
                            .push(secondary(span).with_message("deserialized here"));
                    }
                    diag.notes.push(format!("while parsing {format}"));
                }
                diags
            }
            EvalErrorKind::IncomparableValues {
                eq_pos,
                left,
                right,
            } => {
                let mut labels = Vec::new();

                if let Some(span) = pos_table.get(eq_pos).as_opt_ref() {
                    labels.push(primary(span).with_message("in this equality comparison"));
                }

                // Push the label for the right or left argument and return the type of said
                // argument.
                let mut push_label = |prefix: &str, term: &NickelValue| -> &'static str {
                    let type_of = term.type_of().unwrap_or("<unevaluated>");

                    labels.push(
                        secondary_term(&pos_table, term, files)
                            .with_message(format!("{prefix} argument has type {type_of}")),
                    );

                    type_of
                };

                let left_type = push_label("left", &left);
                let right_type = push_label("right", &right);

                vec![
                    Diagnostic::error()
                        .with_message("cannot compare values for equality")
                        .with_labels(labels)
                        .with_notes(vec![format!(
                            "A {left_type} can't be meaningfully compared with a {right_type}"
                        )]),
                ]
            }
            EvalErrorKind::NonExhaustiveEnumMatch {
                expected,
                found,
                pos,
            } => {
                let tag_list = expected
                    .into_iter()
                    .map(|tag| {
                        // We let the pretty printer handle proper formatting
                        NickelValue::enum_variant_posless(tag, None).to_string()
                    })
                    .collect::<Vec<_>>()
                    .join(", ");

                let mut labels = Vec::new();

                if let Some(span) = pos_table.get(pos).into_opt() {
                    labels.push(primary(&span).with_message("in this match expression"));
                }

                labels.push(
                    secondary_term(&pos_table, &found, files)
                        .with_message("this value doesn't match any branch"),
                );

                vec![Diagnostic::error()
                    .with_message("unmatched pattern")
                    .with_labels(labels)
                    .with_notes(vec![
                        format!("This match expression isn't exhaustive, matching only the following pattern(s): `{tag_list}`"),
                        "But it has been applied to an argument which doesn't match any of those patterns".to_owned(),
                    ])]
            }
            EvalErrorKind::NonExhaustiveMatch { value, pos } => {
                let mut labels = Vec::new();

                if let Some(span) = pos_table.get(pos).into_opt() {
                    labels.push(primary(&span).with_message("in this match expression"));
                }

                labels.push(
                    secondary_term(&pos_table, &value, files)
                        .with_message("this value doesn't match any branch"),
                );

                vec![
                    Diagnostic::error()
                        .with_message("unmatched pattern")
                        .with_labels(labels),
                ]
            }
            EvalErrorKind::FailedDestructuring { value, pattern_pos } => {
                let mut labels = Vec::new();

                if let Some(span) = pos_table.get(pattern_pos).into_opt() {
                    labels.push(primary(&span).with_message("this pattern"));
                }

                labels.push(
                    secondary_term(&pos_table, &value, files)
                        .with_message("this value failed to match"),
                );

                vec![
                    Diagnostic::error()
                        .with_message("destructuring failed")
                        .with_labels(labels),
                ]
            }
            EvalErrorKind::IllegalPolymorphicTailAccess {
                action,
                label: contract_label,
                evaluated_arg,
            } => blame_error::blame_diagnostics(
                &mut pos_table,
                files,
                contract_label,
                evaluated_arg,
                &self.ctxt.call_stack,
                &format!(": {}", &action.message()),
            ),
            EvalErrorKind::UnaryPrimopTypeError {
                primop,
                expected,
                pos_arg,
                arg_evaluated,
            } => EvalErrorData {
                error: EvalErrorKind::TypeError {
                    message: format!("{primop} expects its argument to be a {expected}"),
                    expected,
                    orig_pos: pos_arg,
                    term: arg_evaluated,
                },
                ctxt: EvalCtxt {
                    pos_table,
                    call_stack: self.ctxt.call_stack,
                },
            }
            .into_diagnostics(files),
            EvalErrorKind::NAryPrimopTypeError {
                primop,
                expected,
                arg_number,
                pos_arg,
                arg_evaluated,
                pos_op,
            } => {
                // The parsing of binary subtraction vs unary negation has
                // proven confusing in practice; for example, `add 1 -1` is
                // parsed as `(add 1) - 1`, so the `-` is a subtraction and
                // triggers a type error because `(add 1)` is not a number.
                //
                // We attempt to provide a useful hint for this case.
                //
                // We don't currently attempt to give a good hint for
                // `add -1 1` (parsed as `add - (1 1)`) because the evaluation
                // error hits in a context (the `(1 1)`) where we don't see
                // the `-`.
                let minus_pos = if primop == "(-)"
                    && arg_number == 1
                    && matches!(arg_evaluated.type_of(), Some("Function"))
                {
                    pos_table.get(pos_op).into_opt()
                } else {
                    None
                };

                let diags = EvalErrorData {
                    ctxt: EvalCtxt {
                        pos_table,
                        call_stack: self.ctxt.call_stack,
                    },
                    error: EvalErrorKind::TypeError {
                        message: format!(
                            "{primop} expects its {} argument to be a {expected}",
                            cardinal(arg_number)
                        ),
                        expected,
                        orig_pos: pos_arg,
                        term: arg_evaluated,
                    },
                }
                .into_diagnostics(files);

                if let Some(minus_pos) = minus_pos {
                    let label = secondary(&minus_pos)
                        .with_message("this expression was parsed as a binary subtraction");
                    diags
                        .into_iter()
                        .map(|d| {
                            d.with_label(label.clone())
                                .with_note(
                                    "for unary negation, add parentheses: write `(-42)` instead of `-42`",
                                )
                        })
                        .collect()
                } else {
                    diags
                }
            }
            EvalErrorKind::QueryNonRecord { pos, id, value } => {
                let label = format!(
                    "tried to query field `{}`, but the expression has type {}",
                    id,
                    value.type_of().unwrap_or("<unevaluated>"),
                );

                let label = if let Some(span) = pos_table.get(pos).into_opt() {
                    primary(&span).with_message(label)
                } else {
                    primary_term(&pos_table, &value, files).with_message(label)
                };

                vec![
                    Diagnostic::error()
                        .with_message("tried to query field of a non-record")
                        .with_labels(vec![label]),
                ]
            }
        }
    }
}

/// Common functionality for formatting blame errors.
mod blame_error {
    use codespan_reporting::diagnostic::{Diagnostic, Label};

    use crate::{
        eval::{callstack::CallStack, value::NickelValue},
        files::{FileId, Files},
        label::{
            self, Polarity,
            ty_path::{self, PathSpan},
        },
        position::{PosIdx, PosTable, TermPos},
        typ::Type,
    };

    use super::{primary, secondary, secondary_term};

    /// Returns a title to be used by blame errors based on the `path` and `polarity`
    /// of the label.
    pub fn title(l: &label::Label) -> String {
        if ty_path::has_no_arrow(&l.path) {
            // An empty path or a path that contains only fields necessarily corresponds to
            // a positive blame
            assert_eq!(l.polarity, Polarity::Positive);
            match l.field_name {
                Some(ident) => format!("contract broken by the value of `{ident}`"),
                None => "contract broken by a value".to_owned(),
            }
        } else if l.polarity == Polarity::Positive {
            match l.field_name {
                Some(ident) => format!("contract broken by the function `{ident}`"),
                None => "contract broken by a function".to_owned(),
            }
        } else {
            match l.field_name {
                Some(ident) => format!("contract broken by the caller of `{ident}`"),
                None => "contract broken by the caller".to_owned(),
            }
        }
    }

