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diag: improve closure/generic parameter mismatch

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This commit improves the diagnostic when a type parameter is expected
and a closure is found, noting that each closure has a distinct type and
therefore could not always match the caller-chosen type of the
parameter.

Signed-off-by: David Wood <david@davidtw.co>
This commit is contained in:
David Wood 2020-09-14 15:21:38 +01:00
parent b5f55b7e15
commit 01f65afa4a
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GPG key ID: 2592E76C87381FD9
4 changed files with 37 additions and 5 deletions
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12
compiler/rustc_middle/src/ty/error.rs
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@ -473,6 +473,18 @@ impl<T> Trait<T> for X {
#traits-as-parameters",
);
}
(ty::Param(p), ty::Closure(..) | ty::Generator(..)) => {
let generics = self.generics_of(body_owner_def_id);
let p_span = self.def_span(generics.type_param(p, self).def_id);
if !sp.contains(p_span) {
db.span_label(p_span, "this type parameter");
}
db.help(&format!(
"every closure has a distinct type and so could not always match the \
caller-chosen type of parameter `{}`",
p
));
}
(ty::Param(p), _) | (_, ty::Param(p)) => {
let generics = self.generics_of(body_owner_def_id);
let p_span = self.def_span(generics.type_param(p, self).def_id);