[clang] Support [[guarded_by(mutex)]] attribute inside C struct (PR #94216)

[Pierre d'Herbemont via cfe-commits]

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@@ -3330,6 +3340,63 @@ void Parser::DistributeCLateParsedAttrs(Decl *Dcl,
   }
 }
 
+/// GuardedBy attributes (e.g., guarded_by):
+///   AttrName '(' expression ')'
+void Parser::ParseGuardedByAttribute(IdentifierInfo &AttrName,
+                                     SourceLocation AttrNameLoc,
+                                     ParsedAttributes &Attrs,
+                                     IdentifierInfo *ScopeName,
+                                     SourceLocation ScopeLoc,
+                                     SourceLocation *EndLoc,
+                                     ParsedAttr::Form Form) {
+  assert(Tok.is(tok::l_paren) && "Attribute arg list not starting with '('");
+
+  BalancedDelimiterTracker Parens(*this, tok::l_paren);
+  Parens.consumeOpen();
+
+  if (Tok.is(tok::r_paren)) {
+    Diag(Tok.getLocation(), diag::err_argument_required_after_attribute);
+    Parens.consumeClose();
+    return;
+  }
+
+  ArgsVector ArgExprs;
+  // Don't evaluate argument when the attribute is ignored.
+  using ExpressionKind =
+      Sema::ExpressionEvaluationContextRecord::ExpressionKind;
+  EnterExpressionEvaluationContext EC(
+      Actions, Sema::ExpressionEvaluationContext::PotentiallyEvaluated, nullptr,
+      ExpressionKind::EK_BoundsAttrArgument);
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pdherbemont wrote:

I am looking for guidance here: should I introduce a new `ExpressionKind` for `GuardedByAttr`, or simply rename it?

https://github.com/llvm/llvm-project/pull/94216