    /// Constructs the diagnostic labels used when raising a blame error.
    pub fn build_diagnostic_labels(
        pos_table: &PosTable,
        evaluated_arg: Option<NickelValue>,
        blame_label: &label::Label,
        path_label: Label<FileId>,
        files: &mut Files,
    ) -> Vec<Label<FileId>> {
        let mut labels = vec![path_label];

        if let Some(ref arg_pos) = pos_table.get(blame_label.arg_pos).into_opt() {
            // In some cases, if the blame error is located in an argument or return value
            // of an higher order functions for example, the original argument position can
            // point to the builtin implementation contract like `func` or `record`, so
            // there's no good reason to show it. Note than even in that case, the
            // information contained at the argument index can still be useful.
            if !files.is_stdlib(arg_pos.src_id) {
                labels.push(primary(arg_pos).with_message("applied to this expression"));
            }
        }

        // If we have a reference to the element in the cache that was being tested,
        // we can try to show more information about the final, evaluated value that is
        // responsible for the blame.
        if let Some(mut evaluated_arg) = evaluated_arg {
            match (
                pos_table.get(evaluated_arg.pos_idx()),
                pos_table.get(blame_label.arg_pos).as_opt_ref(),
            ) {
                // Avoid showing a position inside builtin contracts, it's rarely
                // informative.
                (TermPos::Original(val_pos), _) if files.is_stdlib(val_pos.src_id) => {
                    evaluated_arg = evaluated_arg.with_pos_idx(PosIdx::NONE);
                    labels.push(
                        secondary_term(pos_table, &evaluated_arg, files)
                            .with_message("evaluated to this value"),
                    );
                }
                // Do not show the same thing twice: if arg_pos and val_pos are the same,
                // the first label "applied to this value" is sufficient.
                (TermPos::Original(ref val_pos), Some(arg_pos)) if val_pos == arg_pos => {}
                (TermPos::Original(ref val_pos), _) => {
                    labels.push(secondary(val_pos).with_message("evaluated to this expression"))
                }
                // If the final element is a direct reduct of the original value, rather
                // print the actual value than referring to the same position as
                // before.
                (TermPos::Inherited(ref val_pos), Some(arg_pos)) if val_pos == arg_pos => {
                    evaluated_arg = evaluated_arg.with_pos_idx(PosIdx::NONE);
                    labels.push(
                        secondary_term(pos_table, &evaluated_arg, files)
                            .with_message("evaluated to this value"),
                    );
                }
                // Finally, if the parameter reduced to a value which originates from a
                // different expression, show both the expression and the value.
                (TermPos::Inherited(ref val_pos), _) => {
                    if !files.is_stdlib(val_pos.src_id) {
                        labels
                            .push(secondary(val_pos).with_message("evaluated to this expression"));
                    }

                    evaluated_arg = evaluated_arg.with_pos_idx(PosIdx::NONE);
                    labels.push(
                        secondary_term(pos_table, &evaluated_arg, files)
                            .with_message("evaluated to this value"),
                    );
                }
                (TermPos::None, _) => labels.push(
                    secondary_term(pos_table, &evaluated_arg, files)
                        .with_message("evaluated to this value"),
                ),
            }
        }

        labels
    }

    pub trait ExtendWithCallStack {
        fn extend_with_call_stack(
            &mut self,
            pos_table: &PosTable,
            files: &Files,
            call_stack: &CallStack,
        );
    }

    impl ExtendWithCallStack for Vec<Diagnostic<FileId>> {
        fn extend_with_call_stack(
            &mut self,
            pos_table: &PosTable,
            files: &Files,
            call_stack: &CallStack,
        ) {
            let (calls, curr_call) = call_stack.group_by_calls(pos_table, files);
            let diag_curr_call = curr_call.map(|cdescr| {
                let name = cdescr
                    .head
                    .map(|ident| ident.to_string())
                    .unwrap_or_else(|| String::from("<func>"));
                Diagnostic::note().with_labels(vec![
                    primary(&cdescr.span).with_message(format!("While calling to {name}")),
                ])
            });
            let diags = calls.into_iter().enumerate().map(|(i, cdescr)| {
                let name = cdescr
                    .head
                    .map(|ident| ident.to_string())
                    .unwrap_or_else(|| String::from("<func>"));
                Diagnostic::note().with_labels(vec![secondary(&cdescr.span).with_message(format!(
                    "({}) calling {}",
                    i + 1,
                    name
                ))])
            });

            self.extend(diag_curr_call);
            self.extend(diags);
        }
    }

    /// Calls [`crate::label::ty_path::span`], but if the call returns `None` (the position of the
    /// subtype isn't defined), [path_span] pretty-prints the type inside a new source, parses it,
    /// and calls `ty_path::span`. This new type is guaranteed to have all of its positions set,
    /// providing a definite `PathSpan`. This is similar to the behavior of [`super::primary_alt`].
    pub fn path_span<'a, I>(
        pos_table: &mut PosTable,
        files: &mut Files,
        path: I,
        ty: &Type,
    ) -> PathSpan
    where
        I: Iterator<Item = &'a ty_path::Elem> + Clone,
    {
        use crate::parser::{ErrorTolerantParserCompat, grammar::FixedTypeParser, lexer::Lexer};

        ty_path::span(path.clone().peekable(), ty)
            .or_else(|| {
                let type_pprinted = format!("{ty}");
                let file_id = files.add(super::UNKNOWN_SOURCE_NAME, type_pprinted.clone());

                let (ty_with_pos, _) = FixedTypeParser::new()
                    .parse_tolerant_compat(pos_table, file_id, Lexer::new(&type_pprinted))
                    .unwrap();

                ty_path::span(path.peekable(), &ty_with_pos)
            })
            .expect(
                "path_span: we pretty-printed and parsed again the type of a label, \
                so it must have all of its position defined, but `ty_path::span` returned `None`",
            )
    }

    /// Generate a codespan label that describes the [type path][crate::label::ty_path::Path] of a
    /// (Nickel) label.
    pub fn report_ty_path(
        pos_table: &mut PosTable,
        files: &mut Files,
        l: &label::Label,
    ) -> Label<FileId> {
        let PathSpan {
            span,
            last,
            last_arrow_elem,
        } = path_span(pos_table, files, l.path.iter(), &l.typ);

