[clang] Make CXXDefaultArgExpr inherit dependence from the inner Expr

[adamcz]

Summary

Before this change, CXXDefaultArgExpr would always have
ExprDependence::None. This can lead to issues when, for example, the
inner expression is RecoveryExpr and yet containsErrors() on the default
expression is false.

[hokein]

Thanks!

clang/include/clang/AST/ComputeDependence.h

 class CoroutineSuspendExpr;
 class DependentCoawaitExpr;
 class CXXNewExpr;
 class CXXPseudoDestructorExpr;
 class OverloadExpr;
 class DependentScopeDeclRefExpr;
 class CXXConstructExpr;
 class CXXDefaultInitExpr;
+class CXXDefaultArgExpr;
 class LambdaExpr;
 class CXXUnresolvedConstructExpr;
 class CXXDependentScopeMemberExpr;
 class MaterializeTemporaryExpr;
 class CXXFoldExpr;
 class TypeTraitExpr;
 class ConceptSpecializationExpr;
 class SYCLUniqueStableNameExpr;

 ExprDependence computeDependence(CXXNewExpr *E);
 ExprDependence computeDependence(CXXPseudoDestructorExpr *E);
 ExprDependence computeDependence(OverloadExpr *E, bool KnownDependent,
                                  bool KnownInstantiationDependent,
                                  bool KnownContainsUnexpandedParameterPack);
 ExprDependence computeDependence(DependentScopeDeclRefExpr *E);
 ExprDependence computeDependence(CXXConstructExpr *E);
 ExprDependence computeDependence(CXXDefaultInitExpr *E);
+ExprDependence computeDependence(CXXDefaultArgExpr *E);
 ExprDependence computeDependence(LambdaExpr *E,
                                  bool ContainsUnexpandedParameterPack);
 ExprDependence computeDependence(CXXUnresolvedConstructExpr *E);
 ExprDependence computeDependence(CXXDependentScopeMemberExpr *E);
 ExprDependence computeDependence(MaterializeTemporaryExpr *E);
 ExprDependence computeDependence(CXXFoldExpr *E);
 ExprDependence computeDependence(TypeTraitExpr *E);
 ExprDependence computeDependence(ConceptSpecializationExpr *E,

clang/include/clang/AST/ExprCXX.h

CXXDefaultArgExpr(StmtClass SC, SourceLocation Loc, ParmVarDecl *Param,
       : Expr(SC,
              Param->hasUnparsedDefaultArg()
                  ? Param->getType().getNonReferenceType()
                  : Param->getDefaultArg()->getType(),
              Param->getDefaultArg()->getValueKind(),
              Param->getDefaultArg()->getObjectKind()),
         Param(Param), UsedContext(UsedContext) {
     CXXDefaultArgExprBits.Loc = Loc;
-    setDependence(ExprDependence::None);
+    setDependence(computeDependence(this));
   }
 
 public:
   CXXDefaultArgExpr(EmptyShell Empty) : Expr(CXXDefaultArgExprClass, Empty) {}
 
   // \p Param is the parameter whose default argument is used by this
   // expression.
   static CXXDefaultArgExpr *Create(const ASTContext &C, SourceLocation Loc,

clang/lib/AST/ComputeDependence.cpp

for (auto *A : E->arguments())
     D |= A->getDependence() & ~ExprDependence::Type;
   return D;
 }
 
 ExprDependence clang::computeDependence(CXXDefaultInitExpr *E) {
   return E->getExpr()->getDependence();
 }
 
+ExprDependence clang::computeDependence(CXXDefaultArgExpr *E) {
+  return E->getExpr()->getDependence();
+}
+
 ExprDependence clang::computeDependence(LambdaExpr *E,
                                         bool ContainsUnexpandedParameterPack) {
   auto D = toExprDependence(E->getType()->getDependence());
   if (ContainsUnexpandedParameterPack)
     D |= ExprDependence::UnexpandedPack;
   return D;
 }
 

clang/test/AST/ast-dump-default-arg-dep.cpp

+// RUN: not %clang_cc1 -triple x86_64-unknown-unknown -fsyntax-only -ast-dump -frecovery-ast %s | FileCheck %s
+
+// CXXDefaultArgExpr should inherit dependence from the inner Expr, in this case
+// RecoveryExpr.
+void fun(int arg = foo());
+
+void test() {
+  fun();
+}
+// CHECK: -CXXDefaultArgExpr 0x{{[^ ]*}} <<invalid sloc>> '<dependent type>' contains-errors lvalue