mercurial/templater.py

hgweb: refactor the request draining code

The previous code for draining was only invoked in a few places in
the wire protocol. Behavior wasn't consist. Furthermore, it was
difficult to reason about.

With us converting the input stream to a capped reader, it is now
safe to always drain the input stream when its size is known because
we can never overrun the input and read into the next HTTP request.
The only question is "should we?"

This commit changes the draining code so every request is examined.
Draining now kicks in for a few requests where it wouldn't before.
But I think the code is sufficiently restricted so the behavior is
safe. Possibly the most dangerous part of this code is the issuing
of Connection: close for POST and PUT requests that don't have a
Content-Length. I don't think there are any such uses in our WSGI
application, so this should be safe.

In the near future, I plan to significantly refactor the WSGI
response handling. I anticipate this code evolving a bit. So any
minor regressions around draining or connection closing behavior
might be fixed as a result of that work.

All tests pass with this change. That scares me a bit because it
means we are lacking low-level tests for the HTTP protocol.

Differential Revision: https://phab.mercurial-scm.org/D2769

# 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.

from __future__ import absolute_import, print_function

import os
import re
import types

from .i18n import _
from . import (
    color,
    config,
    encoding,
    error,
    minirst,
    obsutil,
    parser,
    pycompat,
    registrar,
    revset as revsetmod,
    revsetlang,
    scmutil,
    templatefilters,
    templatekw,
    util,
)
from .utils import dateutil

class ResourceUnavailable(error.Abort):
    pass

class TemplateNotFound(error.Abort):
    pass

# 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 findsymbolicname(arg):
    """Find symbolic name for the given compiled expression; returns None
    if nothing found reliably"""
    while True:
        func, data = arg
        if func is runsymbol:
            return data
        elif func is runfilter:
            arg = data[0]
        else:
            return None

def evalrawexp(context, mapping, arg):
    """Evaluate given argument as a bare template object which may require
    further processing (such as folding generator of strings)"""
    func, data = arg
    return func(context, mapping, data)

def evalfuncarg(context, mapping, arg):
    """Evaluate given argument as value type"""
    thing = evalrawexp(context, mapping, arg)
    thing = templatekw.unwrapvalue(thing)
    # evalrawexp() may return string, generator of strings or arbitrary object
    # such as date tuple, but filter does not want generator.
    if isinstance(thing, types.GeneratorType):
        thing = stringify(thing)
    return thing

def evalboolean(context, mapping, arg):
    """Evaluate given argument as boolean, but also takes boolean literals"""
    func, data = arg
    if func is runsymbol:
        thing = func(context, mapping, data, default=None)
        if thing is None:
            # not a template keyword, takes as a boolean literal
            thing = util.parsebool(data)
    else:
        thing = func(context, mapping, data)
    thing = templatekw.unwrapvalue(thing)
    if isinstance(thing, bool):
        return thing
    # other objects are evaluated as strings, which means 0 is True, but
    # empty dict/list should be False as they are expected to be ''
    return bool(stringify(thing))

def evalinteger(context, mapping, arg, err=None):
    v = evalfuncarg(context, mapping, arg)
    try:
        return int(v)
    except (TypeError, ValueError):
        raise error.ParseError(err or _('not an integer'))

def evalstring(context, mapping, arg):
    return stringify(evalrawexp(context, mapping, arg))

def evalstringliteral(context, mapping, arg):
    """Evaluate given argument as string template, but returns symbol name
    if it is unknown"""
    func, data = arg
    if func is runsymbol:
        thing = func(context, mapping, data, default=data)
    else:
        thing = func(context, mapping, data)
    return stringify(thing)

_evalfuncbytype = {
    bool: evalboolean,
    bytes: evalstring,
    int: evalinteger,
}

def evalastype(context, mapping, arg, typ):
    """Evaluate given argument and coerce its type"""
    try:
        f = _evalfuncbytype[typ]
    except KeyError:
        raise error.ProgrammingError('invalid type specified: %r' % typ)
    return f(context, mapping, arg)

def runinteger(context, mapping, data):
    return int(data)

def runstring(context, mapping, data):
    return data

def _recursivesymbolblocker(key):
    def showrecursion(**args):
        raise error.Abort(_("recursive reference '%s' in template") % key)
    return showrecursion