        let msg = match (last, last_arrow_elem) {
            // The type path doesn't contain any arrow, and the failing subcontract is the
            // contract for the elements of an array
            (Some(ty_path::Elem::Array), None) => "expected array element type",
            // The type path doesn't contain any arrow, and the failing subcontract is the contract
            // for the fields of a dictionary
            (Some(ty_path::Elem::Dict), None) => "expected dictionary field type",
            // The type path doesn't contain any arrow, and the failing subcontract is the contract
            // for the field of a record
            (Some(ty_path::Elem::Field(_)), None) => "expected field type",
            // The original contract contains an arrow, and the path is only composed of codomains.
            // Then polarity is necessarily true and the cause of the blame is the return value of
            // the function
            (Some(_), Some(ty_path::Elem::Codomain)) if ty_path::has_no_dom(&l.path) => {
                "expected return type"
            }
            // The original contract contains an arrow, the subcontract is the domain of an
            // arrow, and the polarity is positive. The function is to be blamed for calling an
            // argument on a value of the wrong type.
            (Some(_), Some(ty_path::Elem::Domain)) if l.polarity == Polarity::Positive => {
                "expected type of an argument of an inner call"
            }
            // The original contract contains an arrow, the subcontract is the codomain of an
            // arrow, and the polarity is positive. The function is to be blamed for calling a
            // higher-order function argument on a function which returns a value of the wrong
            // type.
            (Some(_), Some(ty_path::Elem::Codomain)) if l.polarity == Polarity::Positive => {
                "expected return type of a sub-function passed as an argument of an inner call"
            }
            // The original contract contains an arrow, the subcontract is the domain of an arrow,
            // and the polarity is negative. The caller is to be blamed for providing an argument
            // of the wrong type.
            (Some(_), Some(ty_path::Elem::Domain)) => {
                "expected type of the argument provided by the caller"
            }
            // The original contract contains an arrow, the subcontract is the codomain of an
            // arrow, and the polarity is negative. The caller is to be blamed for providing a
            // higher-order function argument which returns a value of the wrong type.
            (Some(_), Some(ty_path::Elem::Codomain)) => {
                "expected return type of a function provided by the caller"
            }
            // If there is a last arrow element, then there must be last element
            (None, Some(_)) => panic!(
                "blame error reporting: inconsistent path analysis, last_elem\
is None but last_arrow_elem is Some"
            ),
            _ => "expected type",
        };

        secondary(&span).with_message(msg.to_owned())
    }

    /// Generate codespan diagnostics from blame data. Mostly used by `into_diagnostics`
    /// implementations.
    ///
    /// # Parameters
    ///
    /// The `msg_addendum` is used to customize the main error message. It's inserted between the
    /// leading "contract broken by .." and the custom contract diagnostic message in tail
    /// position.
    pub fn blame_diagnostics(
        pos_table: &mut PosTable,
        files: &mut Files,
        mut label: label::Label,
        evaluated_arg: Option<NickelValue>,
        call_stack: &CallStack,
        msg_addendum: &str,
    ) -> Vec<Diagnostic<FileId>> {
        use std::fmt::Write;

        let mut diagnostics = Vec::new();

        // Contract diagnostics are stacked up in order, which means the last one is
        // usually the latest/most precise/most relevant. We ignore empty diagnostics and
        // iterate in reverse order, to show the most relevant diagnostics first.
        let mut contract_diagnostics = std::mem::take(&mut label.diagnostics)
            .into_iter()
            .rev()
            .filter(|diag| !label::ContractDiagnostic::is_empty(diag));
        let head_contract_diagnostic = contract_diagnostics.next();

        // The addendum and the custom contract diagnostic are important, so we want to display
        // them as part of the main error message. However, they can make the message quite long.
        // To avoid clutter, we display each component on a new line, indented with respect to the
        // initial "error: "
        let new_msg_block = "\n       ";
        let mut msg = title(&label);

        if !msg_addendum.is_empty() {
            // unwrap(): write shouldn't fail on a String
            write!(&mut msg, "{new_msg_block}{msg_addendum}").unwrap();
        }

        if let Some(contract_msg) = head_contract_diagnostic
            .as_ref()
            .and_then(|diag| diag.message.as_ref())
        {
            // unwrap(): write shouldn't fail on a String
            write!(&mut msg, "{new_msg_block}{}", &super::escape(contract_msg)).unwrap();
        }

        let contract_notes = head_contract_diagnostic
            .map(|diag| diag.notes)
            .unwrap_or_default();
        let path_label = report_ty_path(pos_table, files, &label);

        let labels = build_diagnostic_labels(pos_table, evaluated_arg, &label, path_label, files);

        // If there are notes in the head contract diagnostic, we build the first
        // diagnostic using them and will put potential generated notes on higher-order
        // contracts in a following diagnostic.
        if !contract_notes.is_empty() {
            diagnostics.push(
                Diagnostic::error()
                    .with_message(msg)
                    .with_labels(labels)
                    .with_notes(contract_notes),
            );
        } else {
            diagnostics.push(Diagnostic::error().with_message(msg).with_labels(labels));
        }

        for ctr_diag in contract_diagnostics {
            let mut msg = String::from("from a parent contract violation");

            if let Some(msg_contract) = ctr_diag.message {
                msg.push_str(": ");
                msg.push_str(&super::escape(&msg_contract));
            }

            diagnostics.push(
                Diagnostic::note()
                    .with_message(msg)
                    .with_notes(ctr_diag.notes),
            );
        }

        if !ty_path::has_no_dom(&label.path) {
            diagnostics.extend_with_call_stack(pos_table, files, call_stack);
        }

        diagnostics
    }
}

impl IntoDiagnostics for ParseError {
    fn into_diagnostics(self, files: &mut Files) -> Vec<Diagnostic<FileId>> {
        let diagnostic = match self {
            ParseError::UnexpectedEOF(file_id, _expected) => {
                let end = files.source_span(file_id).end;
                Diagnostic::error()
                    .with_message(format!(
                        "unexpected end of file when parsing {}",
                        files.name(file_id).to_string_lossy()
                    ))
                    .with_labels(vec![primary(&RawSpan {
                        start: end,
                        end,
                        src_id: file_id,
                    })])
            }
            ParseError::UnexpectedToken(span, _expected) => Diagnostic::error()
                .with_message("unexpected token")
                .with_labels(vec![primary(&span)]),
            ParseError::ExtraToken(span) => Diagnostic::error()
                .with_message("superfluous unexpected token")
                .with_labels(vec![primary(&span)]),
            ParseError::UnmatchedCloseBrace(span) => Diagnostic::error()
                .with_message("unmatched closing brace \'}\'")
                .with_labels(vec![primary(&span)]),
            ParseError::InvalidEscapeSequence(span) => Diagnostic::error()
                .with_message("invalid escape sequence")
                .with_labels(vec![primary(&span)]),
            ParseError::InvalidAsciiEscapeCode(span) => Diagnostic::error()
                .with_message("invalid ascii escape code")
                .with_labels(vec![primary(&span)]),
            ParseError::InvalidUnicodeEscapeCode(span) => Diagnostic::error()
                .with_message("invalid unicode escape code")
                .with_labels(vec![primary(&span)]),
            ParseError::StringDelimiterMismatch {
                opening_delimiter,
                closing_delimiter,
            } => Diagnostic::error()
                .with_message("string closing delimiter has too many `%`")
                .with_labels(vec![
                    primary(&closing_delimiter).with_message("the closing delimiter"),
                    secondary(&opening_delimiter).with_message("the opening delimiter"),
                ])
                .with_notes(vec![
                    "A special string must be opened and closed with the same number of `%` \
                    in the corresponding delimiters."
                        .into(),
                    "Try removing the superflous `%` in the closing delimiter".into(),
                ]),
            ParseError::ExternalFormatError(format, msg, span_opt) => {
                let labels = span_opt
                    .as_ref()
                    .map(|span| vec![primary(span)])
                    .unwrap_or_default();

