path: root/contrib/python/fonttools/fontTools/voltLib/voltToFea.py

"""\
MS VOLT ``.vtp`` to AFDKO ``.fea`` OpenType Layout converter.

Usage
-----

To convert a VTP project file:


.. code-block:: sh

    $ fonttools voltLib.voltToFea input.vtp output.fea

It is also possible convert font files with `TSIV` table (as saved from Volt),
in this case the glyph names used in the Volt project will be mapped to the
actual glyph names in the font files when written to the feature file:

.. code-block:: sh

    $ fonttools voltLib.voltToFea input.ttf output.fea

The ``--quiet`` option can be used to suppress warnings.

The ``--traceback`` can be used to get Python traceback in case of exceptions,
instead of suppressing the traceback.


Limitations
-----------

* Not all VOLT features are supported, the script will error if it it
  encounters something it does not understand. Please report an issue if this
  happens.
* AFDKO feature file syntax for mark positioning is awkward and does not allow
  setting the mark coverage. It also defines mark anchors globally, as a result
  some mark positioning lookups might cover many marks than what was in the VOLT
  file. This should not be an issue in practice, but if it is then the only way
  is to modify the VOLT file or the generated feature file manually to use unique
  mark anchors for each lookup.
* VOLT allows subtable breaks in any lookup type, but AFDKO feature file
  implementations vary in their support; currently AFDKO’s makeOTF supports
  subtable breaks in pair positioning lookups only, while FontTools’ feaLib
  support it for most substitution lookups and only some positioning lookups.
"""

import logging
import re
from io import StringIO
from graphlib import TopologicalSorter

from fontTools.feaLib import ast
from fontTools.ttLib import TTFont, TTLibError
from fontTools.voltLib import ast as VAst
from fontTools.voltLib.parser import Parser as VoltParser

log = logging.getLogger("fontTools.voltLib.voltToFea")

TABLES = ["GDEF", "GSUB", "GPOS"]


def _flatten_group(group):
    ret = []
    if isinstance(group, (tuple, list)):
        for item in group:
            ret.extend(_flatten_group(item))
    elif hasattr(group, "enum"):
        ret.extend(_flatten_group(group.enum))
    else:
        ret.append(group)
    return ret


# Topologically sort of group definitions to ensure that all groups are defined
# before they are referenced. This is necessary because FEA requires it but
# VOLT does not, see below.
def sort_groups(groups):
    group_map = {group.name.lower(): group for group in groups}
    graph = {
        group.name.lower(): [
            x.group.lower()
            for x in _flatten_group(group)
            if isinstance(x, VAst.GroupName)
        ]
        for group in groups
    }
    sorter = TopologicalSorter(graph)
    return [group_map[name] for name in sorter.static_order()]


class Lookup(ast.LookupBlock):
    def __init__(self, name, use_extension=False, location=None):
        super().__init__(name, use_extension, location)
        self.chained = []


class VoltToFea:
    _NOT_LOOKUP_NAME_RE = re.compile(r"[^A-Za-z_0-9.]")
    _NOT_CLASS_NAME_RE = re.compile(r"[^A-Za-z_0-9.\-]")

    def __init__(self, file_or_path, font=None):
        if isinstance(file_or_path, VAst.VoltFile):
            self._doc, self._file_or_path = file_or_path, None
        else:
            self._doc, self._file_or_path = None, file_or_path
        self._font = font

        self._glyph_map = {}
        self._glyph_order = None

        self._gdef = {}
        self._glyphclasses = {}
        self._features = {}
        self._lookups = {}

        self._marks = set()
        self._ligatures = {}

        self._markclasses = {}
        self._anchors = {}

        self._settings = {}

        self._lookup_names = {}
        self._class_names = {}

    def _lookupName(self, name):
        if name not in self._lookup_names:
            res = self._NOT_LOOKUP_NAME_RE.sub("_", name)
            while res in self._lookup_names.values():
                res += "_"
            self._lookup_names[name] = res
        return self._lookup_names[name]

    def _className(self, name):
        if name not in self._class_names:
            res = self._NOT_CLASS_NAME_RE.sub("_", name)
            while res in self._class_names.values():
                res += "_"
            self._class_names[name] = res
        return self._class_names[name]

    def _collectStatements(self, doc, tables, ignore_unsupported_settings=False):
        # Collect glyph difinitions first, as we need them to map VOLT glyph names to font glyph name.
        for statement in doc.statements:
            if isinstance(statement, VAst.GlyphDefinition):
                self._glyphDefinition(statement)

