fix master ufo paths' file extension if saving as ufoz

plus, make sure when we log 'Saving Font.ufoz' then the file extension actually matches what we are saving on disk

Lib/fontmake/font_project.py

@@ -78,6 +78,12 @@
 INSTANCE_FILENAME_KEY = "com.github.googlefonts.fontmake.instance_filename"
 
 
+UFO_STRUCTURE_EXTENSIONS = {
+    "package": ".ufo",
+    "zip": ".ufoz",
+}
+
+
 def needs_subsetting(ufo):
     if KEEP_GLYPHS_OLD_KEY in ufo.lib or KEEP_GLYPHS_NEW_KEY in ufo.lib:
         return True
@@ -126,6 +132,13 @@ def open_ufo(self, path):
         except Exception as e:
             raise FontmakeError("Reading UFO source failed", path) from e
 
+    @staticmethod
+    def _fix_ufo_path(path, ufo_structure):
+        """Normalizes UFO path and updates extension suffix to match its structure"""
+        return os.path.normpath(
+            Path(path).with_suffix(UFO_STRUCTURE_EXTENSIONS[ufo_structure])
+        )
+
     def save_ufo_as(self, font, path, ufo_structure="package"):
         try:
             font.save(
@@ -198,7 +211,9 @@ def build_master_ufos(
         # multiple sources can have the same font/filename (but different layer),
         # we want to save a font only once
         for source in designspace.sources:
-            ufo_path = os.path.join(master_dir, source.filename)
+            ufo_path = self._fix_ufo_path(
+                os.path.join(master_dir, source.filename), ufo_structure
+            )
             source.path = ufo_path
             # relative 'filename' would be auto-updated upon writing the designspace
             # but we may not always write one out, thus we keep it up-to-date
@@ -851,7 +866,7 @@ def run_from_glyphs(
             raise
 
     def _instance_ufo_path(
-        self, instance, designspace_path, output_dir=None, ext=".ufo"
+        self, instance, designspace_path, output_dir=None, ufo_structure="package"
     ):
         """Return an instance path, optionally overriding output dir or extension"""
         # prefer absolute instance.path over relative instance.filename
@@ -874,8 +889,8 @@ def _instance_ufo_path(
         if instance_dir is None:
             instance_dir = self._output_dir("ufo", is_instance=True)
 
-        instance_path = Path(instance_dir) / f"{Path(instance_path).stem}{ext}"
-        return os.path.normpath(instance_path)
+        instance_path = Path(instance_dir) / Path(instance_path).name
+        return self._fix_ufo_path(instance_path, ufo_structure)
 
     def interpolate_instance_ufos(
         self,
@@ -958,16 +973,18 @@ def interpolate_instance_ufos(
                 apply_instance_data_to_ufo(instance.font, instance, subDoc)
 
                 if save_ufos:
-                    ext = ".ufoz" if ufo_structure == "zip" else ".ufo"
                     if output_path is not None:
                         # we don't know in advance how many instances we will generate
                         # (depends on splitInterpolable and include filter); if we
                         # overwrite or stop in the middle of the build it'd be worse,
                         # so we make the output_path unique using #1, #2, etc. suffix
-                        instance_path = makeOutputFileName(output_path, extension=ext)
+                        instance_path = makeOutputFileName(
+                            output_path,
+                            extension=UFO_STRUCTURE_EXTENSIONS[ufo_structure],
+                        )
                     else:
                         instance_path = self._instance_ufo_path(
-                            instance, designspace.path, output_dir, ext
+                            instance, designspace.path, output_dir, ufo_structure
                         )
                     logger.info("Saving %s", instance_path)
                     self.save_ufo_as(instance.font, instance_path, ufo_structure)