path: root/registry/generator.py

#!/usr/bin/python3 -i
#
# Copyright (c) 2013-2020 The Khronos Group Inc.
#
# SPDX-License-Identifier: Apache-2.0
"""Base class for source/header/doc generators, as well as some utility functions."""

from __future__ import unicode_literals

import io
import os
import pdb
import re
import shutil
import sys
import tempfile
try:
    from pathlib import Path
except ImportError:
    from pathlib2 import Path

from spec_tools.util import getElemName, getElemType


def write(*args, **kwargs):
    file = kwargs.pop('file', sys.stdout)
    end = kwargs.pop('end', '\n')
    file.write(' '.join(str(arg) for arg in args))
    file.write(end)


def noneStr(s):
    """Return string argument, or "" if argument is None.

    Used in converting etree Elements into text.
    s - string to convert"""
    if s:
        return s
    return ""


def enquote(s):
    """Return string argument with surrounding quotes,
      for serialization into Python code."""
    if s:
        return "'{}'".format(s)
    return None


def regSortCategoryKey(feature):
    """Sort key for regSortFeatures.
    Sorts by category of the feature name string:

    - Core API features (those defined with a `<feature>` tag)
    - ARB/KHR/OES (Khronos extensions)
    - other       (EXT/vendor extensions)"""

    if feature.elem.tag == 'feature':
        return 0
    if (feature.category == 'ARB'
        or feature.category == 'KHR'
            or feature.category == 'OES'):
        return 1

    return 2


def regSortOrderKey(feature):
    """Sort key for regSortFeatures - key is the sortorder attribute."""

    # print("regSortOrderKey {} -> {}".format(feature.name, feature.sortorder))
    return feature.sortorder


def regSortFeatureVersionKey(feature):
    """Sort key for regSortFeatures - key is the feature version.
    `<extension>` elements all have version number 0."""

    return float(feature.versionNumber)


def regSortExtensionNumberKey(feature):
    """Sort key for regSortFeatures - key is the extension number.
    `<feature>` elements all have extension number 0."""

    return int(feature.number)


def regSortFeatures(featureList):
    """Default sort procedure for features.

    - Sorts by explicit sort order (default 0) relative to other features
    - then by feature category ('feature' or 'extension'),
    - then by version number (for features)
    - then by extension number (for extensions)"""
    featureList.sort(key=regSortExtensionNumberKey)
    featureList.sort(key=regSortFeatureVersionKey)
    featureList.sort(key=regSortCategoryKey)
    featureList.sort(key=regSortOrderKey)


class GeneratorOptions:
    """Base class for options used during header/documentation production.

    These options are target language independent, and used by
    Registry.apiGen() and by base OutputGenerator objects."""

    def __init__(self,
                 conventions=None,
                 filename=None,
                 directory='.',
                 genpath=None,
                 apiname=None,
                 profile=None,
                 versions='.*',
                 emitversions='.*',
                 defaultExtensions=None,
                 addExtensions=None,
                 removeExtensions=None,
                 emitExtensions=None,
                 reparentEnums=True,
                 sortProcedure=regSortFeatures):
        """Constructor.

        Arguments:

        - conventions - may be mandatory for some generators:
        an object that implements ConventionsBase
        - filename - basename of file to generate, or None to write to stdout.
        - directory - directory in which to generate files
        - genpath - path to previously generated files, such as api.py
        - apiname - string matching `<api>` 'apiname' attribute, e.g. 'gl'.
        - profile - string specifying API profile , e.g. 'core', or None.
        - versions - regex matching API versions to process interfaces for.
        Normally `'.*'` or `'[0-9][.][0-9]'` to match all defined versions.
        - emitversions - regex matching API versions to actually emit
        interfaces for (though all requested versions are considered
        when deciding which interfaces to generate). For GL 4.3 glext.h,
        this might be `'1[.][2-5]|[2-4][.][0-9]'`.
        - defaultExtensions - If not None, a string which must in its
        entirety match the pattern in the "supported" attribute of
        the `<extension>`. Defaults to None. Usually the same as apiname.
        - addExtensions - regex matching names of additional extensions
        to include. Defaults to None.
        - removeExtensions - regex matching names of extensions to
        remove (after defaultExtensions and addExtensions). Defaults
        to None.
        - emitExtensions - regex matching names of extensions to actually emit
        interfaces for (though all requested versions are considered when
        deciding which interfaces to generate).
        - reparentEnums - move <enum> elements which extend an enumerated
        type from <feature> or <extension> elements to the target <enums>
        element. This is required for almost all purposes, but the
        InterfaceGenerator relies on the list of interfaces in the <feature>
        or <extension> being complete. Defaults to True.
        - sortProcedure - takes a list of FeatureInfo objects and sorts
        them in place to a preferred order in the generated output.
        Default is core API versions, ARB/KHR/OES extensions, all other
        extensions, by core API version number or extension number in each
        group.