        # Collect and sort group definitions first, to make sure a group
        # definition that references other groups comes after them since VOLT
        # does not enforce such ordering, and feature file require it.
        groups = [s for s in doc.statements if isinstance(s, VAst.GroupDefinition)]
        for group in sort_groups(groups):
            self._groupDefinition(group)

        for statement in doc.statements:
            if isinstance(statement, VAst.AnchorDefinition):
                if "GPOS" in tables:
                    self._anchorDefinition(statement)
            elif isinstance(statement, VAst.SettingDefinition):
                self._settingDefinition(statement, ignore_unsupported_settings)
            elif isinstance(statement, (VAst.GlyphDefinition, VAst.GroupDefinition)):
                pass  # Handled above
            elif isinstance(statement, VAst.ScriptDefinition):
                self._scriptDefinition(statement)
            elif not isinstance(statement, VAst.LookupDefinition):
                raise NotImplementedError(statement)

        # Lookup definitions need to be handled last as they reference glyph
        # and mark classes that might be defined after them.
        for statement in doc.statements:
            if isinstance(statement, VAst.LookupDefinition):
                if statement.pos and "GPOS" not in tables:
                    continue
                if statement.sub and "GSUB" not in tables:
                    continue
                self._lookupDefinition(statement)

    def _buildFeatureFile(self, tables):
        doc = ast.FeatureFile()
        statements = doc.statements

        if self._glyphclasses:
            statements.append(ast.Comment("# Glyph classes"))
            statements.extend(self._glyphclasses.values())

        if self._markclasses:
            statements.append(ast.Comment("\n# Mark classes"))
            statements.extend(c[1] for c in sorted(self._markclasses.items()))

        if self._lookups:
            statements.append(ast.Comment("\n# Lookups"))
            for lookup in self._lookups.values():
                statements.extend(lookup.chained)
                statements.append(lookup)

        # Prune features
        features = self._features.copy()
        for feature_tag in features:
            scripts = features[feature_tag]
            for script_tag in scripts:
                langs = scripts[script_tag]
                for language_tag in langs:
                    langs[language_tag] = [
                        l for l in langs[language_tag] if l.lower() in self._lookups
                    ]
                scripts[script_tag] = {t: l for t, l in langs.items() if l}
            features[feature_tag] = {t: s for t, s in scripts.items() if s}
        features = {t: f for t, f in features.items() if f}

        if features:
            statements.append(ast.Comment("# Features"))
            for feature_tag, scripts in features.items():
                feature = ast.FeatureBlock(feature_tag)
                script_tags = sorted(scripts, key=lambda k: 0 if k == "DFLT" else 1)
                if feature_tag == "aalt" and len(script_tags) > 1:
                    log.warning(
                        "FEA syntax does not allow script statements in 'aalt' feature, "
                        "so only lookups from the first script will be included."
                    )
                    script_tags = script_tags[:1]
                for script_tag in script_tags:
                    if feature_tag != "aalt":
                        feature.statements.append(ast.ScriptStatement(script_tag))
                    language_tags = sorted(
                        scripts[script_tag],
                        key=lambda k: 0 if k == "dflt" else 1,
                    )
                    if feature_tag == "aalt" and len(language_tags) > 1:
                        log.warning(
                            "FEA syntax does not allow language statements in 'aalt' feature, "
                            "so only lookups from the first language will be included."
                        )
                        language_tags = language_tags[:1]
                    for language_tag in language_tags:
                        if feature_tag != "aalt":
                            include_default = True if language_tag == "dflt" else False
                            feature.statements.append(
                                ast.LanguageStatement(
                                    language_tag.ljust(4),
                                    include_default=include_default,
                                )
                            )
                        for name in scripts[script_tag][language_tag]:
                            lookup = self._lookups[name.lower()]
                            lookupref = ast.LookupReferenceStatement(lookup)
                            feature.statements.append(lookupref)
                statements.append(feature)

