Struct LambdaAnnotationMismatch 

pub struct LambdaAnnotationMismatch {
    pub range: TextRange,
    pub param_name: Option<String>,
    pub expected: Ty,
    pub found: Ty,
}

One incompatibility between a lambda’s own written annotation (a param’s : T or the lambda’s : R return annotation) and its body-derived type (issue #1994, RULED 2026-08-01, closing #1932: “the written annotation takes priority… an incompatible body is an eager error at the lambda, not a deferred surprise at the call site”).

Unlike TypedAssignMismatch/DirectCallArgMismatch (both E063, gradual/advisory — the body-derived type wins regardless, the annotation-vs-body comparison is only ever a warning), a mismatch recorded here is reported unconditionally as an Error-severity E174 by strict::check_lambda_annotation_mismatches — the written annotation replaces the body-derived type at this slot (see body::InferPass::infer_lambda’s own doc for the precedence change), so a disagreement is never merely advisory.

Recorded only when a written annotation exists for this slot and the body-derived type is not itself unresolved (Ty::is_unresolved) — an unannotated slot has nothing to compare against and keeps #1910’s unchanged body-derived-wins behavior, and an Unknown/Conflicted body-derived type never disagrees with anything (mirrors annotations::report_if_mismatched’s identical guard for the fn/flow case).

Fields

range: TextRange

The diagnostic site: the mismatched param’s own : T annotation range, or the lambda’s own : R return-annotation range.

param_name: Option<String>

Some(param name) for a mismatched parameter annotation, None for the lambda’s own return annotation.

expected: Ty

The written annotation’s resolved type — what now governs this slot’s type.

found: Ty

The body’s own independent derivation, which disagreed.

Trait Implementations

impl Clone for LambdaAnnotationMismatch

fn clone(&self) -> LambdaAnnotationMismatch

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl Debug for LambdaAnnotationMismatch

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

Formats the value using the given formatter.

impl Eq for LambdaAnnotationMismatch

impl PartialEq for LambdaAnnotationMismatch

fn eq(&self, other: &LambdaAnnotationMismatch) -> bool

Equality operator ==.

fn ne(&self, other: &Rhs) -> bool

Inequality operator !=.

impl StructuralPartialEq for LambdaAnnotationMismatch