Move output to stderr, pass debug through as an attr

zapp/compiler/__main__.py

@@ -223,8 +223,8 @@ def rezip_wheels(opts, manifest):
                 wf = str(wf)
             else:
                 if opts.debug and False:
-                    print("\n---")
-                    json.dump({"$type": "whl", **w}, sys.stdout, indent=2)
+                    print("\n---", file=sys.stderr)
+                    json.dump({"$type": "whl", **w}, sys.stderr, indent=2)
 
                 wf = zip_wheel(opts.tmpdir, w)
 
@@ -336,7 +336,7 @@ def main():
         manifest = insert_manifest_json(opts, manifest)
 
         if opts.debug:
-            print("\n---")
+            print("\n---", file=sys.stderr)
             json.dump(
                 {
                     "$type": "zapp",
@@ -345,7 +345,7 @@ def main():
                     },
                     "manifest": manifest,
                 },
-                sys.stdout,
+                sys.stderr,
                 indent=2,
             )
 

zapp/zapp.bzl

@@ -142,12 +142,13 @@ def _zapp_impl(ctx):
     )
 
     args = [
-        "--debug",
         "-o", ctx.outputs.executable.path,
         manifest_file.path
     ]
     if ctx.attr.use_wheels:
         args = ["--use-wheels"] + args
+    if ctx.attr.debug:
+        args = ["--debug"] + args
 
     # Run compiler
     ctx.actions.run(
@@ -183,6 +184,7 @@ _zapp_attrs = {
     "prelude_points": attr.string_list(),
     "zip_safe": attr.bool(default = True),
     "use_wheels": attr.bool(default = False),
+    "debug": attr.bool(default = False),
     # FIXME: These are really toolchain parameters, probably.
     "compiler": attr.label(
         default = Label(DEFAULT_COMPILER),