Correct behavior for default mem-initializers used by inherited ctors.

Author: katzdm

clang/lib/AST/ExprConstantMeta.cpp

@@ -989,6 +989,9 @@ static bool getParameterName(ParmVarDecl *PVD, std::string &Out) {
   StringRef FirstNameSeen = PVD->getName();
   unsigned ParamIdx = PVD->getFunctionScopeIndex();
 
+  // TODO(P2996): This will crash if we're in the trailing requires-clause of
+  // a function declaration, since the DeclContext is not the function but the
+  // TranslationUnitDecl.
   FunctionDecl *FD = cast<FunctionDecl>(PVD->getDeclContext());
   FD = FD->getMostRecentDecl();
 
@@ -1019,6 +1022,9 @@ static bool getParameterName(ParmVarDecl *PVD, std::string &Out) {
 }
 
 static ParmVarDecl *getMostRecentParmVarDecl(ParmVarDecl *PVD) {
+  // TODO(P2996): This will crash if we're in the trailing requires-clause of
+  // a function declaration, since the DeclContext is not the function but the
+  // TranslationUnitDecl.
   FunctionDecl *FD = cast<FunctionDecl>(PVD->getDeclContext());
   FD = FD->getMostRecentDecl();
   return FD->getParamDecl(PVD->getFunctionScopeIndex());
@@ -5570,14 +5576,22 @@ bool current_access_context(APValue &Result, ASTContext &C, MetaActions &Meta,
                             SourceRange Range, ArrayRef<Expr *> Args,
                             Decl *ContainingDecl) {
   assert(ResultTy == C.MetaInfoTy);
+  Decl *Ctx = nullptr;
 
   StackLocationExpr *SLE = StackLocationExpr::Create(C, SourceRange(), 1);
-  if (!Evaluator(Result, SLE, true) || !Result.isReflection())
+  if (!Evaluator(Result, SLE, true) || !Result.isReflectedDecl())
     return true;
-  else if (Result.getReflectedDecl() != nullptr)
-    return false;
+  else if (Ctx = Result.getReflectedDecl(); !Ctx)
+    Ctx = Meta.CurrentCtx();
+
+  if (auto *Ctor = dyn_cast<CXXConstructorDecl>(Ctx);
+      Ctor && Ctor->isInheritingConstructor())
+    Ctx = cast<Decl>(Ctor->getDeclContext());
 
-  return SetAndSucceed(Result, makeReflection(Meta.CurrentCtx()));
+  if (auto *RD = dyn_cast<CXXRecordDecl>(Ctx))
+    return SetAndSucceed(Result,
+                         makeReflection(QualType(RD->getTypeForDecl(), 0)));
+  return SetAndSucceed(Result, makeReflection(Ctx));
 }
 
 bool is_accessible(APValue &Result, ASTContext &C, MetaActions &Meta,

clang/lib/Sema/SemaReflect.cpp

@@ -26,6 +26,7 @@
 #include "clang/Sema/Template.h"
 #include "clang/Sema/TemplateDeduction.h"
 #include "llvm/Support/raw_ostream.h"
+#include <iostream>
 
 using namespace clang;
 using namespace sema;

libcxx/test/std/experimental/reflection/member-visibility.pass.cpp

@@ -339,4 +339,22 @@ static_assert(is_accessible(^^a,
               std::meta::access_context::unprivileged()));
 }  // namespace anonymous_structs_unions
 
+                          // ========================
+                          // default_mem_initializers
+                          // ========================
+
+namespace default_mem_initializers {
+struct A {
+  int a;
+  consteval A(int p) : a(p) {}
+};
+struct B : A {
+  using A::A;
+  consteval B(int p, int q) : A(p * q) {}
+  std::meta::info s = std::meta::access_context::current().scope();
+};
+static_assert(B(1).s == ^^B);
+static_assert(is_constructor(B{1, 2}.s) && parent_of(B{1, 2}.s) == ^^B);
+}  // namespace default_mem_initializers
+
 int main() { }