AutoGen: Add test to check for correct AutoMoc dependencies

When using Qt 5.15.0 or above together with Ninja, check that touching
a source file of a dependency does not needlessly re-run AUTOMOC for
the dependee target.

Tests/RunCMake/CMakeLists.txt

@@ -134,6 +134,9 @@ if(CMAKE_GENERATOR MATCHES "Ninja")
   if(CMAKE_Fortran_COMPILER)
     list(APPEND Ninja_ARGS -DTEST_Fortran=1)
   endif()
+  if(CMake_TEST_Qt5 AND Qt5Core_FOUND)
+    list(APPEND Ninja_ARGS -DCMake_TEST_Qt5=1 -DCMAKE_TEST_Qt5Core_Version=${Qt5Core_VERSION})
+  endif()
   add_RunCMake_test(Ninja)
   set(NinjaMultiConfig_ARGS
     -DCYGWIN=${CYGWIN}

Tests/RunCMake/Ninja/Qt5AutoMocDeps.cmake

@@ -0,0 +1,9 @@
+enable_language(CXX)
+
+find_package(Qt5Core REQUIRED)
+
+set(CMAKE_AUTOMOC ON)
+
+add_library(simple_lib SHARED simple_lib.cpp)
+add_executable(app_with_qt app.cpp app_qt.cpp)
+target_link_libraries(app_with_qt PRIVATE simple_lib Qt5::Core)

Tests/RunCMake/Ninja/RunCMakeTest.cmake

@@ -132,6 +132,7 @@ ${ninja_stderr}
     message(FATAL_ERROR
       "top ninja build failed exited with status ${ninja_result}")
   endif()
+  set(ninja_stdout "${ninja_stdout}" PARENT_SCOPE)
 endfunction(run_ninja)
 
 function (run_LooseObjectDepends)
@@ -316,3 +317,23 @@ function (run_ChangeBuildType)
   run_ninja("${RunCMake_TEST_BINARY_DIR}" -w dupbuild=err)
 endfunction()
 run_ChangeBuildType()
+
+function(run_Qt5AutoMocDeps)
+  if(CMake_TEST_Qt5 AND CMAKE_TEST_Qt5Core_Version VERSION_GREATER_EQUAL 5.15.0)
+    set(RunCMake_TEST_BINARY_DIR ${RunCMake_BINARY_DIR}/Qt5AutoMocDeps-build)
+    run_cmake(Qt5AutoMocDeps)
+    unset(RunCMake_TEST_OPTIONS)
+    # Build the project.
+    run_ninja("${RunCMake_TEST_BINARY_DIR}")
+    # Touch just the library source file, which shouldn't cause a rerun of AUTOMOC
+    # for app_with_qt target.
+    touch("${RunCMake_SOURCE_DIR}/simple_lib.cpp")
+    # Build and assert that AUTOMOC was not run for app_with_qt.
+    run_ninja("${RunCMake_TEST_BINARY_DIR}")
+    if(ninja_stdout MATCHES "Automatic MOC for target app_with_qt")
+        message(FATAL_ERROR
+               "AUTOMOC should not have executed for 'app_with_qt' target:\nstdout:\n${ninja_stdout}")
+    endif()
+  endif()
+endfunction()
+run_Qt5AutoMocDeps()

Tests/RunCMake/Ninja/app.cpp

@@ -0,0 +1,6 @@
+int main(int argc, char* argv[])
+{
+  (void)argc;
+  (void)argv;
+  return 0;
+}

Tests/RunCMake/Ninja/app_qt.cpp

@@ -0,0 +1,11 @@
+#include <QObject>
+
+class Mango : public QObject
+{
+  Q_OBJECT
+public:
+Q_SIGNALS:
+  void eatFruit();
+};
+
+#include "app_qt.moc"

Tests/RunCMake/Ninja/simple_lib.cpp

@@ -0,0 +1,6 @@
+#ifdef _WIN32
+__declspec(dllexport)
+#endif
+  void dummy_symbol()
+{
+}