Qt5-Module: Add `moc_extra_arguments` keyword support.

This commit adds support for an additional `moc_extra_arguments` keyword.
It becomes especially handy, when `moc`-ed sources conditionally provide
`slots`, depending on compile time macros (i.e. defines).

3 files changed, 27 insertions, 10 deletions

diff --git a/docs/markdown/Qt5-module.md b/docs/markdown/Qt5-module.md
index a8ad73d..613e5c1 100644
--- a/docs/markdown/Qt5-module.md
+++ b/docs/markdown/Qt5-module.md
@@ -5,11 +5,11 @@ tools and steps required for Qt. The module has one method.
 
 ## preprocess
 
-This method takes five keyword arguments, `moc_headers`,
-`moc_sources`, `ui_files` and `qresources` which define the files that
-require preprocessing with `moc`, `uic` and `rcc` and 'include_directories' which might be needed by moc. It returns an
-opaque object that should be passed to a main build target. A simple
-example would look like this:
+This method takes six keyword arguments, `moc_headers`, `moc_sources`, `ui_files`, `qresources`
+and `moc_extra_arguments` which define the files that require preprocessing with `moc`, `uic`
+and `rcc` and 'include_directories' which might be needed by moc as well as (optional)
+additional arguments. It returns an opaque object that should be passed to a main build target.
+A simple example would look like this:
 
 ```meson
 qt5 = import('qt5')
diff --git a/docs/markdown/snippets/qt5-moc_extra_arguments.md b/docs/markdown/snippets/qt5-moc_extra_arguments.md
new file mode 100644
index 0000000..957c3c7
--- /dev/null
+++ b/docs/markdown/snippets/qt5-moc_extra_arguments.md
@@ -0,0 +1,8 @@
+# Adds support for additional Qt5-Module keyword `moc_extra_arguments`
+
+When `moc`-ing sources, the `moc` tool does not know about any
+preprocessor macros. The generated code might not match the input
+files when the linking with the moc input sources happens.
+
+This amendment allows to specify a a list of additional arguments
+passed to the `moc` tool. They are called `moc_extra_arguments`.
\ No newline at end of file
diff --git a/mesonbuild/modules/qt.py b/mesonbuild/modules/qt.py
index 2f24740..1ff30ef 100644
--- a/mesonbuild/modules/qt.py
+++ b/mesonbuild/modules/qt.py
@@ -84,10 +84,10 @@ class QtBaseModule:
         except Exception:
             return []
 
-    @permittedKwargs({'moc_headers', 'moc_sources', 'include_directories', 'ui_files', 'qresources', 'method'})
+    @permittedKwargs({'moc_headers', 'moc_sources', 'moc_extra_arguments', 'include_directories', 'ui_files', 'qresources', 'method'})
     def preprocess(self, state, args, kwargs):
-        rcc_files, ui_files, moc_headers, moc_sources, sources, include_directories \
-            = extract_as_list(kwargs, 'qresources', 'ui_files', 'moc_headers', 'moc_sources', 'sources', 'include_directories', pop = True)
+        rcc_files, ui_files, moc_headers, moc_sources, moc_extra_arguments, sources, include_directories \
+            = extract_as_list(kwargs, 'qresources', 'ui_files', 'moc_headers', 'moc_sources', 'moc_extra_arguments', 'sources', 'include_directories', pop = True)
         sources += args[1:]
         method = kwargs.get('method', 'auto')
         self._detect_tools(state.environment, method)
@@ -122,14 +122,23 @@ class QtBaseModule:
             sources.append(ui_output)
         inc = get_include_args(include_dirs=include_directories)
         if len(moc_headers) > 0:
+            if len(moc_extra_arguments) > 0:
+                arguments = moc_extra_arguments + inc + ['@INPUT@', '-o', '@OUTPUT@']
+            else:
+                arguments = inc + ['@INPUT@', '-o', '@OUTPUT@']
             moc_kwargs = {'output': 'moc_@BASENAME@.cpp',
-                          'arguments': inc + ['@INPUT@', '-o', '@OUTPUT@']}
+                          'arguments': arguments}
             moc_gen = build.Generator([self.moc], moc_kwargs)
             moc_output = moc_gen.process_files('Qt{} moc header'.format(self.qt_version), moc_headers, state)
             sources.append(moc_output)
         if len(moc_sources) > 0:
+            if len(moc_extra_arguments) > 0:
+                concatinated_moc_extra_arguments = ' '.join(moc_extra_arguments)
+                arguments = [concatinated_moc_extra_arguments, '@INPUT@', '-o', '@OUTPUT@']
+            else:
+                arguments = ['@INPUT@', '-o', '@OUTPUT@']
             moc_kwargs = {'output': '@BASENAME@.moc',
-                          'arguments': ['@INPUT@', '-o', '@OUTPUT@']}
+                          'arguments': arguments}
             moc_gen = build.Generator([self.moc], moc_kwargs)
             moc_output = moc_gen.process_files('Qt{} moc source'.format(self.qt_version), moc_sources, state)
             sources.append(moc_output)