Add ParseContext for diagnostic in Parser and supress false comments suggestion

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

Author: xizheyin

compiler/rustc_parse/src/parser/diagnostics.rs

@@ -45,6 +45,7 @@ use crate::errors::{
     UnexpectedConstParamDeclaration, UnexpectedConstParamDeclarationSugg, UnmatchedAngleBrackets,
     UseEqInstead, WrapType,
 };
+use crate::parser::ParserContext;
 use crate::parser::attr::InnerAttrPolicy;
 use crate::{exp, fluent_generated as fluent};
 
@@ -685,7 +686,9 @@ impl<'a> Parser<'a> {
             );
         }
 
-        if let token::DocComment(kind, style, _) = self.token.kind {
+        if let token::DocComment(kind, style, _) = self.token.kind
+            && self.context != ParserContext::ExpectItemListComma
+        {
             // 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);

compiler/rustc_parse/src/parser/item.rs

@@ -24,6 +24,7 @@ use super::{
     Recovered, Trailing, UsePreAttrPos,
 };
 use crate::errors::{self, MacroExpandsToAdtField};
+use crate::parser::ParserContext;
 use crate::{exp, fluent_generated as fluent};
 
 impl<'a> Parser<'a> {
@@ -1547,8 +1548,10 @@ impl<'a> Parser<'a> {
             self.bump();
             (thin_vec![], Trailing::No)
         } else {
-            self.parse_delim_comma_seq(exp!(OpenBrace), exp!(CloseBrace), |p| {
-                p.parse_enum_variant(ident.span)
+            self.with_context(ParserContext::ExpectItemListComma, |p| {
+                p.parse_delim_comma_seq(exp!(OpenBrace), exp!(CloseBrace), |p| {
+                    p.parse_enum_variant(ident.span)
+                })
             })
             .map_err(|mut err| {
                 err.span_label(ident.span, "while parsing this enum");

compiler/rustc_parse/src/parser/mod.rs

@@ -166,6 +166,18 @@ pub enum Recovery {
     Forbidden,
 }
 
+/// Parser context for diagnostics and etc.
+/// It is used to determine whether to add suggestions.
+/// For example, in an item list, we don't want to add suggestions for doc comments.
+/// FIXME(xizheyin): This is a basic structure, we can add more fields
+#[derive(Copy, Clone, Debug, PartialEq, Eq)]
+pub enum ParserContext {
+    /// empty context
+    Empty,
+    /// enum/struct/union/fields/variants item list
+    ExpectItemListComma,
+}
+
 #[derive(Clone)]
 pub struct Parser<'a> {
     pub psess: &'a ParseSess,
@@ -218,6 +230,7 @@ pub struct Parser<'a> {
     /// Whether the parser is allowed to do recovery.
     /// This is disabled when parsing macro arguments, see #103534
     recovery: Recovery,
+    pub context: ParserContext,
 }
 
 // This type is used a lot, e.g. it's cloned when matching many declarative macro rules with
@@ -367,6 +380,7 @@ impl<'a> Parser<'a> {
             },
             current_closure: None,
             recovery: Recovery::Allowed,
+            context: ParserContext::Empty,
         };
 
         // Make parser point to the first token.
@@ -1638,6 +1652,15 @@ impl<'a> Parser<'a> {
             _ => self.prev_token.span,
         }
     }
+
+    /// Temporarily set the parser context for a closure, restoring it afterwards.
+    pub fn with_context<T>(&mut self, ctx: ParserContext, f: impl FnOnce(&mut Self) -> T) -> T {
+        let old = self.context;
+        self.context = ctx;
+        let res = f(self);
+        self.context = old;
+        res
+    }
 }
 
 // Metavar captures of various kinds.

tests/ui/enum/enum-lack-comma-suggestion-issue-142311.stderr

@@ -2,18 +2,12 @@ error: expected one of `(`, `,`, `=`, `{`, or `}`, found doc comment `/// Like w
   --> $DIR/enum-lack-comma-suggestion-issue-142311.rs:4:5
    |
 LL |     Bar
-   |        - expected one of `(`, `,`, `=`, `{`, or `}`
+   |        -
+   |        |
+   |        expected one of `(`, `,`, `=`, `{`, or `}`
+   |        help: missing `,`
 LL |     /// Like where people drink
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^ unexpected token
-   |
-help: add a space before the last `/` to write a regular comment
-   |
-LL |     // / Like where people drink
-   |       +
-help: missing `,`
-   |
-LL |     Bar,
-   |        +
 
 error: aborting due to 1 previous error