[clang] [clang] Fix a bug with qualified name lookup into current instantiation (PR #73018)

[Mariya Podchishchaeva via cfe-commits]

https://github.com/Fznamznon created https://github.com/llvm/llvm-project/pull/73018

Due to d0d2ee0e4bbe915d649e983c12d37bcfcf58823c clang doesn't perform qualified name lookup into the current instantiation when it has dependent bases, because of that `getTypeName` call always returns null for unknown specialization case. When there is a `typename` keyword, `DependentNameType` is constructed instead of simply returning null.
This change attempts to do the same in case of `typename` absence.

Fixes https://github.com/llvm/llvm-project/issues/13826

>From 0275f3ea777750b3f410d2132d61ea406131de6c Mon Sep 17 00:00:00 2001
From: "Podchishchaeva, Mariya" <mariya.podchishchaeva at intel.com>
Date: Tue, 21 Nov 2023 08:32:36 -0800
Subject: [PATCH] [clang] Fix a bug with qualified name lookup into current
 instantiation

Due to d0d2ee0e4bbe915d649e983c12d37bcfcf58823c clang doesn't perform qualified
name lookup into the current instantiation when it has dependent bases, because
of that `getTypeName` call always returns null for unknown specialization case.
When there is a `typename` keyword, `DependentNameType` is constructed instead
of simply returning null.
This change attempts to do the same in case of `typename` absence.

Fixes https://github.com/llvm/llvm-project/issues/13826
---
 clang/docs/ReleaseNotes.rst                   |  3 +++
 clang/lib/Sema/SemaDecl.cpp                   | 20 ++++++++++++++++---
 .../SemaTemplate/dependent-base-classes.cpp   | 14 +++++++++++++
 3 files changed, 34 insertions(+), 3 deletions(-)

diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index 157afd9e8629152..09ceb591d06eab5 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -610,6 +610,9 @@ Bug Fixes in This Version
   inside a lambda. (`#61460 <https://github.com/llvm/llvm-project/issues/61460>`_)
 - Fix crash during instantiation of some class template specializations within class
   templates. Fixes (`#70375 <https://github.com/llvm/llvm-project/issues/70375>`_)
+- Fixed false positive error emitted by clang when performing qualified name
+  lookup and the current class instantiation has dependent bases.
+  Fixes (`#13826 <https://github.com/llvm/llvm-project/issues/13826>`_)
 
 Bug Fixes to Compiler Builtins
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
diff --git a/clang/lib/Sema/SemaDecl.cpp b/clang/lib/Sema/SemaDecl.cpp
index 4e1857b931cc868..71003c1815c90e4 100644
--- a/clang/lib/Sema/SemaDecl.cpp
+++ b/clang/lib/Sema/SemaDecl.cpp
@@ -442,7 +442,6 @@ ParsedType Sema::getTypeName(const IdentifierInfo &II, SourceLocation NameLoc,
   UsingShadowDecl *FoundUsingShadow = nullptr;
   switch (Result.getResultKind()) {
   case LookupResult::NotFound:
-  case LookupResult::NotFoundInCurrentInstantiation:
     if (CorrectedII) {
       TypeNameValidatorCCC CCC(/*AllowInvalid=*/true, isClassName,
                                AllowDeducedTemplate);
@@ -482,8 +481,23 @@ ParsedType Sema::getTypeName(const IdentifierInfo &II, SourceLocation NameLoc,
         }
       }
     }
-    // If typo correction failed or was not performed, fall through
-    [[fallthrough]];
+    Result.suppressDiagnostics();
+    return nullptr;
+  case LookupResult::NotFoundInCurrentInstantiation: {
+    if (AllowImplicitTypename == ImplicitTypenameContext::Yes) {
+      QualType T;
+      T = Context.getDependentNameType(ElaboratedTypeKeyword::None,
+                                       SS->getScopeRep(), &II);
+      TypeLocBuilder TLB;
+      DependentNameTypeLoc TL = TLB.push<DependentNameTypeLoc>(T);
+      TL.setElaboratedKeywordLoc(SourceLocation());
+      TL.setQualifierLoc(SS->getWithLocInContext(Context));
+      TL.setNameLoc(NameLoc);
+      return CreateParsedType(T, TLB.getTypeSourceInfo(Context, T));
+    }
+    Result.suppressDiagnostics();
+    return nullptr;
+  }
   case LookupResult::FoundOverloaded:
   case LookupResult::FoundUnresolvedValue:
     Result.suppressDiagnostics();
diff --git a/clang/test/SemaTemplate/dependent-base-classes.cpp b/clang/test/SemaTemplate/dependent-base-classes.cpp
index 09f475f8bde9183..92a37efaa7e73f6 100644
--- a/clang/test/SemaTemplate/dependent-base-classes.cpp
+++ b/clang/test/SemaTemplate/dependent-base-classes.cpp
@@ -130,3 +130,17 @@ namespace PR5812 {
 
   Derived<int> di;
 }
+
+namespace GH13826 {
+template <typename T> struct A {
+  typedef int type;
+  struct B;
+};
+
+template <typename T> struct A<T>::B : A<T> {
+  B::type t;
+};
+
+A<int> a;
+A<int>::B b;
+}