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

def runsymbol(context, mapping, key, default=''):
    v = context.symbol(mapping, key)
    if v is None:
        # put poison to cut recursion. we can't move this to parsing phase
        # because "x = {x}" is allowed if "x" is a keyword. (issue4758)
        safemapping = mapping.copy()
        safemapping[key] = _recursivesymbolblocker(key)
        try:
            v = context.process(key, safemapping)
        except TemplateNotFound:
            v = default
    if callable(v) and getattr(v, '_requires', None) is None:
        # old templatekw: expand all keywords and resources
        props = context._resources.copy()
        props.update(mapping)
        return v(**pycompat.strkwargs(props))
    if callable(v):
        # new templatekw
        try:
            return v(context, mapping)
        except ResourceUnavailable:
            # unsupported keyword is mapped to empty just like unknown keyword
            return None
    return v

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

def runtemplate(context, mapping, template):
    for arg in template:
        yield evalrawexp(context, mapping, arg)

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

def runfilter(context, mapping, data):
    arg, filt = data
    thing = evalfuncarg(context, mapping, arg)
    try:
        return filt(thing)
    except (ValueError, AttributeError, TypeError):
        sym = findsymbolicname(arg)
        if sym:
            msg = (_("template filter '%s' is not compatible with keyword '%s'")
                   % (pycompat.sysbytes(filt.__name__), sym))
        else:
            msg = (_("incompatible use of template filter '%s'")
                   % pycompat.sysbytes(filt.__name__))
        raise error.Abort(msg)

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

def runmap(context, mapping, data):
    darg, targ = data
    d = evalrawexp(context, mapping, darg)
    if util.safehasattr(d, 'itermaps'):
        diter = d.itermaps()
    else:
        try:
            diter = iter(d)
        except TypeError:
            sym = findsymbolicname(darg)
            if sym:
                raise error.ParseError(_("keyword '%s' is not iterable") % sym)
            else:
                raise error.ParseError(_("%r is not iterable") % d)

    for i, v in enumerate(diter):
        lm = mapping.copy()
        lm['index'] = i
        if isinstance(v, dict):
            lm.update(v)
            lm['originalnode'] = mapping.get('node')
            yield evalrawexp(context, lm, targ)
        else:
            # v is not an iterable of dicts, this happen when 'key'
            # has been fully expanded already and format is useless.
            # If so, return the expanded value.
            yield v

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

def runmember(context, mapping, data):
    darg, memb = data
    d = evalrawexp(context, mapping, darg)
    if util.safehasattr(d, 'tomap'):
        lm = mapping.copy()
        lm.update(d.tomap())
        return runsymbol(context, lm, memb)
    if util.safehasattr(d, 'get'):
        return _getdictitem(d, memb)

    sym = findsymbolicname(darg)
    if sym:
        raise error.ParseError(_("keyword '%s' has no member") % sym)
    else:
        raise error.ParseError(_("%r has no member") % pycompat.bytestr(d))

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

def runnegate(context, mapping, data):
    data = evalinteger(context, mapping, data,
                       _('negation needs an integer argument'))
    return -data

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

def runarithmetic(context, mapping, data):
    func, left, right = data
    left = evalinteger(context, mapping, left,
                       _('arithmetic only defined on integers'))
    right = evalinteger(context, mapping, right,
                        _('arithmetic only defined on integers'))
    try:
        return func(left, right)
    except ZeroDivisionError:
        raise error.Abort(_('division by zero is not defined'))

def buildfunc(exp, context):
    n = getsymbol(exp[1])
    if n in funcs:
        f = 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 (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: (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"))

# dict of template built-in functions
funcs = {}

templatefunc = registrar.templatefunc(funcs)

