Correctly check if a macro call is actually a macro call in rustdoc highlighter

src/librustdoc/html/highlight.rs

@@ -1246,7 +1246,7 @@ impl<'src> Classifier<'src> {
                 LiteralKind::Float { .. } | LiteralKind::Int { .. } => Class::Number,
             },
             TokenKind::GuardedStrPrefix => return no_highlight(sink),
-            TokenKind::RawIdent if let Some((TokenKind::Bang, _)) = self.peek_non_trivia() => {
+            TokenKind::RawIdent if self.check_if_macro_call("") => {
                 self.new_macro_span(text, sink, before, file_span);
                 return;
             }
@@ -1268,17 +1268,15 @@ impl<'src> Classifier<'src> {
                         // So if it's not a keyword which can be followed by a value (like `if` or
                         // `return`) and the next non-whitespace token is a `!`, then we consider
                         // it's a macro.
-                        if !NON_MACRO_KEYWORDS.contains(&text)
-                            && matches!(self.peek_non_trivia(), Some((TokenKind::Bang, _)))
-                        {
+                        if !NON_MACRO_KEYWORDS.contains(&text) && self.check_if_macro_call(text) {
                             self.new_macro_span(text, sink, before, file_span);
                             return;
                         }
                         Class::KeyWord
                     }
                     // If it's not a keyword and the next non whitespace token is a `!`, then
                     // we consider it's a macro.
-                    _ if matches!(self.peek_non_trivia(), Some((TokenKind::Bang, _))) => {
+                    _ if self.check_if_macro_call(text) => {
                         self.new_macro_span(text, sink, before, file_span);
                         return;
                     }
@@ -1339,6 +1337,37 @@ impl<'src> Classifier<'src> {
         self.tokens.stop_peeking();
         None
     }
+
+    fn check_if_macro_call(&mut self, ident: &str) -> bool {
+        let mut has_bang = false;
+        let is_macro_rule_ident = ident == "macro_rules";
+
+        while let Some((kind, _)) = self.tokens.peek_next() {
+            if let TokenKind::Whitespace
+            | TokenKind::LineComment { doc_style: None }
+            | TokenKind::BlockComment { doc_style: None, .. } = kind
+            {
+                continue;
+            }
+            if !has_bang {
+                if kind != TokenKind::Bang {
+                    break;
+                }
+                has_bang = true;
+                continue;
+            }
+            self.tokens.stop_peeking();
+            if is_macro_rule_ident {
+                return matches!(kind, TokenKind::Ident | TokenKind::RawIdent);
+            }
+            return matches!(
+                kind,
+                TokenKind::OpenParen | TokenKind::OpenBracket | TokenKind::OpenBrace
+            );
+        }
+        self.tokens.stop_peeking();
+        false
+    }
 }
 
 fn is_keyword(symbol: Symbol) -> bool {

tests/rustdoc-html/source-code-pages/macro-call-2.rs

@@ -0,0 +1,18 @@
+// This is yet another test to ensure that only macro calls are considered as such
+// by the rustdoc highlighter, in particular when named `macro_rules`.
+// This is a regression test for <https://github.com/rust-lang/rust/issues/151904>.
+
+#![crate_name = "foo"]
+
+//@ has src/foo/macro-call-2.rs.html
+//@ count - '//code/span[@class="macro"]' 2
+//@ has - '//code/span[@class="macro"]' 'macro_rules!'
+//@ has - '//code/span[@class="macro"]' 'r#macro_rules!'
+
+macro_rules! r#macro_rules {
+    () => {
+        fn main() {}
+    }
+}
+
+r#macro_rules!();

tests/rustdoc-html/source-code-pages/macro-call.rs

@@ -0,0 +1,29 @@
+// This is yet another test to ensure that only macro calls are considered as such
+// by the rustdoc highlighter.
+// This is a regression test for <https://github.com/rust-lang/rust/issues/151904>.
+
+#![crate_name = "foo"]
+
+//@ has src/foo/macro-call.rs.html
+//@ count - '//code/span[@class="macro"]' 2
+//@ has - '//code/span[@class="macro"]' 'panic!'
+//@ has - '//code/span[@class="macro"]' 'macro_rules!'
+
+pub struct Layout;
+
+impl Layout {
+    pub fn new<X: std::fmt::Debug>() {}
+}
+
+pub fn bar() {
+    let layout = Layout::new::<u32>();
+    if layout != Layout::new::<u32>() {
+        panic!();
+    }
+    let macro_rules = 3;
+    if macro_rules != 3 {}
+}
+
+macro_rules! blob {
+    () => {}
+}