Use split-file for the lit test

Author: hokein

clang/docs/ReleaseNotes.rst

@@ -256,6 +256,8 @@ Improvements to Clang's diagnostics
 
 - Improve the diagnostics for shadows template parameter to report correct location (#GH129060).
 
+- Improve the ``-Wundefined-func-template`` warning when a function template is not instantiated due to being unreachable in modules.
+
 Improvements to Clang's time-trace
 ----------------------------------
 

clang/lib/Sema/SemaTemplate.cpp

@@ -763,7 +763,7 @@ bool Sema::DiagnoseUninstantiableTemplate(
     SourceLocation PointOfInstantiation, NamedDecl *Instantiation,
     bool InstantiatedFromMember, const NamedDecl *Pattern,
     const NamedDecl *PatternDef, TemplateSpecializationKind TSK,
-    bool Complain /*= true*/, bool *Unreachable) {
+    bool Complain, bool *Unreachable) {
   assert(isa<TagDecl>(Instantiation) || isa<FunctionDecl>(Instantiation) ||
          isa<VarDecl>(Instantiation));
 

clang/test/Modules/Inputs/undefined-template/hoge.h

@@ -1,8 +1,37 @@
 // RUN: rm -rf %t
-// RUN: %clang_cc1 -std=c++20 -fmodules -fmodules-cache-path=%t -I%S/Inputs/undefined-template \
+// RUN: split-file %s %t
+// RUN: %clang_cc1 -std=c++20 -fmodules -fmodules-cache-path=%t -I%t \
 // RUN:   -Wundefined-func-template \
-// RUN:   -fimplicit-module-maps  %s 2>&1 | grep "unreachable declaration of template entity is her"
+// RUN:   -fimplicit-module-maps %t/main.cpp 2>&1 | grep "unreachable declaration of template entity is here"
 
+// Note that the diagnostics are triggered when building the 'hoge' module, which is imported from the main file.
+// The "-verify" flag doesn't work in this case. Instead, we grep the expected text to verify the test.
+
+//--- shared_ptr2.h
+#pragma once
+
+template<class T>
+void x() { }
+
+//--- hoge.h
+#pragma once
+
+#include "shared_ptr2.h"
+
+inline void f() {
+  x<int>();
+}
+
+//--- module.modulemap
+module hoge {
+  header "hoge.h"
+}
+
+module shared_ptr2 {
+  header "shared_ptr2.h"
+}
+
+//--- main.cpp
 #include "hoge.h"
 
 int main() {