# Source code for fontTools.feaLib.builder

    from fontTools.misc import sstruct
    from fontTools.misc.textTools import Tag, tostr, binary2num, safeEval
    from fontTools.feaLib.error import FeatureLibError
    from fontTools.feaLib.lookupDebugInfo import (
        LookupDebugInfo,
        LOOKUP_DEBUG_INFO_KEY,
        LOOKUP_DEBUG_ENV_VAR,
    )
    from fontTools.feaLib.parser import Parser
    from fontTools.feaLib.ast import FeatureFile
    from fontTools.feaLib.variableScalar import VariableScalar
    from fontTools.otlLib import builder as otl
    from fontTools.otlLib.maxContextCalc import maxCtxFont
    from fontTools.ttLib import newTable, getTableModule
    from fontTools.ttLib.tables import otBase, otTables
    from fontTools.otlLib.builder import (
        AlternateSubstBuilder,
        ChainContextPosBuilder,
        ChainContextSubstBuilder,
        LigatureSubstBuilder,
        MultipleSubstBuilder,
        CursivePosBuilder,
        MarkBasePosBuilder,
        MarkLigPosBuilder,
        MarkMarkPosBuilder,
        ReverseChainSingleSubstBuilder,
        SingleSubstBuilder,
        ClassPairPosSubtableBuilder,
        PairPosBuilder,
        SinglePosBuilder,
        ChainContextualRule,
    )
    from fontTools.otlLib.error import OpenTypeLibError
    from fontTools.varLib.varStore import OnlineVarStoreBuilder
    from fontTools.varLib.builder import buildVarDevTable
    from fontTools.varLib.featureVars import addFeatureVariationsRaw
    from fontTools.varLib.models import normalizeValue
    from collections import defaultdict
    import itertools
    from io import StringIO
    import logging
    import warnings
    import os

    log = logging.getLogger(__name__)

    def addOpenTypeFeatures(font, featurefile, tables=None, debug=False):
        """Add features from a file to a font. Note that this replaces any features
        currently present.

        Args:
            font (feaLib.ttLib.TTFont): The font object.
            featurefile: Either a path or file object (in which case we
                parse it into an AST), or a pre-parsed AST instance.
            tables: If passed, restrict the set of affected tables to those in the
                list.
            debug: Whether to add source debugging information to the font in the
                ``Debg`` table

        """
        builder = Builder(font, featurefile)
        builder.build(tables=tables, debug=debug)

    def addOpenTypeFeaturesFromString(
        font, features, filename=None, tables=None, debug=False
    ):
        """Add features from a string to a font. Note that this replaces any
        features currently present.

        Args:
            font (feaLib.ttLib.TTFont): The font object.
            features: A string containing feature code.
            filename: The directory containing ``filename`` is used as the root of
                relative ``include()`` paths; if ``None`` is provided, the current
                directory is assumed.
            tables: If passed, restrict the set of affected tables to those in the
                list.
            debug: Whether to add source debugging information to the font in the
                ``Debg`` table

        """

        featurefile = StringIO(tostr(features))
        if filename:
            featurefile.name = filename
        addOpenTypeFeatures(font, featurefile, tables=tables, debug=debug)

    class Builder(object):

        supportedTables = frozenset(
            Tag(tag)
            for tag in [
                "BASE",
                "GDEF",
                "GPOS",
                "GSUB",
                "OS/2",
                "head",
                "hhea",
                "name",
                "vhea",
                "STAT",
            ]
        )

        def __init__(self, font, featurefile):
            self.font = font
            # 'featurefile' can be either a path or file object (in which case we
            # parse it into an AST), or a pre-parsed AST instance
            if isinstance(featurefile, FeatureFile):
                self.parseTree, self.file = featurefile, None
            else:
                self.parseTree, self.file = None, featurefile
            self.glyphMap = font.getReverseGlyphMap()
            self.varstorebuilder = None
            if "fvar" in font:
                self.axes = font["fvar"].axes
                self.varstorebuilder = OnlineVarStoreBuilder(
                    [ax.axisTag for ax in self.axes]
                )
            self.default_language_systems_ = set()
            self.script_ = None
            self.lookupflag_ = 0
            self.lookupflag_markFilterSet_ = None
            self.language_systems = set()
            self.seen_non_DFLT_script_ = False
            self.named_lookups_ = {}
            self.cur_lookup_ = None
            self.cur_lookup_name_ = None
            self.cur_feature_name_ = None
            self.lookups_ = []
            self.lookup_locations = {"GSUB": {}, "GPOS": {}}
            self.features_ = {}  # ('latn', 'DEU ', 'smcp') --> [LookupBuilder*]
            self.required_features_ = {}  # ('latn', 'DEU ') --> 'scmp'
            self.feature_variations_ = {}
            # for feature 'aalt'
            self.aalt_features_ = []  # [(location, featureName)*], for 'aalt'
            self.aalt_location_ = None
            self.aalt_alternates_ = {}
            # for 'featureNames'
            self.featureNames_ = set()
            self.featureNames_ids_ = {}
            # for 'cvParameters'
            self.cv_parameters_ = set()
            self.cv_parameters_ids_ = {}
            self.cv_num_named_params_ = {}
            self.cv_characters_ = defaultdict(list)
            # for feature 'size'
            self.size_parameters_ = None
            # for table 'head'
            self.fontRevision_ = None  # 2.71
            # for table 'name'
            self.names_ = []
            # for table 'BASE'
            self.base_horiz_axis_ = None
            self.base_vert_axis_ = None
            # for table 'GDEF'
            self.attachPoints_ = {}  # "a" --> {3, 7}
            self.ligCaretCoords_ = {}  # "f_f_i" --> {300, 600}
            self.ligCaretPoints_ = {}  # "f_f_i" --> {3, 7}
            self.glyphClassDefs_ = {}  # "fi" --> (2, (file, line, column))
            self.markAttach_ = {}  # "acute" --> (4, (file, line, column))
            self.markAttachClassID_ = {}  # frozenset({"acute", "grave"}) --> 4
            self.markFilterSets_ = {}  # frozenset({"acute", "grave"}) --> 4
            # for table 'OS/2'
            self.os2_ = {}
            # for table 'hhea'
            self.hhea_ = {}
            # for table 'vhea'
            self.vhea_ = {}
            # for table 'STAT'
            self.stat_ = {}
            # for conditionsets
            self.conditionsets_ = {}

        def build(self, tables=None, debug=False):
            if self.parseTree is None:
                self.parseTree = Parser(self.file, self.glyphMap).parse()
            self.parseTree.build(self)
            # by default, build all the supported tables
            if tables is None:
                tables = self.supportedTables
            else:
                tables = frozenset(tables)
                unsupported = tables - self.supportedTables
                if unsupported:
                    unsupported_string = ", ".join(sorted(unsupported))
                    raise NotImplementedError(
                        "The following tables were requested but are unsupported: "
                        f"{unsupported_string}."
                    )
            if "GSUB" in tables:
                self.build_feature_aalt_()
            if "head" in tables:
                self.build_head()
            if "hhea" in tables:
                self.build_hhea()
            if "vhea" in tables:
                self.build_vhea()
            if "name" in tables:
                self.build_name()
            if "OS/2" in tables:
                self.build_OS_2()
            if "STAT" in tables:
                self.build_STAT()
            for tag in ("GPOS", "GSUB"):
                if tag not in tables:
                    continue
                table = self.makeTable(tag)
                if self.feature_variations_:
                    self.makeFeatureVariations(table, tag)
                if (
                    table.ScriptList.ScriptCount > 0
                    or table.FeatureList.FeatureCount > 0
                    or table.LookupList.LookupCount > 0
                ):
                    fontTable = self.font[tag] = newTable(tag)
                    fontTable.table = table
                elif tag in self.font:
                    del self.font[tag]
            if any(tag in self.font for tag in ("GPOS", "GSUB")) and "OS/2" in self.font:
                self.font["OS/2"].usMaxContext = maxCtxFont(self.font)
            if "GDEF" in tables:
                gdef = self.buildGDEF()
                if gdef:
                    self.font["GDEF"] = gdef
                elif "GDEF" in self.font:
                    del self.font["GDEF"]
            if "BASE" in tables:
                base = self.buildBASE()
                if base:
                    self.font["BASE"] = base
                elif "BASE" in self.font:
                    del self.font["BASE"]
            if debug or os.environ.get(LOOKUP_DEBUG_ENV_VAR):
                self.buildDebg()