        The regex patterns can be None or empty, in which case they match
        nothing."""
        self.conventions = conventions
        """may be mandatory for some generators:
        an object that implements ConventionsBase"""

        self.filename = filename
        "basename of file to generate, or None to write to stdout."

        self.genpath = genpath
        """path to previously generated files, such as api.py"""

        self.directory = directory
        "directory in which to generate filename"

        self.apiname = apiname
        "string matching `<api>` 'apiname' attribute, e.g. 'gl'."

        self.profile = profile
        "string specifying API profile , e.g. 'core', or None."

        self.versions = self.emptyRegex(versions)
        """regex matching API versions to process interfaces for.
        Normally `'.*'` or `'[0-9][.][0-9]'` to match all defined versions."""

        self.emitversions = self.emptyRegex(emitversions)
        """regex matching API versions to actually emit
        interfaces for (though all requested versions are considered
        when deciding which interfaces to generate). For GL 4.3 glext.h,
        this might be `'1[.][2-5]|[2-4][.][0-9]'`."""

        self.defaultExtensions = defaultExtensions
        """If not None, a string which must in its
        entirety match the pattern in the "supported" attribute of
        the `<extension>`. Defaults to None. Usually the same as apiname."""

        self.addExtensions = self.emptyRegex(addExtensions)
        """regex matching names of additional extensions
        to include. Defaults to None."""

        self.removeExtensions = self.emptyRegex(removeExtensions)
        """regex matching names of extensions to
        remove (after defaultExtensions and addExtensions). Defaults
        to None."""

        self.emitExtensions = self.emptyRegex(emitExtensions)
        """regex matching names of extensions to actually emit
        interfaces for (though all requested versions are considered when
        deciding which interfaces to generate)."""

        self.reparentEnums = reparentEnums
        """boolean specifying whether to remove <enum> elements from
        <feature> or <extension> when extending an <enums> type."""

        self.sortProcedure = sortProcedure
        """takes a list of FeatureInfo objects and sorts
        them in place to a preferred order in the generated output.
        Default is core API versions, ARB/KHR/OES extensions, all
        other extensions, alphabetically within each group."""

        self.codeGenerator = False
        """True if this generator makes compilable code"""

    def emptyRegex(self, pat):
        """Substitute a regular expression which matches no version
        or extension names for None or the empty string."""
        if not pat:
            return '_nomatch_^'

        return pat


class OutputGenerator:
    """Generate specified API interfaces in a specific style, such as a C header.

    Base class for generating API interfaces.
    Manages basic logic, logging, and output file control.
    Derived classes actually generate formatted output.
    """

    # categoryToPath - map XML 'category' to include file directory name
    categoryToPath = {
        'bitmask': 'flags',
        'enum': 'enums',
        'funcpointer': 'funcpointers',
        'handle': 'handles',
        'define': 'defines',
        'basetype': 'basetypes',
    }

    def __init__(self, errFile=sys.stderr, warnFile=sys.stderr, diagFile=sys.stdout):
        """Constructor

        - errFile, warnFile, diagFile - file handles to write errors,
          warnings, diagnostics to. May be None to not write."""
        self.outFile = None
        self.errFile = errFile
        self.warnFile = warnFile
        self.diagFile = diagFile
        # Internal state
        self.featureName = None
        self.genOpts = None
        self.registry = None
        self.featureDictionary = {}
        # Used for extension enum value generation
        self.extBase = 1000000000
        self.extBlockSize = 1000
        self.madeDirs = {}

        # API dictionary, which may be loaded by the beginFile method of
        # derived generators.
        self.apidict = None

    def logMsg(self, level, *args):
        """Write a message of different categories to different
        destinations.

