mercurial/templater.py

filemerge: make the 'local' path match the format that 'base' and 'other' use

If we pass a separate '$output' arg to the merge tool, we produce four files:
local, base, other, and output.  In this situation, 'output' will be the
original filename, 'base' and 'other' are temporary files, and previously
'local' would be the backup file (so if 'output' was foo.txt, 'local' would be
foo.txt.orig).

This change makes it so that 'local' follows the same pattern as 'base' and
'other' - it will be a temporary file either in the
`experimental.mergetempdirprefix`-controlled directory with a name like
foo~local.txt, or in the normal system-wide temp dir with a name like
foo~local.RaNd0m.txt.

For the cases where the merge tool does not use an '$output' arg, 'local' is
still the destination filename, and 'base' and 'other' are unchanged.

The hope is that this is much easier for people to reason about; rather than
having a tool like Meld pop up with three panes, one of them with the filename
"foo.txt.orig", one with the filename "foo.txt", and one with
"foo~other.StuFf2.txt", we can (when the merge temp dir stuff is enabled) make
it show up as "foo~local.txt", "foo.txt" and "foo~other.txt", respectively.

This also opens the door to future customization, such as getting the
operation-provided labels and a hash prefix into the filenames (so we see
something like "foo~dest.abc123", "foo.txt", and "foo~src.d4e5f6").

Differential Revision: https://phab.mercurial-scm.org/D2889

# templater.py - template expansion for output
#
# Copyright 2005, 2006 Matt Mackall <[e-mail]>
#
# This software may be used and distributed according to the terms of the
# GNU General Public License version 2 or any later version.

"""Slightly complicated template engine for commands and hgweb

This module provides low-level interface to the template engine. See the
formatter and cmdutil modules if you are looking for high-level functions
such as ``cmdutil.rendertemplate(ctx, tmpl)``.

Internal Data Types
-------------------

Template keywords and functions take a dictionary of current symbols and
resources (a "mapping") and return result. Inputs and outputs must be one
of the following data types:

bytes
    a byte string, which is generally a human-readable text in local encoding.

generator
    a lazily-evaluated byte string, which is a possibly nested generator of
    values of any printable types, and  will be folded by ``stringify()``
    or ``flatten()``.

    BUG: hgweb overloads this type for mappings (i.e. some hgweb keywords
    returns a generator of dicts.)

None
    sometimes represents an empty value, which can be stringified to ''.

True, False, int, float
    can be stringified as such.

date tuple
    a (unixtime, offset) tuple, which produces no meaningful output by itself.

hybrid
    represents a list/dict of printable values, which can also be converted
    to mappings by % operator.

mappable
    represents a scalar printable value, also supports % operator.
"""

from __future__ import absolute_import, print_function

import abc
import os

from .i18n import _
from . import (
    config,
    encoding,
    error,
    parser,
    pycompat,
    templatefilters,
    templatefuncs,
    templateutil,
    util,
)

# template parsing

elements = {
    # token-type: binding-strength, primary, prefix, infix, suffix
    "(": (20, None, ("group", 1, ")"), ("func", 1, ")"), None),
    ".": (18, None, None, (".", 18), None),
    "%": (15, None, None, ("%", 15), None),
    "|": (15, None, None, ("|", 15), None),
    "*": (5, None, None, ("*", 5), None),
    "/": (5, None, None, ("/", 5), None),
    "+": (4, None, None, ("+", 4), None),
    "-": (4, None, ("negate", 19), ("-", 4), None),
    "=": (3, None, None, ("keyvalue", 3), None),
    ",": (2, None, None, ("list", 2), None),
    ")": (0, None, None, None, None),
    "integer": (0, "integer", None, None, None),
    "symbol": (0, "symbol", None, None, None),
    "string": (0, "string", None, None, None),
    "template": (0, "template", None, None, None),
    "end": (0, None, None, None, None),
}

