Fix recursion for i18n.xgettext

docs/markdown/snippets/xgettext-include-private-dependencies.md

@@ -0,0 +1,24 @@
+## i18n.xgettext recursive option now includes "private" dependencies
+
+Suppose we have:
+
+```
+libA.dll -> libB.dll -> libC.dll
+```
+
+Here, `libA` links with `libB`, and `libB` links with `libC`, but `libA` does
+not link with `libC` directly. So, `libC` is a "private" dependency of `libB`.
+If we collect strings to translate using:
+
+```
+i18n.xgettext(libC)
+i18n.xgettext(libB)
+pot_file = i18n.xgettext(libA, recursive: true)
+```
+
+Previously, strings from `libC` would not be included in `pot_file`, since
+`libC` is not a direct link dependency of `libA`. This has been fixed: when
+the `recursive: true` option is used, `xgettext` now recursively includes
+translations from all dependencies, including those of dependencies. This is
+more logical, as even if `libA` does not directly link with `libC`, it may
+still need translated strings from `libC`.

mesonbuild/modules/i18n.py

@@ -209,9 +209,11 @@ def _get_depends(self, sources: T.Iterable[SourcesType]) -> T.Set[build.CustomTa
         depends = set()
         for source in sources:
             if isinstance(source, build.BuildTarget):
-                for source_id in self._get_source_id(source.get_dependencies()):
+                dependencies = source.get_dependencies()
+                for source_id in self._get_source_id(dependencies):
                     if source_id in self.pot_files:
                         depends.add(self.pot_files[source_id])
+                depends.update(self._get_depends(dependencies))
             elif isinstance(source, build.CustomTarget):
                 # Dependency on another extracted pot file
                 source_id = source.get_id()