        - `level`
          - 'diag' (diagnostic, voluminous)
          - 'warn' (warning)
          - 'error' (fatal error - raises exception after logging)

        - `*args` - print()-style arguments to direct to corresponding log"""
        if level == 'error':
            strfile = io.StringIO()
            write('ERROR:', *args, file=strfile)
            if self.errFile is not None:
                write(strfile.getvalue(), file=self.errFile)
            raise UserWarning(strfile.getvalue())
        elif level == 'warn':
            if self.warnFile is not None:
                write('WARNING:', *args, file=self.warnFile)
        elif level == 'diag':
            if self.diagFile is not None:
                write('DIAG:', *args, file=self.diagFile)
        else:
            raise UserWarning(
                '*** FATAL ERROR in Generator.logMsg: unknown level:' + level)

    def enumToValue(self, elem, needsNum):
        """Parse and convert an `<enum>` tag into a value.

        Returns a list:

        - first element - integer representation of the value, or None
          if needsNum is False. The value must be a legal number
          if needsNum is True.
        - second element - string representation of the value

        There are several possible representations of values.

        - A 'value' attribute simply contains the value.
        - A 'bitpos' attribute defines a value by specifying the bit
          position which is set in that value.
        - An 'offset','extbase','extends' triplet specifies a value
          as an offset to a base value defined by the specified
          'extbase' extension name, which is then cast to the
          typename specified by 'extends'. This requires probing
          the registry database, and imbeds knowledge of the
          API extension enum scheme in this function.
        - An 'alias' attribute contains the name of another enum
          which this is an alias of. The other enum must be
          declared first when emitting this enum."""
        name = elem.get('name')
        numVal = None
        if 'value' in elem.keys():
            value = elem.get('value')
            # print('About to translate value =', value, 'type =', type(value))
            if needsNum:
                numVal = int(value, 0)
            # If there's a non-integer, numeric 'type' attribute (e.g. 'u' or
            # 'ull'), append it to the string value.
            # t = enuminfo.elem.get('type')
            # if t is not None and t != '' and t != 'i' and t != 's':
            #     value += enuminfo.type
            self.logMsg('diag', 'Enum', name, '-> value [', numVal, ',', value, ']')
            return [numVal, value]
        if 'bitpos' in elem.keys():
            value = elem.get('bitpos')
            bitpos = int(value, 0)
            numVal = 1 << bitpos
            value = '0x%08x' % numVal
            if bitpos >= 32:
                value = value + 'ULL'
            self.logMsg('diag', 'Enum', name, '-> bitpos [', numVal, ',', value, ']')
            return [numVal, value]
        if 'offset' in elem.keys():
            # Obtain values in the mapping from the attributes
            enumNegative = False
            offset = int(elem.get('offset'), 0)
            extnumber = int(elem.get('extnumber'), 0)
            extends = elem.get('extends')
            if 'dir' in elem.keys():
                enumNegative = True
            self.logMsg('diag', 'Enum', name, 'offset =', offset,
                        'extnumber =', extnumber, 'extends =', extends,
                        'enumNegative =', enumNegative)
            # Now determine the actual enumerant value, as defined
            # in the "Layers and Extensions" appendix of the spec.
            numVal = self.extBase + (extnumber - 1) * self.extBlockSize + offset
            if enumNegative:
                numVal *= -1
            value = '%d' % numVal
            # More logic needed!
            self.logMsg('diag', 'Enum', name, '-> offset [', numVal, ',', value, ']')
            return [numVal, value]
        if 'alias' in elem.keys():
            return [None, elem.get('alias')]
        return [None, None]

    def checkDuplicateEnums(self, enums):
        """Sanity check enumerated values.