        if self._gdef and "GDEF" in tables:
            classes = []
            for name in ("BASE", "MARK", "LIGATURE", "COMPONENT"):
                if name in self._gdef:
                    classname = "GDEF_" + name.lower()
                    glyphclass = ast.GlyphClassDefinition(classname, self._gdef[name])
                    statements.append(glyphclass)
                    classes.append(ast.GlyphClassName(glyphclass))
                else:
                    classes.append(None)

            gdef = ast.TableBlock("GDEF")
            gdef.statements.append(ast.GlyphClassDefStatement(*classes))
            statements.append(gdef)

        return doc

    def convert(self, tables=None, ignore_unsupported_settings=False):
        if self._doc is None:
            self._doc = VoltParser(self._file_or_path).parse()
        doc = self._doc

        if tables is None:
            tables = TABLES
        if self._font is not None:
            self._glyph_order = self._font.getGlyphOrder()

        self._collectStatements(doc, tables, ignore_unsupported_settings)
        fea = self._buildFeatureFile(tables)
        return fea.asFea()

    def _glyphName(self, glyph):
        try:
            name = glyph.glyph
        except AttributeError:
            name = glyph
        return ast.GlyphName(self._glyph_map.get(name, name))

    def _groupName(self, group):
        try:
            name = group.group
        except AttributeError:
            name = group
        return ast.GlyphClassName(self._glyphclasses[name.lower()])

    def _glyphSet(self, item):
        return [
            (self._glyphName(x) if isinstance(x, (str, VAst.GlyphName)) else x)
            for x in item.glyphSet()
        ]

    def _coverage(self, coverage, flatten=False):
        items = []
        for item in coverage:
            if isinstance(item, VAst.GlyphName):
                items.append(self._glyphName(item))
            elif isinstance(item, VAst.GroupName):
                items.append(self._groupName(item))
            elif isinstance(item, VAst.Enum):
                item = self._coverage(item.enum, flatten=True)
                if flatten:
                    items.extend(item)
                else:
                    items.append(ast.GlyphClass(item))
            elif isinstance(item, VAst.Range):
                item = self._glyphSet(item)
                if flatten:
                    items.extend(item)
                else:
                    items.append(ast.GlyphClass(item))
            else:
                raise NotImplementedError(item)
        return items

    def _context(self, context):
        out = []
        for item in context:
            coverage = self._coverage(item, flatten=True)
            if len(coverage) > 1:
                coverage = ast.GlyphClass(coverage)
            else:
                coverage = coverage[0]
            out.append(coverage)
        return out

    def _groupDefinition(self, group):
        name = self._className(group.name)
        glyphs = self._coverage(group.enum.enum, flatten=True)
        glyphclass = ast.GlyphClass(glyphs)
        classdef = ast.GlyphClassDefinition(name, glyphclass)
        self._glyphclasses[group.name.lower()] = classdef

    def _glyphDefinition(self, glyph):
        try:
            self._glyph_map[glyph.name] = self._glyph_order[glyph.id]
        except TypeError:
            pass

        if glyph.type in ("BASE", "MARK", "LIGATURE", "COMPONENT"):
            if glyph.type not in self._gdef:
                self._gdef[glyph.type] = ast.GlyphClass()
            self._gdef[glyph.type].glyphs.append(self._glyphName(glyph.name))

        if glyph.type == "MARK":
            self._marks.add(glyph.name)
        elif glyph.type == "LIGATURE":
            self._ligatures[glyph.name] = glyph.components

