Bug 1215526 - part 2 - write dependencies to file_generate.py's depfile; r=glandium

python/mozbuild/mozbuild/action/file_generate.py

@@ -15,6 +15,7 @@ import sys
 import traceback
 
 from mozbuild.util import FileAvoidWrite
+from mozbuild.makeutil import Makefile
 
 def main(argv):
     parser = argparse.ArgumentParser('Generate a file from a Python script',
@@ -56,6 +57,16 @@ def main(argv):
     try:
         with FileAvoidWrite(args.output_file) as output:
             ret = module.__dict__[method](output, *args.additional_arguments)
+            # We treat sets as a statement of success.  Everything else
+            # is an error (so scripts can conveniently |return 1| or
+            # similar).
+            if isinstance(ret, set) and ret:
+                mk = Makefile()
+                mk.create_rule([args.output_file]).add_dependencies(ret)
+                with FileAvoidWrite(args.dep_file) as dep_file:
+                    mk.dump(dep_file)
+                # The script succeeded, so reset |ret| to indicate that.
+                ret = None
     except IOError as e:
         print('Error opening file "{0}"'.format(e.filename), file=sys.stderr)
         traceback.print_exc()

python/mozbuild/mozbuild/frontend/context.py

@@ -907,6 +907,9 @@ VARIABLES = {
           GENERATED_FILES += ['bar.c']
           bar = GENERATED_FILES['bar.c']
           bar.script = 'generate.py:make_bar'
+
+        The chosen script entry point may optionally return a set of strings,
+        indicating extra files the output depends on.
         """, 'export'),
 
     'DEFINES': (OrderedDict, dict,