        -  enums - list of `<enum>` Elements

        returns the list with duplicates stripped"""
        # Dictionaries indexed by name and numeric value.
        # Entries are [ Element, numVal, strVal ] matching name or value

        nameMap = {}
        valueMap = {}

        stripped = []
        for elem in enums:
            name = elem.get('name')
            (numVal, strVal) = self.enumToValue(elem, True)

            if name in nameMap:
                # Duplicate name found; check values
                (name2, numVal2, strVal2) = nameMap[name]

                # Duplicate enum values for the same name are benign. This
                # happens when defining the same enum conditionally in
                # several extension blocks.
                if (strVal2 == strVal or (numVal is not None
                                          and numVal == numVal2)):
                    True
                    # self.logMsg('info', 'checkDuplicateEnums: Duplicate enum (' + name +
                    #             ') found with the same value:' + strVal)
                else:
                    self.logMsg('warn', 'checkDuplicateEnums: Duplicate enum (' + name
                                + ') found with different values:' + strVal
                                + ' and ' + strVal2)

                # Don't add the duplicate to the returned list
                continue
            elif numVal in valueMap:
                # Duplicate value found (such as an alias); report it, but
                # still add this enum to the list.
                (name2, numVal2, strVal2) = valueMap[numVal]

                msg = 'Two enums found with the same value: {} = {} = {}'.format(
                    name, name2.get('name'), strVal)
                self.logMsg('error', msg)

            # Track this enum to detect followon duplicates
            nameMap[name] = [elem, numVal, strVal]
            if numVal is not None:
                valueMap[numVal] = [elem, numVal, strVal]

            # Add this enum to the list
            stripped.append(elem)

        # Return the list
        return stripped

    def buildEnumCDecl(self, expand, groupinfo, groupName):
        """Generate the C declaration for an enum"""
        groupElem = groupinfo.elem

        # Determine the required bit width for the enum group.
        # 32 is the default, which generates C enum types for the values.
        bitwidth = 32
        
        # If the constFlagBits preference is set, 64 is the default for bitmasks
        if self.genOpts.conventions.constFlagBits and groupElem.get('type') == 'bitmask':
            bitwidth = 64
        
        # Check for an explicitly defined bitwidth, which will override any defaults.
        if groupElem.get('bitwidth'):
            try:
                bitwidth = int(groupElem.get('bitwidth'))
            except ValueError as ve:
                self.logMsg('error', 'Invalid value for bitwidth attribute (', groupElem.get('bitwidth'), ') for ', groupName, ' - must be an integer value\n')
                exit(1)
        
        # Bitmask types support 64-bit flags, so have different handling
        if groupElem.get('type') == 'bitmask':
        
            # Validate the bitwidth and generate values appropriately
            # Bitmask flags up to 64-bit are generated as static const uint64_t values
            # Bitmask flags up to 32-bit are generated as C enum values
            if bitwidth > 64:
                self.logMsg('error', 'Invalid value for bitwidth attribute (', groupElem.get('bitwidth'), ') for bitmask type ', groupName, ' - must be less than or equal to 64\n')
                exit(1)
            elif bitwidth > 32:
                return self.buildEnumCDecl_Bitmask(groupinfo, groupName)
            else:
                return self.buildEnumCDecl_Enum(expand, groupinfo, groupName)
        else:
            # Validate the bitwidth and generate values appropriately
            # Enum group types up to 32-bit are generated as C enum values
            if bitwidth > 32:
                self.logMsg('error', 'Invalid value for bitwidth attribute (', groupElem.get('bitwidth'), ') for enum type ', groupName, ' - must be less than or equal to 32\n')
                exit(1)
            else:
                return self.buildEnumCDecl_Enum(expand, groupinfo, groupName)

    def buildEnumCDecl_Bitmask(self, groupinfo, groupName):
        """Generate the C declaration for an "enum" that is actually a
        set of flag bits"""
        groupElem = groupinfo.elem
        flagTypeName = groupinfo.flagType.elem.get('name')

        # Prefix
        body = "// Flag bits for " + flagTypeName + "\n"
        
        # Maximum allowable value for a flag (unsigned 64-bit integer)
        maxValidValue = 2**(64) - 1
        minValidValue = 0

        # Loop over the nested 'enum' tags.
        for elem in groupElem.findall('enum'):
            # Convert the value to an integer and use that to track min/max.
            # Values of form -(number) are accepted but nothing more complex.
            # Should catch exceptions here for more complex constructs. Not yet.
            (numVal, strVal) = self.enumToValue(elem, True)
            name = elem.get('name')
            
            # Range check for the enum value
            if numVal is not None and (numVal > maxValidValue or numVal < minValidValue):
                self.logMsg('error', 'Allowable range for flag types in C is [', minValidValue, ',', maxValidValue, '], but', name, 'flag has a value outside of this (', strVal, ')\n')
                exit(1)
            
            body += "static const {} {} = {};\n".format(flagTypeName, name, strVal)

