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

[Aaron Ballman via cfe-commits]

================
@@ -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);
+
+  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 = Tok.getLocation();
+  }
----------------
AaronBallman wrote:

```suggestion
  if (EndLoc)
     *EndLoc = Tok.getLocation();
```

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