rucc-sema 0.2.7

//! The pass: what walks the untyped tree and builds the typed one.
//!
//! Design: `spec/07-types-and-semantics.md`.
//!
//! The shape is the parser's, because the job is the same shape: a context of the things that do
//! not change, a walk that holds the things that do, and one structure handed back at the end.
//! What is different is that this walk has two trees, one it reads and one it writes, and the
//! reason a node is copied across rather than annotated in place is that the two are not the
//! same tree. A `p->x` is one node in the source and two here, an `int` meeting a `long` is
//! three, and an array used as a pointer is a node that the source does not contain at all.
//!
//! # What is here so far
//!
//! Expressions, and only those that do not name a type. A cast, a `sizeof`, a compound literal
//! and `_Generic` each need more than the type: they need the checking of the operator itself,
//! which is the piece after this one, so each of them is reported as not supported rather than
//! quietly given the wrong type. Every other expression is checked, which is where the
//! constraints of 6.5 live.
//!
//! The type a declaration declares is here as well, through [`Checker::declared_type`] and
//! [`Checker::type_name`], which fold a declarator onto the type a specifier list named.
//!
//! Folding is reachable from here through [`Checker::eval_constant`] and
//! [`Checker::eval_integer`], and the checking itself asks for it in one place: an assignment or
//! an initialization of an arithmetic type looks at what the value would become and warns when
//! narrowing it changes it. Everything else that wants a constant is a declaration or a
//! statement, so it is the caller of the next milestone rather than of this one.
//!
//! # Poisoning
//!
//! The rule is the parser's, in `spec/06-lexer-and-parser.md` section 6.8, and it is the same
//! rule for the same reason. An expression that has been diagnosed becomes
//! [`ExprKind::Error`](crate::ExprKind::Error), and an operator whose operand is poisoned is
//! poisoned in turn without a word said about it. That is what keeps one undeclared name from
//! producing an error for every operator it appears under, and it is why nothing below asks
//! whether an error has already been reported: it asks whether the node in its hand is one.

use rucc_ast::Ast;
use rucc_base::{Interner, Symbol};
use rucc_diag::{DEFAULT_ERROR_LIMIT, Diagnostic, Errors, Span};
use rucc_session::Std;
use rucc_target::TargetInfo;
use rucc_types::{IntKind, TypeId, Types, int_width};

use crate::convert::Conv;
use crate::decl::{Decl, DeclId, DeclKind, Definition, Linkage, StorageDuration};
use crate::eval::{Eval, NotConstant};
use crate::expr::{Category, Expr, ExprId, ExprKind};
use crate::scope::Scopes;
use crate::tast::{Const, Tast};

mod expr;
mod ty;

/// What the checking needs and does not change.
#[derive(Debug, Clone, Copy)]
pub struct Context<'a> {
    /// The spellings, for the diagnostics that name an identifier.
    pub names: &'a Interner,
    /// What the target's types are, which every layout and every promotion is decided by.
    pub target: &'a TargetInfo,
    /// The dialect.
    pub std: Std,
    /// Whether the GNU extensions are on.
    pub gnu: bool,
    /// Whether `-pedantic` was given.
    pub pedantic: bool,
    /// How many errors to report before stopping, with zero meaning no limit.
    pub error_limit: usize,
}

impl<'a> Context<'a> {
    /// A context with the defaults, for a caller that has an interner and a target to hand.
    #[must_use]
    pub fn new(names: &'a Interner, target: &'a TargetInfo, std: Std) -> Context<'a> {
        Context { names, target, std, gnu: true, pedantic: false, error_limit: DEFAULT_ERROR_LIMIT }
    }
}

/// What one run of the checking produced.
#[derive(Debug)]
pub struct Checked {
    /// The typed tree, which holds poisoned nodes where the source did not check.
    pub tast: Tast,
    /// The types, which the tree points into and which outlive it.
    pub types: Types,
    /// What went wrong, in the order it was found.
    pub diagnostics: Vec<Diagnostic>,
}

impl Checked {
    /// Whether anything was reported at an error severity.
    #[must_use]
    pub fn failed(&self) -> bool {
        self.diagnostics.iter().any(|d| d.severity.is_fatal())
    }
}

/// The checking pass.
#[derive(Debug)]
pub struct Checker<'a> {
    pub(crate) ast: &'a Ast,
    pub(crate) tast: Tast,
    pub(crate) types: Types,
    pub(crate) scopes: Scopes,
    pub(crate) errors: Errors,
    pub(crate) cx: Context<'a>,
    /// What the type builder has already worked out, which is in `check/ty.rs` with the code
    /// that fills it in.
    pub(crate) built: ty::Built,
}

impl<'a> Checker<'a> {
    /// A checker over one untyped tree.
    #[must_use]
    pub fn new(ast: &'a Ast, cx: Context<'a>) -> Checker<'a> {
        Checker {
            ast,
            tast: Tast::new(),
            types: Types::new(),
            scopes: Scopes::new(),
            errors: Errors::new(cx.error_limit),
            cx,
            built: ty::Built::default(),
        }
    }

