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Pretty-print PatKind::Missing as _.

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Printing "no pattern" as `_` isn't ideal, but better than crashing, and
HIR pretty-printing already has plenty of imperfections. The added `f2`
and `f6` examples are ones that triggered the crash.

Note that some of the added examples are printed badly, e.g.
`fn(, ...)`. The next commit will fix those.

Fixes #139633.
This commit is contained in:
Nicholas Nethercote 2025-04-15 10:05:20 +10:00
parent 092a284ba0
commit f8edc831ca
3 changed files with 56 additions and 3 deletions
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7
compiler/rustc_hir_pretty/src/lib.rs
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@ -1871,10 +1871,11 @@ impl<'a> State<'a> {
fn print_pat(&mut self, pat: &hir::Pat<'_>) {
self.maybe_print_comment(pat.span.lo());
self.ann.pre(self, AnnNode::Pat(pat));
// Pat isn't normalized, but the beauty of it
// is that it doesn't matter
// Pat isn't normalized, but the beauty of it is that it doesn't matter.
match pat.kind {
PatKind::Missing => unreachable!(),
// Printing `_` isn't ideal for a missing pattern, but it's easy and good enough.
// E.g. `fn(u32)` gets printed as `fn(_: u32)`.
PatKind::Missing => self.word("_"),
PatKind::Wild => self.word("_"),
PatKind::Never => self.word("!"),
PatKind::Binding(BindingMode(by_ref, mutbl), _, ident, sub) => {