def tokenize(program, start, end, term=None):
    """Parse a template expression into a stream of tokens, which must end
    with term if specified"""
    pos = start
    program = pycompat.bytestr(program)
    while pos < end:
        c = program[pos]
        if c.isspace(): # skip inter-token whitespace
            pass
        elif c in "(=,).%|+-*/": # handle simple operators
            yield (c, None, pos)
        elif c in '"\'': # handle quoted templates
            s = pos + 1
            data, pos = _parsetemplate(program, s, end, c)
            yield ('template', data, s)
            pos -= 1
        elif c == 'r' and program[pos:pos + 2] in ("r'", 'r"'):
            # handle quoted strings
            c = program[pos + 1]
            s = pos = pos + 2
            while pos < end: # find closing quote
                d = program[pos]
                if d == '\\': # skip over escaped characters
                    pos += 2
                    continue
                if d == c:
                    yield ('string', program[s:pos], s)
                    break
                pos += 1
            else:
                raise error.ParseError(_("unterminated string"), s)
        elif c.isdigit():
            s = pos
            while pos < end:
                d = program[pos]
                if not d.isdigit():
                    break
                pos += 1
            yield ('integer', program[s:pos], s)
            pos -= 1
        elif (c == '\\' and program[pos:pos + 2] in (br"\'", br'\"')
              or c == 'r' and program[pos:pos + 3] in (br"r\'", br'r\"')):
            # handle escaped quoted strings for compatibility with 2.9.2-3.4,
            # where some of nested templates were preprocessed as strings and
            # then compiled. therefore, \"...\" was allowed. (issue4733)
            #
            # processing flow of _evalifliteral() at 5ab28a2e9962:
            # outer template string    -> stringify()  -> compiletemplate()
            # ------------------------    ------------    ------------------
            # {f("\\\\ {g(\"\\\"\")}"}    \\ {g("\"")}    [r'\\', {g("\"")}]
            #             ~~~~~~~~
            #             escaped quoted string
            if c == 'r':
                pos += 1
                token = 'string'
            else:
                token = 'template'
            quote = program[pos:pos + 2]
            s = pos = pos + 2
            while pos < end: # find closing escaped quote
                if program.startswith('\\\\\\', pos, end):
                    pos += 4 # skip over double escaped characters
                    continue
                if program.startswith(quote, pos, end):
                    # interpret as if it were a part of an outer string
                    data = parser.unescapestr(program[s:pos])
                    if token == 'template':
                        data = _parsetemplate(data, 0, len(data))[0]
                    yield (token, data, s)
                    pos += 1
                    break
                pos += 1
            else:
                raise error.ParseError(_("unterminated string"), s)
        elif c.isalnum() or c in '_':
            s = pos
            pos += 1
            while pos < end: # find end of symbol
                d = program[pos]
                if not (d.isalnum() or d == "_"):
                    break
                pos += 1
            sym = program[s:pos]
            yield ('symbol', sym, s)
            pos -= 1
        elif c == term:
            yield ('end', None, pos)
            return
        else:
            raise error.ParseError(_("syntax error"), pos)
        pos += 1
    if term:
        raise error.ParseError(_("unterminated template expansion"), start)
    yield ('end', None, pos)

def _parsetemplate(tmpl, start, stop, quote=''):
    r"""
    >>> _parsetemplate(b'foo{bar}"baz', 0, 12)
    ([('string', 'foo'), ('symbol', 'bar'), ('string', '"baz')], 12)
    >>> _parsetemplate(b'foo{bar}"baz', 0, 12, quote=b'"')
    ([('string', 'foo'), ('symbol', 'bar')], 9)
    >>> _parsetemplate(b'foo"{bar}', 0, 9, quote=b'"')
    ([('string', 'foo')], 4)
    >>> _parsetemplate(br'foo\"bar"baz', 0, 12, quote=b'"')
    ([('string', 'foo"'), ('string', 'bar')], 9)
    >>> _parsetemplate(br'foo\\"bar', 0, 10, quote=b'"')
    ([('string', 'foo\\')], 6)
    """
    parsed = []
    for typ, val, pos in _scantemplate(tmpl, start, stop, quote):
        if typ == 'string':
            parsed.append((typ, val))
        elif typ == 'template':
            parsed.append(val)
        elif typ == 'end':
            return parsed, pos
        else:
            raise error.ProgrammingError('unexpected type: %s' % typ)
    raise error.ProgrammingError('unterminated scanning of template')

def scantemplate(tmpl, raw=False):
    r"""Scan (type, start, end) positions of outermost elements in template

