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Rollup merge of #145234 - dianne:1-tuple-witnesses, r=jackh726

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match exhaustiveness diagnostics: show a trailing comma on singleton tuple consructors in witness patterns (and clean up a little)

Constructor patterns of type `(T,)` are written `(pat,)`, not `(pat)`. However, exhaustiveness/usefulness diagnostics would print them as `(pat)` when e.g. providing a witness of non-exhaustiveness and suggesting adding arms to make matches exhaustive; this would result in an error when applied.
rust-analyzer already prints the trailing comma, so it doesn't need changing.

This also includes some cleanup in the second commit, with justification in the commit message.
This commit is contained in:
Samuel Tardieu
2025-08-23 22:22:15 +02:00
committed by GitHub
parent 982b022b1e 8f649a7e58
commit 5a14685a63
3 changed files with 13 additions and 25 deletions
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22
compiler/rustc_pattern_analysis/src/rustc/print.rs
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@@ -101,23 +101,11 @@ pub(crate) fn write_struct_like<'tcx>(
let num_fields = variant_and_name.as_ref().map_or(subpatterns.len(), |(v, _)| v.fields.len());
if num_fields != 0 || variant_and_name.is_none() {
write!(f, "(")?;
for i in 0..num_fields {
write!(f, "{}", start_or_comma())?;
// Common case: the field is where we expect it.
if let Some(p) = subpatterns.get(i) {
if p.field.index() == i {
write!(f, "{}", p.pattern)?;
continue;
}
}
// Otherwise, we have to go looking for it.
if let Some(p) = subpatterns.iter().find(|p| p.field.index() == i) {
write!(f, "{}", p.pattern)?;
} else {
write!(f, "_")?;
}
for FieldPat { pattern, .. } in subpatterns {
write!(f, "{}{pattern}", start_or_comma())?;
}
if matches!(ty.kind(), ty::Tuple(..)) && num_fields == 1 {
write!(f, ",")?;
}
write!(f, ")")?;
}