Instantiator support for non-default layer sources

Lib/fontmake/__main__.py

@@ -137,7 +137,7 @@ def parse_mutually_exclusive_inputs(parser, args):
         ):
             ufo_paths.append(filename)
         else:
-            parser.error(f"Unknown input file extension: '{filename}'")
+            parser.error(f"Unknown input file extension: {filename!r}")
 
     count = sum(bool(p) for p in (glyphs_path, ufo_paths, designspace_path))
     if count == 0:

Lib/fontmake/errors.py

@@ -26,7 +26,7 @@ def __init__(self, msg, source_file):
 
     def __str__(self):
         trail = " -> ".join(
-            f"'{str(_try_relative_path(s))}'"
+            f"{str(_try_relative_path(s))!r}"
             for s in reversed(self.source_trail)
             if s is not None
         )

Lib/fontmake/font_project.py

@@ -574,6 +574,7 @@ def save_otfs(
             warnings.warn(
                 "the 'subroutinize' argument is deprecated, use 'optimize_cff'",
                 UserWarning,
+                stacklevel=2,
             )
             if subroutinize:
                 optimize_cff = CFFOptimization.SUBROUTINIZE
@@ -909,13 +910,15 @@ def interpolate_instance_ufos(
                 if include is not None and not fullmatch(include, instance.name):
                     continue
 
-                logger.info(f'Generating instance UFO for "{instance.name}"')
+                logger.info("Generating instance UFO for {!r}".format(instance.name))
 
                 try:
                     instance.font = generator.generate_instance(instance)
                 except instantiator.InstantiatorError as e:
                     raise FontmakeError(
-                        f"Interpolating instance '{instance.styleName}' failed.",
+                        "Interpolating instance {!r} failed.".format(
+                            instance.styleName
+                        ),
                         designspace.path,
                     ) from e
 

Lib/fontmake/instantiator.py

@@ -224,21 +224,36 @@ def from_designspace(
         # because the math behind varLib and MutatorMath uses the default font as the
         # point of reference for all data.
         default_font = designspace.default.font
+        non_default_layer_name = designspace.default.layerName
+        default_source_uses_non_default_layer = non_default_layer_name is not None
+
         glyph_names: Set[str] = set(default_font.keys())
 
-        for source in designspace.sources:
-            other_names = set(source.font.keys())
-            diff_names = other_names - glyph_names
-            if diff_names:
-                logger.warning(
-                    "The source %s (%s) contains glyphs that are missing from the "
-                    "default source, which will be ignored: %s. If this is unintended, "
-                    "check that these glyphs have the exact same name as the "
-                    "corresponding glyphs in the default source.",
-                    source.name,
-                    source.filename,
-                    ", ".join(sorted(diff_names)),
-                )
+        if default_source_uses_non_default_layer:
+            try:
+                layer = default_font.layers[non_default_layer_name]
+            except KeyError as e:
+                raise InstantiatorError(
+                    f"Layer {non_default_layer_name!r} not found "
+                    f"in {designspace.default.filename}"
+                ) from e
+            layer = default_font.layers[non_default_layer_name]
+            glyph_names = layer.keys()
+            logger.info(f"Building from layer {layer.name}")
+        else:
+            for source in designspace.sources:
+                other_names = set(source.font.keys())
+                diff_names = other_names - glyph_names
+                if diff_names:
+                    logger.warning(
+                        "The source %s (%s) contains glyphs that are missing from the "
+                        "default source, which will be ignored: %s. If this is unintended, "
+                        "check that these glyphs have the exact same name as the "
+                        "corresponding glyphs in the default source.",
+                        source.name,
+                        source.filename,
+                        ", ".join(sorted(diff_names)),
+                    )
 
         # Construct Variators
         axis_bounds: AxisBounds = {}  # Design space!
@@ -279,7 +294,7 @@ def from_designspace(
                 glyph_mutators[glyph_name] = Variator.from_masters(items, axis_order)
             except varLib.errors.VarLibError as e:
                 raise InstantiatorError(
-                    f"Cannot set up glyph '{glyph_name}' for interpolation: {e}'"
+                    f"Cannot set up glyph {glyph_name} for interpolation: {e}'"
                 ) from e
             glyph_name_to_unicodes[glyph_name] = default_font[glyph_name].unicodes
 
