Handle multiple outs per input (for plugins)

protobuf.bzl

@@ -91,8 +91,10 @@ def _proto_gen_impl(ctx):
         ),  
     )   
 
-  for src, out in zip(srcs, ctx.outputs.outs):
+  for src in srcs:
     args = []
+    src_name = src.basename[:-len(".proto")]
+    outs = [out for out in ctx.outputs.outs if src_name in out.basename]
 
     in_gen_dir = src.root.path == gen_dir.rstrip('/')
     if in_gen_dir:
@@ -126,6 +128,7 @@ def _proto_gen_impl(ctx):
       args += ["--%s_out=%s" % (lang, outdir)]
       inputs += [plugin]
 
+    for out in outs:
       if in_gen_dir:
         orig_command = " ".join(
             ["$(realpath %s)" % ctx.executable.protoc.path] + args +