        def get_chained_lookup_(self, location, builder_class):
            result = builder_class(self.font, location)
            result.lookupflag = self.lookupflag_
            result.markFilterSet = self.lookupflag_markFilterSet_
            self.lookups_.append(result)
            return result

        def add_lookup_to_feature_(self, lookup, feature_name):
            for script, lang in self.language_systems:
                key = (script, lang, feature_name)
                self.features_.setdefault(key, []).append(lookup)

        def get_lookup_(self, location, builder_class):
            if (
                self.cur_lookup_
                and type(self.cur_lookup_) == builder_class
                and self.cur_lookup_.lookupflag == self.lookupflag_
                and self.cur_lookup_.markFilterSet == self.lookupflag_markFilterSet_
            ):
                return self.cur_lookup_
            if self.cur_lookup_name_ and self.cur_lookup_:
                raise FeatureLibError(
                    "Within a named lookup block, all rules must be of "
                    "the same lookup type and flag",
                    location,
                )
            self.cur_lookup_ = builder_class(self.font, location)
            self.cur_lookup_.lookupflag = self.lookupflag_
            self.cur_lookup_.markFilterSet = self.lookupflag_markFilterSet_
            self.lookups_.append(self.cur_lookup_)
            if self.cur_lookup_name_:
                # We are starting a lookup rule inside a named lookup block.
                self.named_lookups_[self.cur_lookup_name_] = self.cur_lookup_
            if self.cur_feature_name_:
                # We are starting a lookup rule inside a feature. This includes
                # lookup rules inside named lookups inside features.
                self.add_lookup_to_feature_(self.cur_lookup_, self.cur_feature_name_)
            return self.cur_lookup_

        def build_feature_aalt_(self):
            if not self.aalt_features_ and not self.aalt_alternates_:
                return
            alternates = {g: set(a) for g, a in self.aalt_alternates_.items()}
            for location, name in self.aalt_features_ + [(None, "aalt")]:
                feature = [
                    (script, lang, feature, lookups)
                    for (script, lang, feature), lookups in self.features_.items()
                    if feature == name
                ]
                # "aalt" does not have to specify its own lookups, but it might.
                if not feature and name != "aalt":
                    raise FeatureLibError(
                        "Feature %s has not been defined" % name, location
                    )
                for script, lang, feature, lookups in feature:
                    for lookuplist in lookups:
                        if not isinstance(lookuplist, list):
                            lookuplist = [lookuplist]
                        for lookup in lookuplist:
                            for glyph, alts in lookup.getAlternateGlyphs().items():
                                alternates.setdefault(glyph, set()).update(alts)
            single = {
                glyph: list(repl)[0] for glyph, repl in alternates.items() if len(repl) == 1
            }
            # TODO: Figure out the glyph alternate ordering used by makeotf.
            # https://github.com/fonttools/fonttools/issues/836
            multi = {
                glyph: sorted(repl, key=self.font.getGlyphID)
                for glyph, repl in alternates.items()
                if len(repl) > 1
            }
            if not single and not multi:
                return
            self.features_ = {
                (script, lang, feature): lookups
                for (script, lang, feature), lookups in self.features_.items()
                if feature != "aalt"
            }
            old_lookups = self.lookups_
            self.lookups_ = []
            self.start_feature(self.aalt_location_, "aalt")
            if single:
                single_lookup = self.get_lookup_(location, SingleSubstBuilder)
                single_lookup.mapping = single
            if multi:
                multi_lookup = self.get_lookup_(location, AlternateSubstBuilder)
                multi_lookup.alternates = multi
            self.end_feature()
            self.lookups_.extend(old_lookups)

        def build_head(self):
            if not self.fontRevision_:
                return
            table = self.font.get("head")
            if not table:  # this only happens for unit tests
                table = self.font["head"] = newTable("head")
                table.decompile(b"\0" * 54, self.font)
                table.tableVersion = 1.0
                table.created = table.modified = 3406620153  # 2011-12-13 11:22:33
            table.fontRevision = self.fontRevision_

        def build_hhea(self):
            if not self.hhea_:
                return
            table = self.font.get("hhea")
            if not table:  # this only happens for unit tests
                table = self.font["hhea"] = newTable("hhea")
                table.decompile(b"\0" * 36, self.font)
                table.tableVersion = 0x00010000
            if "caretoffset" in self.hhea_:
                table.caretOffset = self.hhea_["caretoffset"]
            if "ascender" in self.hhea_:
                table.ascent = self.hhea_["ascender"]
            if "descender" in self.hhea_:
                table.descent = self.hhea_["descender"]
            if "linegap" in self.hhea_:
                table.lineGap = self.hhea_["linegap"]

        def build_vhea(self):
            if not self.vhea_:
                return
            table = self.font.get("vhea")
            if not table:  # this only happens for unit tests
                table = self.font["vhea"] = newTable("vhea")
                table.decompile(b"\0" * 36, self.font)
                table.tableVersion = 0x00011000
            if "verttypoascender" in self.vhea_:
                table.ascent = self.vhea_["verttypoascender"]
            if "verttypodescender" in self.vhea_:
                table.descent = self.vhea_["verttypodescender"]
            if "verttypolinegap" in self.vhea_:
                table.lineGap = self.vhea_["verttypolinegap"]

        def get_user_name_id(self, table):
            # Try to find first unused font-specific name id
            nameIDs = [name.nameID for name in table.names]
            for user_name_id in range(256, 32767):
                if user_name_id not in nameIDs:
                    return user_name_id

        def buildFeatureParams(self, tag):
            params = None
            if tag == "size":
                params = otTables.FeatureParamsSize()
                (
                    params.DesignSize,
                    params.SubfamilyID,
                    params.RangeStart,
                    params.RangeEnd,
                ) = self.size_parameters_
                if tag in self.featureNames_ids_:
                    params.SubfamilyNameID = self.featureNames_ids_[tag]
                else:
                    params.SubfamilyNameID = 0
            elif tag in self.featureNames_:
                if not self.featureNames_ids_:
                    # name table wasn't selected among the tables to build; skip
                    pass
                else:
                    assert tag in self.featureNames_ids_
                    params = otTables.FeatureParamsStylisticSet()
                    params.Version = 0
                    params.UINameID = self.featureNames_ids_[tag]
            elif tag in self.cv_parameters_:
                params = otTables.FeatureParamsCharacterVariants()
                params.Format = 0
                params.FeatUILabelNameID = self.cv_parameters_ids_.get(
                    (tag, "FeatUILabelNameID"), 0
                )
                params.FeatUITooltipTextNameID = self.cv_parameters_ids_.get(
                    (tag, "FeatUITooltipTextNameID"), 0
                )
                params.SampleTextNameID = self.cv_parameters_ids_.get(
                    (tag, "SampleTextNameID"), 0
                )
                params.NumNamedParameters = self.cv_num_named_params_.get(tag, 0)
                params.FirstParamUILabelNameID = self.cv_parameters_ids_.get(
                    (tag, "ParamUILabelNameID_0"), 0
                )
                params.CharCount = len(self.cv_characters_[tag])
                params.Character = self.cv_characters_[tag]
            return params

