Dont suggest converting /// to regular comment when it appears after missing , in list

Signed-off-by: xizheyin <xizheyin@smail.nju.edu.cn>

compiler/rustc_parse/src/parser/diagnostics.rs

@@ -686,6 +686,16 @@ impl<'a> Parser<'a> {
         }
 
         if let token::DocComment(kind, style, _) = self.token.kind {
+            // This is to avoid suggesting converting a doc comment to a regular comment
+            // when missing a comma before the doc comment in lists (#142311):
+            //
+            // ```
+            // enum Foo{
+            //     A /// xxxxxxx
+            //     B,
+            // }
+            // ```
+            if !expected.contains(&TokenType::Comma) {
                 // We have something like `expr //!val` where the user likely meant `expr // !val`
                 let pos = self.token.span.lo() + BytePos(2);
                 let span = self.token.span.with_lo(pos).with_hi(pos);
@@ -701,9 +711,10 @@ impl<'a> Parser<'a> {
                         },
                     ),
                     " ".to_string(),
-                Applicability::MachineApplicable,
+                    Applicability::MaybeIncorrect,
                 );
             }
+        }
 
         let sp = if self.token == token::Eof {
             // This is EOF; don't want to point at the following char, but rather the last token.

tests/ui/parser/doc-comment-after-missing-comma-issue-142311.rs

@@ -0,0 +1,34 @@
+//! Check that if the parser suggests converting `///` to a regular comment
+//! when it appears after a missing comma in an list (e.g. `enum` variants).
+//!
+//! Related issue
+//! - https://github.com/rust-lang/rust/issues/142311
+
+enum Foo {
+    /// Like the noise a sheep makes
+    Bar
+    /// Like where people drink
+    //~^ ERROR expected one of `(`, `,`, `=`, `{`, or `}`, found doc comment `/// Like where people drink`
+    Baa///xxxxxx
+    //~^ ERROR expected one of `(`, `,`, `=`, `{`, or `}`, found doc comment `///xxxxxx`
+    Baz///xxxxxx
+    //~^ ERROR expected one of `(`, `,`, `=`, `{`, or `}`, found doc comment `///xxxxxx`
+}
+
+fn foo() {
+    let a = [
+        1///xxxxxx
+        //~^ ERROR expected one of `,`, `.`, `;`, `?`, `]`, or an operator, found doc comment `///xxxxxx`
+        2
+    ];
+}
+
+fn bar() {
+    let a = [
+        1,
+        2///xxxxxx
+        //~^ ERROR expected one of `,`, `.`, `?`, `]`, or an operator, found doc comment `///xxxxxx`
+    ];
+}
+
+fn main() {}

tests/ui/parser/doc-comment-after-missing-comma-issue-142311.stderr

@@ -0,0 +1,43 @@
+error: expected one of `(`, `,`, `=`, `{`, or `}`, found doc comment `/// Like where people drink`
+  --> $DIR/doc-comment-after-missing-comma-issue-142311.rs:10:5
+   |
+LL |     Bar
+   |        -
+   |        |
+   |        expected one of `(`, `,`, `=`, `{`, or `}`
+   |        help: missing `,`
+LL |     /// Like where people drink
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^ unexpected token
+
+error: expected one of `(`, `,`, `=`, `{`, or `}`, found doc comment `///xxxxxx`
+  --> $DIR/doc-comment-after-missing-comma-issue-142311.rs:12:8
+   |
+LL |     Baa///xxxxxx
+   |        -^^^^^^^^
+   |        |
+   |        expected one of `(`, `,`, `=`, `{`, or `}`
+   |        help: missing `,`
+
+error: expected one of `(`, `,`, `=`, `{`, or `}`, found doc comment `///xxxxxx`
+  --> $DIR/doc-comment-after-missing-comma-issue-142311.rs:14:8
+   |
+LL |     Baz///xxxxxx
+   |        ^^^^^^^^^ expected one of `(`, `,`, `=`, `{`, or `}`
+   |
+   = help: doc comments must come before what they document, if a comment was intended use `//`
+   = help: enum variants can be `Variant`, `Variant = <integer>`, `Variant(Type, ..., TypeN)` or `Variant { fields: Types }`
+
+error: expected one of `,`, `.`, `;`, `?`, `]`, or an operator, found doc comment `///xxxxxx`
+  --> $DIR/doc-comment-after-missing-comma-issue-142311.rs:20:10
+   |
+LL |         1///xxxxxx
+   |          ^^^^^^^^^ expected one of `,`, `.`, `;`, `?`, `]`, or an operator
+
+error: expected one of `,`, `.`, `?`, `]`, or an operator, found doc comment `///xxxxxx`
+  --> $DIR/doc-comment-after-missing-comma-issue-142311.rs:29:10
+   |
+LL |         2///xxxxxx
+   |          ^^^^^^^^^ expected one of `,`, `.`, `?`, `]`, or an operator
+
+error: aborting due to 5 previous errors
+