Struct EvalError 

pub struct EvalError {
    pub kind: EvalErrorKind,
    pub span: Option<Span>,
    pub message: String,
    pub source: Option<Arc<dyn Error + Send + Sync>>,
}

An error that occurs during template evaluation.

Carries a structured EvalErrorKind, a human-readable message, an optional source Span, and an optional underlying error cause.

Error chaining

When a host’s EvalContext implementation catches an underlying error (database, I/O, etc.), it can preserve the original error chain using with_source:

use weaver_lang::EvalError;

fn example() -> Result<(), EvalError> {
    let io_err = std::io::Error::new(std::io::ErrorKind::NotFound, "file missing");
    Err(EvalError::host_error("failed to load entry").with_source(io_err))
}

Fields

kind: EvalErrorKind

span: Option<Span>

message: String

source: Option<Arc<dyn Error + Send + Sync>>

The underlying error that caused this evaluation error, if any.

Wrapped in Arc so that EvalError remains Clone.

Implementations

impl EvalError

pub fn new(kind: EvalErrorKind, message: impl Into<String>) -> Self

pub fn with_span(self, span: Span) -> Self

pub fn with_source(self, source: impl Error + Send + Sync + 'static) -> Self

Attach an underlying error cause to this evaluation error.

This preserves the full error chain for production logging and debugging. The source is wrapped in an Arc so that EvalError remains Clone.

pub fn undefined_variable(scope: &str, name: &str) -> Self

pub fn undefined_processor(namespace: &str, name: &str) -> Self

pub fn undefined_command(name: &str) -> Self

pub fn type_error(expected: &str, got: &str) -> Self

pub fn not_iterable(got: &str) -> Self

pub fn host_error(message: impl Into<String>) -> Self

Trait Implementations

impl Clone for EvalError

fn clone(&self) -> EvalError

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for EvalError

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Display for EvalError

fn fmt(&self, __formatter: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Error for EvalError

fn source(&self) -> Option<&(dyn Error + 'static)>

Returns the lower-level source of this error, if any.

fn description(&self) -> &str

👎Deprecated since 1.42.0:

use the Display impl or to_string()

fn cause(&self) -> Option<&dyn Error>

👎Deprecated since 1.33.0:

replaced by Error::source, which can support downcasting

fn provide<'a>(&'a self, request: &mut Request<'a>)

🔬This is a nightly-only experimental API. (error_generic_member_access)

Provides type-based access to context intended for error reports.