        # Postfix

        return ("bitmask", body)

    def buildEnumCDecl_Enum(self, expand, groupinfo, groupName):
        """Generate the C declaration for an enumerated type"""
        groupElem = groupinfo.elem

        # Break the group name into prefix and suffix portions for range
        # enum generation
        expandName = re.sub(r'([0-9a-z_])([A-Z0-9])', r'\1_\2', groupName).upper()
        expandPrefix = expandName
        expandSuffix = ''
        expandSuffixMatch = re.search(r'[A-Z][A-Z]+$', groupName)
        if expandSuffixMatch:
            expandSuffix = '_' + expandSuffixMatch.group()
            # Strip off the suffix from the prefix
            expandPrefix = expandName.rsplit(expandSuffix, 1)[0]

        # Prefix
        body = ["typedef enum %s {" % groupName]

        # @@ Should use the type="bitmask" attribute instead
        isEnum = ('FLAG_BITS' not in expandPrefix)
        
        # Allowable range for a C enum - which is that of a signed 32-bit integer
        maxValidValue = 2**(32 - 1) - 1
        minValidValue = (maxValidValue * -1) - 1
        

        # Get a list of nested 'enum' tags.
        enums = groupElem.findall('enum')

        # Check for and report duplicates, and return a list with them
        # removed.
        enums = self.checkDuplicateEnums(enums)

        # Loop over the nested 'enum' tags. Keep track of the minimum and
        # maximum numeric values, if they can be determined; but only for
        # core API enumerants, not extension enumerants. This is inferred
        # by looking for 'extends' attributes.
        minName = None

        # Accumulate non-numeric enumerant values separately and append
        # them following the numeric values, to allow for aliases.
        # NOTE: this doesn't do a topological sort yet, so aliases of
        # aliases can still get in the wrong order.
        aliasText = []

        for elem in enums:
            # Convert the value to an integer and use that to track min/max.
            # Values of form -(number) are accepted but nothing more complex.
            # Should catch exceptions here for more complex constructs. Not yet.
            (numVal, strVal) = self.enumToValue(elem, True)
            name = elem.get('name')

            # Extension enumerants are only included if they are required
            if self.isEnumRequired(elem):
                decl = "    {} = {},".format(name, strVal)
                if numVal is not None:
                    body.append(decl)
                else:
                    aliasText.append(decl)

            # Range check for the enum value
            if numVal is not None and (numVal > maxValidValue or numVal < minValidValue):
                self.logMsg('error', 'Allowable range for C enum types is [', minValidValue, ',', maxValidValue, '], but', name, 'has a value outside of this (', strVal, ')\n')
                exit(1)
            

            # Don't track min/max for non-numbers (numVal is None)
            if isEnum and numVal is not None and elem.get('extends') is None:
                if minName is None:
                    minName = maxName = name
                    minValue = maxValue = numVal
                elif numVal < minValue:
                    minName = name
                    minValue = numVal
                elif numVal > maxValue:
                    maxName = name
                    maxValue = numVal

        # Now append the non-numeric enumerant values
        body.extend(aliasText)

        # Generate min/max value tokens - legacy use case.
        if isEnum and expand:
            body.extend(("    {}_BEGIN_RANGE{} = {},".format(expandPrefix, expandSuffix, minName),
                         "    {}_END_RANGE{} = {},".format(
                             expandPrefix, expandSuffix, maxName),
                         "    {}_RANGE_SIZE{} = ({} - {} + 1),".format(expandPrefix, expandSuffix, maxName, minName)))

        # Generate a range-padding value to ensure the enum is 32 bits, but
        # only in code generators, so it doesn't appear in documentation
        if (self.genOpts.codeGenerator or
            self.conventions.generate_max_enum_in_docs):
            body.append("    {}_MAX_ENUM{} = 0x7FFFFFFF".format(
                expandPrefix, expandSuffix))

        # Postfix
        body.append("} %s;" % groupName)

        # Determine appropriate section for this declaration
        if groupElem.get('type') == 'bitmask':
            section = 'bitmask'
        else:
            section = 'group'

        return (section, '\n'.join(body))

    def makeDir(self, path):
        """Create a directory, if not already done.

