[tests] Provide unittest/example for API dispatch mechanism

to be followed up with a section in docs

Author: aaronj0

unittests/CppInterOp/CMakeLists.txt

@@ -11,6 +11,14 @@ else()
   set(EXTRA_PATH_TEST_BINARIES /CppInterOpTests/unittests/bin/$<CONFIG>/)
 endif()
 
+# Add the DispatchAPITest only when building shared libraries
+if (BUILD_SHARED_LIBS)
+  set_source_files_properties(DispatchAPITest.cpp PROPERTIES COMPILE_DEFINITIONS
+    "CPPINTEROP_LIB_DIR=\"${CMAKE_BINARY_DIR}/lib/libclangCppInterOp${CMAKE_SHARED_LIBRARY_SUFFIX}\""
+  )
+  list(APPEND EXTRA_TEST_SOURCE_FILES DispatchAPITest.cpp)
+endif()
+
 add_cppinterop_unittest(CppInterOpTests
   EnumReflectionTest.cpp
   FunctionReflectionTest.cpp

unittests/CppInterOp/DispatchAPITest.cpp

@@ -0,0 +1,67 @@
+#include "Utils.h"
+
+#include "CppInterOp/CppInterOpDispatch.h"
+
+#include "gtest/gtest.h"
+
+#include <dlfcn.h>
+
+using namespace TestUtils;
+using namespace llvm;
+using namespace clang;
+
+static void* dlGetProcAddress(const char* name) {
+  static void* handle = dlopen(CPPINTEROP_LIB_DIR, RTLD_LAZY | RTLD_LOCAL);
+  EXPECT_NE(handle, nullptr) << "Failed to open library: " << dlerror();
+  if (!handle)
+    return nullptr;
+  static void* gpa = dlsym(handle, "CppGetProcAddress");
+  EXPECT_NE(gpa, nullptr) << "Failed to find GetProcAddress: " << dlerror();
+  return reinterpret_cast<void* (*)(const char*)>(gpa)(name);
+}
+
+TEST(DispatchAPITestTest, IsClassSymbolLookup) {
+  CppAPIType::IsClass IsClassFn =
+      reinterpret_cast<CppAPIType::IsClass>(dlGetProcAddress("IsClass"));
+  ASSERT_NE(IsClassFn, nullptr) << "failed to locate symbol: " << dlerror();
+  std::vector<Decl*> Decls;
+  GetAllTopLevelDecls("namespace N {} class C{}; int I;", Decls);
+  EXPECT_FALSE(IsClassFn(Decls[0]));
+  EXPECT_TRUE(IsClassFn(Decls[1]));
+  EXPECT_FALSE(IsClassFn(Decls[2]));
+}
+
+TEST(DispatchAPITestTest, Demangle) {
+
+  std::string code = R"(
+    int add(int x, int y) { return x + y; }
+    int add(double x, double y) { return x + y; }
+  )";
+
+  std::vector<Decl*> Decls;
+  GetAllTopLevelDecls(code, Decls);
+  EXPECT_EQ(Decls.size(), 2);
+
+  auto Add_int = clang::GlobalDecl(static_cast<clang::NamedDecl*>(Decls[0]));
+  auto Add_double = clang::GlobalDecl(static_cast<clang::NamedDecl*>(Decls[1]));
+
+  std::string mangled_add_int;
+  std::string mangled_add_double;
+  compat::maybeMangleDeclName(Add_int, mangled_add_int);
+  compat::maybeMangleDeclName(Add_double, mangled_add_double);
+
+  // CppAPIType:: gives us the specific function pointer types
+  CppAPIType::Demangle DemangleFn =
+      reinterpret_cast<CppAPIType::Demangle>(dlGetProcAddress("Demangle"));
+  CppAPIType::GetQualifiedCompleteName GetQualifiedCompleteNameFn =
+      reinterpret_cast<CppAPIType::GetQualifiedCompleteName>(
+          dlGetProcAddress("GetQualifiedCompleteName"));
+
+  std::string demangled_add_int = DemangleFn(mangled_add_int);
+  std::string demangled_add_double = DemangleFn(mangled_add_double);
+
+  EXPECT_NE(demangled_add_int.find(GetQualifiedCompleteNameFn(Decls[0])),
+            std::string::npos);
+  EXPECT_NE(demangled_add_double.find(GetQualifiedCompleteNameFn(Decls[1])),
+            std::string::npos);
+}