Automoc: Don't create automoc targets if Qt is not used (#13999)

Commit 79568f95 (automoc: Add source file to target early to set the
linker language, 2013-02-20) changed automoc initialization to a two
step process. In the first step, the generated source file was added
to the target, which allows the link language to be determined.

However, this bypassed the check for the availability of Qt itself.
At build-time the automoc file could not be generated because the moc
tool was not available to create it.

The solution is to only add the automoc file to the target if Qt is
found.

Source/cmGlobalGenerator.cxx

@@ -1086,12 +1086,14 @@ void cmGlobalGenerator::CreateAutomocTargets()
         if(target.GetPropertyAsBool("AUTOMOC") && !target.IsImported())
           {
           cmQtAutomoc automoc;
-          automoc.InitializeMocSourceFile(&target);
+          if(automoc.InitializeMocSourceFile(&target))
+            {
             automocs.push_back(std::make_pair(automoc, &target));
             }
           }
         }
       }
+    }
   for (Automocs::iterator it = automocs.begin(); it != automocs.end();
        ++it)
     {

Source/cmQtAutomoc.cxx

@@ -119,10 +119,21 @@ cmQtAutomoc::cmQtAutomoc()
     }
 }
 
-void cmQtAutomoc::InitializeMocSourceFile(cmTarget* target)
+bool cmQtAutomoc::InitializeMocSourceFile(cmTarget* target)
 {
+  cmMakefile* makefile = target->GetMakefile();
+  // don't do anything if there is no Qt4 or Qt5Core (which contains moc):
+  std::string qtMajorVersion = makefile->GetSafeDefinition("QT_VERSION_MAJOR");
+  if (qtMajorVersion == "")
+    {
+    qtMajorVersion = makefile->GetSafeDefinition("Qt5Core_VERSION_MAJOR");
+    }
+  if (qtMajorVersion != "4" && qtMajorVersion != "5")
+    {
+    return false;
+    }
+
   std::string automocTargetName = target->GetName();
-  cmMakefile *makefile = target->GetMakefile();
   automocTargetName += "_automoc";
   std::string mocCppFile = makefile->GetCurrentOutputDirectory();
   mocCppFile += "/";
@@ -134,6 +145,7 @@ void cmQtAutomoc::InitializeMocSourceFile(cmTarget* target)
                            mocCppFile.c_str(), false);
 
   target->AddSourceFile(mocCppSource);
+  return true;
 }
 
 void cmQtAutomoc::SetupAutomocTarget(cmTarget* target)
@@ -141,16 +153,6 @@ void cmQtAutomoc::SetupAutomocTarget(cmTarget* target)
   cmMakefile* makefile = target->GetMakefile();
   cmLocalGenerator* localGen = makefile->GetLocalGenerator();
   const char* targetName = target->GetName();
-  // don't do anything if there is no Qt4 or Qt5Core (which contains moc):
-  std::string qtMajorVersion = makefile->GetSafeDefinition("QT_VERSION_MAJOR");
-  if (qtMajorVersion == "")
-    {
-    qtMajorVersion = makefile->GetSafeDefinition("Qt5Core_VERSION_MAJOR");
-    }
-  if (qtMajorVersion != "4" && qtMajorVersion != "5")
-    {
-    return;
-    }
 
   bool relaxedMode = makefile->IsOn("CMAKE_AUTOMOC_RELAXED_MODE");
 

Source/cmQtAutomoc.h

@@ -23,7 +23,7 @@ public:
   cmQtAutomoc();
   bool Run(const char* targetDirectory);
 
-  void InitializeMocSourceFile(cmTarget* target);
+  bool InitializeMocSourceFile(cmTarget* target);
   void SetupAutomocTarget(cmTarget* target);
 
 private:

Tests/CMakeLists.txt

@@ -970,6 +970,16 @@ ${CMake_BINARY_DIR}/bin/cmake -DVERSION=master -P ${CMake_SOURCE_DIR}/Utilities/
     )
   list(APPEND TEST_BUILD_DIRS "${CMake_BINARY_DIR}/Tests/Environment")
 
+  add_test(QtAutomocNoQt  ${CMAKE_CTEST_COMMAND}
+    --build-and-test
+    "${CMake_SOURCE_DIR}/Tests/QtAutomocNoQt"
+    "${CMake_BINARY_DIR}/Tests/QtAutomocNoQt"
+    ${build_generator_args}
+    --build-project QtAutomocNoQt
+    --build-options -DCMAKE_BUILD_TYPE=\${CTEST_CONFIGURATION_TYPE}
+    )
+  list(APPEND TEST_BUILD_DIRS "${CMake_BINARY_DIR}/Tests/QtAutomocNoQt")
+
   if(QT4_WORKS AND QT_QTGUI_FOUND)
     add_test(QtAutomoc ${CMAKE_CTEST_COMMAND}
       --build-and-test

Tests/QtAutomocNoQt/CMakeLists.txt

@@ -0,0 +1,7 @@
+cmake_minimum_required(VERSION 2.8)
+
+project(QtAutomocNoQt)
+
+set(CMAKE_AUTOMOC ON)
+
+add_executable(hello main.c)

Tests/QtAutomocNoQt/main.c

@@ -0,0 +1,4 @@
+int main(void)
+{
+  return 0;
+}