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Fix a common false-positive type mismatch

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E.g. for `&{ some_string() }` in a context where a `&str` is expected, we
reported a mismatch inside the block. The problem is that we're passing an
expectation of `str` down, but the expectation is more of a hint in this case.
There's a long comment in rustc about this, which I just copied.

Also, fix reported location for type mismatches in macros.
This commit is contained in:
Florian Diebold 2020-02-29 15:31:07 +01:00
parent 0ec7f760fc
commit 5fe220b987
4 changed files with 86 additions and 18 deletions
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8
crates/ra_hir_ty/src/infer/expr.rs
View file

@ -42,14 +42,14 @@ impl<'a, D: HirDatabase> InferenceContext<'a, D> {
/// Return the type after possible coercion.
pub(super) fn infer_expr_coerce(&mut self, expr: ExprId, expected: &Expectation) -> Ty {
let ty = self.infer_expr_inner(expr, &expected);
let ty = if !self.coerce(&ty, &expected.ty) {
let ty = if !self.coerce(&ty, &expected.coercion_target()) {
self.result
.type_mismatches
.insert(expr, TypeMismatch { expected: expected.ty.clone(), actual: ty.clone() });
// Return actual type when type mismatch.
// This is needed for diagnostic when return type mismatch.
ty
} else if expected.ty == Ty::Unknown {
} else if expected.coercion_target() == &Ty::Unknown {
ty
} else {
expected.ty.clone()
@ -297,7 +297,7 @@ impl<'a, D: HirDatabase> InferenceContext<'a, D> {
// FIXME: throw type error - expected mut reference but found shared ref,
// which cannot be coerced
}
Expectation::has_type(Ty::clone(exp_inner))
Expectation::rvalue_hint(Ty::clone(exp_inner))
} else {
Expectation::none()
};
@ -542,7 +542,7 @@ impl<'a, D: HirDatabase> InferenceContext<'a, D> {
let ty = if let Some(expr) = tail {
self.infer_expr_coerce(expr, expected)
} else {
self.coerce(&Ty::unit(), &expected.ty);
self.coerce(&Ty::unit(), expected.coercion_target());
Ty::unit()
};
if diverges {