        Generally called from derived generators creating hierarchies."""
        self.logMsg('diag', 'OutputGenerator::makeDir(' + path + ')')
        if path not in self.madeDirs:
            # This can get race conditions with multiple writers, see
            # https://stackoverflow.com/questions/273192/
            if not os.path.exists(path):
                os.makedirs(path)
            self.madeDirs[path] = None

    def beginFile(self, genOpts):
        """Start a new interface file

        - genOpts - GeneratorOptions controlling what's generated and how"""
        self.genOpts = genOpts
        self.should_insert_may_alias_macro = \
            self.genOpts.conventions.should_insert_may_alias_macro(self.genOpts)

        # Try to import the API dictionary, api.py, if it exists. Nothing in
        # api.py cannot be extracted directly from the XML, and in the
        # future we should do that.
        if self.genOpts.genpath is not None:
            try:
                sys.path.insert(0, self.genOpts.genpath)
                import api
                self.apidict = api
            except ImportError:
                self.apidict = None

        self.conventions = genOpts.conventions

        # Open a temporary file for accumulating output.
        if self.genOpts.filename is not None:
            self.outFile = tempfile.NamedTemporaryFile(mode='w', encoding='utf-8', newline='\n', delete=False)
        else:
            self.outFile = sys.stdout

    def endFile(self):
        if self.errFile:
            self.errFile.flush()
        if self.warnFile:
            self.warnFile.flush()
        if self.diagFile:
            self.diagFile.flush()
        self.outFile.flush()
        if self.outFile != sys.stdout and self.outFile != sys.stderr:
            self.outFile.close()

        # On successfully generating output, move the temporary file to the
        # target file.
        if self.genOpts.filename is not None:
            if sys.platform == 'win32':
                directory = Path(self.genOpts.directory)
                if not Path.exists(directory):
                    os.makedirs(directory)
            shutil.copy(self.outFile.name, self.genOpts.directory + '/' + self.genOpts.filename)
            os.remove(self.outFile.name)
        self.genOpts = None

    def beginFeature(self, interface, emit):
        """Write interface for a feature and tag generated features as having been done.

        - interface - element for the `<version>` / `<extension>` to generate
        - emit - actually write to the header only when True"""
        self.emit = emit
        self.featureName = interface.get('name')
        # If there's an additional 'protect' attribute in the feature, save it
        self.featureExtraProtect = interface.get('protect')

    def endFeature(self):
        """Finish an interface file, closing it when done.

        Derived classes responsible for emitting feature"""
        self.featureName = None
        self.featureExtraProtect = None

    def validateFeature(self, featureType, featureName):
        """Validate we're generating something only inside a `<feature>` tag"""
        if self.featureName is None:
            raise UserWarning('Attempt to generate', featureType,
                              featureName, 'when not in feature')

    def genType(self, typeinfo, name, alias):
        """Generate interface for a type

        - typeinfo - TypeInfo for a type

        Extend to generate as desired in your derived class."""
        self.validateFeature('type', name)

    def genStruct(self, typeinfo, typeName, alias):
        """Generate interface for a C "struct" type.

        - typeinfo - TypeInfo for a type interpreted as a struct

        Extend to generate as desired in your derived class."""
        self.validateFeature('struct', typeName)

        # The mixed-mode <member> tags may contain no-op <comment> tags.
        # It is convenient to remove them here where all output generators
        # will benefit.
        for member in typeinfo.elem.findall('.//member'):
            for comment in member.findall('comment'):
                member.remove(comment)

    def genGroup(self, groupinfo, groupName, alias):
        """Generate interface for a group of enums (C "enum")

        - groupinfo - GroupInfo for a group.

        Extend to generate as desired in your derived class."""

        self.validateFeature('group', groupName)

    def genEnum(self, enuminfo, typeName, alias):
        """Generate interface for an enum (constant).

        - enuminfo - EnumInfo for an enum
        - name - enum name

        Extend to generate as desired in your derived class."""
        self.validateFeature('enum', typeName)

    def genCmd(self, cmd, cmdinfo, alias):
        """Generate interface for a command.

        - cmdinfo - CmdInfo for a command

        Extend to generate as desired in your derived class."""
        self.validateFeature('command', cmdinfo)

    def makeProtoName(self, name, tail):
        """Turn a `<proto>` `<name>` into C-language prototype
        and typedef declarations for that name.

