Revert "[clang] Substitute alias templates from correct context (llvm#75069)"

This reverts commit dbf67ea.

It caused spurious "out-of-line definition of 'operator=' does not match
any declaration in" error.
llvm#75069 (comment)

Author: MaskRay

clang/docs/ReleaseNotes.rst

@@ -685,9 +685,6 @@ Bug Fixes in This Version
   (`#62157 <https://github.com/llvm/llvm-project/issues/62157>`_) and
   (`#64885 <https://github.com/llvm/llvm-project/issues/64885>`_) and
   (`#65568 <https://github.com/llvm/llvm-project/issues/65568>`_)
-- Fixed false positive error emitted when templated alias inside a class
-  used private members of the same class.
-  Fixes (`#41693 <https://github.com/llvm/llvm-project/issues/41693>`_)
 
 Bug Fixes to Compiler Builtins
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

clang/include/clang/Sema/Sema.h

@@ -8737,7 +8737,7 @@ class Sema final {
                              SourceLocation IILoc,
                              bool DeducedTSTContext = true);
 
-  bool RebuildingTypesInCurrentInstantiation = false;
+
   TypeSourceInfo *RebuildTypeInCurrentInstantiation(TypeSourceInfo *T,
                                                     SourceLocation Loc,
                                                     DeclarationName Name);

clang/lib/Sema/SemaCXXScopeSpec.cpp

@@ -30,33 +30,17 @@ static CXXRecordDecl *getCurrentInstantiationOf(QualType T,
     return nullptr;
 
   const Type *Ty = T->getCanonicalTypeInternal().getTypePtr();
-  if (isa<TemplateSpecializationType>(Ty)) {
-    if (auto *Record = dyn_cast<CXXRecordDecl>(CurContext)) {
-      if (isa<ClassTemplatePartialSpecializationDecl>(Record) ||
-          Record->getDescribedClassTemplate()) {
-        const Type *ICNT = Record->getTypeForDecl();
-        QualType Injected =
-            cast<InjectedClassNameType>(ICNT)->getInjectedSpecializationType();
-
-        if (Ty == Injected->getCanonicalTypeInternal().getTypePtr())
-          return Record;
-      }
-    }
-  }
-
   if (const RecordType *RecordTy = dyn_cast<RecordType>(Ty)) {
     CXXRecordDecl *Record = cast<CXXRecordDecl>(RecordTy->getDecl());
     if (!Record->isDependentContext() ||
         Record->isCurrentInstantiation(CurContext))
       return Record;
 
     return nullptr;
-  }
-
-  if (auto *ICNT = dyn_cast<InjectedClassNameType>(Ty))
-    return ICNT->getDecl();
-
-  return nullptr;
+  } else if (isa<InjectedClassNameType>(Ty))
+    return cast<InjectedClassNameType>(Ty)->getDecl();
+  else
+    return nullptr;
 }
 
 /// Compute the DeclContext that is associated with the given type.

clang/lib/Sema/SemaTemplate.cpp

@@ -39,7 +39,6 @@
 #include "llvm/ADT/SmallBitVector.h"
 #include "llvm/ADT/SmallString.h"
 #include "llvm/ADT/StringExtras.h"
-#include "llvm/Support/SaveAndRestore.h"
 
 #include <iterator>
 #include <optional>
@@ -3991,14 +3990,9 @@ QualType Sema::CheckTemplateIdType(TemplateName Name,
     if (Inst.isInvalid())
       return QualType();
 
-    {
-      Sema::ContextRAII SavedContext(*this, Pattern->getDeclContext());
-      if (RebuildingTypesInCurrentInstantiation)
-        SavedContext.pop();
-      CanonType =
-          SubstType(Pattern->getUnderlyingType(), TemplateArgLists,
-                    AliasTemplate->getLocation(), AliasTemplate->getDeclName());
-    }
+    CanonType = SubstType(Pattern->getUnderlyingType(),
+                          TemplateArgLists, AliasTemplate->getLocation(),
+                          AliasTemplate->getDeclName());
     if (CanonType.isNull()) {
       // If this was enable_if and we failed to find the nested type
       // within enable_if in a SFINAE context, dig out the specific
@@ -11398,8 +11392,6 @@ TypeSourceInfo *Sema::RebuildTypeInCurrentInstantiation(TypeSourceInfo *T,
   if (!T || !T->getType()->isInstantiationDependentType())
     return T;
 
-  llvm::SaveAndRestore DisableContextSwitchForTypeAliases(
-      RebuildingTypesInCurrentInstantiation, true);
   CurrentInstantiationRebuilder Rebuilder(*this, Loc, Name);
   return Rebuilder.TransformType(T);
 }

clang/test/CXX/temp/temp.decls/temp.alias/p3.cpp

@@ -2,12 +2,11 @@
 
 // The example given in the standard (this is rejected for other reasons anyway).
 template<class T> struct A;
-template<class T> using B = typename A<T>::U; // expected-error {{no type named 'U' in 'A<short>'}}
-                                              // expected-note@-1 {{in instantiation of template class 'A<short>' requested here}}
+template<class T> using B = typename A<T>::U; // expected-error {{no type named 'U' in 'A<T>'}}
 template<class T> struct A {
   typedef B<T> U; // expected-note {{in instantiation of template type alias 'B' requested here}}
 };
-B<short> b; // expected-note {{in instantiation of template type alias 'B' requested here}}
+B<short> b;
 
 template<typename T> using U = int;
 

clang/test/SemaCXX/alias-template.cpp

@@ -192,68 +192,3 @@ int g = sfinae_me<int>(); // expected-error{{no matching function for call to 's
 namespace NullExceptionDecl {
 template<int... I> auto get = []() { try { } catch(...) {}; return I; }; // expected-error{{initializer contains unexpanded parameter pack 'I'}}
 }
-
-namespace GH41693 {
-// No errors when a type alias defined in a class or a friend of a class
-// accesses private members of the same class.
-struct S {
-private:
-  template <typename> static constexpr void Impl() {}
-
-public:
-  template <typename X> using U = decltype(Impl<X>());
-};
-
-using X = S::U<void>;
-struct Y {
-private:
-  static constexpr int x=0;
-
-  template <typename>
-  static constexpr int y=0;
-
-  template <typename>
-  static constexpr int foo();
-
-public:
-  template <typename U>
-  using bar1 = decltype(foo<U>());
-  using bar2 = decltype(x);
-  template <typename U>
-  using bar3 = decltype(y<U>);
-};
-
-
-using type1 = Y::bar1<float>;
-using type2 = Y::bar2;
-using type3 = Y::bar3<float>;
-
-struct theFriend{
-  template<class T>
-  using theAlias = decltype(&T::i);
-};
-
-class theC{
-  int i;
-  public:
-  friend struct theFriend;
-};
-
-int foo(){
-  (void)sizeof(theFriend::theAlias<theC>);
-}
-
-// Test case that regressed with the first iteration of the fix for GH41693.
-template <typename T> class SP {
-    T* data;
-};
-
-template <typename T> class A {
-    static SP<A> foo();
-};
-
-template<typename T> using TRet = SP<A<T>>;
-
-template<typename T> TRet<T> A<T>::foo() { return TRet<T>{};};
-
-}