From 77975524be1927008b87bbb15a5a09fd091cb85b Mon Sep 17 00:00:00 2001
From: Egor Zhdan <e_zhdan@apple.com>
Date: Tue, 19 Aug 2025 17:24:04 +0100
Subject: [PATCH] [cxx-interop] Do not import partial specializations of
 variables

They do not get imported correctly and trigger linker errors.

rdar://149232900 / resolves https://github.com/swiftlang/swift/issues/80802
---
 lib/ClangImporter/ImportDecl.cpp                             | 5 +++++
 test/ClangImporter/const_values_cxx.swift                    | 3 ---
 test/Interop/Cxx/templates/Inputs/module.modulemap           | 5 +++++
 test/Interop/Cxx/templates/Inputs/variable-template.h        | 5 +++++
 .../Cxx/templates/variable-template-typechecker.swift        | 5 +++++
 5 files changed, 20 insertions(+), 3 deletions(-)
 create mode 100644 test/Interop/Cxx/templates/Inputs/variable-template.h
 create mode 100644 test/Interop/Cxx/templates/variable-template-typechecker.swift

diff --git a/lib/ClangImporter/ImportDecl.cpp b/lib/ClangImporter/ImportDecl.cpp
index 096c8d7315876..40f44f97cf2d8 100644
--- a/lib/ClangImporter/ImportDecl.cpp
+++ b/lib/ClangImporter/ImportDecl.cpp
@@ -4638,6 +4638,11 @@ namespace {
       return result;
     }
 
+    Decl *VisitVarTemplatePartialSpecializationDecl(
+        const clang::VarTemplatePartialSpecializationDecl *decl) {
+      return nullptr;
+    }
+
     Decl *VisitImplicitParamDecl(const clang::ImplicitParamDecl *decl) {
       // Parameters are never directly imported.
       return nullptr;
diff --git a/test/ClangImporter/const_values_cxx.swift b/test/ClangImporter/const_values_cxx.swift
index 3283d68e19e97..e1a0c75502444 100644
--- a/test/ClangImporter/const_values_cxx.swift
+++ b/test/ClangImporter/const_values_cxx.swift
@@ -55,9 +55,6 @@ func foo() {
 
   print(MyClass().class_const_int)
   print(MyClass.class_static_const_int)
-
-  // TODO: This seems to be incorrectly imported, this test here is just to check that the compiler doesn't crash.
-  print(template_gcd)
 }
 
 // Only imported as external declarations:
diff --git a/test/Interop/Cxx/templates/Inputs/module.modulemap b/test/Interop/Cxx/templates/Inputs/module.modulemap
index b2764d9204b53..88d4bdd22085f 100644
--- a/test/Interop/Cxx/templates/Inputs/module.modulemap
+++ b/test/Interop/Cxx/templates/Inputs/module.modulemap
@@ -177,3 +177,8 @@ module UninstantiatableSpecialMembers {
   header "uninstantiatable-special-members.h"
   requires cplusplus
 }
+
+module VariableTemplate {
+  header "variable-template.h"
+  requires cplusplus
+}
diff --git a/test/Interop/Cxx/templates/Inputs/variable-template.h b/test/Interop/Cxx/templates/Inputs/variable-template.h
new file mode 100644
index 0000000000000..ffe1432a24199
--- /dev/null
+++ b/test/Interop/Cxx/templates/Inputs/variable-template.h
@@ -0,0 +1,5 @@
+template <int N, int M>
+inline const int template_gcd = template_gcd<M, N % M>;
+
+template <int N>
+inline const int template_gcd<N, 0> = N;
diff --git a/test/Interop/Cxx/templates/variable-template-typechecker.swift b/test/Interop/Cxx/templates/variable-template-typechecker.swift
new file mode 100644
index 0000000000000..3e628d34b1873
--- /dev/null
+++ b/test/Interop/Cxx/templates/variable-template-typechecker.swift
@@ -0,0 +1,5 @@
+// RUN: %target-typecheck-verify-swift -cxx-interoperability-mode=default -I %S/Inputs
+
+import VariableTemplate
+
+let _: CInt = template_gcd // expected-error {{cannot find 'template_gcd' in scope}}