    def _scriptDefinition(self, script):
        stag = script.tag
        for lang in script.langs:
            ltag = lang.tag
            for feature in lang.features:
                lookups = {l.split("\\")[0]: True for l in feature.lookups}
                ftag = feature.tag
                if ftag not in self._features:
                    self._features[ftag] = {}
                if stag not in self._features[ftag]:
                    self._features[ftag][stag] = {}
                assert ltag not in self._features[ftag][stag]
                self._features[ftag][stag][ltag] = lookups.keys()

    def _settingDefinition(self, setting, ignore_unsupported=False):
        if setting.name.startswith("COMPILER_"):
            self._settings[setting.name] = setting.value
        elif not ignore_unsupported:
            log.warning(f"Unsupported setting ignored: {setting.name}")

    def _adjustment(self, adjustment):
        adv, dx, dy, adv_adjust_by, dx_adjust_by, dy_adjust_by = adjustment

        adv_device = adv_adjust_by and adv_adjust_by.items() or None
        dx_device = dx_adjust_by and dx_adjust_by.items() or None
        dy_device = dy_adjust_by and dy_adjust_by.items() or None

        return ast.ValueRecord(
            xPlacement=dx,
            yPlacement=dy,
            xAdvance=adv,
            xPlaDevice=dx_device,
            yPlaDevice=dy_device,
            xAdvDevice=adv_device,
        )

    def _anchor(self, adjustment):
        adv, dx, dy, adv_adjust_by, dx_adjust_by, dy_adjust_by = adjustment

        assert not adv_adjust_by
        dx_device = dx_adjust_by and dx_adjust_by.items() or None
        dy_device = dy_adjust_by and dy_adjust_by.items() or None

        return ast.Anchor(
            dx or 0,
            dy or 0,
            xDeviceTable=dx_device or None,
            yDeviceTable=dy_device or None,
        )

    def _anchorDefinition(self, anchordef):
        anchorname = anchordef.name
        glyphname = anchordef.glyph_name
        anchor = self._anchor(anchordef.pos)

        if glyphname not in self._anchors:
            self._anchors[glyphname] = {}
        if anchorname.startswith("MARK_"):
            anchorname = anchorname[:5] + anchorname[5:].lower()
        else:
            anchorname = anchorname.lower()
        if anchorname not in self._anchors[glyphname]:
            self._anchors[glyphname][anchorname] = {}
        self._anchors[glyphname][anchorname][anchordef.component] = anchor

    def _gposLookup(self, lookup, fealookup):
        statements = fealookup.statements

        pos = lookup.pos
        if isinstance(pos, VAst.PositionAdjustPairDefinition):
            for (idx1, idx2), (pos1, pos2) in pos.adjust_pair.items():
                coverage_1 = pos.coverages_1[idx1 - 1]
                coverage_2 = pos.coverages_2[idx2 - 1]

                # If not both are groups, use “enum pos” otherwise makeotf will
                # fail.
                enumerated = False
                for item in coverage_1 + coverage_2:
                    if not isinstance(item, VAst.GroupName):
                        enumerated = True

                glyphs1 = self._coverage(coverage_1)
                glyphs2 = self._coverage(coverage_2)
                record1 = self._adjustment(pos1)
                record2 = self._adjustment(pos2)
                assert len(glyphs1) == 1
                assert len(glyphs2) == 1
                statements.append(
                    ast.PairPosStatement(
                        glyphs1[0], record1, glyphs2[0], record2, enumerated=enumerated
                    )
                )
        elif isinstance(pos, VAst.PositionAdjustSingleDefinition):
            for a, b in pos.adjust_single:
                glyphs = self._coverage(a)
                record = self._adjustment(b)
                assert len(glyphs) == 1
                statements.append(
                    ast.SinglePosStatement([(glyphs[0], record)], [], [], False)
                )
        elif isinstance(pos, VAst.PositionAttachDefinition):
            anchors = {}
            allmarks = set()
            for coverage, anchorname in pos.coverage_to:
                # In feature files mark classes are global, but in VOLT they
                # are defined per-lookup. If we output mark class definitions
                # for all marks that use a given anchor, we might end up with a
                # mark used in two different classes in the same lookup, which
                # is causes feature file compilation error.
                # At the expense of uglier feature code, we make the mark class
                # name by appending the current lookup name not the anchor
                # name, and output mark class definitions only for marks used
                # in this lookup.
                classname = self._className(f"{anchorname}.{lookup.name}")
                markclass = ast.MarkClass(classname)