                Diagnostic::error()
                    .with_message(format!("{format} parse error: {msg}"))
                    .with_labels(labels)
            }
            ParseError::UnboundTypeVariables(idents) => Diagnostic::error()
                .with_message(format!(
                    "unbound type variable(s): {}",
                    idents
                        .iter()
                        .map(|x| format!("`{x}`"))
                        .collect::<Vec<_>>()
                        .join(",")
                ))
                .with_labels(
                    idents
                        .into_iter()
                        .filter_map(|id| id.pos.into_opt())
                        .map(|span| primary(&span).with_message("this identifier is unbound"))
                        .collect(),
                ),
            ParseError::InvalidRecordType {
                record_span,
                tail_span,
                cause,
            } => {
                let mut labels: Vec<_> = std::iter::once(primary(&record_span))
                    .chain(cause.labels())
                    .collect();
                let mut notes: Vec<_> = std::iter::once(
                    "A record type is a literal composed only of type annotations, of the \
                        form `<field>: <type>`."
                        .into(),
                )
                .chain(cause.notes())
                .collect();

                if let Some(tail_span) = tail_span {
                    labels.push(secondary(&tail_span).with_message("tail"));
                    notes.push(
                        "This literal was interpreted as a record type because it has a \
                        polymorphic tail; record values cannot have tails."
                            .into(),
                    );
                } else {
                    notes.push(
                        "This literal was interpreted as a record type because it has \
                        fields with type annotations but no value definitions; to make \
                        this a record value, assign values to its fields."
                            .into(),
                    );
                };
                Diagnostic::error()
                    .with_message("invalid record literal")
                    .with_labels(labels)
                    .with_notes(notes)
            }
            ParseError::RecursiveLetPattern(span) => Diagnostic::error()
                .with_message("recursive destructuring is not supported")
                .with_labels(vec![primary(&span)])
                .with_notes(vec![
                    "A destructuring let-binding can't be recursive. Try removing the `rec` \
                        from `let rec`."
                        .into(),
                    "You can reference other fields of a record recursively \
                        from within a field, so you might not need the recursive let."
                        .into(),
                ]),
            ParseError::PatternInLetBlock(span) => Diagnostic::error()
                .with_message("destructuring patterns are not currently permitted in let blocks")
                .with_labels(vec![primary(&span)])
                .with_notes(vec!["Try re-writing your let block as nested `let ... in` expressions.".into()]),
            ParseError::TypeVariableKindMismatch { ty_var, span } => Diagnostic::error()
                .with_message(format!(
                    "the type variable `{ty_var}` is used in conflicting ways"
                ))
                .with_labels(vec![primary(&span)])
                .with_notes(vec![
                    "Type variables may be used either as types, polymorphic record tails, \
                    or polymorphic enum tails."
                        .into(),
                    "Using the same type variable as more than one category at the same time \
                    is forbidden."
                        .into(),
                ]),
            ParseError::TypedFieldWithoutDefinition {
                field_span,
                annot_span,
            } => Diagnostic::error()
                .with_message("statically typed field without a definition")
                .with_labels(vec![
                    primary(&field_span).with_message("this field doesn't have a definition"),
                    secondary(&annot_span).with_message("but it has a type annotation"),
                ])
                .with_notes(vec![
                    "A static type annotation must be attached to an expression but \
                    this field doesn't have a definition."
                        .into(),
                    "Did you mean to use `|` instead of `:`, for example when defining a \
                    record contract?"
                        .into(),
                    "Typed fields without definitions are only allowed inside \
                    record types, but the enclosing record literal doesn't qualify as a \
                    record type. Please refer to the manual for the defining conditions of a \
                    record type."
                        .into(),
                ]),
            ParseError::InterpolationInStaticPath {
                input: _,
                path_elem_span,
            } => Diagnostic::error()
                .with_message("string interpolation is forbidden within a query")
                .with_labels(vec![primary(&path_elem_span)])
                .with_notes(vec![
                    "Field paths don't support string interpolation when querying \
                        metadata."
                        .into(),
                    "Only identifiers and simple string literals are allowed.".into(),
                ]),
            ParseError::DuplicateIdentInRecordPattern { ident, prev_ident } => Diagnostic::error()
                .with_message(format!(
                    "duplicated binding `{}` in record pattern",
                    ident.label()
                ))
                .with_labels(vec![
                    secondary(&prev_ident.pos.unwrap()).with_message("previous binding here"),
                    primary(&ident.pos.unwrap()).with_message("duplicated binding here"),
                ]),
            ParseError::DuplicateIdentInLetBlock { ident, prev_ident } => Diagnostic::error()
                .with_message(format!(
                    "duplicated binding `{}` in let block",
                    ident.label()
                ))
                .with_labels(vec![
                    secondary(&prev_ident.pos.unwrap()).with_message("previous binding here"),
                    primary(&ident.pos.unwrap()).with_message("duplicated binding here"),
                ]),
            ParseError::DisabledFeature { feature, span } => Diagnostic::error()
                .with_message("interpreter compiled without required features")
                .with_labels(vec![primary(&span).with_message(format!(
                    "this syntax is only supported with the `{feature}` feature enabled"
                ))])
                .with_notes(vec![format!(
                    "Recompile nickel with `--features {}`",
                    feature
                )]),
            ParseError::InvalidContract(span) => Diagnostic::error()
                .with_message("invalid contract expression")
                .with_labels(vec![primary(&span).with_message("this can't be used as a contract")])
                .with_notes(vec![
                    "This expression is used as a contract as part of an annotation or a type expression."
                        .to_owned(),
                    "Only functions and records might be valid contracts".to_owned(),
                ]),
            ParseError::InvalidImportFormat{span} => Diagnostic::error()
                .with_message("unknown import format tag")
                .with_labels(vec![primary(&span)])
                .with_notes(vec![
                    "Examples of valid format tags: 'Nickel, 'Json, 'Yaml, 'Toml, 'Text"
                        .to_owned()
                ]),
            ParseError::UnknownSigilSelector { selector, span } => {
                Diagnostic::error()
                .with_message(format!("unknown sigil selector `{selector}`"))
                .with_labels(vec![primary(&span)])
                .with_note("Available selectors are currently: `env`")
            }
            ParseError::UnknownSigilAttribute { selector, attribute, span } => {
                Diagnostic::error()
                .with_message(format!("unknown sigil attribute `{attribute}`"))
                .with_labels(vec![primary(&span).with_message(format!("unknown attribute for sigil selector `{selector}`"))])
                .with_note(available_sigil_attrs_note(&selector))
            }
            ParseError::SigilExprMissingColon(span) => {
                Diagnostic::error()
                .with_message("missing sigil expression separator `:`")
                .with_labels(vec![primary(&span)])
                .with_notes(vec![
                    "The CLI sigil expression syntax is `@<selector>:<argument>` or `@<selector>/<attribute>:<argument>`".to_owned(),
                    "The provided sigil expression is missing the `:` separator.".to_owned(),
                ])
            }
            ParseError::MultipleFieldDecls { ident, include_span, other_span } => Diagnostic::error()
                .with_message(format!(
                    "multiple declarations for included field `{ident}`",
                ))
                .with_labels(vec![
                    primary(&include_span).with_message("included here"),
                    secondary(&other_span).with_message("but also declared here"),
                ])
                .with_notes(vec![
                    "Piecewise definitions involving an included field are currently not supported".to_owned()
                ]),
        };