    If raw=True, a backslash is not taken as an escape character just like
    r'' string in Python. Note that this is different from r'' literal in
    template in that no template fragment can appear in r'', e.g. r'{foo}'
    is a literal '{foo}', but ('{foo}', raw=True) is a template expression
    'foo'.

    >>> list(scantemplate(b'foo{bar}"baz'))
    [('string', 0, 3), ('template', 3, 8), ('string', 8, 12)]
    >>> list(scantemplate(b'outer{"inner"}outer'))
    [('string', 0, 5), ('template', 5, 14), ('string', 14, 19)]
    >>> list(scantemplate(b'foo\\{escaped}'))
    [('string', 0, 5), ('string', 5, 13)]
    >>> list(scantemplate(b'foo\\{escaped}', raw=True))
    [('string', 0, 4), ('template', 4, 13)]
    """
    last = None
    for typ, val, pos in _scantemplate(tmpl, 0, len(tmpl), raw=raw):
        if last:
            yield last + (pos,)
        if typ == 'end':
            return
        else:
            last = (typ, pos)
    raise error.ProgrammingError('unterminated scanning of template')

def _scantemplate(tmpl, start, stop, quote='', raw=False):
    """Parse template string into chunks of strings and template expressions"""
    sepchars = '{' + quote
    unescape = [parser.unescapestr, pycompat.identity][raw]
    pos = start
    p = parser.parser(elements)
    try:
        while pos < stop:
            n = min((tmpl.find(c, pos, stop) for c in sepchars),
                    key=lambda n: (n < 0, n))
            if n < 0:
                yield ('string', unescape(tmpl[pos:stop]), pos)
                pos = stop
                break
            c = tmpl[n:n + 1]
            bs = 0  # count leading backslashes
            if not raw:
                bs = (n - pos) - len(tmpl[pos:n].rstrip('\\'))
            if bs % 2 == 1:
                # escaped (e.g. '\{', '\\\{', but not '\\{')
                yield ('string', unescape(tmpl[pos:n - 1]) + c, pos)
                pos = n + 1
                continue
            if n > pos:
                yield ('string', unescape(tmpl[pos:n]), pos)
            if c == quote:
                yield ('end', None, n + 1)
                return

            parseres, pos = p.parse(tokenize(tmpl, n + 1, stop, '}'))
            if not tmpl.startswith('}', pos):
                raise error.ParseError(_("invalid token"), pos)
            yield ('template', parseres, n)
            pos += 1

        if quote:
            raise error.ParseError(_("unterminated string"), start)
    except error.ParseError as inst:
        if len(inst.args) > 1:  # has location
            loc = inst.args[1]
            # Offset the caret location by the number of newlines before the
            # location of the error, since we will replace one-char newlines
            # with the two-char literal r'\n'.
            offset = tmpl[:loc].count('\n')
            tmpl = tmpl.replace('\n', br'\n')
            # We want the caret to point to the place in the template that
            # failed to parse, but in a hint we get a open paren at the
            # start. Therefore, we print "loc + 1" spaces (instead of "loc")
            # to line up the caret with the location of the error.
            inst.hint = (tmpl + '\n'
                         + ' ' * (loc + 1 + offset) + '^ ' + _('here'))
        raise
    yield ('end', None, pos)

