Move where doc comment meant as comment check

The new place makes more sense and covers more cases beyond individual
statements.

```
error: expected one of `.`, `;`, `?`, `else`, or an operator, found doc comment `//!foo
  --> $DIR/doc-comment-in-stmt.rs:25:22
   |
LL |     let y = x.max(1) //!foo
   |                      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected one of `.`, `;`, `?`, `else`, or an operator
   |
help: add a space before `!` to write a regular comment
   |
LL |     let y = x.max(1) // !foo
   |                        +
```

Fix #65329.

2 files changed, 21 insertions, 18 deletions

diff --git a/compiler/rustc_parse/src/parser/diagnostics.rs b/compiler/rustc_parse/src/parser/diagnostics.rs
index 75e3393aa96..9f8361a4b1e 100644
--- a/compiler/rustc_parse/src/parser/diagnostics.rs
+++ b/compiler/rustc_parse/src/parser/diagnostics.rs
@@ -39,7 +39,7 @@ use rustc_errors::{
 use rustc_session::errors::ExprParenthesesNeeded;
 use rustc_span::source_map::Spanned;
 use rustc_span::symbol::{kw, sym, Ident};
-use rustc_span::{Span, SpanSnippetError, Symbol, DUMMY_SP};
+use rustc_span::{BytePos, Span, SpanSnippetError, Symbol, DUMMY_SP};
 use std::mem::take;
 use std::ops::{Deref, DerefMut};
 use thin_vec::{thin_vec, ThinVec};
@@ -648,6 +648,26 @@ impl<'a> Parser<'a> {
             );
         }
 
+        if let token::DocComment(kind, style, _) = self.token.kind {
+            // 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);
+            err.span_suggestion_verbose(
+                span,
+                format!(
+                    "add a space before {} to write a regular comment",
+                    match (kind, style) {
+                        (token::CommentKind::Line, ast::AttrStyle::Inner) => "`!`",
+                        (token::CommentKind::Block, ast::AttrStyle::Inner) => "`!`",
+                        (token::CommentKind::Line, ast::AttrStyle::Outer) => "the last `/`",
+                        (token::CommentKind::Block, ast::AttrStyle::Outer) => "the last `*`",
+                    },
+                ),
+                " ".to_string(),
+                Applicability::MachineApplicable,
+            );
+        }
+
         // Add suggestion for a missing closing angle bracket if '>' is included in expected_tokens
         // there are unclosed angle brackets
         if self.unmatched_angle_bracket_count > 0
diff --git a/compiler/rustc_parse/src/parser/stmt.rs b/compiler/rustc_parse/src/parser/stmt.rs
index e2f59cb2071..8e3c4568694 100644
--- a/compiler/rustc_parse/src/parser/stmt.rs
+++ b/compiler/rustc_parse/src/parser/stmt.rs
@@ -632,23 +632,6 @@ impl<'a> Parser<'a> {
                         // Recover from parser, skip type error to avoid extra errors.
                         Ok(true) => true,
                         Err(mut e) => {
-                            if let TokenKind::DocComment(..) = self.token.kind
-                                && let Ok(snippet) = self.span_to_snippet(self.token.span)
-                            {
-                                let sp = self.token.span;
-                                let marker = &snippet[..3];
-                                let (comment_marker, doc_comment_marker) = marker.split_at(2);
-
-                                e.span_suggestion(
-                                    sp.with_hi(sp.lo() + BytePos(marker.len() as u32)),
-                                    format!(
-                                        "add a space before `{doc_comment_marker}` to use a regular comment",
-                                    ),
-                                    format!("{comment_marker} {doc_comment_marker}"),
-                                    Applicability::MaybeIncorrect,
-                                );
-                            }
-
                             if self.recover_colon_as_semi() {
                                 // recover_colon_as_semi has already emitted a nicer error.
                                 e.delay_as_bug();