Rollup merge of #65410 - Centril:intersection-pat-recover, r=davidtwco,varkor
syntax: add parser recovery for intersection- / and-patterns `p1 @ p2` Fixes https://github.com/rust-lang/rust/issues/65400. The recovery comes in two flavors: 1. We know that `p2` is a binding so we can invert as `p2 @ p1`: ```rust error: pattern on wrong side of `@` --> $DIR/intersection-patterns.rs:13:9 | LL | Some(x) @ y => {} | -------^^^- | | | | | binding on the right, should be to the left | pattern on the left, should be to the right | help: switch the order: `y @ Some(x)` ``` 2. Otherwise we emit a generic diagnostic for the lack of support for intersection patterns: ```rust error: left-hand side of `@` must be a binding --> $DIR/intersection-patterns.rs:23:9 | LL | Some(x) @ Some(y) => {} | -------^^^------- | | | | | also a pattern | interpreted as a pattern, not a binding | = note: bindings are `x`, `mut x`, `ref x`, and `ref mut x` ``` For more on and-patterns, see e.g. https://docs.microsoft.com/en-us/dotnet/fsharp/language-reference/pattern-matching#and-pattern. r? @davidtwco cc @varkor @lzutao
This commit is contained in:
Tyler Mandry
GitHub
commit
1b182371e1
4 changed files with 135 additions and 1 deletions
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@ -367,6 +367,7 @@ impl<'a> Parser<'a> {
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let pat = self.mk_pat(lo.to(self.prev_span), pat);
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let pat = self.maybe_recover_from_bad_qpath(pat, true)?;
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let pat = self.recover_intersection_pat(pat)?;
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if !allow_range_pat {
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self.ban_pat_range_if_ambiguous(&pat)?
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@ -375,6 +376,65 @@ impl<'a> Parser<'a> {
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Ok(pat)
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}
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/// Try to recover the more general form `intersect ::= $pat_lhs @ $pat_rhs`.
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///
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/// Allowed binding patterns generated by `binding ::= ref? mut? $ident @ $pat_rhs`
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/// should already have been parsed by now at this point,
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/// if the next token is `@` then we can try to parse the more general form.
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///
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/// Consult `parse_pat_ident` for the `binding` grammar.
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///
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/// The notion of intersection patterns are found in
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/// e.g. [F#][and] where they are called AND-patterns.
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///
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/// [and]: https://docs.microsoft.com/en-us/dotnet/fsharp/language-reference/pattern-matching
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fn recover_intersection_pat(&mut self, lhs: P<Pat>) -> PResult<'a, P<Pat>> {
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if self.token.kind != token::At {
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// Next token is not `@` so it's not going to be an intersection pattern.
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return Ok(lhs);
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}
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// At this point we attempt to parse `@ $pat_rhs` and emit an error.
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self.bump(); // `@`
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let mut rhs = self.parse_pat(None)?;
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let sp = lhs.span.to(rhs.span);
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if let PatKind::Ident(_, _, ref mut sub @ None) = rhs.kind {
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// The user inverted the order, so help them fix that.
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let mut applicability = Applicability::MachineApplicable;
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lhs.walk(&mut |p| match p.kind {
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// `check_match` is unhappy if the subpattern has a binding anywhere.
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PatKind::Ident(..) => {
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applicability = Applicability::MaybeIncorrect;
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false // Short-circuit.
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},
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_ => true,
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});
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let lhs_span = lhs.span;
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// Move the LHS into the RHS as a subpattern.
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// The RHS is now the full pattern.
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*sub = Some(lhs);
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self.struct_span_err(sp, "pattern on wrong side of `@`")
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.span_label(lhs_span, "pattern on the left, should be on the right")
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.span_label(rhs.span, "binding on the right, should be on the left")
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.span_suggestion(sp, "switch the order", pprust::pat_to_string(&rhs), applicability)
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.emit();
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} else {
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// The special case above doesn't apply so we may have e.g. `A(x) @ B(y)`.
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rhs.kind = PatKind::Wild;
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self.struct_span_err(sp, "left-hand side of `@` must be a binding")
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.span_label(lhs.span, "interpreted as a pattern, not a binding")
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.span_label(rhs.span, "also a pattern")
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.note("bindings are `x`, `mut x`, `ref x`, and `ref mut x`")
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.emit();
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}
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rhs.span = sp;
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Ok(rhs)
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}
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/// Ban a range pattern if it has an ambiguous interpretation.
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fn ban_pat_range_if_ambiguous(&self, pat: &Pat) -> PResult<'a, ()> {
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match pat.kind {
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@ -2381,7 +2381,8 @@ impl<'a> State<'a> {
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}
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self.print_ident(ident);
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if let Some(ref p) = *sub {
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self.s.word("@");
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self.s.space();
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self.s.word_space("@");
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self.print_pat(p);
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}
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}
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40
src/test/ui/parser/intersection-patterns.rs
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40
src/test/ui/parser/intersection-patterns.rs
Normal file
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@ -0,0 +1,40 @@
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// This tests the parser recovery in `recover_intersection_pat`
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// and serves as a regression test for the diagnostics issue #65400.
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//
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// The general idea is that for `$pat_lhs @ $pat_rhs` where
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// `$pat_lhs` is not generated by `ref? mut? $ident` we want
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// to suggest either switching the order or note that intersection
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// patterns are not allowed.
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fn main() {
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let s: Option<u8> = None;
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match s {
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Some(x) @ y => {}
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//~^ ERROR pattern on wrong side of `@`
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//~| pattern on the left, should be on the right
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//~| binding on the right, should be on the left
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//~| HELP switch the order
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//~| SUGGESTION y @ Some(x)
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_ => {}
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}
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match s {
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Some(x) @ Some(y) => {}
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//~^ ERROR left-hand side of `@` must be a binding
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//~| interpreted as a pattern, not a binding
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//~| also a pattern
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//~| NOTE bindings are `x`, `mut x`, `ref x`, and `ref mut x`
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_ => {}
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}
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match 2 {
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1 ..= 5 @ e => {}
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//~^ ERROR pattern on wrong side of `@`
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//~| pattern on the left, should be on the right
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//~| binding on the right, should be on the left
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//~| HELP switch the order
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//~| SUGGESTION e @ 1 ..=5
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_ => {}
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}
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}
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33
src/test/ui/parser/intersection-patterns.stderr
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33
src/test/ui/parser/intersection-patterns.stderr
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@ -0,0 +1,33 @@
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error: pattern on wrong side of `@`
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--> $DIR/intersection-patterns.rs:13:9
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LL | Some(x) @ y => {}
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| -------^^^-
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| | |
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| | binding on the right, should be on the left
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| pattern on the left, should be on the right
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| help: switch the order: `y @ Some(x)`
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error: left-hand side of `@` must be a binding
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--> $DIR/intersection-patterns.rs:23:9
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LL | Some(x) @ Some(y) => {}
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| -------^^^-------
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| | |
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| | also a pattern
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| interpreted as a pattern, not a binding
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= note: bindings are `x`, `mut x`, `ref x`, and `ref mut x`
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error: pattern on wrong side of `@`
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--> $DIR/intersection-patterns.rs:32:9
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LL | 1 ..= 5 @ e => {}
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| -------^^^-
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| | |
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| | binding on the right, should be on the left
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| pattern on the left, should be on the right
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| help: switch the order: `e @ 1 ..=5`
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error: aborting due to 3 previous errors
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