def _unnesttemplatelist(tree):
    """Expand list of templates to node tuple

    >>> def f(tree):
    ...     print(pycompat.sysstr(prettyformat(_unnesttemplatelist(tree))))
    >>> f((b'template', []))
    (string '')
    >>> f((b'template', [(b'string', b'foo')]))
    (string 'foo')
    >>> f((b'template', [(b'string', b'foo'), (b'symbol', b'rev')]))
    (template
      (string 'foo')
      (symbol 'rev'))
    >>> f((b'template', [(b'symbol', b'rev')]))  # template(rev) -> str
    (template
      (symbol 'rev'))
    >>> f((b'template', [(b'template', [(b'string', b'foo')])]))
    (string 'foo')
    """
    if not isinstance(tree, tuple):
        return tree
    op = tree[0]
    if op != 'template':
        return (op,) + tuple(_unnesttemplatelist(x) for x in tree[1:])

    assert len(tree) == 2
    xs = tuple(_unnesttemplatelist(x) for x in tree[1])
    if not xs:
        return ('string', '')  # empty template ""
    elif len(xs) == 1 and xs[0][0] == 'string':
        return xs[0]  # fast path for string with no template fragment "x"
    else:
        return (op,) + xs

def parse(tmpl):
    """Parse template string into tree"""
    parsed, pos = _parsetemplate(tmpl, 0, len(tmpl))
    assert pos == len(tmpl), 'unquoted template should be consumed'
    return _unnesttemplatelist(('template', parsed))

def _parseexpr(expr):
    """Parse a template expression into tree

    >>> _parseexpr(b'"foo"')
    ('string', 'foo')
    >>> _parseexpr(b'foo(bar)')
    ('func', ('symbol', 'foo'), ('symbol', 'bar'))
    >>> _parseexpr(b'foo(')
    Traceback (most recent call last):
      ...
    ParseError: ('not a prefix: end', 4)
    >>> _parseexpr(b'"foo" "bar"')
    Traceback (most recent call last):
      ...
    ParseError: ('invalid token', 7)
    """
    p = parser.parser(elements)
    tree, pos = p.parse(tokenize(expr, 0, len(expr)))
    if pos != len(expr):
        raise error.ParseError(_('invalid token'), pos)
    return _unnesttemplatelist(tree)

def prettyformat(tree):
    return parser.prettyformat(tree, ('integer', 'string', 'symbol'))

def compileexp(exp, context, curmethods):
    """Compile parsed template tree to (func, data) pair"""
    if not exp:
        raise error.ParseError(_("missing argument"))
    t = exp[0]
    if t in curmethods:
        return curmethods[t](exp, context)
    raise error.ParseError(_("unknown method '%s'") % t)

# template evaluation

def getsymbol(exp):
    if exp[0] == 'symbol':
        return exp[1]
    raise error.ParseError(_("expected a symbol, got '%s'") % exp[0])

def getlist(x):
    if not x:
        return []
    if x[0] == 'list':
        return getlist(x[1]) + [x[2]]
    return [x]

def gettemplate(exp, context):
    """Compile given template tree or load named template from map file;
    returns (func, data) pair"""
    if exp[0] in ('template', 'string'):
        return compileexp(exp, context, methods)
    if exp[0] == 'symbol':
        # unlike runsymbol(), here 'symbol' is always taken as template name
        # even if it exists in mapping. this allows us to override mapping
        # by web templates, e.g. 'changelogtag' is redefined in map file.
        return context._load(exp[1])
    raise error.ParseError(_("expected template specifier"))

def _runrecursivesymbol(context, mapping, key):
    raise error.Abort(_("recursive reference '%s' in template") % key)

def buildtemplate(exp, context):
    ctmpl = [compileexp(e, context, methods) for e in exp[1:]]
    return (templateutil.runtemplate, ctmpl)

def buildfilter(exp, context):
    n = getsymbol(exp[2])
    if n in context._filters:
        filt = context._filters[n]
        arg = compileexp(exp[1], context, methods)
        return (templateutil.runfilter, (arg, filt))
    if n in context._funcs:
        f = context._funcs[n]
        args = _buildfuncargs(exp[1], context, methods, n, f._argspec)
        return (f, args)
    raise error.ParseError(_("unknown function '%s'") % n)

def buildmap(exp, context):
    darg = compileexp(exp[1], context, methods)
    targ = gettemplate(exp[2], context)
    return (templateutil.runmap, (darg, targ))

