Add subset adder (needs merge of googlefonts#730)

Lib/gftools/builder/file.py

@@ -38,7 +38,11 @@ def is_ufo(self):
     @property
     def is_designspace(self):
         return self.extension == "designspace"
-
+
+    @property
+    def is_font_source(self):
+        return (self.is_glyphs or self.is_ufo or self.is_designspace)
+
     @cached_property
     def gsfont(self):
         if self.is_glyphs:

Lib/gftools/builder/operations/addSubset.py

@@ -0,0 +1,38 @@
+import os
+import sys
+from tempfile import NamedTemporaryFile, TemporaryDirectory
+
+import yaml
+
+from gftools.builder.file import File
+from gftools.builder.operations import OperationBase
+
+
+class AddSubset(OperationBase):
+    description = "Add a subset from another font"
+    rule = "gftools-add-ds-subsets -y $yaml -o $out $in"
+
+    def validate(self):
+        # Ensure there is a new name
+        if not self.first_source.is_font_source:
+            raise ValueError("%s is not a font source file" % self.first_source)
+        if "subsets" not in self.original:
+            raise ValueError("No subsets defined")
+
+    def convert_dependencies(self, builder):
+        self._target = TemporaryDirectory() # Stow object
+        self._orig = NamedTemporaryFile(delete=False, mode="w")
+        yaml.dump(self.original["subsets"], self._orig)
+        self._orig.close()
+
+    @property
+    def targets(self):
+        dspath = os.path.join(self._target.name, self.first_source.basename.rsplit(".", 1)[0] + ".designspace")
+        return [ File(dspath) ]
+
+    @property
+    def variables(self):
+        return {
+            "yaml": self._orig.name,
+        }
+