Port fontc' propagate_anchors.rs to .py, apply as preflight transform…

… on GSFont

Fixes #368

Translate fontc' propagate_anchors.rs from Rust to Python and apply to the GSFont in the 'preflight' step before it's passed on to UFOBuilder
The Rust code was based off the original Glyphs.app's Objective-C code (Georg shared a snippet with us privately) and is as such more 'correct' then the old, reverse-engineered implementation.
The old glyphsLib.builder.anchor_propagation module is deprecated but kept around in case users may instantiate the UFOBuilder class directly with propagate_anchors=True.
Also, the existing `propagate_anchors` parameters of `to_designspace`, `to_ufos` and other high-level methods continues to have an equivalent effect but now controls the **new** propagate anchors logic. Clients such as fontmake do not need to do anything besides upgrading glyphsLib to use this.

Lib/glyphsLib/builder/__init__.py

@@ -18,7 +18,7 @@
 from glyphsLib import classes
 
 from .builders import UFOBuilder, GlyphsBuilder
-from .transformations import TRANSFORMATIONS
+from .transformations import TRANSFORMATIONS, TRANSFORMATION_CUSTOM_PARAMS
 
 logger = logging.getLogger(__name__)
 
@@ -64,11 +64,13 @@ def to_ufos(
     """
     if preserve_original:
         font = copy.deepcopy(font)
+    font = preflight_glyphs(
+        font, glyph_data=glyph_data, do_propagate_all_anchors=propagate_anchors
+    )
     builder = UFOBuilder(
-        preflight_glyphs(font),
+        font,
         ufo_module=ufo_module,
         family_name=family_name,
-        propagate_anchors=propagate_anchors,
         minimize_glyphs_diffs=minimize_glyphs_diffs,
         generate_GDEF=generate_GDEF,
         store_editor_state=store_editor_state,
@@ -129,13 +131,14 @@ def to_designspace(
     """
     if preserve_original:
         font = copy.deepcopy(font)
-
+    font = preflight_glyphs(
+        font, glyph_data=glyph_data, do_propagate_all_anchors=propagate_anchors
+    )
     builder = UFOBuilder(
-        preflight_glyphs(font),
+        font,
         ufo_module=ufo_module,
         family_name=family_name,
         instance_dir=instance_dir,
-        propagate_anchors=propagate_anchors,
         use_designspace=True,
         minimize_glyphs_diffs=minimize_glyphs_diffs,
         generate_GDEF=generate_GDEF,
@@ -148,12 +151,49 @@ def to_designspace(
     return builder.designspace
 
 
-def preflight_glyphs(font):
+def preflight_glyphs(font, *, glyph_data=None, **todos):
     """Run a set of transformations over a GSFont object to make
-    it easier to convert to UFO; resolve all the "smart stuff"."""
+    it easier to convert to UFO; resolve all the "smart stuff".
+
+    Currently, the transformations are:
+        - `propagate_all_anchors`: copy anchors from components to their parent
+
+    More transformations may be added in the future.
+
+    Some transformations may have custom parameters that can be set in the
+    font. For example, the `propagate_all_anchors` transformation can be
+    disabled by setting the custom parameter "Propagate Anchors" to False
+    (see `TRANSFORMATION_CUSTOM_PARAMS`).
+
+    Args:
+        font: a GSFont object
+        glyph_data: an optional GlyphData object associating various properties to
+            glyph names (e.g. category) that overrides the default one
+        **todos: a set of boolean flags to enable/disable specific transformations,
+            named `do_<transformation_name>`, e.g. `do_propagate_all_anchors=False`
+            will disable the propagation of anchors.
+
+    Returns:
+        the modified GSFont object
+    """
 
     for transform in TRANSFORMATIONS:
-        transform(font)
+        do_transform = todos.pop("do_" + transform.__name__, None)
+        if do_transform is True:
+            pass
+        elif do_transform is False:
+            continue
+        elif do_transform is None:
+            if transform in TRANSFORMATION_CUSTOM_PARAMS:
+                param = TRANSFORMATION_CUSTOM_PARAMS[transform]
+                if not font.customParameters.get(param.name, param.default):
+                    continue
+        else:
+            raise ValueError(f"Invalid value for do_{transform.__name__}")
+        logger.info(f"Running '{transform.__name__}' transformation")
+        transform(font, glyph_data=glyph_data)
+    if todos:
+        logger.warning(f"preflight_glyphs has unused `todos` arguments: {todos}")
     return font
 
 

Lib/glyphsLib/builder/anchor_propagation.py

@@ -1,3 +1,11 @@
+"""This module is DEPRECATED and will be removed in a future release.
+
+For anchor propagation on GSFont objects, you can use the
+`glyphsLib.builder.transformations.propagate_anchors` module.
+For anchor propagation on UFO font objects, you can try the
+`ufo2ft.filters.propagateAnchors` filter.
+"""
+
 from fontTools.misc.transform import Transform
 import fontTools.pens.boundsPen
 

