Be more clever about subsetting:

* Find appropriate master from subset font by matching source location to subset location
* Write changed files in a temporary directory

Lib/gftools/actions/notobuilder.py

@@ -12,6 +12,8 @@
 import os
 import re
 import sys
+import shutil
+import tempfile
 from pathlib import Path
 
 import pygit2
@@ -118,20 +120,39 @@ def build(self):
         for key in ["vfDir", "otDir", "ttDir"]:
             self.config[key] = self.config[key].replace("unhinted", "full")
 
+        new_builder_sources = []
+        temporaries = []
+
         for ds_file in self.config["sources"]:
+            new_ds_file_dir = tempfile.TemporaryDirectory()
+            temporaries.append(new_ds_file_dir)
             ds = designspaceLib.DesignSpaceDocument.fromfile(ds_file)
-            for subset in self.config["includeSubsets"]:
-                if len(ds.sources) == 1:
-                    self.add_subset(ds.sources[0], subset, mapping="Regular")
-                else:
-                    for master in ds.sources:
-                        self.add_subset(ds.sources[0], subset)
+            for master in ds.sources:
+                # Save a copy to temporary UFO
+                newpath = os.path.join(new_ds_file_dir.name, os.path.basename(master.path))
+                original_ufo = ufoLib2.Font.open(master.path)
+                original_ufo.save(newpath, overwrite=True)
+
+                master.path = newpath
+
+                for subset in self.config["includeSubsets"]:
+                    self.add_subset(master, subset)
+            # # Set instance filenames to temporary
+            for instance in ds.instances:
+                instance.filename = instance.path = os.path.join(new_ds_file_dir.name, os.path.basename(instance.filename))
+
+            # Save new designspace to temporary
+            new_ds_file = os.path.join(new_ds_file_dir.name, os.path.basename(ds_file))
+            ds.write(new_ds_file)
+
+            new_builder_sources.append(new_ds_file)
+
+        self.config["sources"] = new_builder_sources
 
         super().build()
+        # Temporaries should get cleaned here.
 
-    def add_subset(self, ds_source, subset, mapping=None):
-        if mapping is None:
-            raise NotImplementedError
+    def add_subset(self, ds_source, subset):
         if "name" in subset:
             # Resolve to glyphset
             unicodes = CodepointsInSubset(subset["name"])
@@ -140,33 +161,55 @@ def add_subset(self, ds_source, subset, mapping=None):
             for r in subset["ranges"]:
                 for cp in range(r["start"], r["end"] + 1):
                     unicodes.append(cp)
-        source_ufo = self.obtain_noto_ufo(subset["from"], mapping)
+        source_ufo = self.obtain_noto_ufo(subset["from"], ds_source.location)
         target_ufo = ufoLib2.Font.open(ds_source.path)
         merge_ufos(
             target_ufo, source_ufo, codepoints=unicodes, existing_handling="skip",
         )
         target_ufo.save(ds_source.path, overwrite=True)
 
-    def obtain_noto_ufo(self, font_name, mapping):
+    def obtain_noto_ufo(self, font_name, location):
         if font_name == "Noto Sans":
             self.clone_for_subsetting("latin-greek-cyrillic")
             path = "../subset-files/latin-greek-cyrillic/sources/NotoSans-MM.glyphs"
+        if font_name == "Noto Serif":
+            self.clone_for_subsetting("latin-greek-cyrillic")
+            path = "../subset-files/latin-greek-cyrillic/sources/NotoSerif-MM.glyphs"
         if font_name == "Noto Sans Devanagari":
             self.clone_for_subsetting("devanagari")
             path = "../subset-files/devanagari/sources/NotoSansDevanagari.glyphs"
 
         if path.endswith(".glyphs"):
-            # Check if UFO already exists
-            path = self.glyphs_to_ufo(path)
+            ds_path = path.replace(".glyphs", ".designspace")
+            if os.path.exists(ds_path):
+                path = ds_path
+            else:
+                self.logger.info("Building UFO file for subset font "+font_name)
+                path = self.glyphs_to_ufo(path)
         source_ds = designspaceLib.DesignSpaceDocument.fromfile(path)
-        regs = [
-            source.path
-            for source in source_ds.sources
-            if source.name.endswith("Regular")
-        ]
-        if not regs:
-            regs = [source_ds.sources[0].path]
-        return ufoLib2.Font.open(regs[0])
+
+        # Find a source for this location
+        return ufoLib2.Font.open(self.find_source(source_ds, location, font_name).path)
+
+    def find_source(self, source_ds, location, font_name):
+        source_mappings = {
+            ax.name: ax.map_forward for ax in source_ds.axes
+        }
+        target = None
+        for source in source_ds.sources:
+            match = True
+            for axis, loc in location.items():
+                if axis in source.location and axis in source_mappings and source.location[axis] != source_mappings[axis](loc):
+                    match = False
+            if match:
+                target = source
+                break
+        if target:
+            self.logger.info(f"Adding subset from {target} for location {location}")
+            return target
+        self.logger.error(f"Could not find master in {font_name} for location {location}")
+        import IPython;IPython.embed()
+        raise ValueError("Could not add subset")
 
     def clone_for_subsetting(self, repo):
         dest = "../subset-files/" + repo