vala: Fix compiled object extraction

Fixes #791

mesonbuild/backend/backends.py

@@ -271,6 +271,9 @@ class Backend():
     def object_filename_from_source(self, target, source):
         if isinstance(source, mesonlib.File):
             source = source.fname
+        # foo.vala files compile down to foo.c and then foo.c.o, not foo.vala.o
+        if source.endswith('.vala'):
+            source = os.path.join(self.get_target_private_dir(target), source[:-5] + '.c')
         return source.replace('/', '_').replace('\\', '_') + '.' + self.environment.get_object_suffix()
 
     def determine_ext_objs(self, extobj, proj_dir_to_build_root):

test cases/vala/6 static library/installed_files.txt

@@ -0,0 +1 @@
+usr/lib/libextractedlib.a

test cases/vala/6 static library/meson.build

@@ -3,6 +3,12 @@ project('valastatic', 'vala', 'c')
 valadeps = [dependency('glib-2.0'), dependency('gobject-2.0')]
 
 l = static_library('valalib', 'mylib.vala', dependencies : valadeps)
+# NOTE: This static library is not usable from Vala because it does not carry
+# forward the .vapi and .h files generated by Valac to the next BuildTarget.
+# Will have to be fixed with https://github.com/mesonbuild/meson/issues/891
+m = static_library('extractedlib',
+  objects : l.extract_all_objects(),
+  install : true)
 
 e = executable('valaprog', 'prog.vala',
 link_with : l,