[clang] Allow attributes on first constructor argument in pre-C++11 (#157300)

Resolves GH-156809

Modifies decl parser to allow C++11 style [[attributes]] on the first
argument in constructors in all C++ standards. They are already allowed
on later arguments.

---------

Co-authored-by: Shafik Yaghmour <[email protected]>

Author: camc

clang/docs/ReleaseNotes.rst

@@ -365,6 +365,8 @@ Bug Fixes to C++ Support
   authentication enabled. (#GH152601)
 - Fix the check for narrowing int-to-float conversions, so that they are detected in
   cases where converting the float back to an integer is undefined behaviour (#GH157067).
+- Stop rejecting C++11-style attributes on the first argument of constructors in older
+  standards. (#GH156809).
 - Fix a crash when applying binary or ternary operators to two same function types with different spellings,
   where at least one of the function parameters has an attribute which affects
   the function type.

clang/lib/Parse/ParseDecl.cpp

@@ -6007,10 +6007,9 @@ bool Parser::isConstructorDeclarator(bool IsUnqualified, bool DeductionGuide,
 
   // A C++11 attribute here signals that we have a constructor, and is an
   // attribute on the first constructor parameter.
-  if (getLangOpts().CPlusPlus11 &&
-      isCXX11AttributeSpecifier(/*Disambiguate*/ false,
-                                /*OuterMightBeMessageSend*/ true) !=
-          CXX11AttributeKind::NotAttributeSpecifier) {
+  if (isCXX11AttributeSpecifier(/*Disambiguate=*/false,
+                                /*OuterMightBeMessageSend=*/true) !=
+      CXX11AttributeKind::NotAttributeSpecifier) {
     return true;
   }
 

clang/test/Parser/cxx03-attributes.cpp

@@ -0,0 +1,6 @@
+// RUN: %clang_cc1 -fsyntax-only -verify -std=c++03 %s
+// expected-no-diagnostics
+
+struct S {
+    S([[clang::lifetimebound]] int&) {}
+};