        def build_name(self):
            if not self.names_:
                return
            table = self.font.get("name")
            if not table:  # this only happens for unit tests
                table = self.font["name"] = newTable("name")
                table.names = []
            for name in self.names_:
                nameID, platformID, platEncID, langID, string = name
                # For featureNames block, nameID is 'feature tag'
                # For cvParameters blocks, nameID is ('feature tag', 'block name')
                if not isinstance(nameID, int):
                    tag = nameID
                    if tag in self.featureNames_:
                        if tag not in self.featureNames_ids_:
                            self.featureNames_ids_[tag] = self.get_user_name_id(table)
                            assert self.featureNames_ids_[tag] is not None
                        nameID = self.featureNames_ids_[tag]
                    elif tag[0] in self.cv_parameters_:
                        if tag not in self.cv_parameters_ids_:
                            self.cv_parameters_ids_[tag] = self.get_user_name_id(table)
                            assert self.cv_parameters_ids_[tag] is not None
                        nameID = self.cv_parameters_ids_[tag]
                table.setName(string, nameID, platformID, platEncID, langID)

        def build_OS_2(self):
            if not self.os2_:
                return
            table = self.font.get("OS/2")
            if not table:  # this only happens for unit tests
                table = self.font["OS/2"] = newTable("OS/2")
                data = b"\0" * sstruct.calcsize(getTableModule("OS/2").OS2_format_0)
                table.decompile(data, self.font)
            version = 0
            if "fstype" in self.os2_:
                table.fsType = self.os2_["fstype"]
            if "panose" in self.os2_:
                panose = getTableModule("OS/2").Panose()
                (
                    panose.bFamilyType,
                    panose.bSerifStyle,
                    panose.bWeight,
                    panose.bProportion,
                    panose.bContrast,
                    panose.bStrokeVariation,
                    panose.bArmStyle,
                    panose.bLetterForm,
                    panose.bMidline,
                    panose.bXHeight,
                ) = self.os2_["panose"]
                table.panose = panose
            if "typoascender" in self.os2_:
                table.sTypoAscender = self.os2_["typoascender"]
            if "typodescender" in self.os2_:
                table.sTypoDescender = self.os2_["typodescender"]
            if "typolinegap" in self.os2_:
                table.sTypoLineGap = self.os2_["typolinegap"]
            if "winascent" in self.os2_:
                table.usWinAscent = self.os2_["winascent"]
            if "windescent" in self.os2_:
                table.usWinDescent = self.os2_["windescent"]
            if "vendor" in self.os2_:
                table.achVendID = safeEval("'''" + self.os2_["vendor"] + "'''")
            if "weightclass" in self.os2_:
                table.usWeightClass = self.os2_["weightclass"]
            if "widthclass" in self.os2_:
                table.usWidthClass = self.os2_["widthclass"]
            if "unicoderange" in self.os2_:
                table.setUnicodeRanges(self.os2_["unicoderange"])
            if "codepagerange" in self.os2_:
                pages = self.build_codepages_(self.os2_["codepagerange"])
                table.ulCodePageRange1, table.ulCodePageRange2 = pages
                version = 1
            if "xheight" in self.os2_:
                table.sxHeight = self.os2_["xheight"]
                version = 2
            if "capheight" in self.os2_:
                table.sCapHeight = self.os2_["capheight"]
                version = 2
            if "loweropsize" in self.os2_:
                table.usLowerOpticalPointSize = self.os2_["loweropsize"]
                version = 5
            if "upperopsize" in self.os2_:
                table.usUpperOpticalPointSize = self.os2_["upperopsize"]
                version = 5

            def checkattr(table, attrs):
                for attr in attrs:
                    if not hasattr(table, attr):
                        setattr(table, attr, 0)

            table.version = max(version, table.version)
            # this only happens for unit tests
            if version >= 1:
                checkattr(table, ("ulCodePageRange1", "ulCodePageRange2"))
            if version >= 2:
                checkattr(
                    table,
                    (
                        "sxHeight",
                        "sCapHeight",
                        "usDefaultChar",
                        "usBreakChar",
                        "usMaxContext",
                    ),
                )
            if version >= 5:
                checkattr(table, ("usLowerOpticalPointSize", "usUpperOpticalPointSize"))

        def setElidedFallbackName(self, value, location):
            # ElidedFallbackName is a convenience method for setting
            # ElidedFallbackNameID so only one can be allowed
            for token in ("ElidedFallbackName", "ElidedFallbackNameID"):
                if token in self.stat_:
                    raise FeatureLibError(
                        f"{token} is already set.",
                        location,
                    )
            if isinstance(value, int):
                self.stat_["ElidedFallbackNameID"] = value
            elif isinstance(value, list):
                self.stat_["ElidedFallbackName"] = value
            else:
                raise AssertionError(value)

        def addDesignAxis(self, designAxis, location):
            if "DesignAxes" not in self.stat_:
                self.stat_["DesignAxes"] = []
            if designAxis.tag in (r.tag for r in self.stat_["DesignAxes"]):
                raise FeatureLibError(
                    f'DesignAxis already defined for tag "{designAxis.tag}".',
                    location,
                )
            if designAxis.axisOrder in (r.axisOrder for r in self.stat_["DesignAxes"]):
                raise FeatureLibError(
                    f"DesignAxis already defined for axis number {designAxis.axisOrder}.",
                    location,
                )
            self.stat_["DesignAxes"].append(designAxis)

        def addAxisValueRecord(self, axisValueRecord, location):
            if "AxisValueRecords" not in self.stat_:
                self.stat_["AxisValueRecords"] = []
            # Check for duplicate AxisValueRecords
            for record_ in self.stat_["AxisValueRecords"]:
                if (
                    {n.asFea() for n in record_.names}
                    == {n.asFea() for n in axisValueRecord.names}
                    and {n.asFea() for n in record_.locations}
                    == {n.asFea() for n in axisValueRecord.locations}
                    and record_.flags == axisValueRecord.flags
                ):
                    raise FeatureLibError(
                        "An AxisValueRecord with these values is already defined.",
                        location,
                    )
            self.stat_["AxisValueRecords"].append(axisValueRecord)

        def build_STAT(self):
            if not self.stat_:
                return

            axes = self.stat_.get("DesignAxes")
            if not axes:
                raise FeatureLibError("DesignAxes not defined", None)
            axisValueRecords = self.stat_.get("AxisValueRecords")
            axisValues = {}
            format4_locations = []
            for tag in axes:
                axisValues[tag.tag] = []
            if axisValueRecords is not None:
                for avr in axisValueRecords:
                    valuesDict = {}
                    if avr.flags > 0:
                        valuesDict["flags"] = avr.flags
                    if len(avr.locations) == 1:
                        location = avr.locations[0]
                        values = location.values
                        if len(values) == 1:  # format1
                            valuesDict.update({"value": values[0], "name": avr.names})
                        if len(values) == 2:  # format3
                            valuesDict.update(
                                {
                                    "value": values[0],
                                    "linkedValue": values[1],
                                    "name": avr.names,
                                }
                            )
                        if len(values) == 3:  # format2
                            nominal, minVal, maxVal = values
                            valuesDict.update(
                                {
                                    "nominalValue": nominal,
                                    "rangeMinValue": minVal,
                                    "rangeMaxValue": maxVal,
                                    "name": avr.names,
                                }
                            )
                        axisValues[location.tag].append(valuesDict)
                    else:
                        valuesDict.update(
                            {
                                "location": {i.tag: i.values[0] for i in avr.locations},
                                "name": avr.names,
                            }
                        )
                        format4_locations.append(valuesDict)

