Expose and fix mistranslation from python that can lead to bad avar

glyphs-reader/src/font.rs

@@ -1882,7 +1882,7 @@ impl UserToDesignMapping {
     fn new(from: &RawFont, instances: &[Instance]) -> Self {
         let from_axis_mapping = user_to_design_from_axis_mapping(from);
         let from_axis_location = user_to_design_from_axis_location(from);
-        let (result, add_instance_mappings) = match (from_axis_mapping, from_axis_location) {
+        let (result, incomplete_mapping) = match (from_axis_mapping, from_axis_location) {
             (Some(from_mapping), Some(..)) => {
                 warn!("Axis Mapping *and* Axis Location are defined; using Axis Mapping");
                 (from_mapping, false)
@@ -1892,10 +1892,10 @@ impl UserToDesignMapping {
             (None, None) => (BTreeMap::new(), true),
         };
         let mut result = Self(result);
-        if add_instance_mappings {
+        if incomplete_mapping {
             result.add_instance_mappings_if_new(instances);
+            result.add_master_mappings_if_new(from);
         }
-        result.add_master_mappings_if_new(from);
         result
     }
 
@@ -3622,4 +3622,18 @@ mod tests {
             }
         }
     }
+
+    // We had a bug where if a master wasn't at a mapping point the Axis Mapping was modified
+    #[test]
+    fn ignore_masters_if_axis_mapping() {
+        let font = Font::load(&glyphs2_dir().join("MasterNotMapped.glyphs")).unwrap();
+        let mapping = &font.axis_mappings.0.get("Weight").unwrap().0;
+        assert_eq!(
+            vec![
+                (OrderedFloat(400_f64), OrderedFloat(40.0)),
+                (OrderedFloat(700_f64), OrderedFloat(70.0))
+            ],
+            *mapping
+        );
+    }
 }

resources/testdata/glyphs2/MasterNotMapped.glyphs

@@ -0,0 +1,60 @@
+{
+customParameters = (
+{
+name = Axes;
+value = (
+{
+Name = Weight;
+Tag = wght;
+}
+);
+},
+{
+name = "Axis Mappings";
+value = {
+wght = {
+400 = 40;
+700 = 70;
+};
+};
+}
+);
+
+familyName = MnM;
+fontMaster = (
+{
+id = regular;
+weightValue = 40;
+},
+{
+id = "medium";
+weightValue = 50;
+},
+{
+id = "bold";
+weightValue = 70;
+}
+);
+
+glyphs = (
+{
+glyphname = space;
+layers = (
+{
+layerId = regular;
+width = 200;
+},
+{
+layerId = medium;
+width = 400;
+},
+{
+layerId = "bold";
+width = 600;
+}
+);
+unicode = 0020;
+}
+);
+unitsPerEm = 1000;
+}