def buildmember(exp, context):
    darg = compileexp(exp[1], context, methods)
    memb = getsymbol(exp[2])
    return (templateutil.runmember, (darg, memb))

def buildnegate(exp, context):
    arg = compileexp(exp[1], context, exprmethods)
    return (templateutil.runnegate, arg)

def buildarithmetic(exp, context, func):
    left = compileexp(exp[1], context, exprmethods)
    right = compileexp(exp[2], context, exprmethods)
    return (templateutil.runarithmetic, (func, left, right))

def buildfunc(exp, context):
    n = getsymbol(exp[1])
    if n in context._funcs:
        f = context._funcs[n]
        args = _buildfuncargs(exp[2], context, exprmethods, n, f._argspec)
        return (f, args)
    if n in context._filters:
        args = _buildfuncargs(exp[2], context, exprmethods, n, argspec=None)
        if len(args) != 1:
            raise error.ParseError(_("filter %s expects one argument") % n)
        f = context._filters[n]
        return (templateutil.runfilter, (args[0], f))
    raise error.ParseError(_("unknown function '%s'") % n)

def _buildfuncargs(exp, context, curmethods, funcname, argspec):
    """Compile parsed tree of function arguments into list or dict of
    (func, data) pairs

    >>> context = engine(lambda t: (templateutil.runsymbol, t))
    >>> def fargs(expr, argspec):
    ...     x = _parseexpr(expr)
    ...     n = getsymbol(x[1])
    ...     return _buildfuncargs(x[2], context, exprmethods, n, argspec)
    >>> list(fargs(b'a(l=1, k=2)', b'k l m').keys())
    ['l', 'k']
    >>> args = fargs(b'a(opts=1, k=2)', b'**opts')
    >>> list(args.keys()), list(args[b'opts'].keys())
    (['opts'], ['opts', 'k'])
    """
    def compiledict(xs):
        return util.sortdict((k, compileexp(x, context, curmethods))
                             for k, x in xs.iteritems())
    def compilelist(xs):
        return [compileexp(x, context, curmethods) for x in xs]

    if not argspec:
        # filter or function with no argspec: return list of positional args
        return compilelist(getlist(exp))

    # function with argspec: return dict of named args
    _poskeys, varkey, _keys, optkey = argspec = parser.splitargspec(argspec)
    treeargs = parser.buildargsdict(getlist(exp), funcname, argspec,
                                    keyvaluenode='keyvalue', keynode='symbol')
    compargs = util.sortdict()
    if varkey:
        compargs[varkey] = compilelist(treeargs.pop(varkey))
    if optkey:
        compargs[optkey] = compiledict(treeargs.pop(optkey))
    compargs.update(compiledict(treeargs))
    return compargs

def buildkeyvaluepair(exp, content):
    raise error.ParseError(_("can't use a key-value pair in this context"))

# methods to interpret function arguments or inner expressions (e.g. {_(x)})
exprmethods = {
    "integer": lambda e, c: (templateutil.runinteger, e[1]),
    "string": lambda e, c: (templateutil.runstring, e[1]),
    "symbol": lambda e, c: (templateutil.runsymbol, e[1]),
    "template": buildtemplate,
    "group": lambda e, c: compileexp(e[1], c, exprmethods),
    ".": buildmember,
    "|": buildfilter,
    "%": buildmap,
    "func": buildfunc,
    "keyvalue": buildkeyvaluepair,
    "+": lambda e, c: buildarithmetic(e, c, lambda a, b: a + b),
    "-": lambda e, c: buildarithmetic(e, c, lambda a, b: a - b),
    "negate": buildnegate,
    "*": lambda e, c: buildarithmetic(e, c, lambda a, b: a * b),
    "/": lambda e, c: buildarithmetic(e, c, lambda a, b: a // b),
    }

# methods to interpret top-level template (e.g. {x}, {x|_}, {x % "y"})
methods = exprmethods.copy()
methods["integer"] = exprmethods["symbol"]  # '{1}' as variable

class _aliasrules(parser.basealiasrules):
    """Parsing and expansion rule set of template aliases"""
    _section = _('template alias')
    _parse = staticmethod(_parseexpr)