Lib/glyphsLib/builder/builders.py

@@ -28,7 +28,7 @@
     FONT_CUSTOM_PARAM_PREFIX,
 )
 from .axes import WEIGHT_AXIS_DEF, WIDTH_AXIS_DEF, find_base_style, class_to_value
-from glyphsLib.util import LoggerMixin
+from glyphsLib.util import LoggerMixin, _DeprecatedArgument
 
 
 class UFOBuilder(LoggerMixin):
@@ -41,7 +41,7 @@ def __init__(
         designspace_module=designspaceLib,
         family_name=None,
         instance_dir=None,
-        propagate_anchors=None,
+        propagate_anchors=_DeprecatedArgument,  # DEPRECATED
         use_designspace=False,
         minimize_glyphs_diffs=False,
         generate_GDEF=True,
@@ -66,9 +66,8 @@ def __init__(
                        only instances with this name will be returned.
         instance_dir -- if provided, instance UFOs will be located in this
                         directory, according to their Designspace filenames.
-        propagate_anchors -- set to True or False to explicitly control anchor
-                             propagation, the default is to check for
-                             "Propagate Anchors" custom parameter.
+        propagate_anchors -- DEPRECATED. Use preflight_glyphs to propagate anchors on
+                             the GSFont before building UFOs.
         use_designspace -- set to True to make optimal use of the designspace:
                            data that is common to all ufos will go there.
         minimize_glyphs_diffs -- set to True to store extra info in UFOs
@@ -106,9 +105,18 @@ def __init__(
         self.expand_includes = expand_includes
         self.minimal = minimal
 
-        if propagate_anchors is None:
-            propagate_anchors = font.customParameters["Propagate Anchors"]
-            propagate_anchors = bool(propagate_anchors is None or propagate_anchors)
+        if propagate_anchors is not _DeprecatedArgument:
+            from warnings import warn
+
+            warn(
+                "The 'propagate_anchors' argument is deprecated and will be removed "
+                "in a future version. "
+                "Use glyphsLib.builder.preflight_glyphs to propagate anchors on the "
+                "GSFont before building UFOs.",
+                DeprecationWarning,
+            )
+        else:
+            propagate_anchors = False
         self.propagate_anchors = propagate_anchors
 
         # The set of (SourceDescriptor + UFO)s that will be built,
@@ -215,7 +223,7 @@ def masters(self):
         for master_id, source in self._sources.items():
             ufo = source.font
             master = self.font.masters[master_id]
-            if self.propagate_anchors:
+            if self.propagate_anchors:  # deprecated, will be removed one day
                 self.to_ufo_propagate_font_anchors(ufo)  # .anchor_propagation
             if not self.minimal:
                 for layer in list(ufo.layers):

Lib/glyphsLib/builder/transformations/__init__.py

@@ -1 +1,20 @@
-TRANSFORMATIONS = []
+from types import MappingProxyType
+from typing import NamedTuple
+
+from .propagate_anchors import propagate_all_anchors
+
+TRANSFORMATIONS = [
+    propagate_all_anchors,
+]
+
+
+class _CustomParameter(NamedTuple):
+    name: str
+    default: bool
+
+
+TRANSFORMATION_CUSTOM_PARAMS = MappingProxyType(
+    {
+        propagate_all_anchors: _CustomParameter("Propagate Anchors", True),
+    }
+)

Lib/glyphsLib/util.py

@@ -176,3 +176,7 @@ def __next__(self):
 
     def peek(self, n=0):
         return self.list[self.index + n]
+
+
+# sentinel object to indicate a deprecated argument
+_DeprecatedArgument = object()

tests/builder/designspace_gen_test.py

@@ -26,6 +26,7 @@
 import glyphsLib
 from glyphsLib import to_designspace, to_glyphs
 from glyphsLib.util import open_ufo
+from glyphsLib.types import Point
 
 
 def test_designspace_generation_regular_same_family_name(tmpdir, ufo_module):
@@ -481,7 +482,7 @@ def test_designspace_generation_bracket_GDEF(datadir, ufo_module):
     for layer in font.glyphs["x"].layers:
         anchor = glyphsLib.classes.GSAnchor()
         anchor.name = "top"
-        anchor.position = (0, 0)
+        anchor.position = Point(0, 0)
         layer.anchors.append(anchor)
 
     designspace = to_designspace(font, ufo_module=ufo_module, generate_GDEF=True)

tests/classes_test.py

@@ -115,7 +115,7 @@ def add_anchor(font, glyphname, anchorname, x, y):
                 layer.anchors = getattr(layer, "anchors", [])
                 anchor = GSAnchor()
                 anchor.name = anchorname
-                anchor.position = (x, y)
+                anchor.position = Point(x, y)
                 layer.anchors.append(anchor)