@templatefunc('date(date[, fmt])')
def date(context, mapping, args):
    """Format a date. See :hg:`help dates` for formatting
    strings. The default is a Unix date format, including the timezone:
    "Mon Sep 04 15:13:13 2006 0700"."""
    if not (1 <= len(args) <= 2):
        # i18n: "date" is a keyword
        raise error.ParseError(_("date expects one or two arguments"))

    date = evalfuncarg(context, mapping, args[0])
    fmt = None
    if len(args) == 2:
        fmt = evalstring(context, mapping, args[1])
    try:
        if fmt is None:
            return dateutil.datestr(date)
        else:
            return dateutil.datestr(date, fmt)
    except (TypeError, ValueError):
        # i18n: "date" is a keyword
        raise error.ParseError(_("date expects a date information"))

@templatefunc('dict([[key=]value...])', argspec='*args **kwargs')
def dict_(context, mapping, args):
    """Construct a dict from key-value pairs. A key may be omitted if
    a value expression can provide an unambiguous name."""
    data = util.sortdict()

    for v in args['args']:
        k = findsymbolicname(v)
        if not k:
            raise error.ParseError(_('dict key cannot be inferred'))
        if k in data or k in args['kwargs']:
            raise error.ParseError(_("duplicated dict key '%s' inferred") % k)
        data[k] = evalfuncarg(context, mapping, v)

    data.update((k, evalfuncarg(context, mapping, v))
                for k, v in args['kwargs'].iteritems())
    return templatekw.hybriddict(data)

@templatefunc('diff([includepattern [, excludepattern]])')
def diff(context, mapping, args):
    """Show a diff, optionally
    specifying files to include or exclude."""
    if len(args) > 2:
        # i18n: "diff" is a keyword
        raise error.ParseError(_("diff expects zero, one, or two arguments"))

    def getpatterns(i):
        if i < len(args):
            s = evalstring(context, mapping, args[i]).strip()
            if s:
                return [s]
        return []

    ctx = context.resource(mapping, 'ctx')
    chunks = ctx.diff(match=ctx.match([], getpatterns(0), getpatterns(1)))

    return ''.join(chunks)

@templatefunc('extdata(source)', argspec='source')
def extdata(context, mapping, args):
    """Show a text read from the specified extdata source. (EXPERIMENTAL)"""
    if 'source' not in args:
        # i18n: "extdata" is a keyword
        raise error.ParseError(_('extdata expects one argument'))

    source = evalstring(context, mapping, args['source'])
    cache = context.resource(mapping, 'cache').setdefault('extdata', {})
    ctx = context.resource(mapping, 'ctx')
    if source in cache:
        data = cache[source]
    else:
        data = cache[source] = scmutil.extdatasource(ctx.repo(), source)
    return data.get(ctx.rev(), '')

@templatefunc('files(pattern)')
def files(context, mapping, args):
    """All files of the current changeset matching the pattern. See
    :hg:`help patterns`."""
    if not len(args) == 1:
        # i18n: "files" is a keyword
        raise error.ParseError(_("files expects one argument"))

    raw = evalstring(context, mapping, args[0])
    ctx = context.resource(mapping, 'ctx')
    m = ctx.match([raw])
    files = list(ctx.matches(m))
    return templatekw.compatlist(context, mapping, "file", files)

@templatefunc('fill(text[, width[, initialident[, hangindent]]])')
def fill(context, mapping, args):
    """Fill many
    paragraphs with optional indentation. See the "fill" filter."""
    if not (1 <= len(args) <= 4):
        # i18n: "fill" is a keyword
        raise error.ParseError(_("fill expects one to four arguments"))

    text = evalstring(context, mapping, args[0])
    width = 76
    initindent = ''
    hangindent = ''
    if 2 <= len(args) <= 4:
        width = evalinteger(context, mapping, args[1],
                            # i18n: "fill" is a keyword
                            _("fill expects an integer width"))
        try:
            initindent = evalstring(context, mapping, args[2])
            hangindent = evalstring(context, mapping, args[3])
        except IndexError:
            pass

    return templatefilters.fill(text, width, initindent, hangindent)

@templatefunc('formatnode(node)')
def formatnode(context, mapping, args):
    """Obtain the preferred form of a changeset hash. (DEPRECATED)"""
    if len(args) != 1:
        # i18n: "formatnode" is a keyword
        raise error.ParseError(_("formatnode expects one argument"))

    ui = context.resource(mapping, 'ui')
    node = evalstring(context, mapping, args[0])
    if ui.debugflag:
        return node
    return templatefilters.short(node)

