[fontc] Add --experimental-simple-output flag

This turns on the same target simplification that we do in fontc mode,
without using fontc. (This ensures we generate the same set of targets
with both compilers.)

Lib/gftools/builder/__init__.py

@@ -36,7 +36,7 @@ class GFBuilder:
     config: dict
     recipe: Recipe
 
-    def __init__(self, config: Union[dict, str], use_fontc=False):
+    def __init__(self, config: Union[dict, str], use_fontc=False, simple_outputs=False):
         if isinstance(config, str):
             parentpath = Path(config).resolve().parent
             with open(config, "r") as file:
@@ -55,9 +55,7 @@ def __init__(self, config: Union[dict, str], use_fontc=False):
             self._orig_config = yaml.dump(config)
             self.config = config
 
-        # TODO(colin) we also want to suppress instancing when running fontmake
-        # if we're using it to compare with fontc
-        if use_fontc:
+        if use_fontc or simple_outputs:
             # we stash this flag here to pass it down to the recipe provider
             self.config["use_fontc"] = use_fontc
             self.config["buildWebfont"] = False
@@ -404,6 +402,12 @@ def main(args=None):
         action="store_true",
     )
 
+    parser.add_argument(
+        "--experimental-simple-output",
+        help="For comparison with fontc: skip instancing, webfonts, and OTF (if building TTF)",
+        action="store_true",
+    )
+
     parser.add_argument("config", help="Path to config file or source file", nargs="+")
     args = parser.parse_args(args)
     yaml_files = []
@@ -427,7 +431,7 @@ def main(args=None):
             raise ValueError("Only one config file can be given for now")
         config = args.config[0]
 
-    pd = GFBuilder(config, use_fontc=args.experimental_fontc)
+    pd = GFBuilder(config, use_fontc=args.experimental_fontc, simple_outputs=args.experimental_simple_output)
     if args.generate:
         config = pd.config
         config["recipe"] = pd.recipe