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Rollup merge of #78235 - Aaron1011:closure-ret-infer, r=varkor

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Explain where the closure return type was inferred

Fixes #78193
This commit is contained in:
Yuki Okushi 2020-10-23 18:26:39 +09:00 • committed by GitHub
commit 3f462c22b5
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22
compiler/rustc_typeck/src/check/coercion.rs
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@ -1475,6 +1475,28 @@ impl<'tcx, 'exprs, E: AsCoercionSite> CoerceMany<'tcx, 'exprs, E> {
if let (Some(sp), Some(fn_output)) = (fcx.ret_coercion_span.borrow().as_ref(), fn_output) {
self.add_impl_trait_explanation(&mut err, cause, fcx, expected, *sp, fn_output);
}
if let Some(sp) = fcx.ret_coercion_span.borrow().as_ref() {
// If the closure has an explicit return type annotation,
// then a type error may occur at the first return expression we
// see in the closure (if it conflicts with the declared
// return type). Skip adding a note in this case, since it
// would be incorrect.
if !err.span.primary_spans().iter().any(|span| span == sp) {
let hir = fcx.tcx.hir();
let body_owner = hir.body_owned_by(hir.enclosing_body_owner(fcx.body_id));
if fcx.tcx.is_closure(hir.body_owner_def_id(body_owner).to_def_id()) {
err.span_note(
*sp,
&format!(
"return type inferred to be `{}` here",
fcx.resolve_vars_if_possible(&expected)
),
);
}
}
}
err
}