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

[Dan Liew via cfe-commits]

================
@@ -3330,6 +3340,112 @@ 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_AttrArgument);
+
+  ExprResult ArgExpr(
+      Actions.CorrectDelayedTyposInExpr(ParseAssignmentExpression()));
+
+  if (ArgExpr.isInvalid()) {
+    Parens.skipToEnd();
+    return;
+  }
+
+  ArgExprs.push_back(ArgExpr.get());
+
+  auto RParens = Tok.getLocation();
+  auto &AL =
+      *Attrs.addNew(&AttrName, SourceRange(AttrNameLoc, RParens), ScopeName,
+                    ScopeLoc, ArgExprs.data(), ArgExprs.size(), Form);
+
+  if (EndLoc)
+    *EndLoc = RParens;
+
+  if (!Tok.is(tok::r_paren)) {
+    Diag(Tok.getLocation(), diag::err_attribute_wrong_number_arguments)
----------------
delcypher wrote:

@pdherbemont Could you add a test case for this path?

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