[builder] Reorder .notdef and space glyphs in public.glyphOrder

Unless "Keep GlyphOrder" (or the older "TrueType Keep GlyphOrder")
custom parameter is set to True.

Lib/glyphsLib/builder/custom_params.py

@@ -858,6 +858,26 @@ def to_ufo(self, builder, glyphs, ufo):
                 ]
                 ufo.set_lib_value(GLYPH_ORDER_KEY, glyphs_glyphOrder)
 
+            # if "Keep GlyphOrder" is not set, we reorder ".notdef"
+            # and "space" to the beginning of the glyph order.
+            #
+            # There is an older "TrueType Keep GlyphOrder" that is specific to
+            # TrueType export, but we don't know what the export format is so we
+            # treat it the same as "Keep GlyphOrder".
+            keep_glyphOrder = glyphs.get_custom_value(
+                "Keep GlyphOrder"
+            ) or glyphs.get_custom_value("TrueType Keep GlyphOrder")
+            ufo_glyphOrder = ufo.get_lib_value(GLYPH_ORDER_KEY)
+            if not keep_glyphOrder and ufo_glyphOrder:
+                space_index = 0
+                if ".notdef" in ufo_glyphOrder:
+                    ufo_glyphOrder.remove(".notdef")
+                    ufo_glyphOrder.insert(0, ".notdef")
+                    space_index = 1
+                if "space" in ufo_glyphOrder:
+                    ufo_glyphOrder.remove("space")
+                    ufo_glyphOrder.insert(space_index, "space")
+
 
 register(GlyphOrderParamHandler())
 

tests/builder/builder_test.py

@@ -2758,3 +2758,64 @@ def test_glyphs_to_ufo_with_partial_glyphOrder(self, ufo_module):
         ufo = self.from_glyphs(ufo_module)
         assert ["xxx1", "f", "xxx2", "c", "a"] == ufo.lib["public.glyphOrder"]
         assert GLYPHS_PREFIX + "glyphOrder" not in ufo.lib
+
+    def test_glyphs_to_ufo_with_keepGlyphOrder(self, ufo_module):
+        self.prepare(ufo_module)
+        self.font.glyphs.append(GSGlyph("space"))
+
+        # If "Keep GlyphOrder" is True, no reordering happens
+        self.font.customParameters["Keep GlyphOrder"] = True
+        ufo = self.from_glyphs(ufo_module)
+        assert ["c", "a", "f", "space"] == ufo.lib["public.glyphOrder"]
+
+        # If "Keep GlyphOrder" is False, space is reordered
+        self.font.customParameters["Keep GlyphOrder"] = False
+        ufo = self.from_glyphs(ufo_module)
+        assert ["space", "c", "a", "f"] == ufo.lib["public.glyphOrder"]
+
+        # Absence of "Keep GlyphOrder" is equivalent to False
+        del self.font.customParameters["Keep GlyphOrder"]
+        ufo = self.from_glyphs(ufo_module)
+        assert ["space", "c", "a", "f"] == ufo.lib["public.glyphOrder"]
+
+    def test_glyphs_to_ufo_with_keepGlyphOrder_and_notdef(self, ufo_module):
+        self.prepare(ufo_module)
+        self.font.glyphs.append(GSGlyph("space"))
+        self.font.glyphs.append(GSGlyph(".notdef"))
+
+        # If "Keep GlyphOrder" is True, no reordering happens
+        self.font.customParameters["Keep GlyphOrder"] = True
+        ufo = self.from_glyphs(ufo_module)
+        assert ["c", "a", "f", "space", ".notdef"] == ufo.lib["public.glyphOrder"]
+
+        # If "Keep GlyphOrder" is False, space is reordered
+        self.font.customParameters["Keep GlyphOrder"] = False
+        ufo = self.from_glyphs(ufo_module)
+        assert [".notdef", "space", "c", "a", "f"] == ufo.lib["public.glyphOrder"]
+
+        # Absence of "Keep GlyphOrder" is equivalent to False
+        del self.font.customParameters["Keep GlyphOrder"]
+        ufo = self.from_glyphs(ufo_module)
+        assert [".notdef", "space", "c", "a", "f"] == ufo.lib["public.glyphOrder"]
+
+    def test_glyphs_to_ufo_with_keepGlyphOrder_and_explicit_glyphOrder(
+        self, ufo_module
+    ):
+        self.prepare(ufo_module)
+        self.font.glyphs.append(GSGlyph("space"))
+        self.font.customParameters["glyphOrder"] = ["c", "a", "space", "f"]
+
+        # If "Keep GlyphOrder" is True, no reordering happens
+        self.font.customParameters["Keep GlyphOrder"] = True
+        ufo = self.from_glyphs(ufo_module)
+        assert ["c", "a", "space", "f"] == ufo.lib["public.glyphOrder"]
+
+        # If "Keep GlyphOrder" is False, space is reordered
+        self.font.customParameters["Keep GlyphOrder"] = False
+        ufo = self.from_glyphs(ufo_module)
+        assert ["space", "c", "a", "f"] == ufo.lib["public.glyphOrder"]
+
+        # Absence of "Keep GlyphOrder" is equivalent to False
+        del self.font.customParameters["Keep GlyphOrder"]
+        ufo = self.from_glyphs(ufo_module)
+        assert ["space", "c", "a", "f"] == ufo.lib["public.glyphOrder"]