        vec![diagnostic]
    }
}

/// Returns the available attributes for each supported sigil
// It's currently trivial, but might be expanded in the future
fn available_sigil_attrs_note(selector: &str) -> String {
    format!(
        "No attributes are available for sigil selector `{selector}`. Use the selector directly as in `@{selector}:<argument>`"
    )
}

impl IntoDiagnostics for TypecheckErrorData {
    fn into_diagnostics(self, files: &mut Files) -> Vec<Diagnostic<FileId>> {
        self.borrow_error().into_diagnostics(files)
    }
}

impl<'ast> IntoDiagnostics for &'_ TypecheckErrorKind<'ast> {
    fn into_diagnostics(self, files: &mut Files) -> Vec<Diagnostic<FileId>> {
        fn mk_expr_label(span_opt: &TermPos) -> Vec<Label<FileId>> {
            mk_expr_label_with_msg(span_opt, "this expression".into())
        }

        fn mk_expr_label_with_msg(span_opt: &TermPos, msg: String) -> Vec<Label<FileId>> {
            span_opt
                .as_opt_ref()
                .map(|span| vec![primary(span).with_message(msg)])
                .unwrap_or_default()
        }

        fn mk_expected_msg<T: std::fmt::Display>(expected: &T) -> String {
            format!("Expected an expression of type `{expected}`")
        }

        fn mk_inferred_msg<T: std::fmt::Display>(inferred: &T) -> String {
            format!("Found an expression of type `{inferred}`")
        }

        match self {
            TypecheckErrorKind::UnboundIdentifier(id) =>
            // Use the same diagnostic as `EvalError::UnboundIdentifier` for consistency.
            {
                EvalErrorData {
                    ctxt: Default::default(),
                    error: EvalErrorKind::UnboundIdentifier(*id, id.pos),
                }
                .into_diagnostics(files)
            }
            TypecheckErrorKind::MissingRow {
                id,
                kind: RowKind::Record,
                expected,
                inferred,
                pos,
            } => {
                let id_access = match &expected.typ {
                    TypeF::Record(r) => {
                        r.find_row(id.ident()).and_then(|row| row.id.pos.into_opt())
                    }
                    _ => None,
                };
                let mut labels = mk_expr_label_with_msg(pos, format!("this record lacks `{id}`"));
                if let Some(id_access) = id_access {
                    labels
                        .push(secondary(&id_access).with_message(format!("`{id}` required here")));
                }
                vec![
                    Diagnostic::error()
                        .with_message(format!("type error: missing field `{id}`"))
                        .with_labels(labels)
                        .with_notes(vec![format!(
                            "Attempted to access field `{id}` on an expression of type `{inferred}`"
                        )]),
                ]
            }
            TypecheckErrorKind::MissingRow {
                id,
                kind: RowKind::Enum,
                expected,
                inferred,
                pos,
            } => vec![
                Diagnostic::error()
                    .with_message(format!("type error: missing row `{id}`"))
                    .with_labels(mk_expr_label(pos))
                    .with_notes(vec![
                        format!(
                            "{}, which contains the field `{id}`",
                            mk_expected_msg(expected)
                        ),
                        format!(
                            "{}, which does not contain the field `{id}`",
                            mk_inferred_msg(inferred)
                        ),
                    ]),
            ],
            TypecheckErrorKind::MissingDynTail {
                expected,
                inferred,
                pos,
            } => vec![
                Diagnostic::error()
                    .with_message(String::from("type error: missing dynamic tail `; Dyn`"))
                    .with_labels(mk_expr_label(pos))
                    .with_notes(vec![
                        format!(
                            "{}, which contains the tail `; Dyn`",
                            mk_expected_msg(expected)
                        ),
                        format!(
                            "{}, which does not contain the tail `; Dyn`",
                            mk_inferred_msg(inferred)
                        ),
                    ]),
            ],
            TypecheckErrorKind::ExtraRow {
                id,
                expected,
                inferred,
                pos,
            } => vec![
                Diagnostic::error()
                    .with_message(format!("type error: extra row `{id}`"))
                    .with_labels(mk_expr_label(pos))
                    .with_notes(vec![
                        format!(
                            "{}, which does not contain the field `{id}`",
                            mk_expected_msg(expected)
                        ),
                        format!(
                            "{}, which contains the extra field `{id}`",
                            mk_inferred_msg(inferred)
                        ),
                    ]),
            ],
            TypecheckErrorKind::ExtraDynTail {
                expected,
                inferred,
                pos,
            } => vec![
                Diagnostic::error()
                    .with_message(String::from("type error: extra dynamic tail `; Dyn`"))
                    .with_labels(mk_expr_label(pos))
                    .with_notes(vec![
                        format!(
                            "{}, which does not contain the tail `; Dyn`",
                            mk_expected_msg(expected)
                        ),
                        format!(
                            "{}, which contains the extra tail `; Dyn`",
                            mk_inferred_msg(inferred)
                        ),
                    ]),
            ],
            TypecheckErrorKind::UnboundTypeVariable(ident) => {
                vec![Diagnostic::error()
                    .with_message(format!("unbound type variable `{ident}`"))
                    .with_labels(vec![primary_alt(
                        ident.pos.into_opt(),
                        ident.to_string(),
                        files,
                    )
                    .with_message("this type variable is unbound")])
                    .with_notes(vec![format!(
                    "Did you forget to put a `forall {ident}.` somewhere in the enclosing type?"
                )])]
            }
            TypecheckErrorKind::TypeMismatch {
                expected,
                inferred,
                pos,
            } => {
                fn addendum<'ast>(ty: &Type<'ast>) -> &'static str {
                    if ty.typ.is_contract() {
                        " (a contract)"
                    } else {
                        ""
                    }
                }
                let last_note = if expected.typ.is_contract() ^ inferred.typ.is_contract() {
                    "Static types and contracts are not compatible"
                } else {
                    "These types are not compatible"
                };

                vec![
                    Diagnostic::error()
                        .with_message("incompatible types")
                        .with_labels(mk_expr_label(pos))
                        .with_notes(vec![
                            format!("{}{}", mk_expected_msg(expected), addendum(expected),),
                            format!("{}{}", mk_inferred_msg(inferred), addendum(inferred),),
                            String::from(last_note),
                        ]),
                ]
            }
            TypecheckErrorKind::RecordRowMismatch {
                id,
                expected,
                inferred,
                cause: err,
                pos,
            } => {
                let mut err = err;
                // If the unification error is on a nested field, we will have a succession of
                // `RowMismatch` errors wrapping the underlying error. In this case, instead of
                // showing a cascade of similar error messages, we determine the full path of the
                // nested field (e.g. `pkg.subpkg1.meta.url`) and only show once the row mismatch
                // error followed by the underlying error.
                let mut path = vec![id.ident()];

                while let TypecheckErrorKind::RecordRowMismatch {
                    id: id_next,
                    cause: next,
                    ..
                } = &**err
                {
                    path.push(id_next.ident());
                    err = next;
                }

                let path_str: Vec<String> = path
                    .clone()
                    .into_iter()
                    .map(|ident| format!("{ident}"))
                    .collect();
                let field = path_str.join(".");

                let mk_expected_row_msg = |field, ty| {
                    format!("Expected an expression of a record type with the row `{field}: {ty}`")
                };
                let mk_inferred_row_msg = |field, ty| {
                    format!("Found an expression of a record type with the row `{field}: {ty}`")
                };

