Suggests turbofish in patterns

Author: mu001999

compiler/rustc_parse/messages.ftl

@@ -270,6 +270,8 @@ parse_found_expr_would_be_stmt = expected expression, found `{$token}`
 parse_function_body_equals_expr = function body cannot be `= expression;`
     .suggestion = surround the expression with `{"{"}` and `{"}"}` instead of `=` and `;`
 
+parse_generic_args_in_pat_require_turbofish_syntax = generic args in patterns require the turbofish syntax
+
 parse_generic_parameters_without_angle_brackets = generic parameters without surrounding angle brackets
     .suggestion = surround the type parameters with angle brackets
 

compiler/rustc_parse/src/errors.rs

@@ -2731,3 +2731,17 @@ pub(crate) struct WhereClauseBeforeConstBodySugg {
     #[suggestion_part(code = "")]
     pub right: Span,
 }
+
+#[derive(Diagnostic)]
+#[diag(parse_generic_args_in_pat_require_turbofish_syntax)]
+pub(crate) struct GenericArgsInPatRequireTurbofishSyntax {
+    #[primary_span]
+    pub span: Span,
+    #[suggestion(
+        parse_sugg_turbofish_syntax,
+        style = "verbose",
+        code = "::",
+        applicability = "maybe-incorrect"
+    )]
+    pub suggest_turbofish: Span,
+}

compiler/rustc_parse/src/parser/pat.rs

@@ -805,6 +805,7 @@ impl<'a> Parser<'a> {
             | token::DotDotDot | token::DotDotEq | token::DotDot // A range pattern.
             | token::ModSep // A tuple / struct variant pattern.
             | token::Not)) // A macro expanding to a pattern.
+        && !(self.look_ahead(1, |t| t.kind == token::Lt) && self.look_ahead(2, |t| t.can_begin_type())) // May suggest the turbofish syntax for generics, only valid for recoveries.
     }
 
     /// Parses `ident` or `ident @ pat`.

compiler/rustc_parse/src/parser/path.rs

@@ -1,6 +1,6 @@
 use super::ty::{AllowPlus, RecoverQPath, RecoverReturnSign};
 use super::{Parser, Restrictions, TokenType};
-use crate::errors::PathSingleColon;
+use crate::errors::{GenericArgsInPatRequireTurbofishSyntax, PathSingleColon};
 use crate::{errors, maybe_whole};
 use rustc_ast::ptr::P;
 use rustc_ast::token::{self, Delimiter, Token, TokenKind};
@@ -382,6 +382,14 @@ impl<'a> Parser<'a> {
                 };
 
                 PathSegment { ident, args: Some(args), id: ast::DUMMY_NODE_ID }
+            } else if style == PathStyle::Pat
+                && self.check_noexpect(&token::Lt)
+                && self.look_ahead(1, |t| t.can_begin_type())
+            {
+                return Err(self.sess.create_err(GenericArgsInPatRequireTurbofishSyntax {
+                    span: self.token.span,
+                    suggest_turbofish: self.token.span.shrink_to_lo(),
+                }));
             } else {
                 // Generic arguments are not found.
                 PathSegment::from_ident(ident)

tests/ui/did_you_mean/issue-114112.rs

@@ -0,0 +1,11 @@
+enum E<T> {
+    A(T)
+}
+
+fn main() {
+    match E::<i32>::A(1) {
+        E<i32>::A(v) => { //~ ERROR generic args in patterns require the turbofish syntax
+            println!("{v:?}");
+        },
+    }
+}

tests/ui/did_you_mean/issue-114112.stderr

@@ -0,0 +1,13 @@
+error: generic args in patterns require the turbofish syntax
+  --> $DIR/issue-114112.rs:7:10
+   |
+LL |         E<i32>::A(v) => {
+   |          ^
+   |
+help: use `::<...>` instead of `<...>` to specify lifetime, type, or const arguments
+   |
+LL |         E::<i32>::A(v) => {
+   |          ++
+
+error: aborting due to previous error
+

tests/ui/parser/issues/issue-22647.rs

@@ -1,5 +1,5 @@
 fn main() {
-    let caller<F> = |f: F|  //~ ERROR expected one of `:`, `;`, `=`, `@`, or `|`, found `<`
+    let caller<F> = |f: F|  //~ ERROR generic args in patterns require the turbofish syntax
     where F: Fn() -> i32
     {
         let x = f();

tests/ui/parser/issues/issue-22647.stderr

@@ -1,8 +1,13 @@
-error: expected one of `:`, `;`, `=`, `@`, or `|`, found `<`
+error: generic args in patterns require the turbofish syntax
   --> $DIR/issue-22647.rs:2:15
    |
 LL |     let caller<F> = |f: F|
-   |               ^ expected one of `:`, `;`, `=`, `@`, or `|`
+   |               ^
+   |
+help: use `::<...>` instead of `<...>` to specify lifetime, type, or const arguments
+   |
+LL |     let caller::<F> = |f: F|
+   |               ++
 
 error: aborting due to previous error
 

tests/ui/parser/issues/issue-22712.rs

@@ -3,7 +3,7 @@ struct Foo<B> {
 }
 
 fn bar() {
-    let Foo<Vec<u8>>  //~ ERROR expected one of `:`, `;`, `=`, `@`, or `|`, found `<`
+    let Foo<Vec<u8>> //~ ERROR generic args in patterns require the turbofish syntax
 }
 
 fn main() {}

tests/ui/parser/issues/issue-22712.stderr

@@ -1,8 +1,13 @@
-error: expected one of `:`, `;`, `=`, `@`, or `|`, found `<`
+error: generic args in patterns require the turbofish syntax
   --> $DIR/issue-22712.rs:6:12
    |
 LL |     let Foo<Vec<u8>>
-   |            ^ expected one of `:`, `;`, `=`, `@`, or `|`
+   |            ^
+   |
+help: use `::<...>` instead of `<...>` to specify lifetime, type, or const arguments
+   |
+LL |     let Foo::<Vec<u8>>
+   |            ++
 
 error: aborting due to previous error