modules/qt: use append rather than extend in preprocess

Because that's what we need, of course

mesonbuild/modules/qt.py

@@ -428,11 +428,11 @@ class QtBaseModule(ExtensionModule):
                 if not isinstance(args[0], str):
                     raise build.InvalidArguments('First argument to qt.preprocess must be a string')
                 rcc_kwargs['name'] = args[0]
-            sources.extend(self.compile_resources(state, tuple(), rcc_kwargs).return_value)
+            sources.append(self.compile_resources(state, tuple(), rcc_kwargs).return_value)
 
         if kwargs['ui_files']:
             ui_kwargs: 'UICompilerKwArgs' = {'sources': kwargs['ui_files'], 'extra_args': kwargs['uic_extra_arguments'], 'method': method}
-            sources.extend(self.compile_ui(state, tuple(), ui_kwargs).return_value)
+            sources.append(self.compile_ui(state, tuple(), ui_kwargs).return_value)
 
         if kwargs['moc_headers'] or kwargs['moc_sources']:
             moc_kwargs: 'MocCompilerKwArgs' = {
@@ -443,7 +443,7 @@ class QtBaseModule(ExtensionModule):
                 'dependencies': kwargs['dependencies'],
                 'method': method,
             }
-            sources.extend(self.compile_moc(state, tuple(), moc_kwargs).return_value)
+            sources.append(self.compile_moc(state, tuple(), moc_kwargs).return_value)
 
         return ModuleReturnValue(sources, [sources])
 

test cases/frameworks/4 qt/meson.build

@@ -57,6 +57,10 @@ foreach qt : ['qt4', 'qt5', 'qt6']
     # XML files that need to be compiled with the uic tol.
     prep += qtmodule.compile_ui(sources : 'mainWindow.ui', method: get_option('method'))
 
+    qtmodule.preprocess(
+      ui_files : 'mainWindow.ui',
+      method: get_option('method'))
+
     # Resource file(s) for rcc compiler
     extra_cpp_args = []
     if meson.is_unity()
@@ -100,6 +104,12 @@ foreach qt : ['qt4', 'qt5', 'qt6']
     # The build system needs to include the cpp files from
     # headers but the user must manually include moc
     # files from sources.
+    qtmodule.preprocess(
+      moc_extra_arguments : ['-DMOC_EXTRA_FLAG'], # This is just a random macro to test `extra_arguments`
+      moc_sources : 'manualinclude.cpp',
+      moc_headers : 'manualinclude.h',
+      method : get_option('method'))
+
     manpreprocessed = qtmodule.compile_moc(
       extra_args : ['-DMOC_EXTRA_FLAG'], # This is just a random macro to test `extra_arguments`
       sources : 'manualinclude.cpp',