    @staticmethod
    def _trygetfunc(tree):
        """Return (name, args) if tree is func(...) or ...|filter; otherwise
        None"""
        if tree[0] == 'func' and tree[1][0] == 'symbol':
            return tree[1][1], getlist(tree[2])
        if tree[0] == '|' and tree[2][0] == 'symbol':
            return tree[2][1], [tree[1]]

def expandaliases(tree, aliases):
    """Return new tree of aliases are expanded"""
    aliasmap = _aliasrules.buildmap(aliases)
    return _aliasrules.expand(aliasmap, tree)

# template engine

def _flatten(thing):
    '''yield a single stream from a possibly nested set of iterators'''
    thing = templateutil.unwraphybrid(thing)
    if isinstance(thing, bytes):
        yield thing
    elif isinstance(thing, str):
        # We can only hit this on Python 3, and it's here to guard
        # against infinite recursion.
        raise error.ProgrammingError('Mercurial IO including templates is done'
                                     ' with bytes, not strings, got %r' % thing)
    elif thing is None:
        pass
    elif not util.safehasattr(thing, '__iter__'):
        yield pycompat.bytestr(thing)
    else:
        for i in thing:
            i = templateutil.unwraphybrid(i)
            if isinstance(i, bytes):
                yield i
            elif i is None:
                pass
            elif not util.safehasattr(i, '__iter__'):
                yield pycompat.bytestr(i)
            else:
                for j in _flatten(i):
                    yield j

def unquotestring(s):
    '''unwrap quotes if any; otherwise returns unmodified string'''
    if len(s) < 2 or s[0] not in "'\"" or s[0] != s[-1]:
        return s
    return s[1:-1]

class resourcemapper(object):
    """Mapper of internal template resources"""

    __metaclass__ = abc.ABCMeta

    @abc.abstractmethod
    def availablekeys(self, context, mapping):
        """Return a set of available resource keys based on the given mapping"""

    @abc.abstractmethod
    def knownkeys(self):
        """Return a set of supported resource keys"""

    @abc.abstractmethod
    def lookup(self, context, mapping, key):
        """Return a resource for the key if available; otherwise None"""

class nullresourcemapper(resourcemapper):
    def availablekeys(self, context, mapping):
        return set()

    def knownkeys(self):
        return set()

    def lookup(self, context, mapping, key):
        return None

class engine(object):
    '''template expansion engine.

    template expansion works like this. a map file contains key=value
    pairs. if value is quoted, it is treated as string. otherwise, it
    is treated as name of template file.

    templater is asked to expand a key in map. it looks up key, and
    looks for strings like this: {foo}. it expands {foo} by looking up
    foo in map, and substituting it. expansion is recursive: it stops
    when there is no more {foo} to replace.

    expansion also allows formatting and filtering.

    format uses key to expand each item in list. syntax is
    {key%format}.

    filter uses function to transform value. syntax is
    {key|filter1|filter2|...}.'''

    def __init__(self, loader, filters=None, defaults=None, resources=None,
                 aliases=()):
        self._loader = loader
        if filters is None:
            filters = {}
        self._filters = filters
        self._funcs = templatefuncs.funcs  # make this a parameter if needed
        if defaults is None:
            defaults = {}
        if resources is None:
            resources = nullresourcemapper()
        self._defaults = defaults
        self._resources = resources
        self._aliasmap = _aliasrules.buildmap(aliases)
        self._cache = {}  # key: (func, data)

    def overlaymap(self, origmapping, newmapping):
        """Create combined mapping from the original mapping and partial
        mapping to override the original"""
        # do not copy symbols which overrides the defaults depending on
        # new resources, so the defaults will be re-evaluated (issue5612)
        knownres = self._resources.knownkeys()
        newres = self._resources.availablekeys(self, newmapping)
        mapping = {k: v for k, v in origmapping.iteritems()
                   if (k in knownres  # not a symbol per self.symbol()
                       or newres.isdisjoint(self._defaultrequires(k)))}
        mapping.update(newmapping)
        return mapping

