filters: sort glyphs by decreasing component depth to avoid order-dep…

…endent issues

Fixes #621

Lib/ufo2ft/filters/base.py

@@ -3,7 +3,7 @@
 
 from fontTools.misc.loggingTools import Timer
 
-from ufo2ft.util import _GlyphSet, _LazyFontName
+from ufo2ft.util import _GlyphSet, _LazyFontName, getMaxComponentDepth
 
 logger = logging.getLogger(__name__)
 
@@ -186,9 +186,16 @@ def __call__(self, font, glyphSet=None):
         include = self.include
         modified = context.modified
 
+        # process composite glyphs in decreasing component depth order (i.e. composites
+        # with more deeply nested components before shallower ones) to avoid
+        # order-dependent interferences while filtering glyphs with nested components
+        # https://github.com/googlefonts/ufo2ft/issues/621
+        orderedGlyphs = sorted(
+            glyphSet.keys(), key=lambda g: -getMaxComponentDepth(glyphSet[g], glyphSet)
+        )
+
         with Timer() as t:
-            # we sort the glyph names to make loop deterministic
-            for glyphName in sorted(glyphSet.keys()):
+            for glyphName in orderedGlyphs:
                 if glyphName in modified:
                     continue
                 glyph = glyphSet[glyphName]

Lib/ufo2ft/util.py

@@ -546,3 +546,28 @@ def ensure_all_sources_have_names(doc: DesignSpaceDocument) -> None:
             source.name = f"temp_master.{counter}"
             counter += 1
         used_names.add(source.name)
+
+
+def getMaxComponentDepth(glyph, glyphSet, maxComponentDepth=0):
+    """Return the height of a composite glyph's tree of components.
+
+    This is equal to the depth of its deepest node, where the depth
+    means the number of edges (component references) from the node
+    to the tree's root.
+
+    For glyphs that contain no components, only contours, this is 0.
+    Composite glyphs have max component depth of 1 or greater.
+    """
+    if not glyph.components:
+        return maxComponentDepth
+
+    maxComponentDepth += 1
+
+    initialMaxComponentDepth = maxComponentDepth
+    for component in glyph.components:
+        componentDepth = getMaxComponentDepth(
+            glyphSet[component.baseGlyph], glyphSet, initialMaxComponentDepth
+        )
+        maxComponentDepth = max(maxComponentDepth, componentDepth)
+
+    return maxComponentDepth