                # Anchor names are case-insensitive in VOLT
                anchorname = anchorname.lower()

                # We might still end in marks used in two different anchor
                # classes, so we filter out already used marks.
                marks = set()
                for mark in coverage:
                    marks.update(mark.glyphSet())
                if not marks.isdisjoint(allmarks):
                    marks.difference_update(allmarks)
                    if not marks:
                        continue
                allmarks.update(marks)

                for glyphname in marks:
                    glyph = self._glyphName(glyphname)
                    anchor = self._anchors[glyphname][f"MARK_{anchorname}"][1]
                    markdef = ast.MarkClassDefinition(markclass, anchor, glyph)
                    self._markclasses[(glyphname, classname)] = markdef

                for base in pos.coverage:
                    for name in base.glyphSet():
                        if name not in anchors:
                            anchors[name] = []
                        if (anchorname, classname) not in anchors[name]:
                            anchors[name].append((anchorname, classname))

            is_ligature = all(n in self._ligatures for n in anchors)
            is_mark = all(n in self._marks for n in anchors)
            for name in anchors:
                components = 1
                if is_ligature:
                    components = self._ligatures[name]

                marks = [[] for _ in range(components)]
                for mark, classname in anchors[name]:
                    markclass = ast.MarkClass(classname)
                    for component in range(1, components + 1):
                        if component in self._anchors[name][mark]:
                            anchor = self._anchors[name][mark][component]
                            marks[component - 1].append((anchor, markclass))

                base = self._glyphName(name)
                if is_mark:
                    mark = ast.MarkMarkPosStatement(base, marks[0])
                elif is_ligature:
                    mark = ast.MarkLigPosStatement(base, marks)
                else:
                    mark = ast.MarkBasePosStatement(base, marks[0])
                statements.append(mark)
        elif isinstance(pos, VAst.PositionAttachCursiveDefinition):
            # Collect enter and exit glyphs
            enter_coverage = []
            for coverage in pos.coverages_enter:
                for base in coverage:
                    for name in base.glyphSet():
                        enter_coverage.append(name)
            exit_coverage = []
            for coverage in pos.coverages_exit:
                for base in coverage:
                    for name in base.glyphSet():
                        exit_coverage.append(name)

            # Write enter anchors, also check if the glyph has exit anchor and
            # write it, too.
            for name in enter_coverage:
                glyph = self._glyphName(name)
                entry = self._anchors[name]["entry"][1]
                exit = None
                if name in exit_coverage:
                    exit = self._anchors[name]["exit"][1]
                    exit_coverage.pop(exit_coverage.index(name))
                statements.append(ast.CursivePosStatement(glyph, entry, exit))

            # Write any remaining exit anchors.
            for name in exit_coverage:
                glyph = self._glyphName(name)
                exit = self._anchors[name]["exit"][1]
                statements.append(ast.CursivePosStatement(glyph, None, exit))
        else:
            raise NotImplementedError(pos)

    def _gposContextLookup(self, lookup, prefix, suffix, ignore, fealookup, chained):
        statements = fealookup.statements

        pos = lookup.pos
        if isinstance(pos, VAst.PositionAdjustPairDefinition):
            for (idx1, idx2), (pos1, pos2) in pos.adjust_pair.items():
                glyphs1 = self._coverage(pos.coverages_1[idx1 - 1])
                glyphs2 = self._coverage(pos.coverages_2[idx2 - 1])
                assert len(glyphs1) == 1
                assert len(glyphs2) == 1
                glyphs = (glyphs1[0], glyphs2[0])

