[clang] 4556813 - [Sema] Use lexical DC for friend functions when getting constraint instantiation args (#77552)

[via cfe-commits]

Author: antangelo
Date: 2024-01-12T09:02:01-05:00
New Revision: 45568135cbb31bb3b345a8355134970742248120

URL: https://github.com/llvm/llvm-project/commit/45568135cbb31bb3b345a8355134970742248120
DIFF: https://github.com/llvm/llvm-project/commit/45568135cbb31bb3b345a8355134970742248120.diff

LOG: [Sema] Use lexical DC for friend functions when getting constraint instantiation args (#77552)

Fixes a crash where the template argument depth computed in the semantic
context for a friend FunctionDecl with a constrained parameter is
compared against arguments in the lexical context for the purpose of
checking if the constraint depends on enclosing template parameters.

Since getTemplateInstantiationArgs in this case follows the semantic DC
for friend FunctionDecls, the resulting depth is incorrect and trips an
assertion.

Fixes #75426

Added: 
    clang/test/SemaTemplate/GH75426.cpp

Modified: 
    clang/docs/ReleaseNotes.rst
    clang/lib/Sema/SemaTemplateInstantiate.cpp

Removed: 
    


################################################################################
diff  --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index 4aba054e252af2..10e426a30d98f9 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -723,6 +723,10 @@ Bug Fixes in This Version
 - Clang now emits correct source location for code-coverage regions in `if constexpr`
   and `if consteval` branches.
   Fixes (`#54419 <https://github.com/llvm/llvm-project/issues/54419>`_)
+- Fix assertion failure when declaring a template friend function with
+  a constrained parameter in a template class that declares a class method
+  or lambda at 
diff erent depth.
+  Fixes (`#75426 <https://github.com/llvm/llvm-project/issues/75426>`_)
 - Fix an issue where clang cannot find conversion function with template
   parameter when instantiation of template class.
   Fixes (`#77583 <https://github.com/llvm/llvm-project/issues/77583>`_)

diff  --git a/clang/lib/Sema/SemaTemplateInstantiate.cpp b/clang/lib/Sema/SemaTemplateInstantiate.cpp
index 7f20413c104e97..fc80515b45e35b 100644
--- a/clang/lib/Sema/SemaTemplateInstantiate.cpp
+++ b/clang/lib/Sema/SemaTemplateInstantiate.cpp
@@ -223,6 +223,9 @@ Response HandleFunction(const FunctionDecl *Function,
       (!Pattern || !Pattern->getLexicalDeclContext()->isFileContext())) {
     return Response::ChangeDecl(Function->getLexicalDeclContext());
   }
+
+  if (ForConstraintInstantiation && Function->getFriendObjectKind())
+    return Response::ChangeDecl(Function->getLexicalDeclContext());
   return Response::UseNextDecl(Function);
 }
 

diff  --git a/clang/test/SemaTemplate/GH75426.cpp b/clang/test/SemaTemplate/GH75426.cpp
new file mode 100644
index 00000000000000..faf70699f9c5f0
--- /dev/null
+++ b/clang/test/SemaTemplate/GH75426.cpp
@@ -0,0 +1,16 @@
+// RUN: %clang_cc1 -std=c++20 -fsyntax-only -verify %s
+// expected-no-diagnostics
+
+template<typename T> concept C = true;
+
+struct A {
+    template<C T> void f();
+};
+
+auto L = []<C T>{};
+
+template<typename X>
+class Friends {
+    template<C T> friend void A::f();
+    template<C T> friend void decltype(L)::operator()();
+};