                //TODO: we should rather have RowMismatch hold a rows, instead of a general type,
                //than doing this match.
                let note1 = if let TypeF::Record(rrows) = &expected.typ {
                    match rrows.find_path(path.as_slice()) {
                        Some(row) => mk_expected_row_msg(&field, row.typ),
                        None => mk_expected_msg(&expected),
                    }
                } else {
                    mk_expected_msg(&expected)
                };

                let note2 = if let TypeF::Record(rrows) = &inferred.typ {
                    match rrows.find_path(path.as_slice()) {
                        Some(row) => mk_inferred_row_msg(&field, row.typ),
                        None => mk_inferred_msg(&inferred),
                    }
                } else {
                    mk_inferred_msg(inferred)
                };

                let mut diags = vec![
                    Diagnostic::error()
                        .with_message("incompatible record rows declaration")
                        .with_labels(mk_expr_label(pos))
                        .with_notes(vec![
                            note1,
                            note2,
                            format!("Could not match the two declarations of `{field}`"),
                        ]),
                ];

                // We generate a diagnostic for the underlying error, but append a prefix to the
                // error message to make it clear that this is not a separate error but a more
                // precise description of why the unification of a row failed.
                diags.extend(err.into_diagnostics(files).into_iter().map(|mut diag| {
                    diag.message = format!("while typing field `{}`: {}", field, diag.message);
                    diag
                }));
                diags
            }
            TypecheckErrorKind::EnumRowMismatch {
                id,
                expected,
                inferred,
                cause,
                pos,
            } => {
                let mk_expected_row_msg = |row| {
                    format!("Expected an expression of an enum type with the enum row `{row}`")
                };
                let mk_inferred_row_msg =
                    |row| format!("Found an expression of an enum type with the enum row `{row}`");

                //TODO: we should rather have RowMismatch hold enum rows, instead of a general
                //type, to avoid doing this match.
                let note1 = if let TypeF::Enum(erows) = &expected.typ {
                    if let Some(row) = erows.find_row(id.ident()) {
                        mk_expected_row_msg(row)
                    } else {
                        mk_expected_msg(expected)
                    }
                } else {
                    mk_expected_msg(expected)
                };

                let note2 = if let TypeF::Enum(erows) = &inferred.typ {
                    if let Some(row) = erows.find_row(id.ident()) {
                        mk_inferred_row_msg(row)
                    } else {
                        mk_inferred_msg(expected)
                    }
                } else {
                    mk_inferred_msg(inferred)
                };

                let mut diags = vec![
                    Diagnostic::error()
                        .with_message("incompatible enum rows declaration")
                        .with_labels(mk_expr_label(pos))
                        .with_notes(vec![
                            note1,
                            note2,
                            format!("Could not match the two declarations of `{id}`"),
                        ]),
                ];

                // We generate a diagnostic for the underlying error if any, but append a prefix to
                // the error message to make it clear that this is not a separate error but a more
                // precise description of why the unification of a row failed.
                if let Some(err) = cause {
                    diags.extend((*err).into_diagnostics(files).into_iter().map(|mut diag| {
                        diag.message = format!("while typing enum row `{id}`: {}", diag.message);
                        diag
                    }));
                }

                diags
            }
            TypecheckErrorKind::RecordRowConflict {
                row,
                expected,
                inferred,
                pos,
            } => {
                let mut diags = Vec::new();

                diags.push(
                    Diagnostic::error()
                        .with_message("multiple record row declarations")
                        .with_labels(mk_expr_label(pos))
                        .with_notes(vec![
                            format!("Found an expression with the row `{row}`"),
                            format!(
                                "But this row appears inside another record type, \
                                which already has a diffent declaration for the field `{}`",
                                row.id
                            ),
                            String::from(
                                "A type cannot have two conflicting declarations for the same row",
                            ),
                        ]),
                );

                diags.push(
                    Diagnostic::note()
                        .with_message("while matching types")
                        .with_notes(vec![
                            format!("Expected type {expected}"),
                            format!("With inferred type {inferred}"),
                        ]),
                );

                diags
            }
            TypecheckErrorKind::EnumRowConflict {
                row,
                expected,
                inferred,
                pos,
            } => {
                let mut diags = Vec::new();

                diags.push(
                    Diagnostic::error()
                        .with_message("multiple enum row declarations")
                        .with_labels(mk_expr_label(pos))
                        .with_notes(vec![
                            format!("Found an expression with the row `{row}`"),
                            format!(
                                "But this row appears inside another enum type, \
                                which already has a diffent declaration for the tag `{}`",
                                row.id
                            ),
                            String::from(
                                "A type cannot have two conflicting declarations for the same row",
                            ),
                        ]),
                );

                diags.push(
                    Diagnostic::note()
                        .with_message("while matching types")
                        .with_notes(vec![
                            format!("Expected type {expected}"),
                            format!("With inferred type {inferred}"),
                        ]),
                );

                diags
            }
            TypecheckErrorKind::ArrowTypeMismatch {
                expected,
                inferred,
                type_path,
                cause,
                pos,
            } => {
                // We locally convert the type to their runtime representation as a way to reuse
                // the code of `blame_error::path_span`, which works on the latter.
                let mut pos_table = PosTable::new();
                let expected_mline = expected.to_mainline(&mut pos_table);
                let inferred_mline = inferred.to_mainline(&mut pos_table);

                let PathSpan {
                    span: expd_span, ..
                } = blame_error::path_span(
                    &mut pos_table,
                    files,
                    type_path.iter(),
                    &expected_mline,
                );
                let PathSpan {
                    span: actual_span, ..
                } = blame_error::path_span(
                    &mut pos_table,
                    files,
                    type_path.iter(),
                    &inferred_mline,
                );

                let mut labels = vec![
                    secondary(&expd_span).with_message("this part of the expected type"),
                    secondary(&actual_span)
                        .with_message("does not match this part of the inferred type"),
                ];
                labels.extend(mk_expr_label(pos));

                let mut diags = vec![
                    Diagnostic::error()
                        .with_message("function types mismatch")
                        .with_labels(labels)
                        .with_notes(vec![
                            mk_expected_msg(expected),
                            mk_inferred_msg(inferred),
                            String::from("Could not match the two function types"),
                        ]),
                ];