            designAxes = [
                {
                    "ordering": a.axisOrder,
                    "tag": a.tag,
                    "name": a.names,
                    "values": axisValues[a.tag],
                }
                for a in axes
            ]

            nameTable = self.font.get("name")
            if not nameTable:  # this only happens for unit tests
                nameTable = self.font["name"] = newTable("name")
                nameTable.names = []

            if "ElidedFallbackNameID" in self.stat_:
                nameID = self.stat_["ElidedFallbackNameID"]
                name = nameTable.getDebugName(nameID)
                if not name:
                    raise FeatureLibError(
                        f"ElidedFallbackNameID {nameID} points "
                        "to a nameID that does not exist in the "
                        '"name" table',
                        None,
                    )
            elif "ElidedFallbackName" in self.stat_:
                nameID = self.stat_["ElidedFallbackName"]

            otl.buildStatTable(
                self.font,
                designAxes,
                locations=format4_locations,
                elidedFallbackName=nameID,
            )

        def build_codepages_(self, pages):
            pages2bits = {
                1252: 0,
                1250: 1,
                1251: 2,
                1253: 3,
                1254: 4,
                1255: 5,
                1256: 6,
                1257: 7,
                1258: 8,
                874: 16,
                932: 17,
                936: 18,
                949: 19,
                950: 20,
                1361: 21,
                869: 48,
                866: 49,
                865: 50,
                864: 51,
                863: 52,
                862: 53,
                861: 54,
                860: 55,
                857: 56,
                855: 57,
                852: 58,
                775: 59,
                737: 60,
                708: 61,
                850: 62,
                437: 63,
            }
            bits = [pages2bits[p] for p in pages if p in pages2bits]
            pages = []
            for i in range(2):
                pages.append("")
                for j in range(i * 32, (i + 1) * 32):
                    if j in bits:
                        pages[i] += "1"
                    else:
                        pages[i] += "0"
            return [binary2num(p[::-1]) for p in pages]

        def buildBASE(self):
            if not self.base_horiz_axis_ and not self.base_vert_axis_:
                return None
            base = otTables.BASE()
            base.Version = 0x00010000
            base.HorizAxis = self.buildBASEAxis(self.base_horiz_axis_)
            base.VertAxis = self.buildBASEAxis(self.base_vert_axis_)

            result = newTable("BASE")
            result.table = base
            return result

        def buildBASEAxis(self, axis):
            if not axis:
                return
            bases, scripts = axis
            axis = otTables.Axis()
            axis.BaseTagList = otTables.BaseTagList()
            axis.BaseTagList.BaselineTag = bases
            axis.BaseTagList.BaseTagCount = len(bases)
            axis.BaseScriptList = otTables.BaseScriptList()
            axis.BaseScriptList.BaseScriptRecord = []
            axis.BaseScriptList.BaseScriptCount = len(scripts)
            for script in sorted(scripts):
                record = otTables.BaseScriptRecord()
                record.BaseScriptTag = script[0]
                record.BaseScript = otTables.BaseScript()
                record.BaseScript.BaseLangSysCount = 0
                record.BaseScript.BaseValues = otTables.BaseValues()
                record.BaseScript.BaseValues.DefaultIndex = bases.index(script[1])
                record.BaseScript.BaseValues.BaseCoord = []
                record.BaseScript.BaseValues.BaseCoordCount = len(script[2])
                for c in script[2]:
                    coord = otTables.BaseCoord()
                    coord.Format = 1
                    coord.Coordinate = c
                    record.BaseScript.BaseValues.BaseCoord.append(coord)
                axis.BaseScriptList.BaseScriptRecord.append(record)
            return axis

        def buildGDEF(self):
            gdef = otTables.GDEF()
            gdef.GlyphClassDef = self.buildGDEFGlyphClassDef_()
            gdef.AttachList = otl.buildAttachList(self.attachPoints_, self.glyphMap)
            gdef.LigCaretList = otl.buildLigCaretList(
                self.ligCaretCoords_, self.ligCaretPoints_, self.glyphMap
            )
            gdef.MarkAttachClassDef = self.buildGDEFMarkAttachClassDef_()
            gdef.MarkGlyphSetsDef = self.buildGDEFMarkGlyphSetsDef_()
            gdef.Version = 0x00010002 if gdef.MarkGlyphSetsDef else 0x00010000
            if self.varstorebuilder:
                store = self.varstorebuilder.finish()
                if store:
                    gdef.Version = 0x00010003
                    gdef.VarStore = store
                    varidx_map = store.optimize()

                    gdef.remap_device_varidxes(varidx_map)
                    if 'GPOS' in self.font:
                        self.font['GPOS'].table.remap_device_varidxes(varidx_map)
                VariableScalar.clear_cache()
            if any(
                (
                    gdef.GlyphClassDef,
                    gdef.AttachList,
                    gdef.LigCaretList,
                    gdef.MarkAttachClassDef,
                    gdef.MarkGlyphSetsDef,
                )
            ) or hasattr(gdef, "VarStore"):
                result = newTable("GDEF")
                result.table = gdef
                return result
            else:
                return None

        def buildGDEFGlyphClassDef_(self):
            if self.glyphClassDefs_:
                classes = {g: c for (g, (c, _)) in self.glyphClassDefs_.items()}
            else:
                classes = {}
                for lookup in self.lookups_:
                    classes.update(lookup.inferGlyphClasses())
                for markClass in self.parseTree.markClasses.values():
                    for markClassDef in markClass.definitions:
                        for glyph in markClassDef.glyphSet():
                            classes[glyph] = 3
            if classes:
                result = otTables.GlyphClassDef()
                result.classDefs = classes
                return result
            else:
                return None

        def buildGDEFMarkAttachClassDef_(self):
            classDefs = {g: c for g, (c, _) in self.markAttach_.items()}
            if not classDefs:
                return None
            result = otTables.MarkAttachClassDef()
            result.classDefs = classDefs
            return result

        def buildGDEFMarkGlyphSetsDef_(self):
            sets = []
            for glyphs, id_ in sorted(
                self.markFilterSets_.items(), key=lambda item: item[1]
            ):
                sets.append(glyphs)
            return otl.buildMarkGlyphSetsDef(sets, self.glyphMap)

        def buildDebg(self):
            if "Debg" not in self.font:
                self.font["Debg"] = newTable("Debg")
                self.font["Debg"].data = {}
            self.font["Debg"].data[LOOKUP_DEBUG_INFO_KEY] = self.lookup_locations

        def buildLookups_(self, tag):
            assert tag in ("GPOS", "GSUB"), tag
            for lookup in self.lookups_:
                lookup.lookup_index = None
            lookups = []
            for lookup in self.lookups_:
                if lookup.table != tag:
                    continue
                lookup.lookup_index = len(lookups)
                self.lookup_locations[tag][str(lookup.lookup_index)] = LookupDebugInfo(
                    location=str(lookup.location),
                    name=self.get_lookup_name_(lookup),
                    feature=None,
                )
                lookups.append(lookup)
            try:
                otLookups = [l.build() for l in lookups]
            except OpenTypeLibError as e:
                raise FeatureLibError(str(e), e.location) from e
            return otLookups

        def makeTable(self, tag):
            table = getattr(otTables, tag, None)()
            table.Version = 0x00010000
            table.ScriptList = otTables.ScriptList()
            table.ScriptList.ScriptRecord = []
            table.FeatureList = otTables.FeatureList()
            table.FeatureList.FeatureRecord = []
            table.LookupList = otTables.LookupList()
            table.LookupList.Lookup = self.buildLookups_(tag)