    def _defaultrequires(self, key):
        """Resource keys required by the specified default symbol function"""
        v = self._defaults.get(key)
        if v is None or not callable(v):
            return ()
        return getattr(v, '_requires', ())

    def symbol(self, mapping, key):
        """Resolve symbol to value or function; None if nothing found"""
        v = None
        if key not in self._resources.knownkeys():
            v = mapping.get(key)
        if v is None:
            v = self._defaults.get(key)
        return v

    def resource(self, mapping, key):
        """Return internal data (e.g. cache) used for keyword/function
        evaluation"""
        v = self._resources.lookup(self, mapping, key)
        if v is None:
            raise templateutil.ResourceUnavailable(
                _('template resource not available: %s') % key)
        return v

    def _load(self, t):
        '''load, parse, and cache a template'''
        if t not in self._cache:
            # put poison to cut recursion while compiling 't'
            self._cache[t] = (_runrecursivesymbol, t)
            try:
                x = parse(self._loader(t))
                if self._aliasmap:
                    x = _aliasrules.expand(self._aliasmap, x)
                self._cache[t] = compileexp(x, self, methods)
            except: # re-raises
                del self._cache[t]
                raise
        return self._cache[t]

    def preload(self, t):
        """Load, parse, and cache the specified template if available"""
        try:
            self._load(t)
            return True
        except templateutil.TemplateNotFound:
            return False

    def process(self, t, mapping):
        '''Perform expansion. t is name of map element to expand.
        mapping contains added elements for use during expansion. Is a
        generator.'''
        func, data = self._load(t)
        return _flatten(func(self, mapping, data))

engines = {'default': engine}

def stylelist():
    paths = templatepaths()
    if not paths:
        return _('no templates found, try `hg debuginstall` for more info')
    dirlist = os.listdir(paths[0])
    stylelist = []
    for file in dirlist:
        split = file.split(".")
        if split[-1] in ('orig', 'rej'):
            continue
        if split[0] == "map-cmdline":
            stylelist.append(split[1])
    return ", ".join(sorted(stylelist))

def _readmapfile(mapfile):
    """Load template elements from the given map file"""
    if not os.path.exists(mapfile):
        raise error.Abort(_("style '%s' not found") % mapfile,
                          hint=_("available styles: %s") % stylelist())

    base = os.path.dirname(mapfile)
    conf = config.config(includepaths=templatepaths())
    conf.read(mapfile, remap={'': 'templates'})

    cache = {}
    tmap = {}
    aliases = []

    val = conf.get('templates', '__base__')
    if val and val[0] not in "'\"":
        # treat as a pointer to a base class for this style
        path = util.normpath(os.path.join(base, val))

        # fallback check in template paths
        if not os.path.exists(path):
            for p in templatepaths():
                p2 = util.normpath(os.path.join(p, val))
                if os.path.isfile(p2):
                    path = p2
                    break
                p3 = util.normpath(os.path.join(p2, "map"))
                if os.path.isfile(p3):
                    path = p3
                    break

        cache, tmap, aliases = _readmapfile(path)

    for key, val in conf['templates'].items():
        if not val:
            raise error.ParseError(_('missing value'),
                                   conf.source('templates', key))
        if val[0] in "'\"":
            if val[0] != val[-1]:
                raise error.ParseError(_('unmatched quotes'),
                                       conf.source('templates', key))
            cache[key] = unquotestring(val)
        elif key != '__base__':
            val = 'default', val
            if ':' in val[1]:
                val = val[1].split(':', 1)
            tmap[key] = val[0], os.path.join(base, val[1])
    aliases.extend(conf['templatealias'].items())
    return cache, tmap, aliases

class templater(object):

    def __init__(self, filters=None, defaults=None, resources=None,
                 cache=None, aliases=(), minchunk=1024, maxchunk=65536):
        """Create template engine optionally with preloaded template fragments

