Fix problem where axis with no mappings was erroring out during roundtrip

Lib/glyphsLib/builder/builders.py

@@ -749,6 +749,19 @@ def _valid_designspace(self, designspace, ufo_module):
  )
  )
  setattr(source, name, getattr(source.font.info, name))
+ # An axis without a mapping will see its range information (min and max
+ # values) lost when converted to a Glyps.app file. To combat this we
+ # add an explicit identity mapping.
+ for axis in copy.axes:
+ if axis.map:
+ continue
+ if axis.minimum == axis.maximum:
+ axis.map = [(axis.minimum, axis.minimum)]
+ else:
+ axis.map = [
+ (axis.minimum, axis.minimum),
+ (axis.maximum, axis.maximum),
+ ]
  return copy
 
  def _fake_designspace(self, ufos):

tests/builder/axes_test.py

@@ -13,6 +13,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+from copy import deepcopy
 import os.path
 
 import pytest
@@ -81,6 +82,9 @@ def _make_designspace_with_axes(axes, ufo_module):
  axis = doc.newAxisDescriptor()
  axis.tag = tag
  axis.name = name
+ axis.minimum = 0
+ axis.default = 0
+ axis.maximum = 100
  doc.addAxis(axis)
 
  extreme = doc.newSourceDescriptor()
@@ -347,8 +351,60 @@ def test_axis_mapping(ufo_module):
  assert doc.axes[1].map != wdth_mapping
  assert doc.axes[1].map == []
 
- # When we convert back to glyphs, the wdth mapping isn't present because
- # it was removed during the designspace conversion.
  font = to_glyphs(doc)
- axis_mappings["wdth"] = {}
  assert font.customParameters["Axis Mappings"] == axis_mappings
+
+
+def test_axis_with_no_mapping_does_not_error_in_roundtrip(ufo_module):
+ """Tests that a custom axis without a mapping and without sources on its
+ extremes does not generate an error during roundtrip. Also tests that
+ during a to_glyphs, to_designspace roundtrip the min and max axis
+ information is not lost.
+ """
+ doc = designspaceLib.DesignSpaceDocument()
+
+ # Add a "Regular" source
+ regular = doc.newSourceDescriptor()
+ regular.font = ufo_module.Font()
+ regular.location = {"Style": 0}
+ doc.addSource(regular)
+
+ axis = doc.newAxisDescriptor()
+ axis.tag = "styl"
+ axis.name = "Style"
+ doc.addAxis(axis)
+
+ # This axis spans a range of 0 to 1 but only has a source at {"Style": 0}
+ # and no explicit mapping. The point of this test is to see if the min and
+ # max are still the same after round tripping.
+ doc.axes[0].minimum = 0
+ doc.axes[0].maximum = 1
+ doc.axes[0].default = 0
+ doc.axes[0].map = []
+
+ doc2 = deepcopy(doc)
+ font = to_glyphs(doc2)
+ doc_rt = to_designspace(font)
+
+ assert doc_rt.axes[0].serialize() == doc.axes[0].serialize()
+
+
+def test_axis_with_no_mapping_does_not_error_in_roundtrip_with_2_axes(ufo_module):
+ """Tests that a designspace with 2 axis, one with a mapping and one
+ without a mapping, roundtrips correctly without error. The axis without a
+ mapping should generate an identity mapping on the fly so that the
+ Glyphs.app customParameter field does not lose min/max infromation about
+ the axis.
+ """
+ doc = _make_designspace_with_axes(
+ [("wght", "Weight with mapping"), ("wdth", "Width without mapping")], ufo_module
+ )
+ # Add mapping to weight axis
+ doc.axes[0].map = [(0, 0), (50, 350), (100, 1000)]
+
+ doc2 = deepcopy(doc)
+ font = to_glyphs(doc2)
+ doc_rt = to_designspace(font)
+
+ assert doc_rt.axes[0].serialize() == doc.axes[0].serialize()
+ assert doc_rt.axes[1].serialize() == doc.axes[1].serialize()