parse guard patterns and use correct pattern parsers throughout rustc

Author: max-niederman

compiler/rustc_expand/src/expand.rs

@@ -987,7 +987,7 @@ pub fn parse_ast_fragment<'a>(
             }
         }
         AstFragmentKind::Ty => AstFragment::Ty(this.parse_ty()?),
-        AstFragmentKind::Pat => AstFragment::Pat(this.parse_pat_no_top_guard(
+        AstFragmentKind::Pat => AstFragment::Pat(this.parse_pat_allow_top_guard(
             None,
             RecoverComma::No,
             RecoverColon::Yes,

compiler/rustc_parse/src/parser/expr.rs

@@ -2770,7 +2770,7 @@ impl<'a> Parser<'a> {
         };
         // Try to parse the pattern `for ($PAT) in $EXPR`.
         let pat = match (
-            self.parse_pat_no_top_guard(
+            self.parse_pat_allow_top_guard(
                 None,
                 RecoverComma::Yes,
                 RecoverColon::Yes,

compiler/rustc_parse/src/parser/pat.rs

@@ -99,12 +99,19 @@ impl<'a> Parser<'a> {
     /// `PatternNoTopAlt` (see below) are used.
     pub fn parse_pat_allow_top_guard(
         &mut self,
-        _expected: Option<Expected>,
-        _rc: RecoverComma,
-        _ra: RecoverColon,
-        _rt: CommaRecoveryMode,
+        expected: Option<Expected>,
+        rc: RecoverComma,
+        ra: RecoverColon,
+        rt: CommaRecoveryMode,
     ) -> PResult<'a, P<Pat>> {
-        todo!()
+        let pat = self.parse_pat_no_top_guard(expected, rc, ra, rt)?;
+
+        if self.eat_keyword(kw::If) {
+            let cond = self.parse_expr()?;
+            Ok(self.mk_pat(pat.span.to(cond.span), PatKind::Guard(pat, cond)))
+        } else {
+            Ok(pat)
+        }
     }
 
     /// Parses a pattern.
@@ -123,8 +130,8 @@ impl<'a> Parser<'a> {
     /// Parses a pattern.
     ///
     /// Corresponds to `PatternNoTopGuard` in RFC 3637 and allows or-patterns, but not
-    /// guard patterns, at the top level. Used for parsing patterns in `pat` fragments and
-    /// `let`, `if let`, and `while let` expressions.
+    /// guard patterns, at the top level. Used for parsing patterns in `pat` fragments (until
+    /// the next edition) and `let`, `if let`, and `while let` expressions.
     ///
     /// Note that after the FCP in <https://github.com/rust-lang/rust/issues/81415>,
     /// a leading vert is allowed in nested or-patterns, too. This allows us to
@@ -477,7 +484,7 @@ impl<'a> Parser<'a> {
         } else if self.check(&token::OpenDelim(Delimiter::Bracket)) {
             // Parse `[pat, pat,...]` as a slice pattern.
             let (pats, _) = self.parse_delim_comma_seq(Delimiter::Bracket, |p| {
-                p.parse_pat_no_top_guard(
+                p.parse_pat_allow_top_guard(
                     None,
                     RecoverComma::No,
                     RecoverColon::No,
@@ -725,7 +732,7 @@ impl<'a> Parser<'a> {
         let open_paren = self.token.span;
 
         let (fields, trailing_comma) = self.parse_paren_comma_seq(|p| {
-            p.parse_pat_no_top_guard(
+            p.parse_pat_allow_top_guard(
                 None,
                 RecoverComma::No,
                 RecoverColon::No,
@@ -1134,7 +1141,7 @@ impl<'a> Parser<'a> {
         path: Path,
     ) -> PResult<'a, PatKind> {
         let (fields, _) = self.parse_paren_comma_seq(|p| {
-            p.parse_pat_no_top_guard(
+            p.parse_pat_allow_top_guard(
                 None,
                 RecoverComma::No,
                 RecoverColon::No,
@@ -1169,7 +1176,7 @@ impl<'a> Parser<'a> {
         self.parse_builtin(|self_, _lo, ident| {
             Ok(match ident.name {
                 // builtin#deref(PAT)
-                sym::deref => Some(ast::PatKind::Deref(self_.parse_pat_no_top_guard(
+                sym::deref => Some(ast::PatKind::Deref(self_.parse_pat_allow_top_guard(
                     None,
                     RecoverComma::Yes,
                     RecoverColon::Yes,
@@ -1417,7 +1424,7 @@ impl<'a> Parser<'a> {
             // Parsing a pattern of the form `fieldname: pat`.
             let fieldname = self.parse_field_name()?;
             self.bump();
-            let pat = self.parse_pat_no_top_guard(
+            let pat = self.parse_pat_allow_top_guard(
                 None,
                 RecoverComma::No,
                 RecoverColon::No,