            # Build a table for mapping (tag, lookup_indices) to feature_index.
            # For example, ('liga', (2,3,7)) --> 23.
            feature_indices = {}
            required_feature_indices = {}  # ('latn', 'DEU') --> 23
            scripts = {}  # 'latn' --> {'DEU': [23, 24]} for feature #23,24
            # Sort the feature table by feature tag:
            # https://github.com/fonttools/fonttools/issues/568
            sortFeatureTag = lambda f: (f[0][2], f[0][1], f[0][0], f[1])
            for key, lookups in sorted(self.features_.items(), key=sortFeatureTag):
                script, lang, feature_tag = key
                # l.lookup_index will be None when a lookup is not needed
                # for the table under construction. For example, substitution
                # rules will have no lookup_index while building GPOS tables.
                lookup_indices = tuple(
                    [l.lookup_index for l in lookups if l.lookup_index is not None]
                )

                size_feature = tag == "GPOS" and feature_tag == "size"
                force_feature = self.any_feature_variations(feature_tag, tag)
                if len(lookup_indices) == 0 and not size_feature and not force_feature:
                    continue

                for ix in lookup_indices:
                    try:
                        self.lookup_locations[tag][str(ix)] = self.lookup_locations[tag][
                            str(ix)
                        ]._replace(feature=key)
                    except KeyError:
                        warnings.warn(
                            "feaLib.Builder subclass needs upgrading to "
                            "stash debug information. See fonttools#2065."
                        )

                feature_key = (feature_tag, lookup_indices)
                feature_index = feature_indices.get(feature_key)
                if feature_index is None:
                    feature_index = len(table.FeatureList.FeatureRecord)
                    frec = otTables.FeatureRecord()
                    frec.FeatureTag = feature_tag
                    frec.Feature = otTables.Feature()
                    frec.Feature.FeatureParams = self.buildFeatureParams(feature_tag)
                    frec.Feature.LookupListIndex = list(lookup_indices)
                    frec.Feature.LookupCount = len(lookup_indices)
                    table.FeatureList.FeatureRecord.append(frec)
                    feature_indices[feature_key] = feature_index
                scripts.setdefault(script, {}).setdefault(lang, []).append(feature_index)
                if self.required_features_.get((script, lang)) == feature_tag:
                    required_feature_indices[(script, lang)] = feature_index

            # Build ScriptList.
            for script, lang_features in sorted(scripts.items()):
                srec = otTables.ScriptRecord()
                srec.ScriptTag = script
                srec.Script = otTables.Script()
                srec.Script.DefaultLangSys = None
                srec.Script.LangSysRecord = []
                for lang, feature_indices in sorted(lang_features.items()):
                    langrec = otTables.LangSysRecord()
                    langrec.LangSys = otTables.LangSys()
                    langrec.LangSys.LookupOrder = None

                    req_feature_index = required_feature_indices.get((script, lang))
                    if req_feature_index is None:
                        langrec.LangSys.ReqFeatureIndex = 0xFFFF
                    else:
                        langrec.LangSys.ReqFeatureIndex = req_feature_index

                    langrec.LangSys.FeatureIndex = [
                        i for i in feature_indices if i != req_feature_index
                    ]
                    langrec.LangSys.FeatureCount = len(langrec.LangSys.FeatureIndex)

                    if lang == "dflt":
                        srec.Script.DefaultLangSys = langrec.LangSys
                    else:
                        langrec.LangSysTag = lang
                        srec.Script.LangSysRecord.append(langrec)
                srec.Script.LangSysCount = len(srec.Script.LangSysRecord)
                table.ScriptList.ScriptRecord.append(srec)

            table.ScriptList.ScriptCount = len(table.ScriptList.ScriptRecord)
            table.FeatureList.FeatureCount = len(table.FeatureList.FeatureRecord)
            table.LookupList.LookupCount = len(table.LookupList.Lookup)
            return table

        def makeFeatureVariations(self, table, table_tag):
            feature_vars = {}
            has_any_variations = False
            # Sort out which lookups to build, gather their indices
            for (
                script_,
                language,
                feature_tag,
            ), variations in self.feature_variations_.items():
                feature_vars[feature_tag] = []
                for conditionset, builders in variations.items():
                    raw_conditionset = self.conditionsets_[conditionset]
                    indices = []
                    for b in builders:
                        if b.table != table_tag:
                            continue
                        assert b.lookup_index is not None
                        indices.append(b.lookup_index)
                        has_any_variations = True
                    feature_vars[feature_tag].append((raw_conditionset, indices))

            if has_any_variations:
                for feature_tag, conditions_and_lookups in feature_vars.items():
                    addFeatureVariationsRaw(
                        self.font, table, conditions_and_lookups, feature_tag
                    )

        def any_feature_variations(self, feature_tag, table_tag):
            for (_, _, feature), variations in self.feature_variations_.items():
                if feature != feature_tag:
                    continue
                for conditionset, builders in variations.items():
                    if any(b.table == table_tag for b in builders):
                        return True
            return False

        def get_lookup_name_(self, lookup):
            rev = {v: k for k, v in self.named_lookups_.items()}
            if lookup in rev:
                return rev[lookup]
            return None

        def add_language_system(self, location, script, language):
            # OpenType Feature File Specification, section 4.b.i
            if script == "DFLT" and language == "dflt" and self.default_language_systems_:
                raise FeatureLibError(
                    'If "languagesystem DFLT dflt" is present, it must be '
                    "the first of the languagesystem statements",
                    location,
                )
            if script == "DFLT":
                if self.seen_non_DFLT_script_:
                    raise FeatureLibError(
                        'languagesystems using the "DFLT" script tag must '
                        "precede all other languagesystems",
                        location,
                    )
            else:
                self.seen_non_DFLT_script_ = True
            if (script, language) in self.default_language_systems_:
                raise FeatureLibError(
                    '"languagesystem %s %s" has already been specified'
                    % (script.strip(), language.strip()),
                    location,
                )
            self.default_language_systems_.add((script, language))

        def get_default_language_systems_(self):
            # OpenType Feature File specification, 4.b.i. languagesystem:
            # If no "languagesystem" statement is present, then the
            # implementation must behave exactly as though the following
            # statement were present at the beginning of the feature file:
            # languagesystem DFLT dflt;
            if self.default_language_systems_:
                return frozenset(self.default_language_systems_)
            else:
                return frozenset({("DFLT", "dflt")})

        def start_feature(self, location, name):
            self.language_systems = self.get_default_language_systems_()
            self.script_ = "DFLT"
            self.cur_lookup_ = None
            self.cur_feature_name_ = name
            self.lookupflag_ = 0
            self.lookupflag_markFilterSet_ = None
            if name == "aalt":
                self.aalt_location_ = location

        def end_feature(self):
            assert self.cur_feature_name_ is not None
            self.cur_feature_name_ = None
            self.language_systems = None
            self.cur_lookup_ = None
            self.lookupflag_ = 0
            self.lookupflag_markFilterSet_ = None

        def start_lookup_block(self, location, name):
            if name in self.named_lookups_:
                raise FeatureLibError(
                    'Lookup "%s" has already been defined' % name, location
                )
            if self.cur_feature_name_ == "aalt":
                raise FeatureLibError(
                    "Lookup blocks cannot be placed inside 'aalt' features; "
                    "move it out, and then refer to it with a lookup statement",
                    location,
                )
            self.cur_lookup_name_ = name
            self.named_lookups_[name] = None
            self.cur_lookup_ = None
            if self.cur_feature_name_ is None:
                self.lookupflag_ = 0
                self.lookupflag_markFilterSet_ = None