                if ignore:
                    statement = ast.IgnorePosStatement([(prefix, glyphs, suffix)])
                else:
                    statement = ast.ChainContextPosStatement(
                        prefix, glyphs, suffix, [chained, chained]
                    )
                statements.append(statement)
        elif isinstance(pos, VAst.PositionAdjustSingleDefinition):
            glyphs = [ast.GlyphClass()]
            for a, _ in pos.adjust_single:
                glyphs[0].extend(self._coverage(a, flatten=True))

            if ignore:
                statement = ast.IgnorePosStatement([(prefix, glyphs, suffix)])
            else:
                statement = ast.ChainContextPosStatement(
                    prefix, glyphs, suffix, [chained]
                )
            statements.append(statement)
        elif isinstance(pos, VAst.PositionAttachDefinition):
            glyphs = [ast.GlyphClass()]
            for coverage, _ in pos.coverage_to:
                glyphs[0].extend(self._coverage(coverage, flatten=True))

            if ignore:
                statement = ast.IgnorePosStatement([(prefix, glyphs, suffix)])
            else:
                statement = ast.ChainContextPosStatement(
                    prefix, glyphs, suffix, [chained]
                )
            statements.append(statement)
        else:
            raise NotImplementedError(pos)

    def _gsubLookup(self, lookup, fealookup):
        statements = fealookup.statements

        sub = lookup.sub

        # Alternate substitutions are represented by adding multiple
        # substitutions for the same glyph, so we need to collect them into one
        # to many mapping.
        if isinstance(sub, VAst.SubstitutionAlternateDefinition):
            alternates = {}
            for key, val in sub.mapping.items():
                if not key or not val:
                    path, line, column = sub.location
                    log.warning(f"{path}:{line}:{column}: Ignoring empty substitution")
                    continue
                glyphs = self._coverage(key)
                replacements = self._coverage(val)
                assert len(glyphs) == 1
                for src_glyph, repl_glyph in zip(
                    glyphs[0].glyphSet(), replacements[0].glyphSet()
                ):
                    alternates.setdefault(str(self._glyphName(src_glyph)), []).append(
                        str(self._glyphName(repl_glyph))
                    )

            for glyph, replacements in alternates.items():
                statement = ast.AlternateSubstStatement(
                    [], glyph, [], ast.GlyphClass(replacements)
                )
                statements.append(statement)
            return

        for key, val in sub.mapping.items():
            if not key or not val:
                path, line, column = sub.location
                log.warning(f"{path}:{line}:{column}: Ignoring empty substitution")
                continue
            glyphs = self._coverage(key)
            replacements = self._coverage(val)
            if isinstance(sub, VAst.SubstitutionSingleDefinition):
                assert len(glyphs) == 1
                assert len(replacements) == 1
                statements.append(
                    ast.SingleSubstStatement(glyphs, replacements, [], [], False)
                )
            elif isinstance(sub, VAst.SubstitutionReverseChainingSingleDefinition):
                # This is handled in gsubContextLookup()
                pass
            elif isinstance(sub, VAst.SubstitutionMultipleDefinition):
                assert len(glyphs) == 1
                statements.append(
                    ast.MultipleSubstStatement([], glyphs[0], [], replacements)
                )
            elif isinstance(sub, VAst.SubstitutionLigatureDefinition):
                assert len(replacements) == 1
                statement = ast.LigatureSubstStatement(
                    [], glyphs, [], replacements[0], False
                )

                # If any of the input glyphs is a group, we need to
                # explode the substitution into multiple ligature substitutions
                # since feature file syntax does not support classes in
                # ligature substitutions.
                n = max(len(x.glyphSet()) for x in glyphs)
                if n > 1:
                    # All input should either be groups of the same length or single glyphs
                    assert all(len(x.glyphSet()) in (n, 1) for x in glyphs)
                    glyphs = [x.glyphSet() for x in glyphs]
                    glyphs = [([x[0]] * n if len(x) == 1 else x) for x in glyphs]