compiler/rustc_parse/src/parser/path.rs

@@ -457,7 +457,7 @@ impl<'a> Parser<'a> {
             PathStyle::Pat
                 if let Ok(_) = self
                     .parse_paren_comma_seq(|p| {
-                        p.parse_pat_no_top_guard(
+                        p.parse_pat_allow_top_guard(
                             None,
                             RecoverComma::No,
                             RecoverColon::No,

tests/ui/parser/issues/issue-72373.rs

@@ -3,7 +3,7 @@ fn foo(c: &[u32], n: u32) -> u32 {
         [h, ..] if h > n => 0,
         [h, ..] if h == n => 1,
         [h, ref ts..] => foo(c, n - h) + foo(ts, n),
-        //~^ ERROR expected one of `,`, `@`, `]`, or `|`, found `..`
+        //~^ ERROR expected one of `,`, `@`, `]`, `if`, or `|`, found `..`
         [] => 0,
     }
 }

tests/ui/parser/issues/issue-72373.stderr

@@ -1,8 +1,8 @@
-error: expected one of `,`, `@`, `]`, or `|`, found `..`
+error: expected one of `,`, `@`, `]`, `if`, or `|`, found `..`
   --> $DIR/issue-72373.rs:5:19
    |
 LL |         [h, ref ts..] => foo(c, n - h) + foo(ts, n),
-   |                   ^^ expected one of `,`, `@`, `]`, or `|`
+   |                   ^^ expected one of `,`, `@`, `]`, `if`, or `|`
    |
 help: if you meant to bind the contents of the rest of the array pattern into `ts`, use `@`
    |

tests/ui/parser/misspelled-keywords/ref.stderr

@@ -1,8 +1,8 @@
-error: expected one of `)`, `,`, `@`, or `|`, found `list`
+error: expected one of `)`, `,`, `@`, `if`, or `|`, found `list`
   --> $DIR/ref.rs:4:19
    |
 LL |         Some(refe list) => println!("{list:?}"),
-   |                   ^^^^ expected one of `)`, `,`, `@`, or `|`
+   |                   ^^^^ expected one of `)`, `,`, `@`, `if`, or `|`
    |
 help: there is a keyword `ref` with a similar name
    |

tests/ui/parser/pat-lt-bracket-7.rs

@@ -3,7 +3,7 @@ fn main() {
     let foo = core::iter::empty();
 
     for Thing(x[]) in foo {}
-    //~^ ERROR: expected one of `)`, `,`, `@`, or `|`, found `[`
+    //~^ ERROR: expected one of `)`, `,`, `@`, `if`, or `|`, found `[`
 }
 
 const RECOVERY_WITNESS: () = 0; //~ ERROR mismatched types

tests/ui/parser/pat-lt-bracket-7.stderr

@@ -1,10 +1,10 @@
-error: expected one of `)`, `,`, `@`, or `|`, found `[`
+error: expected one of `)`, `,`, `@`, `if`, or `|`, found `[`
   --> $DIR/pat-lt-bracket-7.rs:5:16
    |
 LL |     for Thing(x[]) in foo {}
    |                ^
    |                |
-   |                expected one of `)`, `,`, `@`, or `|`
+   |                expected one of `)`, `,`, `@`, `if`, or `|`
    |                help: missing `,`
 
 error[E0308]: mismatched types

tests/ui/parser/pat-recover-exprs.rs

@@ -17,12 +17,12 @@ fn main() {
         f?() => (),
         //~^ error: expected a pattern, found an expression
         (_ + 1) => (),
-        //~^ error: expected one of `)`, `,`, or `|`, found `+`
+        //~^ error: expected one of `)`, `,`, `if`, or `|`, found `+`
     }
 
     let 1 + 1 = 2;
     //~^ error: expected a pattern, found an expression
 
     let b = matches!(x, (x * x | x.f()) | x[0]);
-    //~^ error: expected one of `)`, `,`, `@`, or `|`, found `*`
+    //~^ error: expected one of `)`, `,`, `@`, `if`, or `|`, found `*`
 }