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Merge #3938

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3938: fix missing match arm false positive r=flodiebold a=JoshMcguigan

This fixes #3932 by skipping the missing match arm diagnostic in the case any of the match arms don't type check properly against the match expression. 

I think this is the appropriate behavior for this diagnostic, since `is_useful` relies on all match arms being well formed, and the case of a malformed match arm should probably be handled by a different diagnostic.

Co-authored-by: Josh Mcguigan <joshmcg88@gmail.com>
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bors[bot] 2020-04-12 08:30:24 +00:00 • committed by GitHub
commit 268b798729
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2 changed files with 253 additions and 12 deletions
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13
crates/ra_hir_ty/src/expr.rs
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@ -161,12 +161,6 @@ impl<'a, 'b> ExprValidator<'a, 'b> {
let mut seen = Matrix::empty();
for pat in pats {
// We skip any patterns whose type we cannot resolve.
//
// This could lead to false positives in this diagnostic, so
// it might be better to skip the entire diagnostic if we either
// cannot resolve a match arm or determine that the match arm has
// the wrong type.
if let Some(pat_ty) = infer.type_of_pat.get(pat) {
// We only include patterns whose type matches the type
// of the match expression. If we had a InvalidMatchArmPattern
@ -189,8 +183,15 @@ impl<'a, 'b> ExprValidator<'a, 'b> {
// to the matrix here.
let v = PatStack::from_pattern(pat);
seen.push(&cx, v);
continue;
}
}
// If we can't resolve the type of a pattern, or the pattern type doesn't
// fit the match expression, we skip this diagnostic. Skipping the entire
// diagnostic rather than just not including this match arm is preferred
// to avoid the chance of false positives.
return;
}
match is_useful(&cx, &seen, &PatStack::from_wild()) {