        def end_lookup_block(self):
            assert self.cur_lookup_name_ is not None
            self.cur_lookup_name_ = None
            self.cur_lookup_ = None
            if self.cur_feature_name_ is None:
                self.lookupflag_ = 0
                self.lookupflag_markFilterSet_ = None

        def add_lookup_call(self, lookup_name):
            assert lookup_name in self.named_lookups_, lookup_name
            self.cur_lookup_ = None
            lookup = self.named_lookups_[lookup_name]
            if lookup is not None:  # skip empty named lookup
                self.add_lookup_to_feature_(lookup, self.cur_feature_name_)

        def set_font_revision(self, location, revision):
            self.fontRevision_ = revision

        def set_language(self, location, language, include_default, required):
            assert len(language) == 4
            if self.cur_feature_name_ in ("aalt", "size"):
                raise FeatureLibError(
                    "Language statements are not allowed "
                    'within "feature %s"' % self.cur_feature_name_,
                    location,
                )
            if self.cur_feature_name_ is None:
                raise FeatureLibError(
                    "Language statements are not allowed "
                    "within standalone lookup blocks",
                    location,
                )
            self.cur_lookup_ = None

            key = (self.script_, language, self.cur_feature_name_)
            lookups = self.features_.get((key[0], "dflt", key[2]))
            if (language == "dflt" or include_default) and lookups:
                self.features_[key] = lookups[:]
            else:
                self.features_[key] = []
            self.language_systems = frozenset([(self.script_, language)])

            if required:
                key = (self.script_, language)
                if key in self.required_features_:
                    raise FeatureLibError(
                        "Language %s (script %s) has already "
                        "specified feature %s as its required feature"
                        % (
                            language.strip(),
                            self.script_.strip(),
                            self.required_features_[key].strip(),
                        ),
                        location,
                    )
                self.required_features_[key] = self.cur_feature_name_

        def getMarkAttachClass_(self, location, glyphs):
            glyphs = frozenset(glyphs)
            id_ = self.markAttachClassID_.get(glyphs)
            if id_ is not None:
                return id_
            id_ = len(self.markAttachClassID_) + 1
            self.markAttachClassID_[glyphs] = id_
            for glyph in glyphs:
                if glyph in self.markAttach_:
                    _, loc = self.markAttach_[glyph]
                    raise FeatureLibError(
                        "Glyph %s already has been assigned "
                        "a MarkAttachmentType at %s" % (glyph, loc),
                        location,
                    )
                self.markAttach_[glyph] = (id_, location)
            return id_

        def getMarkFilterSet_(self, location, glyphs):
            glyphs = frozenset(glyphs)
            id_ = self.markFilterSets_.get(glyphs)
            if id_ is not None:
                return id_
            id_ = len(self.markFilterSets_)
            self.markFilterSets_[glyphs] = id_
            return id_

        def set_lookup_flag(self, location, value, markAttach, markFilter):
            value = value & 0xFF
            if markAttach:
                markAttachClass = self.getMarkAttachClass_(location, markAttach)
                value = value | (markAttachClass << 8)
            if markFilter:
                markFilterSet = self.getMarkFilterSet_(location, markFilter)
                value = value | 0x10
                self.lookupflag_markFilterSet_ = markFilterSet
            else:
                self.lookupflag_markFilterSet_ = None
            self.lookupflag_ = value

        def set_script(self, location, script):
            if self.cur_feature_name_ in ("aalt", "size"):
                raise FeatureLibError(
                    "Script statements are not allowed "
                    'within "feature %s"' % self.cur_feature_name_,
                    location,
                )
            if self.cur_feature_name_ is None:
                raise FeatureLibError(
                    "Script statements are not allowed " "within standalone lookup blocks",
                    location,
                )
            if self.language_systems == {(script, "dflt")}:
                # Nothing to do.
                return
            self.cur_lookup_ = None
            self.script_ = script
            self.lookupflag_ = 0
            self.lookupflag_markFilterSet_ = None
            self.set_language(location, "dflt", include_default=True, required=False)

        def find_lookup_builders_(self, lookups):
            """Helper for building chain contextual substitutions

            Given a list of lookup names, finds the LookupBuilder for each name.
            If an input name is None, it gets mapped to a None LookupBuilder.
            """
            lookup_builders = []
            for lookuplist in lookups:
                if lookuplist is not None:
                    lookup_builders.append(
                        [self.named_lookups_.get(l.name) for l in lookuplist]
                    )
                else:
                    lookup_builders.append(None)
            return lookup_builders

        def add_attach_points(self, location, glyphs, contourPoints):
            for glyph in glyphs:
                self.attachPoints_.setdefault(glyph, set()).update(contourPoints)

        def add_feature_reference(self, location, featureName):
            if self.cur_feature_name_ != "aalt":
                raise FeatureLibError(
                    'Feature references are only allowed inside "feature aalt"', location
                )
            self.aalt_features_.append((location, featureName))

        def add_featureName(self, tag):
            self.featureNames_.add(tag)

        def add_cv_parameter(self, tag):
            self.cv_parameters_.add(tag)

        def add_to_cv_num_named_params(self, tag):
            """Adds new items to ``self.cv_num_named_params_``
            or increments the count of existing items."""
            if tag in self.cv_num_named_params_:
                self.cv_num_named_params_[tag] += 1
            else:
                self.cv_num_named_params_[tag] = 1

        def add_cv_character(self, character, tag):
            self.cv_characters_[tag].append(character)

        def set_base_axis(self, bases, scripts, vertical):
            if vertical:
                self.base_vert_axis_ = (bases, scripts)
            else:
                self.base_horiz_axis_ = (bases, scripts)

        def set_size_parameters(
            self, location, DesignSize, SubfamilyID, RangeStart, RangeEnd
        ):
            if self.cur_feature_name_ != "size":
                raise FeatureLibError(
                    "Parameters statements are not allowed "
                    'within "feature %s"' % self.cur_feature_name_,
                    location,
                )
            self.size_parameters_ = [DesignSize, SubfamilyID, RangeStart, RangeEnd]
            for script, lang in self.language_systems:
                key = (script, lang, self.cur_feature_name_)
                self.features_.setdefault(key, [])

        # GSUB rules

        # GSUB 1
        def add_single_subst(self, location, prefix, suffix, mapping, forceChain):
            if self.cur_feature_name_ == "aalt":
                for (from_glyph, to_glyph) in mapping.items():
                    alts = self.aalt_alternates_.setdefault(from_glyph, set())
                    alts.add(to_glyph)
                return
            if prefix or suffix or forceChain:
                self.add_single_subst_chained_(location, prefix, suffix, mapping)
                return
            lookup = self.get_lookup_(location, SingleSubstBuilder)
            for (from_glyph, to_glyph) in mapping.items():
                if from_glyph in lookup.mapping:
                    if to_glyph == lookup.mapping[from_glyph]:
                        log.info(
                            "Removing duplicate single substitution from glyph"
                            ' "%s" to "%s" at %s',
                            from_glyph,
                            to_glyph,
                            location,
                        )
                    else:
                        raise FeatureLibError(
                            'Already defined rule for replacing glyph "%s" by "%s"'
                            % (from_glyph, lookup.mapping[from_glyph]),
                            location,
                        )
                lookup.mapping[from_glyph] = to_glyph

        # GSUB 2
        def add_multiple_subst(
            self, location, prefix, glyph, suffix, replacements, forceChain=False
        ):
            if prefix or suffix or forceChain:
                chain = self.get_lookup_(location, ChainContextSubstBuilder)
                sub = self.get_chained_lookup_(location, MultipleSubstBuilder)
                sub.mapping[glyph] = replacements
                chain.rules.append(ChainContextualRule(prefix, [{glyph}], suffix, [sub]))
                return
            lookup = self.get_lookup_(location, MultipleSubstBuilder)
            if glyph in lookup.mapping:
                if replacements == lookup.mapping[glyph]:
                    log.info(
                        "Removing duplicate multiple substitution from glyph"
                        ' "%s" to %s%s',
                        glyph,
                        replacements,
                        f" at {location}" if location else "",
                    )
                else:
                    raise FeatureLibError(
                        'Already defined substitution for glyph "%s"' % glyph, location
                    )
            lookup.mapping[glyph] = replacements