@templatefunc('pad(text, width[, fillchar=\' \'[, left=False]])',
              argspec='text width fillchar left')
def pad(context, mapping, args):
    """Pad text with a
    fill character."""
    if 'text' not in args or 'width' not in args:
        # i18n: "pad" is a keyword
        raise error.ParseError(_("pad() expects two to four arguments"))

    width = evalinteger(context, mapping, args['width'],
                        # i18n: "pad" is a keyword
                        _("pad() expects an integer width"))

    text = evalstring(context, mapping, args['text'])

    left = False
    fillchar = ' '
    if 'fillchar' in args:
        fillchar = evalstring(context, mapping, args['fillchar'])
        if len(color.stripeffects(fillchar)) != 1:
            # i18n: "pad" is a keyword
            raise error.ParseError(_("pad() expects a single fill character"))
    if 'left' in args:
        left = evalboolean(context, mapping, args['left'])

    fillwidth = width - encoding.colwidth(color.stripeffects(text))
    if fillwidth <= 0:
        return text
    if left:
        return fillchar * fillwidth + text
    else:
        return text + fillchar * fillwidth

@templatefunc('indent(text, indentchars[, firstline])')
def indent(context, mapping, args):
    """Indents all non-empty lines
    with the characters given in the indentchars string. An optional
    third parameter will override the indent for the first line only
    if present."""
    if not (2 <= len(args) <= 3):
        # i18n: "indent" is a keyword
        raise error.ParseError(_("indent() expects two or three arguments"))

    text = evalstring(context, mapping, args[0])
    indent = evalstring(context, mapping, args[1])

    if len(args) == 3:
        firstline = evalstring(context, mapping, args[2])
    else:
        firstline = indent

    # the indent function doesn't indent the first line, so we do it here
    return templatefilters.indent(firstline + text, indent)

@templatefunc('get(dict, key)')
def get(context, mapping, args):
    """Get an attribute/key from an object. Some keywords
    are complex types. This function allows you to obtain the value of an
    attribute on these types."""
    if len(args) != 2:
        # i18n: "get" is a keyword
        raise error.ParseError(_("get() expects two arguments"))

    dictarg = evalfuncarg(context, mapping, args[0])
    if not util.safehasattr(dictarg, 'get'):
        # i18n: "get" is a keyword
        raise error.ParseError(_("get() expects a dict as first argument"))

    key = evalfuncarg(context, mapping, args[1])
    return _getdictitem(dictarg, key)

def _getdictitem(dictarg, key):
    val = dictarg.get(key)
    if val is None:
        return
    return templatekw.wraphybridvalue(dictarg, key, val)

@templatefunc('if(expr, then[, else])')
def if_(context, mapping, args):
    """Conditionally execute based on the result of
    an expression."""
    if not (2 <= len(args) <= 3):
        # i18n: "if" is a keyword
        raise error.ParseError(_("if expects two or three arguments"))

    test = evalboolean(context, mapping, args[0])
    if test:
        yield evalrawexp(context, mapping, args[1])
    elif len(args) == 3:
        yield evalrawexp(context, mapping, args[2])

@templatefunc('ifcontains(needle, haystack, then[, else])')
def ifcontains(context, mapping, args):
    """Conditionally execute based
    on whether the item "needle" is in "haystack"."""
    if not (3 <= len(args) <= 4):
        # i18n: "ifcontains" is a keyword
        raise error.ParseError(_("ifcontains expects three or four arguments"))

    haystack = evalfuncarg(context, mapping, args[1])
    try:
        needle = evalastype(context, mapping, args[0],
                            getattr(haystack, 'keytype', None) or bytes)
        found = (needle in haystack)
    except error.ParseError:
        found = False

    if found:
        yield evalrawexp(context, mapping, args[2])
    elif len(args) == 4:
        yield evalrawexp(context, mapping, args[3])

