[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 2bb165ac6264b36f72716cb35ed2e1b4f72f3eaa 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         |  3 +++
 clang/lib/Sema/SemaAccess.cpp       |  9 +++++++++
 clang/test/SemaTemplate/PR25708.cpp | 23 +++++++++++++++++++++++
 3 files changed, 35 insertions(+)
 create mode 100644 clang/test/SemaTemplate/PR25708.cpp

diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index 1b901a27fd19d1..38cbe421fd485c 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -241,6 +241,9 @@ Bug Fixes in This Version
   for variables created through copy initialization having side-effects in C++17 and later.
   Fixes (#GH64356) (#GH79518).
 
+- Allow access to a public template alias declaration that refers to friend's
+  private nested type (`#25708 <https://github.com/llvm/llvm-project/issues/25708>`).
+
 Bug Fixes to Compiler Builtins
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
diff --git a/clang/lib/Sema/SemaAccess.cpp b/clang/lib/Sema/SemaAccess.cpp
index 4af3c0f30a8e8a..0c8d15210f439c 100644
--- a/clang/lib/Sema/SemaAccess.cpp
+++ b/clang/lib/Sema/SemaAccess.cpp
@@ -1481,6 +1481,15 @@ static Sema::AccessResult CheckAccess(Sema &S, SourceLocation Loc,
   }
 
   EffectiveContext EC(S.CurContext);
+  if (!S.CodeSynthesisContexts.empty()) {
+    auto &Active = S.CodeSynthesisContexts.back();
+    if (Active.Kind == Sema::CodeSynthesisContext::TemplateInstantiation &&
+        Active.Entity)
+      if (auto *RD =
+              dyn_cast_or_null<CXXRecordDecl>(Active.Entity->getDeclContext()))
+        EC.Records.push_back(RD);
+  }
+
   switch (CheckEffectiveAccess(S, EC, Loc, Entity)) {
   case AR_accessible: return Sema::AR_accessible;
   case AR_inaccessible: return Sema::AR_inaccessible;
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;
+}