                // We generate a diagnostic for the underlying error, but append a prefix to the
                // error message to make it clear that this is not a separated error but a more
                // precise description of why the unification of the row failed.
                match &**cause {
                    // If the underlying error is a type mismatch, printing won't add any useful
                    // information, so we just ignore it.
                    TypecheckErrorKind::TypeMismatch { .. } => (),
                    error => {
                        diags.extend(error.into_diagnostics(files).into_iter().map(|mut diag| {
                            diag.message =
                                format!("while matching function types: {}", diag.message);
                            diag
                        }));
                    }
                }

                diags
            }
            TypecheckErrorKind::ForallParametricityViolation {
                kind,
                tail,
                violating_type,
                pos,
            } => {
                let tail_kind = match kind {
                    VarKindDiscriminant::Type => "type",
                    VarKindDiscriminant::EnumRows => "enum tail",
                    VarKindDiscriminant::RecordRows => "record tail",
                };
                vec![
                    Diagnostic::error()
                        .with_message(format!(
                            "values of type `{violating_type}` are not guaranteed to be compatible \
                        with polymorphic {tail_kind} `{tail}`"
                        ))
                        .with_labels(mk_expr_label(pos))
                        .with_notes(vec![
                        "Type variables introduced in a `forall` range over all possible types."
                            .to_owned(),
                    ]),
                ]
            }
            TypecheckErrorKind::CtrTypeInTermPos { contract, pos_type } => {
                vec![Diagnostic::error()
                    .with_message(
                        "types containing user-defined contracts cannot be converted into contracts"
                    )
                    .with_labels(
                        pos_type.as_opt_ref()
                            .map(|span| {
                                primary(span).with_message("This type (in contract position)")
                            })
                            .into_iter()
                            .chain(contract.pos.as_opt_ref().map(|span| {
                                secondary(span).with_message("contains this user-defined contract")
                            }))
                            .collect(),
                    )]
            }
            TypecheckErrorKind::VarLevelMismatch {
                type_var: constant,
                pos,
            } => {
                let mut labels = mk_expr_label(pos);

                if let Some(span) = constant.pos.as_opt_ref() {
                    labels.push(secondary(span).with_message("this polymorphic type variable"));
                }

                vec![
                    Diagnostic::error()
                        .with_message("invalid polymorphic generalization".to_string())
                        .with_labels(labels)
                        .with_notes(vec![
                            "While the type of this expression is still undetermined, it appears \
                            indirectly in the type of another expression introduced before \
                            the `forall` block."
                                .into(),
                            format!(
                                "The type of this expression escapes the scope of the \
                                corresponding `forall` and can't be generalized to the \
                                polymorphic type variable `{constant}`"
                            ),
                        ]),
                ]
            }
            TypecheckErrorKind::InhomogeneousRecord {
                pos,
                row_a: expected,
                row_b: inferred,
            } => {
                vec![Diagnostic::error()
                    .with_message("incompatible types")
                    .with_labels(mk_expr_label(pos))
                    .with_notes(vec![
                        "Expected a dictionary type".into(),
                        format!("Found a record with a field of type {expected} and a field of type {inferred}"),
                        "Records are compatible with dicts only if all their fields have the same type".into(),
                    ])]
            }
            TypecheckErrorKind::OrPatternVarsMismatch { var, pos } => {
                let mut labels = vec![
                    primary_alt(var.pos.into_opt(), var.into_label(), files)
                        .with_message("this variable must occur in all branches"),
                ];

                if let Some(span) = pos.as_opt_ref() {
                    labels.push(secondary(span).with_message("in this or-pattern"));
                }

                vec![
                    Diagnostic::error()
                        .with_message("or-pattern variable mismatch".to_string())
                        .with_labels(labels)
                        .with_notes(vec![
                        "All branches of an or-pattern must bind exactly the same set of variables"
                            .into(),
                    ]),
                ]
            }
            // clone() here is unfortunate, but I haven't found a better way to interface typecheck
            // errors - which can generate a diagnostic by reference - from other errors (import
            // errors can themselves hide parsing errors), where `into_diagnostics` consume `self`
            // in the current implementation. Maybe we should migrate from `into_diagnostics` to
            // `to_diagnostic`, taking the error by reference, but this might cause more copying.
            TypecheckErrorKind::ImportError(err) => err.clone().into_diagnostics(files),
        }
    }
}

impl IntoDiagnostics for ImportErrorKind {
    fn into_diagnostics(self, files: &mut Files) -> Vec<Diagnostic<FileId>> {
        match self {
            ImportErrorKind::IOError(path, error, span_opt) => {
                let labels = span_opt
                    .as_opt_ref()
                    .map(|span| vec![secondary(span).with_message("imported here")])
                    .unwrap_or_default();

                vec![
                    Diagnostic::error()
                        .with_message(format!("import of {path} failed: {error}"))
                        .with_labels(labels),
                ]
            }
            ImportErrorKind::ParseErrors(error, span_opt) => {
                let mut diagnostic: Vec<Diagnostic<FileId>> = error
                    .errors
                    .into_iter()
                    .flat_map(|e| e.into_diagnostics(files))
                    .collect();

                if let Some(span) = span_opt.as_opt_ref() {
                    diagnostic[0]
                        .labels
                        .push(secondary(span).with_message("imported here"));
                }

                diagnostic
            }
            ImportErrorKind::MissingDependency {
                parent,
                missing,
                pos,
            } => {
                let labels = pos
                    .as_opt_ref()
                    .map(|span| vec![primary(span).with_message("imported here")])
                    .unwrap_or_default();
                let msg = if let Some(parent_path) = parent.as_deref() {
                    format!(
                        "unknown package {missing}, imported from package {}",
                        parent_path.display()
                    )
                } else {
                    format!("unknown package {missing}")
                };

                vec![Diagnostic::error().with_message(msg).with_labels(labels)]
            }
            ImportErrorKind::NoPackageMap { pos } => {
                let labels = pos
                    .as_opt_ref()
                    .map(|span| vec![primary(span).with_message("imported here")])
                    .unwrap_or_default();
                vec![
                    Diagnostic::error()
                        .with_message(
                            "tried to import from a package, but no package manifest found",
                        )
                        .with_labels(labels)
                        .with_notes(vec![
                            "did you forget a --manifest-path argument?".to_owned(),
                        ]),
                ]
            }
        }
    }
}

impl IntoDiagnostics for ExportErrorData {
    fn into_diagnostics(self, files: &mut Files) -> Vec<Diagnostic<FileId>> {
        let mut notes = if !self.data.path.0.is_empty() {
            vec![format!("When exporting field `{}`", self.data.path)]
        } else {
            vec![]
        };

        let pos_table = self.pos_table;

        match self.data.error {
            ExportErrorKind::NotAString(rt) => vec![
                Diagnostic::error()
                    .with_message(format!(
                        "raw export expects a String value, but got {}",
                        rt.type_of().unwrap_or("<unevaluated>")
                    ))
                    .with_labels(vec![primary_term(&pos_table, &rt, files)])
                    .with_notes(notes),
            ],
            ExportErrorKind::UnsupportedNull(format, rt) => vec![
                Diagnostic::error()
                    .with_message(format!("{format} format doesn't support null values"))
                    .with_labels(vec![primary_term(&pos_table, &rt, files)])
                    .with_notes(notes),
            ],
            ExportErrorKind::NonSerializable(rt) => {
                notes.extend([
                    "Nickel only supports serializing to and from strings, booleans, numbers, \
                    enum tags, `null` (depending on the format), as well as records and arrays \
                    of serializable values."
                        .into(),
                    "Functions and special values (such as contract labels) aren't \
                    serializable."
                        .into(),
                    "If you want serialization to ignore a specific value, please use the \
                    `not_exported` metadata."
                        .into(),
                ]);

                vec![
                    Diagnostic::error()
                        .with_message("non serializable term")
                        .with_labels(vec![primary_term(&pos_table, &rt, files)])
                        .with_notes(notes),
                ]
            }
            ExportErrorKind::NoDocumentation(rt) => {
                notes.push("documentation can only be collected from a record.".to_owned());

                vec![
                    Diagnostic::error()
                        .with_message("no documentation found")
                        .with_labels(vec![primary_term(&pos_table, &rt, files)])
                        .with_notes(notes),
                ]
            }
            ExportErrorKind::NumberOutOfRange { term, value } => {
                notes.push(format!(
                    "Only numbers in the range {:e} to {:e} can be portably serialized",
                    f64::MIN,
                    f64::MAX
                ));