        # GSUB 3
        def add_alternate_subst(self, location, prefix, glyph, suffix, replacement):
            if self.cur_feature_name_ == "aalt":
                alts = self.aalt_alternates_.setdefault(glyph, set())
                alts.update(replacement)
                return
            if prefix or suffix:
                chain = self.get_lookup_(location, ChainContextSubstBuilder)
                lookup = self.get_chained_lookup_(location, AlternateSubstBuilder)
                chain.rules.append(ChainContextualRule(prefix, [{glyph}], suffix, [lookup]))
            else:
                lookup = self.get_lookup_(location, AlternateSubstBuilder)
            if glyph in lookup.alternates:
                raise FeatureLibError(
                    'Already defined alternates for glyph "%s"' % glyph, location
                )
            # We allow empty replacement glyphs here.
            lookup.alternates[glyph] = replacement

        # GSUB 4
        def add_ligature_subst(
            self, location, prefix, glyphs, suffix, replacement, forceChain
        ):
            if prefix or suffix or forceChain:
                chain = self.get_lookup_(location, ChainContextSubstBuilder)
                lookup = self.get_chained_lookup_(location, LigatureSubstBuilder)
                chain.rules.append(ChainContextualRule(prefix, glyphs, suffix, [lookup]))
            else:
                lookup = self.get_lookup_(location, LigatureSubstBuilder)

            if not all(glyphs):
                raise FeatureLibError("Empty glyph class in substitution", location)

            # OpenType feature file syntax, section 5.d, "Ligature substitution":
            # "Since the OpenType specification does not allow ligature
            # substitutions to be specified on target sequences that contain
            # glyph classes, the implementation software will enumerate
            # all specific glyph sequences if glyph classes are detected"
            for g in sorted(itertools.product(*glyphs)):
                lookup.ligatures[g] = replacement

        # GSUB 5/6
        def add_chain_context_subst(self, location, prefix, glyphs, suffix, lookups):
            if not all(glyphs) or not all(prefix) or not all(suffix):
                raise FeatureLibError("Empty glyph class in contextual substitution", location)
            lookup = self.get_lookup_(location, ChainContextSubstBuilder)
            lookup.rules.append(
                ChainContextualRule(
                    prefix, glyphs, suffix, self.find_lookup_builders_(lookups)
                )
            )

        def add_single_subst_chained_(self, location, prefix, suffix, mapping):
            if not mapping or not all(prefix) or not all(suffix):
                raise FeatureLibError("Empty glyph class in contextual substitution", location)
            # https://github.com/fonttools/fonttools/issues/512
            chain = self.get_lookup_(location, ChainContextSubstBuilder)
            sub = chain.find_chainable_single_subst(set(mapping.keys()))
            if sub is None:
                sub = self.get_chained_lookup_(location, SingleSubstBuilder)
            sub.mapping.update(mapping)
            chain.rules.append(
                ChainContextualRule(prefix, [list(mapping.keys())], suffix, [sub])
            )

        # GSUB 8
        def add_reverse_chain_single_subst(self, location, old_prefix, old_suffix, mapping):
            if not mapping:
                raise FeatureLibError("Empty glyph class in substitution", location)
            lookup = self.get_lookup_(location, ReverseChainSingleSubstBuilder)
            lookup.rules.append((old_prefix, old_suffix, mapping))

        # GPOS rules

        # GPOS 1
        def add_single_pos(self, location, prefix, suffix, pos, forceChain):
            if prefix or suffix or forceChain:
                self.add_single_pos_chained_(location, prefix, suffix, pos)
            else:
                lookup = self.get_lookup_(location, SinglePosBuilder)
                for glyphs, value in pos:
                    if not glyphs:
                        raise FeatureLibError("Empty glyph class in positioning rule", location)
                    otValueRecord = self.makeOpenTypeValueRecord(location, value, pairPosContext=False)
                    for glyph in glyphs:
                        try:
                            lookup.add_pos(location, glyph, otValueRecord)
                        except OpenTypeLibError as e:
                            raise FeatureLibError(str(e), e.location) from e

        # GPOS 2
        def add_class_pair_pos(self, location, glyphclass1, value1, glyphclass2, value2):
            if not glyphclass1 or not glyphclass2:
                raise FeatureLibError(
                    "Empty glyph class in positioning rule", location
                )
            lookup = self.get_lookup_(location, PairPosBuilder)
            v1 = self.makeOpenTypeValueRecord(location, value1, pairPosContext=True)
            v2 = self.makeOpenTypeValueRecord(location, value2, pairPosContext=True)
            lookup.addClassPair(location, glyphclass1, v1, glyphclass2, v2)

        def add_specific_pair_pos(self, location, glyph1, value1, glyph2, value2):
            if not glyph1 or not glyph2:
                raise FeatureLibError("Empty glyph class in positioning rule", location)
            lookup = self.get_lookup_(location, PairPosBuilder)
            v1 = self.makeOpenTypeValueRecord(location, value1, pairPosContext=True)
            v2 = self.makeOpenTypeValueRecord(location, value2, pairPosContext=True)
            lookup.addGlyphPair(location, glyph1, v1, glyph2, v2)

        # GPOS 3
        def add_cursive_pos(self, location, glyphclass, entryAnchor, exitAnchor):
            if not glyphclass:
                raise FeatureLibError("Empty glyph class in positioning rule", location)
            lookup = self.get_lookup_(location, CursivePosBuilder)
            lookup.add_attachment(
                location,
                glyphclass,
                self.makeOpenTypeAnchor(location, entryAnchor),
                self.makeOpenTypeAnchor(location, exitAnchor),
            )

        # GPOS 4
        def add_mark_base_pos(self, location, bases, marks):
            builder = self.get_lookup_(location, MarkBasePosBuilder)
            self.add_marks_(location, builder, marks)
            if not bases:
                raise FeatureLibError("Empty glyph class in positioning rule", location)
            for baseAnchor, markClass in marks:
                otBaseAnchor = self.makeOpenTypeAnchor(location, baseAnchor)
                for base in bases:
                    builder.bases.setdefault(base, {})[markClass.name] = otBaseAnchor

        # GPOS 5
        def add_mark_lig_pos(self, location, ligatures, components):
            builder = self.get_lookup_(location, MarkLigPosBuilder)
            componentAnchors = []
            if not ligatures:
                raise FeatureLibError("Empty glyph class in positioning rule", location)
            for marks in components:
                anchors = {}
                self.add_marks_(location, builder, marks)
                for ligAnchor, markClass in marks:
                    anchors[markClass.name] = self.makeOpenTypeAnchor(location, ligAnchor)
                componentAnchors.append(anchors)
            for glyph in ligatures:
                builder.ligatures[glyph] = componentAnchors

        # GPOS 6
        def add_mark_mark_pos(self, location, baseMarks, marks):
            builder = self.get_lookup_(location, MarkMarkPosBuilder)
            self.add_marks_(location, builder, marks)
            if not baseMarks:
                raise FeatureLibError("Empty glyph class in positioning rule", location)
            for baseAnchor, markClass in marks:
                otBaseAnchor = self.makeOpenTypeAnchor(location, baseAnchor)
                for baseMark in baseMarks:
                    builder.baseMarks.setdefault(baseMark, {})[
                        markClass.name
                    ] = otBaseAnchor

