remove glyph names from post table when converting to CFF1

Fixes adobe-type-tools#8

src/cffsubr/__init__.py

@@ -170,7 +170,8 @@ def subroutinize(
     if not inplace:
         otf = copy.deepcopy(otf)
 
-    glyphOrder = otf.getGlyphOrder()
+    # ensure the glyph order is decompiled before CFF table is replaced
+    _ = otf.getGlyphOrder()
 
     buf = io.BytesIO()
     otf.save(buf)
@@ -190,16 +191,36 @@ def subroutinize(
         and keep_glyph_names
     ):
         # set 'post' to format 2 to keep the glyph names dropped from CFF2
-        post_table = otf.get("post")
-        if post_table and post_table.formatType != 2.0:
-            post_table.formatType = 2.0
-            post_table.extraNames = []
-            post_table.mapping = {}
-            post_table.glyphOrder = glyphOrder
+        set_post_table_format(otf, 2.0)
+    elif (
+        input_format == CFFTableTag.CFF2
+        and output_format == CFFTableTag.CFF
+    ):
+        # set 'post' to format 3 so CFF glyph names are not stored twice
+        # TODO convert to CID when keep_glyph_names=False?
+        set_post_table_format(otf, 3.0)
 
     return otf
 
 
+def set_post_table_format(otf, formatType):
+    if formatType not in (2.0, 3.0):
+        raise NotImplementedError(formatType)
+
+    post = otf.get("post")
+    if post and post.formatType != formatType:
+        post.formatType = formatType
+        if formatType == 2.0:
+            post.extraNames = []
+            post.mapping = {}
+            post.glyphOrder = otf.getGlyphOrder()
+        else:
+            for attr in ("extraNames", "mapping"):
+                if hasattr(post, attr):
+                    delattr(post, attr)
+            post.glyphOrder = None
+
+
 def has_subroutines(otf: ttLib.TTFont) -> bool:
     """Return True if the font's CFF or CFF2 table contains any subroutines."""
     table_tag = _sniff_cff_table_format(otf)

tests/cffsubr_test.py

@@ -17,6 +17,13 @@ def load_test_font(name):
     return ttLib.TTFont(buf)
 
 
+def recompile_font(otf):
+    buf = io.BytesIO()
+    otf.save(buf)
+    buf.seek(0)
+    return ttLib.TTFont(buf)
+
+
 class TestSubroutinize:
     @pytest.mark.parametrize(
         "testfile, table_tag",
@@ -74,13 +81,21 @@ def test_keep_glyph_names(self):
         assert font["post"].formatType == 2.0
         assert font["post"].glyphOrder == glyph_order
 
-        buf = io.BytesIO()
-        font.save(buf)
-        buf.seek(0)
-        font2 = ttLib.TTFont(buf)
+        font2 = recompile_font(font)
 
         assert font2.getGlyphOrder() == glyph_order
 
+        # now convert from CFF2 to CFF1 and check post format is set to 3.0
+        # https://github.com/adobe-type-tools/cffsubr/issues/8
+        cffsubr.subroutinize(font2, cff_version=1)
+
+        assert font2["post"].formatType == 3.0
+        assert font2["post"].glyphOrder == None
+
+        font3 = recompile_font(font2)
+
+        assert font3.getGlyphOrder() == glyph_order
+
     def test_drop_glyph_names(self):
         font = load_test_font("SourceSansPro-Regular.subset.ttx")
         glyph_order = font.getGlyphOrder()