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Auto merge of #85233 - FabianWolff:issue-85227, r=petrochenkov

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Improve error message for non-exhaustive matches on non-exhaustive enums

This pull request fixes #85227. For an enum marked with `#[non_exhaustive]` and not defined in the current crate, the error message for non-exhaustive matches now mentions the fact that the enum is marked as non-exhaustive:
```
error[E0004]: non-exhaustive patterns: `_` not covered
  --> main.rs:12:11
   |
12 |     match e {
   |           ^ pattern `_` not covered
   |
   = help: ensure that all possible cases are being handled, possibly by adding wildcards or more match arms
   = note: the matched value is of type `E`, which is marked as non-exhaustive
```
This commit is contained in:
bors 2021-05-14 06:53:45 +00:00
commit 69b352ef77
7 changed files with 88 additions and 6 deletions
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11
compiler/rustc_mir_build/src/thir/pattern/check_match.rs
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@ -496,12 +496,21 @@ fn non_exhaustive_match<'p, 'tcx>(
err.span_label(sp, pattern_not_covered_label(&witnesses, &joined_patterns));
};
let is_variant_list_non_exhaustive = match scrut_ty.kind() {
ty::Adt(def, _) if def.is_variant_list_non_exhaustive() && !def.did.is_local() => true,
_ => false,
};
adt_defined_here(cx, &mut err, scrut_ty, &witnesses);
err.help(
"ensure that all possible cases are being handled, \
possibly by adding wildcards or more match arms",
);
err.note(&format!("the matched value is of type `{}`", scrut_ty));
err.note(&format!(
"the matched value is of type `{}`{}",
scrut_ty,
if is_variant_list_non_exhaustive { ", which is marked as non-exhaustive" } else { "" }
));
if (scrut_ty == cx.tcx.types.usize || scrut_ty == cx.tcx.types.isize)
&& !is_empty_match
&& witnesses.len() == 1