[clang] [Clang][Sema] Allow access to a public template alias declaration that refers to friend's private nested type (PR #83847)

[Qizhi Hu via cfe-commits]

https://github.com/jcsxky updated https://github.com/llvm/llvm-project/pull/83847

>From 8541506bdbe26b9f24e47e5a372fe89124eaff47 Mon Sep 17 00:00:00 2001
From: huqizhi <huqizhi at feysh.com>
Date: Mon, 4 Mar 2024 21:51:07 +0800
Subject: [PATCH] [Clang][Sema] Allow access to a public template alias
 declaration that refers to friend's private nested type

---
 clang/docs/ReleaseNotes.rst         |  6 +++++-
 clang/lib/Sema/SemaTemplate.cpp     | 13 ++++++++++---
 clang/test/SemaTemplate/PR25708.cpp | 23 +++++++++++++++++++++++
 3 files changed, 38 insertions(+), 4 deletions(-)
 create mode 100644 clang/test/SemaTemplate/PR25708.cpp

diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index f61dca9bbc8467..b015367329194c 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -259,6 +259,10 @@ Bug Fixes in This Version
   operator.
   Fixes (#GH83267).
 
+- Allow access to a public template alias declaration that refers to friend's
+  private nested type.
+  Fixes (#GH25708).
+
 Bug Fixes to Compiler Builtins
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
@@ -409,7 +413,7 @@ RISC-V Support
 CUDA/HIP Language Changes
 ^^^^^^^^^^^^^^^^^^^^^^^^^
 
-- PTX is no longer included by default when compiling for CUDA. Using 
+- PTX is no longer included by default when compiling for CUDA. Using
   ``--cuda-include-ptx=all`` will return the old behavior.
 
 CUDA Support
diff --git a/clang/lib/Sema/SemaTemplate.cpp b/clang/lib/Sema/SemaTemplate.cpp
index d62095558d0ffb..4981aa7c5fc739 100644
--- a/clang/lib/Sema/SemaTemplate.cpp
+++ b/clang/lib/Sema/SemaTemplate.cpp
@@ -4342,10 +4342,17 @@ QualType Sema::CheckTemplateIdType(TemplateName Name,
     InstantiatingTemplate Inst(*this, TemplateLoc, Template);
     if (Inst.isInvalid())
       return QualType();
+    if (!AliasTemplate->getDeclContext()->isFileContext()) {
+      ContextRAII SavedContext(*this, AliasTemplate->getDeclContext());
+      CanonType =
+          SubstType(Pattern->getUnderlyingType(), TemplateArgLists,
+                    AliasTemplate->getLocation(), AliasTemplate->getDeclName());
+    } else {
 
-    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
diff --git a/clang/test/SemaTemplate/PR25708.cpp b/clang/test/SemaTemplate/PR25708.cpp
new file mode 100644
index 00000000000000..cc2e7551a6abaa
--- /dev/null
+++ b/clang/test/SemaTemplate/PR25708.cpp
@@ -0,0 +1,23 @@
+// RUN: %clang_cc1 -std=c++11 -verify %s
+// RUN: %clang_cc1 -std=c++14 -verify %s
+// RUN: %clang_cc1 -std=c++17 -verify %s
+// RUN: %clang_cc1 -std=c++20 -verify %s
+// expected-no-diagnostics
+
+struct FooAccessor
+{
+    template <typename T>
+    using Foo = typename T::Foo;
+};
+
+class Type
+{
+    friend struct FooAccessor;
+
+    using Foo = int;
+};
+
+int main()
+{
+    FooAccessor::Foo<Type> t;
+}