Recover _ as .. in field pattern

Author: compiler-errors

compiler/rustc_parse/src/parser/pat.rs

@@ -1013,12 +1013,15 @@ impl<'a> Parser<'a> {
             }
             ate_comma = false;
 
-            if self.check(&token::DotDot) || self.token == token::DotDotDot {
+            if self.check(&token::DotDot)
+                || self.check_noexpect(&token::DotDotDot)
+                || self.check_keyword(kw::Underscore)
+            {
                 etc = true;
                 let mut etc_sp = self.token.span;
 
-                self.recover_one_fewer_dotdot();
-                self.bump(); // `..` || `...`
+                self.recover_bad_dot_dot();
+                self.bump(); // `..` || `...` || `_`
 
                 if self.token == token::CloseDelim(Delimiter::Brace) {
                     etc_span = Some(etc_sp);
@@ -1111,21 +1114,25 @@ impl<'a> Parser<'a> {
         Ok((fields, etc))
     }
 
-    /// Recover on `...` as if it were `..` to avoid further errors.
+    /// Recover on `...` or `_` as if it were `..` to avoid further errors.
     /// See issue #46718.
-    fn recover_one_fewer_dotdot(&self) {
-        if self.token != token::DotDotDot {
+    fn recover_bad_dot_dot(&self) {
+        if self.token == token::DotDot {
             return;
         }
 
-        self.struct_span_err(self.token.span, "expected field pattern, found `...`")
-            .span_suggestion(
-                self.token.span,
-                "to omit remaining fields, use one fewer `.`",
-                "..",
-                Applicability::MachineApplicable,
-            )
-            .emit();
+        let token_str = pprust::token_to_string(&self.token);
+        self.struct_span_err(
+            self.token.span,
+            format!("expected field pattern, found `{token_str}`"),
+        )
+        .span_suggestion_verbose(
+            self.token.span,
+            "to omit remaining fields, use `..`",
+            "..",
+            Applicability::MachineApplicable,
+        )
+        .emit();
     }
 
     fn parse_pat_field(&mut self, lo: Span, attrs: AttrVec) -> PResult<'a, PatField> {

tests/ui/did_you_mean/issue-46718-struct-pattern-dotdotdot.stderr

@@ -2,7 +2,12 @@ error: expected field pattern, found `...`
   --> $DIR/issue-46718-struct-pattern-dotdotdot.rs:11:55
    |
 LL |             PersonalityInventory { expressivity: exp, ... } => exp
-   |                                                       ^^^ help: to omit remaining fields, use one fewer `.`: `..`
+   |                                                       ^^^
+   |
+help: to omit remaining fields, use `..`
+   |
+LL |             PersonalityInventory { expressivity: exp, .. } => exp
+   |                                                       ~~
 
 error: aborting due to previous error
 

tests/ui/parser/issue-102806.stderr

@@ -32,7 +32,12 @@ error: expected field pattern, found `...`
   --> $DIR/issue-102806.rs:21:22
    |
 LL |     let V3 { z: val, ... } = v;
-   |                      ^^^ help: to omit remaining fields, use one fewer `.`: `..`
+   |                      ^^^
+   |
+help: to omit remaining fields, use `..`
+   |
+LL |     let V3 { z: val, .. } = v;
+   |                      ~~
 
 error[E0063]: missing fields `x` and `y` in initializer of `V3`
   --> $DIR/issue-102806.rs:17:13

tests/ui/parser/issues/issue-63135.stderr

@@ -20,7 +20,12 @@ error: expected field pattern, found `...`
   --> $DIR/issue-63135.rs:3:8
    |
 LL | fn i(n{...,f #
-   |        ^^^ help: to omit remaining fields, use one fewer `.`: `..`
+   |        ^^^
+   |
+help: to omit remaining fields, use `..`
+   |
+LL | fn i(n{..,f #
+   |        ~~
 
 error: expected `}`, found `,`
   --> $DIR/issue-63135.rs:3:11

tests/ui/structs-enums/struct-enum-ignoring-field-with-underscore.rs

@@ -7,6 +7,5 @@ fn main() {
     let foo = Some(Foo::Other);
 
     if let Some(Foo::Bar {_}) = foo {}
-    //~^ ERROR expected identifier, found reserved identifier `_`
-    //~| ERROR pattern does not mention field `bar` [E0027]
+    //~^ ERROR expected field pattern, found `_`
 }

tests/ui/structs-enums/struct-enum-ignoring-field-with-underscore.stderr

@@ -1,24 +1,13 @@
-error: expected identifier, found reserved identifier `_`
+error: expected field pattern, found `_`
   --> $DIR/struct-enum-ignoring-field-with-underscore.rs:9:27
    |
 LL |     if let Some(Foo::Bar {_}) = foo {}
-   |                           ^ expected identifier, found reserved identifier
-
-error[E0027]: pattern does not mention field `bar`
-  --> $DIR/struct-enum-ignoring-field-with-underscore.rs:9:17
-   |
-LL |     if let Some(Foo::Bar {_}) = foo {}
-   |                 ^^^^^^^^^^^^ missing field `bar`
-   |
-help: include the missing field in the pattern
+   |                           ^
    |
-LL |     if let Some(Foo::Bar {_, bar }) = foo {}
-   |                            ~~~~~~~
-help: if you don't care about this missing field, you can explicitly ignore it
+help: to omit remaining fields, use `..`
    |
-LL |     if let Some(Foo::Bar {_, .. }) = foo {}
-   |                            ~~~~~~
+LL |     if let Some(Foo::Bar {..}) = foo {}
+   |                           ~~
 
-error: aborting due to 2 previous errors
+error: aborting due to previous error
 
-For more information about this error, try `rustc --explain E0027`.