        - ``filters``: a dict of functions to transform a value into another.
        - ``defaults``: a dict of symbol values/functions; may be overridden
          by a ``mapping`` dict.
        - ``resources``: a resourcemapper object to look up internal data
          (e.g. cache), inaccessible from user template.
        - ``cache``: a dict of preloaded template fragments.
        - ``aliases``: a list of alias (name, replacement) pairs.

        self.cache may be updated later to register additional template
        fragments.
        """
        if filters is None:
            filters = {}
        if defaults is None:
            defaults = {}
        if cache is None:
            cache = {}
        self.cache = cache.copy()
        self.map = {}
        self.filters = templatefilters.filters.copy()
        self.filters.update(filters)
        self.defaults = defaults
        self._resources = resources
        self._aliases = aliases
        self.minchunk, self.maxchunk = minchunk, maxchunk
        self.ecache = {}

    @classmethod
    def frommapfile(cls, mapfile, filters=None, defaults=None, resources=None,
                    cache=None, minchunk=1024, maxchunk=65536):
        """Create templater from the specified map file"""
        t = cls(filters, defaults, resources, cache, [], minchunk, maxchunk)
        cache, tmap, aliases = _readmapfile(mapfile)
        t.cache.update(cache)
        t.map = tmap
        t._aliases = aliases
        return t

    def __contains__(self, key):
        return key in self.cache or key in self.map

    def load(self, t):
        '''Get the template for the given template name. Use a local cache.'''
        if t not in self.cache:
            try:
                self.cache[t] = util.readfile(self.map[t][1])
            except KeyError as inst:
                raise templateutil.TemplateNotFound(
                    _('"%s" not in template map') % inst.args[0])
            except IOError as inst:
                reason = (_('template file %s: %s')
                          % (self.map[t][1], util.forcebytestr(inst.args[1])))
                raise IOError(inst.args[0], encoding.strfromlocal(reason))
        return self.cache[t]

    def renderdefault(self, mapping):
        """Render the default unnamed template and return result as string"""
        return self.render('', mapping)

    def render(self, t, mapping):
        """Render the specified named template and return result as string"""
        return templateutil.stringify(self.generate(t, mapping))

    def generate(self, t, mapping):
        """Return a generator that renders the specified named template and
        yields chunks"""
        ttype = t in self.map and self.map[t][0] or 'default'
        if ttype not in self.ecache:
            try:
                ecls = engines[ttype]
            except KeyError:
                raise error.Abort(_('invalid template engine: %s') % ttype)
            self.ecache[ttype] = ecls(self.load, self.filters, self.defaults,
                                      self._resources, self._aliases)
        proc = self.ecache[ttype]

        stream = proc.process(t, mapping)
        if self.minchunk:
            stream = util.increasingchunks(stream, min=self.minchunk,
                                           max=self.maxchunk)
        return stream

def templatepaths():
    '''return locations used for template files.'''
    pathsrel = ['templates']
    paths = [os.path.normpath(os.path.join(util.datapath, f))
             for f in pathsrel]
    return [p for p in paths if os.path.isdir(p)]

def templatepath(name):
    '''return location of template file. returns None if not found.'''
    for p in templatepaths():
        f = os.path.join(p, name)
        if os.path.exists(f):
            return f
    return None

def stylemap(styles, paths=None):
    """Return path to mapfile for a given style.

    Searches mapfile in the following locations:
    1. templatepath/style/map
    2. templatepath/map-style
    3. templatepath/map
    """

    if paths is None:
        paths = templatepaths()
    elif isinstance(paths, bytes):
        paths = [paths]

    if isinstance(styles, bytes):
        styles = [styles]

    for style in styles:
        # only plain name is allowed to honor template paths
        if (not style
            or style in (pycompat.oscurdir, pycompat.ospardir)
            or pycompat.ossep in style
            or pycompat.osaltsep and pycompat.osaltsep in style):
            continue
        locations = [os.path.join(style, 'map'), 'map-' + style]
        locations.append('map')

        for path in paths:
            for location in locations:
                mapfile = os.path.join(path, location)
                if os.path.isfile(mapfile):
                    return style, mapfile

    raise RuntimeError("No hgweb templates found in %r" % paths)