        - name - contents of `<name>` tag
        - tail - whatever text follows that tag in the Element"""
        return self.genOpts.apientry + name + tail

    def makeTypedefName(self, name, tail):
        """Make the function-pointer typedef name for a command."""
        return '(' + self.genOpts.apientryp + 'PFN_' + name + tail + ')'

    def makeCParamDecl(self, param, aligncol):
        """Return a string which is an indented, formatted
        declaration for a `<param>` or `<member>` block (e.g. function parameter
        or structure/union member).

        - param - Element (`<param>` or `<member>`) to format
        - aligncol - if non-zero, attempt to align the nested `<name>` element
          at this column"""
        indent = '    '
        paramdecl = indent + noneStr(param.text)
        for elem in param:
            text = noneStr(elem.text)
            tail = noneStr(elem.tail)

            if self.should_insert_may_alias_macro and self.genOpts.conventions.is_voidpointer_alias(elem.tag, text, tail):
                # OpenXR-specific macro insertion - but not in apiinc for the spec
                tail = self.genOpts.conventions.make_voidpointer_alias(tail)
            if elem.tag == 'name' and aligncol > 0:
                self.logMsg('diag', 'Aligning parameter', elem.text, 'to column', self.genOpts.alignFuncParam)
                # Align at specified column, if possible
                paramdecl = paramdecl.rstrip()
                oldLen = len(paramdecl)
                # This works around a problem where very long type names -
                # longer than the alignment column - would run into the tail
                # text.
                paramdecl = paramdecl.ljust(aligncol - 1) + ' '
                newLen = len(paramdecl)
                self.logMsg('diag', 'Adjust length of parameter decl from', oldLen, 'to', newLen, ':', paramdecl)
            paramdecl += text + tail
        if aligncol == 0:
            # Squeeze out multiple spaces other than the indentation
            paramdecl = indent + ' '.join(paramdecl.split())
        return paramdecl

    def getCParamTypeLength(self, param):
        """Return the length of the type field is an indented, formatted
        declaration for a `<param>` or `<member>` block (e.g. function parameter
        or structure/union member).

        - param - Element (`<param>` or `<member>`) to identify"""

        # Allow for missing <name> tag
        newLen = 0
        paramdecl = '    ' + noneStr(param.text)
        for elem in param:
            text = noneStr(elem.text)
            tail = noneStr(elem.tail)

            if self.should_insert_may_alias_macro and self.genOpts.conventions.is_voidpointer_alias(elem.tag, text, tail):
                # OpenXR-specific macro insertion
                tail = self.genOpts.conventions.make_voidpointer_alias(tail)
            if elem.tag == 'name':
                # Align at specified column, if possible
                newLen = len(paramdecl.rstrip())
                self.logMsg('diag', 'Identifying length of', elem.text, 'as', newLen)
            paramdecl += text + tail

        return newLen

    def getMaxCParamTypeLength(self, info):
        """Return the length of the longest type field for a member/parameter.

        - info - TypeInfo or CommandInfo.
        """
        lengths = (self.getCParamTypeLength(member)
                   for member in info.getMembers())
        return max(lengths)

    def getHandleParent(self, typename):
        """Get the parent of a handle object."""
        info = self.registry.typedict.get(typename)
        if info is None:
            return None

        elem = info.elem
        if elem is not None:
            return elem.get('parent')

        return None

    def iterateHandleAncestors(self, typename):
        """Iterate through the ancestors of a handle type."""
        current = self.getHandleParent(typename)
        while current is not None:
            yield current
            current = self.getHandleParent(current)

    def getHandleAncestors(self, typename):
        """Get the ancestors of a handle object."""
        return list(self.iterateHandleAncestors(typename))

    def getTypeCategory(self, typename):
        """Get the category of a type."""
        info = self.registry.typedict.get(typename)
        if info is None:
            return None

        elem = info.elem
        if elem is not None:
            return elem.get('category')
        return None

    def isStructAlwaysValid(self, structname):
        """Try to do check if a structure is always considered valid (i.e. there's no rules to its acceptance)."""
        # A conventions object is required for this call.
        if not self.conventions:
            raise RuntimeError("To use isStructAlwaysValid, be sure your options include a Conventions object.")