                    # In this case ligature replacements must be a group of the same length
                    # as the input groups, or a single glyph. VOLT
                    # allows the replacement glyphs to be longer and truncates them.
                    # So well allow that and zip() below will do the truncation
                    # for us.
                    replacement = replacements[0].glyphSet()
                    if len(replacement) == 1:
                        replacement = [replacement[0]] * n
                    assert len(replacement) >= n

                    # Add the unexploded statement commented out for reference.
                    statements.append(ast.Comment(f"# {statement}"))

                    for zipped in zip(*glyphs, replacement):
                        zipped = [self._glyphName(x) for x in zipped]
                        statements.append(
                            ast.LigatureSubstStatement(
                                [], zipped[:-1], [], zipped[-1], False
                            )
                        )
                else:
                    statements.append(statement)
            else:
                raise NotImplementedError(sub)

    def _gsubContextLookup(self, lookup, prefix, suffix, ignore, fealookup, chained):
        statements = fealookup.statements

        sub = lookup.sub

        if isinstance(sub, VAst.SubstitutionReverseChainingSingleDefinition):
            # Reverse substitutions is a special case, it can’t use chained lookups.
            for key, val in sub.mapping.items():
                if not key or not val:
                    path, line, column = sub.location
                    log.warning(f"{path}:{line}:{column}: Ignoring empty substitution")
                    continue
                glyphs = self._coverage(key)
                replacements = self._coverage(val)
                statements.append(
                    ast.ReverseChainSingleSubstStatement(
                        prefix, suffix, glyphs, replacements
                    )
                )
            fealookup.chained = []
            return

        if not isinstance(
            sub,
            (
                VAst.SubstitutionSingleDefinition,
                VAst.SubstitutionMultipleDefinition,
                VAst.SubstitutionLigatureDefinition,
                VAst.SubstitutionAlternateDefinition,
            ),
        ):
            raise NotImplementedError(type(sub))

        glyphs = []
        for key, val in sub.mapping.items():
            if not key or not val:
                path, line, column = sub.location
                log.warning(f"{path}:{line}:{column}: Ignoring empty substitution")
                continue
            glyphs.extend(self._coverage(key, flatten=True))

        if len(glyphs) > 1:
            glyphs = [ast.GlyphClass(glyphs)]
        if ignore:
            statements.append(ast.IgnoreSubstStatement([(prefix, glyphs, suffix)]))
        else:
            statements.append(
                ast.ChainContextSubstStatement(prefix, glyphs, suffix, [chained])
            )

    def _lookupDefinition(self, lookup):
        mark_attachement = None
        mark_filtering = None

        flags = 0
        if lookup.direction == "RTL":
            flags |= 1
        if not lookup.process_base:
            flags |= 2
        # FIXME: Does VOLT support this?
        # if not lookup.process_ligatures:
        #     flags |= 4
        if not lookup.process_marks:
            flags |= 8
        elif isinstance(lookup.process_marks, str):
            mark_attachement = self._groupName(lookup.process_marks)
        elif lookup.mark_glyph_set is not None:
            mark_filtering = self._groupName(lookup.mark_glyph_set)

        lookupflags = None
        if flags or mark_attachement is not None or mark_filtering is not None:
            lookupflags = ast.LookupFlagStatement(
                flags, mark_attachement, mark_filtering
            )

        use_extension = False
        if self._settings.get("COMPILER_USEEXTENSIONLOOKUPS"):
            use_extension = True

