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9f089e080c
"Missing" patterns are possible in bare fn types (`fn f(u32)`) and
similar places. Currently these are represented in the AST with
`ast::PatKind::Ident` with no `by_ref`, no `mut`, an empty ident, and no
sub-pattern. This flows through to `{hir,thir}::PatKind::Binding` for
HIR and THIR.
This is a bit nasty. It's very non-obvious, and easy to forget to check
for the exceptional empty identifier case.
This commit adds a new variant, `PatKind::Missing`, to do it properly.
The process I followed:
- Add a `Missing` variant to `{ast,hir,thir}::PatKind`.
- Chang `parse_param_general` to produce `ast::PatKind::Missing`
instead of `ast::PatKind::Missing`.
- Look through `kw::Empty` occurrences to find functions where an
existing empty ident check needs replacing with a `PatKind::Missing`
check: `print_param`, `check_trait_item`, `is_named_param`.
- Add a `PatKind::Missing => unreachable!(),` arm to every exhaustive
match identified by the compiler.
- Find which arms are actually reachable by running the test suite,
changing them to something appropriate, usually by looking at what
would happen to a `PatKind::Ident`/`PatKind::Binding` with no ref, no
`mut`, an empty ident, and no subpattern.
Quite a few of the `unreachable!()` arms were never reached. This makes
sense because `PatKind::Missing` can't happen in every pattern, only
in places like bare fn tys and trait fn decls.
I also tried an alternative approach: modifying `ast::Param::pat` to
hold an `Option<P<Pat>>` instead of a `P<Pat>`, but that quickly turned
into a very large and painful change. Adding `PatKind::Missing` is much
easier.
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| .. | ||
| auxiliary | ||
| ast-const-trait-bound.rs | ||
| ast-const-trait-bound.stdout | ||
| avoid-crash.rs | ||
| avoid-crash.stderr | ||
| bad-literal.rs | ||
| bad-literal.stderr | ||
| bad-literal.stdout | ||
| box.rs | ||
| box.stdout | ||
| debug-fmt-hir.rs | ||
| debug-fmt-hir.stdout | ||
| deprecated-attr.rs | ||
| deprecated-attr.stdout | ||
| diagnostic-attr.rs | ||
| diagnostic-attr.stdout | ||
| expanded-exhaustive.rs | ||
| expanded-exhaustive.stdout | ||
| expanded-interpolation.rs | ||
| expanded-interpolation.stdout | ||
| extern-static.rs | ||
| extern-static.stdout | ||
| flattened-format-args.rs | ||
| flattened-format-args.stdout | ||
| hir-tree.rs | ||
| let-else-hir.rs | ||
| let-else-hir.stdout | ||
| mir-unpretty.rs | ||
| mir-unpretty.stderr | ||
| self-hir.rs | ||
| self-hir.stdout | ||
| staged-api-invalid-path-108697.rs | ||
| staged-api-invalid-path-108697.stderr | ||
| unpretty-expr-fn-arg.rs | ||
| unpretty-expr-fn-arg.stdout | ||
| unsafe-attr.rs | ||
| unsafe-attr.stdout | ||