        # GPOS 7/8
        def add_chain_context_pos(self, location, prefix, glyphs, suffix, lookups):
            if not all(glyphs) or not all(prefix) or not all(suffix):
                raise FeatureLibError("Empty glyph class in contextual positioning rule", location)
            lookup = self.get_lookup_(location, ChainContextPosBuilder)
            lookup.rules.append(
                ChainContextualRule(
                    prefix, glyphs, suffix, self.find_lookup_builders_(lookups)
                )
            )

        def add_single_pos_chained_(self, location, prefix, suffix, pos):
            if not pos or not all(prefix) or not all(suffix):
                raise FeatureLibError("Empty glyph class in contextual positioning rule", location)
            # https://github.com/fonttools/fonttools/issues/514
            chain = self.get_lookup_(location, ChainContextPosBuilder)
            targets = []
            for _, _, _, lookups in chain.rules:
                targets.extend(lookups)
            subs = []
            for glyphs, value in pos:
                if value is None:
                    subs.append(None)
                    continue
                otValue = self.makeOpenTypeValueRecord(location, value, pairPosContext=False)
                sub = chain.find_chainable_single_pos(targets, glyphs, otValue)
                if sub is None:
                    sub = self.get_chained_lookup_(location, SinglePosBuilder)
                    targets.append(sub)
                for glyph in glyphs:
                    sub.add_pos(location, glyph, otValue)
                subs.append(sub)
            assert len(pos) == len(subs), (pos, subs)
            chain.rules.append(
                ChainContextualRule(prefix, [g for g, v in pos], suffix, subs)
            )

        def add_marks_(self, location, lookupBuilder, marks):
            """Helper for add_mark_{base,liga,mark}_pos."""
            for _, markClass in marks:
                for markClassDef in markClass.definitions:
                    for mark in markClassDef.glyphs.glyphSet():
                        if mark not in lookupBuilder.marks:
                            otMarkAnchor = self.makeOpenTypeAnchor(location, markClassDef.anchor)
                            lookupBuilder.marks[mark] = (markClass.name, otMarkAnchor)
                        else:
                            existingMarkClass = lookupBuilder.marks[mark][0]
                            if markClass.name != existingMarkClass:
                                raise FeatureLibError(
                                    "Glyph %s cannot be in both @%s and @%s"
                                    % (mark, existingMarkClass, markClass.name),
                                    location,
                                )

        def add_subtable_break(self, location):
            self.cur_lookup_.add_subtable_break(location)

        def setGlyphClass_(self, location, glyph, glyphClass):
            oldClass, oldLocation = self.glyphClassDefs_.get(glyph, (None, None))
            if oldClass and oldClass != glyphClass:
                raise FeatureLibError(
                    "Glyph %s was assigned to a different class at %s"
                    % (glyph, oldLocation),
                    location,
                )
            self.glyphClassDefs_[glyph] = (glyphClass, location)

        def add_glyphClassDef(
            self, location, baseGlyphs, ligatureGlyphs, markGlyphs, componentGlyphs
        ):
            for glyph in baseGlyphs:
                self.setGlyphClass_(location, glyph, 1)
            for glyph in ligatureGlyphs:
                self.setGlyphClass_(location, glyph, 2)
            for glyph in markGlyphs:
                self.setGlyphClass_(location, glyph, 3)
            for glyph in componentGlyphs:
                self.setGlyphClass_(location, glyph, 4)

        def add_ligatureCaretByIndex_(self, location, glyphs, carets):
            for glyph in glyphs:
                if glyph not in self.ligCaretPoints_:
                    self.ligCaretPoints_[glyph] = carets

        def add_ligatureCaretByPos_(self, location, glyphs, carets):
            for glyph in glyphs:
                if glyph not in self.ligCaretCoords_:
                    self.ligCaretCoords_[glyph] = carets

        def add_name_record(self, location, nameID, platformID, platEncID, langID, string):
            self.names_.append([nameID, platformID, platEncID, langID, string])

        def add_os2_field(self, key, value):
            self.os2_[key] = value

        def add_hhea_field(self, key, value):
            self.hhea_[key] = value

        def add_vhea_field(self, key, value):
            self.vhea_[key] = value

        def add_conditionset(self, key, value):
            if not "fvar" in self.font:
                raise FeatureLibError(
                    "Cannot add feature variations to a font without an 'fvar' table"
                )

            # Normalize
            axisMap = {
                axis.axisTag: (axis.minValue, axis.defaultValue, axis.maxValue)
                for axis in self.axes
            }

            value = {
                tag: (
                    normalizeValue(bottom, axisMap[tag]),
                    normalizeValue(top, axisMap[tag]),
                )
                for tag, (bottom, top) in value.items()
            }

            self.conditionsets_[key] = value

        def makeOpenTypeAnchor(self, location, anchor):
            """ast.Anchor --> otTables.Anchor"""
            if anchor is None:
                return None
            variable = False
            deviceX, deviceY = None, None
            if anchor.xDeviceTable is not None:
                deviceX = otl.buildDevice(dict(anchor.xDeviceTable))
            if anchor.yDeviceTable is not None:
                deviceY = otl.buildDevice(dict(anchor.yDeviceTable))
            for dim in ("x", "y"):
                if not isinstance(getattr(anchor, dim), VariableScalar):
                    continue
                if getattr(anchor, dim+"DeviceTable") is not None:
                    raise FeatureLibError("Can't define a device coordinate and variable scalar", location)
                if not self.varstorebuilder:
                    raise FeatureLibError("Can't define a variable scalar in a non-variable font", location)
                varscalar = getattr(anchor,dim)
                varscalar.axes = self.axes
                default, index = varscalar.add_to_variation_store(self.varstorebuilder)
                setattr(anchor, dim, default)
                if index is not None and index != 0xFFFFFFFF:
                    if dim == "x":
                        deviceX = buildVarDevTable(index)
                    else:
                        deviceY = buildVarDevTable(index)
                    variable = True

            otlanchor = otl.buildAnchor(anchor.x, anchor.y, anchor.contourpoint, deviceX, deviceY)
            if variable:
                otlanchor.Format = 3
            return otlanchor

        _VALUEREC_ATTRS = {
            name[0].lower() + name[1:]: (name, isDevice)
            for _, name, isDevice, _ in otBase.valueRecordFormat
            if not name.startswith("Reserved")
        }

        def makeOpenTypeValueRecord(self, location, v, pairPosContext):
            """ast.ValueRecord --> otBase.ValueRecord"""
            if not v:
                return None

            vr = {}
            variable = False
            for astName, (otName, isDevice) in self._VALUEREC_ATTRS.items():
                val = getattr(v, astName, None)
                if not val:
                    continue
                if isDevice:
                    vr[otName] = otl.buildDevice(dict(val))
                elif isinstance(val, VariableScalar):
                    otDeviceName = otName[0:4] + "Device"
                    feaDeviceName = otDeviceName[0].lower() + otDeviceName[1:]
                    if getattr(v, feaDeviceName):
                        raise FeatureLibError("Can't define a device coordinate and variable scalar", location)
                    if not self.varstorebuilder:
                        raise FeatureLibError("Can't define a variable scalar in a non-variable font", location)
                    val.axes = self.axes
                    default, index = val.add_to_variation_store(self.varstorebuilder)
                    vr[otName] = default
                    if index is not None and index != 0xFFFFFFFF:
                        vr[otDeviceName] = buildVarDevTable(index)
                        variable = True
                else:
                    vr[otName] = val

            if pairPosContext and not vr:
                vr = {"YAdvance": 0} if v.vertical else {"XAdvance": 0}
            valRec = otl.buildValue(vr)
            return valRec