        if "\\" in lookup.name:
            # Merge sub lookups as subtables (lookups named “base\sub”),
            # makeotf/feaLib will issue a warning and ignore the subtable
            # statement if it is not a pairpos lookup, though.
            name = lookup.name.split("\\")[0]
            if name.lower() not in self._lookups:
                fealookup = Lookup(
                    self._lookupName(name),
                    use_extension=use_extension,
                )
                if lookupflags is not None:
                    fealookup.statements.append(lookupflags)
                fealookup.statements.append(ast.Comment("# " + lookup.name))
            else:
                fealookup = self._lookups[name.lower()]
                fealookup.statements.append(ast.SubtableStatement())
                fealookup.statements.append(ast.Comment("# " + lookup.name))
            self._lookups[name.lower()] = fealookup
        else:
            fealookup = Lookup(
                self._lookupName(lookup.name),
                use_extension=use_extension,
            )
            if lookupflags is not None:
                fealookup.statements.append(lookupflags)
            self._lookups[lookup.name.lower()] = fealookup

        if lookup.comments is not None:
            fealookup.statements.append(ast.Comment("# " + lookup.comments))

        contexts = []
        for context in lookup.context:
            prefix = self._context(context.left)
            suffix = self._context(context.right)
            ignore = context.ex_or_in == "EXCEPT_CONTEXT"
            contexts.append([prefix, suffix, ignore])
            # It seems that VOLT will create contextual substitution using
            # only the input if there is no other contexts in this lookup.
            if ignore and len(lookup.context) == 1:
                contexts.append([[], [], False])

        if contexts:
            chained = ast.LookupBlock(
                self._lookupName(lookup.name + " chained"),
                use_extension=use_extension,
            )
            fealookup.chained.append(chained)
            if lookup.sub is not None:
                self._gsubLookup(lookup, chained)
            elif lookup.pos is not None:
                self._gposLookup(lookup, chained)
            for prefix, suffix, ignore in contexts:
                if lookup.sub is not None:
                    self._gsubContextLookup(
                        lookup, prefix, suffix, ignore, fealookup, chained
                    )
                elif lookup.pos is not None:
                    self._gposContextLookup(
                        lookup, prefix, suffix, ignore, fealookup, chained
                    )
        else:
            if lookup.sub is not None:
                self._gsubLookup(lookup, fealookup)
            elif lookup.pos is not None:
                self._gposLookup(lookup, fealookup)


def main(args=None):
    """Convert MS VOLT to AFDKO feature files."""

    import argparse
    from pathlib import Path

    from fontTools import configLogger

    parser = argparse.ArgumentParser(
        "fonttools voltLib.voltToFea", description=main.__doc__
    )
    parser.add_argument(
        "input", metavar="INPUT", type=Path, help="input font/VTP file to process"
    )
    parser.add_argument(
        "featurefile", metavar="OUTPUT", type=Path, help="output feature file"
    )
    parser.add_argument(
        "-t",
        "--table",
        action="append",
        choices=TABLES,
        dest="tables",
        help="List of tables to write, by default all tables are written",
    )
    parser.add_argument(
        "-q", "--quiet", action="store_true", help="Suppress non-error messages"
    )
    parser.add_argument(
        "--traceback", action="store_true", help="Don’t catch exceptions"
    )

    options = parser.parse_args(args)

    configLogger(level=("ERROR" if options.quiet else "INFO"))

    file_or_path = options.input
    font = None
    try:
        font = TTFont(file_or_path)
        if "TSIV" in font:
            file_or_path = StringIO(font["TSIV"].data.decode("utf-8"))
        else:
            log.error('"TSIV" table is missing, font was not saved from VOLT?')
            return 1
    except TTLibError:
        pass

    converter = VoltToFea(file_or_path, font)
    try:
        fea = converter.convert(options.tables)
    except NotImplementedError as e:
        if options.traceback:
            raise
        location = getattr(e.args[0], "location", None)
        message = f'"{e}" is not supported'
        if location:
            path, line, column = location
            log.error(f"{path}:{line}:{column}: {message}")
        else:
            log.error(message)
        return 1
    with open(options.featurefile, "w") as feafile:
        feafile.write(fea)


if __name__ == "__main__":
    import sys

    sys.exit(main())