[clang][modules] Re-add the unit test from #121245.

Author: mpark

clang/test/Modules/pr121245.cpp

@@ -0,0 +1,93 @@
+// If this test fails, it should be investigated under Debug builds.
+// Before the PR, this test was encountering an `llvm_unreachable()`.
+
+// RUN: rm -rf %t
+// RUN: mkdir -p %t
+// RUN: split-file %s %t
+// RUN: cd %t
+
+// RUN: %clang_cc1 -std=c++20 -emit-header-unit -xc++-user-header %t/hu-01.h \
+// RUN:  -fcxx-exceptions -o %t/hu-01.pcm
+
+// RUN: %clang_cc1 -std=c++20 -emit-header-unit -xc++-user-header %t/hu-02.h \
+// RUN:  -Wno-experimental-header-units -fcxx-exceptions \
+// RUN:  -fmodule-file=%t/hu-01.pcm -o %t/hu-02.pcm
+
+// RUN: %clang_cc1 -std=c++20 -emit-header-unit -xc++-user-header %t/hu-03.h \
+// RUN:  -Wno-experimental-header-units -fcxx-exceptions \
+// RUN:  -fmodule-file=%t/hu-01.pcm -o %t/hu-03.pcm
+
+// RUN: %clang_cc1 -std=c++20 -emit-header-unit -xc++-user-header %t/hu-04.h \
+// RUN:  -Wno-experimental-header-units -fcxx-exceptions \
+// RUN:  -fmodule-file=%t/hu-01.pcm -o %t/hu-04.pcm
+
+// RUN: %clang_cc1 -std=c++20 -emit-header-unit -xc++-user-header %t/hu-05.h \
+// RUN:  -Wno-experimental-header-units -fcxx-exceptions \
+// RUN:  -fmodule-file=%t/hu-03.pcm -fmodule-file=%t/hu-04.pcm \
+// RUN:  -fmodule-file=%t/hu-01.pcm -o %t/hu-05.pcm
+
+// RUN: %clang_cc1 -std=c++20 -emit-obj %t/main.cpp \
+// RUN:  -Wno-experimental-header-units -fcxx-exceptions \
+// RUN:  -fmodule-file=%t/hu-02.pcm -fmodule-file=%t/hu-05.pcm \
+// RUN:  -fmodule-file=%t/hu-04.pcm -fmodule-file=%t/hu-03.pcm \
+// RUN:  -fmodule-file=%t/hu-01.pcm
+
+//--- hu-01.h
+template <typename T>
+struct A {
+  A() {}
+  ~A() {}
+};
+
+template <typename T>
+struct EBO : T {
+  EBO() = default;
+};
+
+template <typename T>
+struct HT : EBO<A<T>> {};
+
+//--- hu-02.h
+import "hu-01.h";
+
+inline void f() {
+  HT<int>();
+}
+
+//--- hu-03.h
+import "hu-01.h";
+
+struct C {
+  C();
+
+  HT<long> _;
+};
+
+//--- hu-04.h
+import "hu-01.h";
+
+void g(HT<long> = {});
+
+//--- hu-05.h
+import "hu-03.h";
+import "hu-04.h";
+import "hu-01.h";
+
+struct B {
+  virtual ~B() = default;
+
+  virtual void f() {
+    HT<long>();
+  }
+};
+
+//--- main.cpp
+import "hu-02.h";
+import "hu-05.h";
+import "hu-03.h";
+
+int main() {
+  f();
+  C();
+  B();
+}