        if self.conventions.type_always_valid(structname):
            return True

        category = self.getTypeCategory(structname)
        if self.conventions.category_requires_validation(category):
            return False

        info = self.registry.typedict.get(structname)
        assert(info is not None)

        members = info.getMembers()

        for member in members:
            member_name = getElemName(member)
            if member_name in (self.conventions.structtype_member_name,
                               self.conventions.nextpointer_member_name):
                return False

            if member.get('noautovalidity'):
                return False

            member_type = getElemType(member)

            if member_type in ('void', 'char') or self.paramIsArray(member) or self.paramIsPointer(member):
                return False

            if self.conventions.type_always_valid(member_type):
                continue

            member_category = self.getTypeCategory(member_type)

            if self.conventions.category_requires_validation(member_category):
                return False

            if member_category in ('struct', 'union'):
                if self.isStructAlwaysValid(member_type) is False:
                    return False

        return True

    def isEnumRequired(self, elem):
        """Return True if this `<enum>` element is
        required, False otherwise

        - elem - `<enum>` element to test"""
        required = elem.get('required') is not None
        self.logMsg('diag', 'isEnumRequired:', elem.get('name'),
                    '->', required)
        return required

        # @@@ This code is overridden by equivalent code now run in
        # @@@ Registry.generateFeature

        required = False

        extname = elem.get('extname')
        if extname is not None:
            # 'supported' attribute was injected when the <enum> element was
            # moved into the <enums> group in Registry.parseTree()
            if self.genOpts.defaultExtensions == elem.get('supported'):
                required = True
            elif re.match(self.genOpts.addExtensions, extname) is not None:
                required = True
        elif elem.get('version') is not None:
            required = re.match(self.genOpts.emitversions, elem.get('version')) is not None
        else:
            required = True

        return required

    def makeCDecls(self, cmd):
        """Return C prototype and function pointer typedef for a
        `<command>` Element, as a two-element list of strings.

        - cmd - Element containing a `<command>` tag"""
        proto = cmd.find('proto')
        params = cmd.findall('param')
        # Begin accumulating prototype and typedef strings
        pdecl = self.genOpts.apicall
        tdecl = 'typedef '

        # Insert the function return type/name.
        # For prototypes, add APIENTRY macro before the name
        # For typedefs, add (APIENTRY *<name>) around the name and
        #   use the PFN_cmdnameproc naming convention.
        # Done by walking the tree for <proto> element by element.
        # etree has elem.text followed by (elem[i], elem[i].tail)
        #   for each child element and any following text
        # Leading text
        pdecl += noneStr(proto.text)
        tdecl += noneStr(proto.text)
        # For each child element, if it's a <name> wrap in appropriate
        # declaration. Otherwise append its contents and tail contents.
        for elem in proto:
            text = noneStr(elem.text)
            tail = noneStr(elem.tail)
            if elem.tag == 'name':
                pdecl += self.makeProtoName(text, tail)
                tdecl += self.makeTypedefName(text, tail)
            else:
                pdecl += text + tail
                tdecl += text + tail

        if self.genOpts.alignFuncParam == 0:
            # Squeeze out multiple spaces - there is no indentation
            pdecl = ' '.join(pdecl.split())
            tdecl = ' '.join(tdecl.split())

        # Now add the parameter declaration list, which is identical
        # for prototypes and typedefs. Concatenate all the text from
        # a <param> node without the tags. No tree walking required
        # since all tags are ignored.
        # Uses: self.indentFuncProto
        # self.indentFuncPointer
        # self.alignFuncParam
        n = len(params)
        # Indented parameters
        if n > 0:
            indentdecl = '(\n'
            indentdecl += ',\n'.join(self.makeCParamDecl(p, self.genOpts.alignFuncParam)
                                     for p in params)
            indentdecl += ');'
        else:
            indentdecl = '(void);'
        # Non-indented parameters
        paramdecl = '('
        if n > 0:
            paramnames = (''.join(t for t in p.itertext())
                          for p in params)
            paramdecl += ', '.join(paramnames)
        else:
            paramdecl += 'void'
        paramdecl += ");"
        return [pdecl + indentdecl, tdecl + paramdecl]

    def newline(self):
        """Print a newline to the output file (utility function)"""
        write('', file=self.outFile)

    def setRegistry(self, registry):
        self.registry = registry