@@ -382,7 +397,7 @@ def generate_instance(
                 # whatever reason (usually outline incompatibility)...
                 if glyph_name not in self.skip_export_glyphs:
                     raise InstantiatorError(
-                        f"Failed to generate instance of glyph '{glyph_name}': "
+                        f"Failed to generate instance of glyph {glyph_name!r}: "
                         f"{str(e)}. (Note: the most common cause for an error here is "
                         "that the glyph outlines are not point-for-point compatible or "
                         "have the same starting point or are in the same order in all "
@@ -494,9 +509,9 @@ def _error_msg_no_default(designspace: designspaceLib.DesignSpaceDocument) -> st
 
     return (
         "Can't generate UFOs from this Designspace because there is no default "
-        f"master source at location '{default_location}'. Check that all 'default' "
+        "master source at location {!r}. Check that all 'default' "
         "values of all axes together point to a single actual master source. "
-        f"{bonus_msg}"
+        "{!s}".format(default_location, bonus_msg)
     )
 
 
@@ -517,9 +532,11 @@ def collect_info_masters(
 ) -> List[Tuple[Location, FontMathObject]]:
     """Return master Info objects wrapped by MathInfo."""
     locations_and_masters = []
+
     for source in designspace.sources:
         if source.layerName is not None:
-            continue  # No font info in source layers.
+            if source is not designspace.default:
+                continue  # No font info in source layers.
 
         normalized_location = varLib.models.normalizeLocation(
             source.location, axis_bounds
@@ -541,9 +558,11 @@ def collect_kerning_masters(
     groups = designspace.default.font.groups
 
     locations_and_masters = []
+
     for source in designspace.sources:
         if source.layerName is not None:
-            continue  # No kerning in source layers.
+            if source is not designspace.default:
+                continue  # No kerning in source layers.
 
         # If a source has groups, they should match the default's.
         if source.font.groups and source.font.groups != groups:
@@ -665,8 +684,9 @@ def swap_glyph_names(font: ufoLib2.Font, name_old: str, name_new: str):
 
     if name_old not in font or name_new not in font:
         raise InstantiatorError(
-            f"Cannot swap glyphs '{name_old}' and '{name_new}', as either or both are "
-            "missing."
+            "Cannot swap glyphs {!r} and {!r}, as either or both are missing".format(
+                name_old, name_new
+            )
         )
 
     # 1. Swap outlines and glyph width. Ignore lib content and other properties.

tests/data/MutatorSans/MutatorSans-non-default-layer.designspace

@@ -0,0 +1,29 @@
+<?xml version='1.0' encoding='UTF-8'?>
+<designspace format="4.0">
+  <axes>
+    <axis tag="wdth" name="width" minimum="0" maximum="1000" default="0"/>
+    <axis tag="wght" name="weight" minimum="0" maximum="1000" default="0"/>
+  </axes>
+  <sources>
+    <source filename="MutatorSansLightCondensed.ufo" name="master.MutatorMathTest.LightCondensed.0" familyname="MutatorMathTest" stylename="LightCondensed" layer="support">
+      <lib copy="1"/>
+      <groups copy="1"/>
+      <features copy="1"/>
+      <info copy="1"/>
+      <location>
+        <dimension name="width" xvalue="0"/>
+        <dimension name="weight" xvalue="0"/>
+      </location>
+    </source>
+  </sources>
+  <instances>
+    <instance familyname="MutatorMathTest" stylename="LightCondensed" filename="instances/MutatorMathTest-LightCondensed.ufo" postscriptfontname="MutatorMathTest-LightCondensed">
+      <location>
+        <dimension name="width" xvalue="0"/>
+        <dimension name="weight" xvalue="0"/>
+      </location>
+      <kerning/>
+      <info/>
+    </instance>
+  </instances>
+</designspace>

tests/test_instantiator.py

@@ -420,6 +420,18 @@ def test_interpolation_masters_as_instances(data_dir):
     assert instance_font["l"].width == 280
 
 
+def test_non_default_layer(data_dir, caplog):
+    designspace = designspaceLib.DesignSpaceDocument.fromfile(
+        data_dir / "MutatorSans" / "MutatorSans-non-default-layer.designspace"
+    )
+    designspace.loadSourceFonts(ufoLib2.Font.open)
+    generator = fontmake.instantiator.Instantiator.from_designspace(
+        designspace, round_geometry=True
+    )
+    instance_font = generator.generate_instance(designspace.instances[0])
+    assert {g.name for g in instance_font} == {"A", "S", "W"}
+
+
 def test_instance_attributes(data_dir):
     designspace = designspaceLib.DesignSpaceDocument.fromfile(
         data_dir / "DesignspaceTest" / "DesignspaceTest-instance-attrs.designspace"