    /// Checks one expression and gives back the node it became.
    ///
    /// Always gives back a node. An expression that does not check is poisoned rather than
    /// absent, so that the operators around it are still checked and the diagnostics they would
    /// produce are still held back.
    pub fn check_expr(&mut self, id: rucc_ast::ExprId) -> ExprId {
        self.expr(id)
    }

    /// Folds a checked expression, reporting whatever the folding itself found wrong.
    ///
    /// # Errors
    ///
    /// [`NotConstant`] when the expression is not one. It is handed back rather than reported
    /// because the message names the context: `case label does not reduce to an integer
    /// constant` and `enumerator value for 'x' is not an integer constant` are two sentences
    /// about the same failure, and only the caller knows which one to write.
    pub fn eval_constant(&mut self, expr: ExprId) -> Result<Const, NotConstant> {
        let mut eval = self.eval();
        let value = eval.constant(expr);
        self.absorb(eval.finish());
        value
    }

    /// The same, for a context that needs an integer constant expression.
    ///
    /// # Errors
    ///
    /// [`NotConstant`] when the expression is not one, or is a constant of some other type.
    pub fn eval_integer(&mut self, expr: ExprId) -> Result<i128, NotConstant> {
        let mut eval = self.eval();
        let value = eval.integer(expr);
        self.absorb(eval.finish());
        value
    }

    /// The tree, the types and the diagnostics.
    #[must_use]
    pub fn finish(self) -> Checked {
        Checked { tast: self.tast, types: self.types, diagnostics: self.errors.finish() }
    }

    /// Declares an object or a function in the current scope, and puts it in the tree.
    ///
    /// This is what declaration checking will call once it exists, and it is public in the
    /// meantime because [`Checker::check_expr`] is: without a way to put a name in scope the
    /// only expression a caller could check is one made entirely of constants.
    pub fn declare_object(&mut self, name: Symbol, ty: TypeId, span: Span) -> DeclId {
        let kind = if rucc_types::is_function(&self.types, ty) {
            DeclKind::Function
        } else {
            DeclKind::Object
        };
        let decl = self.tast.decl(
            Decl {
                name: Some(name),
                ty,
                kind,
                linkage: Linkage::None,
                duration: StorageDuration::Automatic,
                state: Definition::Defined,
                alignment: None,
                init: None,
                body: None,
            },
            span,
        );
        self.scopes.declare(name, crate::scope::Binding::Decl(decl));
        decl
    }

    /// The conversions, over this tree and these types.
    pub(crate) fn conv(&mut self) -> Conv<'_> {
        // The target is copied out first because it is a shared reference living as long as the
        // context, so taking it does not borrow the checker the two mutable ones are taken from.
        let target = self.cx.target;
        Conv { tast: &mut self.tast, types: &mut self.types, target }
    }

    /// The constant folding, over this tree and these types.
    pub(crate) fn eval(&self) -> Eval<'_> {
        Eval::new(&self.tast, &self.types, self.cx.target, self.cx.names)
    }

    /// Reports a diagnostic.
    pub(crate) fn report(&mut self, diagnostic: Diagnostic) {
        self.errors.push(diagnostic);
    }

    /// Reports everything the folding found, which it collects rather than pushing itself
    /// because it holds the tree while it runs and the error list is beside the tree.
    pub(crate) fn absorb(&mut self, diagnostics: Vec<Diagnostic>) {
        for diagnostic in diagnostics {
            self.errors.push(diagnostic);
        }
    }

    /// Whether a checked expression is one that was already the subject of a diagnostic.
    pub(crate) fn is_poisoned(&self, id: ExprId) -> bool {
        matches!(self.tast[id].kind, ExprKind::Error)
    }

    /// A poisoned expression, for the operand that did not check.
    ///
    /// Its type is `int` because every node has a type and there is no type meaning "no idea".
    /// Nothing reads it, since every operator that meets a poisoned operand poisons itself
    /// before it looks at what type the operand had.
    pub(crate) fn poison(&mut self, span: Span) -> ExprId {
        let int = self.types.int(IntKind::Int);
        self.tast.expr(Expr::new(ExprKind::Error, int, Category::Rvalue), span)
    }

    /// How a type is written, for a diagnostic that names one.
    pub(crate) fn spell(&self, ty: TypeId) -> String {
        rucc_types::spell(&self.types, self.cx.names, ty)
    }

    /// What a name is spelled, for a diagnostic that quotes one.
    pub(crate) fn text(&self, name: Symbol) -> &str {
        self.cx.names.resolve(name)
    }

    /// `int`, which is the type of every comparison and of `!`.
    pub(crate) fn int(&self) -> TypeId {
        self.types.int(IntKind::Int)
    }

    /// The type of the difference between two pointers.
    ///
    /// Derived rather than stored, because `ptrdiff_t` is whatever signed type is as wide as a
    /// pointer and that is `long` on every LP64 target and `long long` on Windows, which is the
    /// same fact `long_width` already records. Asking the widths keeps the two from disagreeing.
    pub(crate) fn ptrdiff(&self) -> TypeId {
        let width = self.cx.target.pointer_width;
        for kind in [IntKind::Int, IntKind::Long, IntKind::LongLong] {
            if int_width(kind, self.cx.target) >= width {
                return self.types.int(kind);
            }
        }
        self.types.int(IntKind::LongLong)
    }
}