                vec![
                    Diagnostic::error()
                        .with_message(format!(
                            "The number {} is too large (in absolute value) to be serialized.",
                            value.to_sci()
                        ))
                        .with_labels(vec![primary_term(&pos_table, &term, files)])
                        .with_notes(notes),
                ]
            }
            ExportErrorKind::Other(msg) => {
                notes.push(msg);

                vec![
                    Diagnostic::error()
                        .with_message("serialization failed")
                        .with_notes(notes),
                ]
            }
            ExportErrorKind::ExpectedArray { value } => {
                vec![
                    Diagnostic::error()
                        .with_message("yaml-documents export expects an array")
                        .with_labels(vec![primary_term(&pos_table, &value, files)])
                        .with_notes(notes),
                ]
            }
        }
    }
}

impl IntoDiagnostics for IOError {
    fn into_diagnostics(self, _fil: &mut Files) -> Vec<Diagnostic<FileId>> {
        match self {
            IOError(msg) => vec![Diagnostic::error().with_message(msg)],
        }
    }
}

impl IntoDiagnostics for ReplErrorKind {
    fn into_diagnostics(self, files: &mut Files) -> Vec<Diagnostic<FileId>> {
        match self {
            ReplErrorKind::UnknownCommand(s) => vec![
                Diagnostic::error()
                    .with_message(format!("unknown command `{s}`"))
                    .with_notes(vec![String::from(
                        "type `:?` or `:help` for a list of available commands.",
                    )]),
            ],
            ReplErrorKind::InvalidQueryPath(err) => err.into_diagnostics(files),
            ReplErrorKind::MissingArg { cmd, msg_opt } => {
                let mut notes = msg_opt
                    .as_ref()
                    .map(|msg| vec![msg.clone()])
                    .unwrap_or_default();
                notes.push(format!(
                    "type `:? {cmd}` or `:help {cmd}` for more information."
                ));

                vec![
                    Diagnostic::error()
                        .with_message(format!("{cmd}: missing argument"))
                        .with_notes(notes),
                ]
            }
        }
    }
}

impl CloneTo for TypecheckErrorKind<'_> {
    type Data<'ast> = TypecheckErrorKind<'ast>;

    fn clone_to<'to>(data: Self::Data<'_>, dest: &'to AstAlloc) -> Self::Data<'to> {
        match data {
            TypecheckErrorKind::UnboundIdentifier(loc_ident) => {
                TypecheckErrorKind::UnboundIdentifier(loc_ident)
            }
            TypecheckErrorKind::MissingRow {
                id,
                kind,
                expected,
                inferred,
                pos,
            } => TypecheckErrorKind::MissingRow {
                id,
                kind,
                expected: Type::clone_to(expected, dest),
                inferred: Type::clone_to(inferred, dest),
                pos,
            },
            TypecheckErrorKind::MissingDynTail {
                expected,
                inferred,
                pos,
            } => TypecheckErrorKind::MissingDynTail {
                expected: Type::clone_to(expected, dest),
                inferred: Type::clone_to(inferred, dest),
                pos,
            },
            TypecheckErrorKind::ExtraRow {
                id,
                expected,
                inferred,
                pos,
            } => TypecheckErrorKind::ExtraRow {
                id,
                expected: Type::clone_to(expected, dest),
                inferred: Type::clone_to(inferred, dest),
                pos,
            },
            TypecheckErrorKind::ExtraDynTail {
                expected,
                inferred,
                pos,
            } => TypecheckErrorKind::ExtraDynTail {
                expected: Type::clone_to(expected, dest),
                inferred: Type::clone_to(inferred, dest),
                pos,
            },
            TypecheckErrorKind::ForallParametricityViolation {
                kind,
                tail,
                violating_type,
                pos,
            } => TypecheckErrorKind::ForallParametricityViolation {
                kind,
                tail: Type::clone_to(tail, dest),
                violating_type: Type::clone_to(violating_type, dest),
                pos,
            },
            TypecheckErrorKind::UnboundTypeVariable(loc_ident) => {
                TypecheckErrorKind::UnboundTypeVariable(loc_ident)
            }
            TypecheckErrorKind::TypeMismatch {
                expected,
                inferred,
                pos,
            } => TypecheckErrorKind::TypeMismatch {
                expected: Type::clone_to(expected, dest),
                inferred: Type::clone_to(inferred, dest),
                pos,
            },
            TypecheckErrorKind::RecordRowMismatch {
                id,
                expected,
                inferred,
                cause,
                pos,
            } => TypecheckErrorKind::RecordRowMismatch {
                id,
                expected: Type::clone_to(expected, dest),
                inferred: Type::clone_to(inferred, dest),
                cause: Box::new(TypecheckErrorKind::clone_to(*cause, dest)),
                pos,
            },
            TypecheckErrorKind::EnumRowMismatch {
                id,
                expected,
                inferred,
                cause,
                pos,
            } => TypecheckErrorKind::EnumRowMismatch {
                id,
                expected: Type::clone_to(expected, dest),
                inferred: Type::clone_to(inferred, dest),
                cause: cause.map(|cause| Box::new(TypecheckErrorKind::clone_to(*cause, dest))),
                pos,
            },
            TypecheckErrorKind::RecordRowConflict {
                row,
                expected,
                inferred,
                pos,
            } => TypecheckErrorKind::RecordRowConflict {
                row: RecordRow::clone_to(row, dest),
                expected: Type::clone_to(expected, dest),
                inferred: Type::clone_to(inferred, dest),
                pos,
            },
            TypecheckErrorKind::EnumRowConflict {
                row,
                expected,
                inferred,
                pos,
            } => TypecheckErrorKind::EnumRowConflict {
                row: EnumRow::clone_to(row, dest),
                expected: Type::clone_to(expected, dest),
                inferred: Type::clone_to(inferred, dest),
                pos,
            },
            TypecheckErrorKind::ArrowTypeMismatch {
                expected,
                inferred,
                type_path,
                cause,
                pos,
            } => TypecheckErrorKind::ArrowTypeMismatch {
                expected: Type::clone_to(expected, dest),
                inferred: Type::clone_to(inferred, dest),
                type_path,
                cause: Box::new(TypecheckErrorKind::clone_to(*cause, dest)),
                pos,
            },
            TypecheckErrorKind::CtrTypeInTermPos { contract, pos_type } => {
                TypecheckErrorKind::CtrTypeInTermPos {
                    contract: Ast::clone_to(contract, dest),
                    pos_type,
                }
            }
            TypecheckErrorKind::VarLevelMismatch { type_var, pos } => {
                TypecheckErrorKind::VarLevelMismatch { type_var, pos }
            }
            TypecheckErrorKind::InhomogeneousRecord { row_a, row_b, pos } => {
                TypecheckErrorKind::InhomogeneousRecord {
                    row_a: Type::clone_to(row_a, dest),
                    row_b: Type::clone_to(row_b, dest),
                    pos,
                }
            }
            TypecheckErrorKind::OrPatternVarsMismatch { var, pos } => {
                TypecheckErrorKind::OrPatternVarsMismatch { var, pos }
            }
            TypecheckErrorKind::ImportError(import_error) => {
                TypecheckErrorKind::ImportError(import_error)
            }
        }
    }
}