@templatefunc('ifeq(expr1, expr2, then[, else])')
def ifeq(context, mapping, args):
    """Conditionally execute based on
    whether 2 items are equivalent."""
    if not (3 <= len(args) <= 4):
        # i18n: "ifeq" is a keyword
        raise error.ParseError(_("ifeq expects three or four arguments"))

    test = evalstring(context, mapping, args[0])
    match = evalstring(context, mapping, args[1])
    if test == match:
        yield evalrawexp(context, mapping, args[2])
    elif len(args) == 4:
        yield evalrawexp(context, mapping, args[3])

@templatefunc('join(list, sep)')
def join(context, mapping, args):
    """Join items in a list with a delimiter."""
    if not (1 <= len(args) <= 2):
        # i18n: "join" is a keyword
        raise error.ParseError(_("join expects one or two arguments"))

    # TODO: perhaps this should be evalfuncarg(), but it can't because hgweb
    # abuses generator as a keyword that returns a list of dicts.
    joinset = evalrawexp(context, mapping, args[0])
    joinset = templatekw.unwrapvalue(joinset)
    joinfmt = getattr(joinset, 'joinfmt', pycompat.identity)
    joiner = " "
    if len(args) > 1:
        joiner = evalstring(context, mapping, args[1])

    first = True
    for x in pycompat.maybebytestr(joinset):
        if first:
            first = False
        else:
            yield joiner
        yield joinfmt(x)

@templatefunc('label(label, expr)')
def label(context, mapping, args):
    """Apply a label to generated content. Content with
    a label applied can result in additional post-processing, such as
    automatic colorization."""
    if len(args) != 2:
        # i18n: "label" is a keyword
        raise error.ParseError(_("label expects two arguments"))

    ui = context.resource(mapping, 'ui')
    thing = evalstring(context, mapping, args[1])
    # preserve unknown symbol as literal so effects like 'red', 'bold',
    # etc. don't need to be quoted
    label = evalstringliteral(context, mapping, args[0])

    return ui.label(thing, label)

@templatefunc('latesttag([pattern])')
def latesttag(context, mapping, args):
    """The global tags matching the given pattern on the
    most recent globally tagged ancestor of this changeset.
    If no such tags exist, the "{tag}" template resolves to
    the string "null"."""
    if len(args) > 1:
        # i18n: "latesttag" is a keyword
        raise error.ParseError(_("latesttag expects at most one argument"))

    pattern = None
    if len(args) == 1:
        pattern = evalstring(context, mapping, args[0])
    return templatekw.showlatesttags(context, mapping, pattern)

@templatefunc('localdate(date[, tz])')
def localdate(context, mapping, args):
    """Converts a date to the specified timezone.
    The default is local date."""
    if not (1 <= len(args) <= 2):
        # i18n: "localdate" is a keyword
        raise error.ParseError(_("localdate expects one or two arguments"))

    date = evalfuncarg(context, mapping, args[0])
    try:
        date = dateutil.parsedate(date)
    except AttributeError:  # not str nor date tuple
        # i18n: "localdate" is a keyword
        raise error.ParseError(_("localdate expects a date information"))
    if len(args) >= 2:
        tzoffset = None
        tz = evalfuncarg(context, mapping, args[1])
        if isinstance(tz, bytes):
            tzoffset, remainder = dateutil.parsetimezone(tz)
            if remainder:
                tzoffset = None
        if tzoffset is None:
            try:
                tzoffset = int(tz)
            except (TypeError, ValueError):
                # i18n: "localdate" is a keyword
                raise error.ParseError(_("localdate expects a timezone"))
    else:
        tzoffset = dateutil.makedate()[1]
    return (date[0], tzoffset)

@templatefunc('max(iterable)')
def max_(context, mapping, args, **kwargs):
    """Return the max of an iterable"""
    if len(args) != 1:
        # i18n: "max" is a keyword
        raise error.ParseError(_("max expects one argument"))

    iterable = evalfuncarg(context, mapping, args[0])
    try:
        x = max(pycompat.maybebytestr(iterable))
    except (TypeError, ValueError):
        # i18n: "max" is a keyword
        raise error.ParseError(_("max first argument should be an iterable"))
    return templatekw.wraphybridvalue(iterable, x, x)

@templatefunc('min(iterable)')
def min_(context, mapping, args, **kwargs):
    """Return the min of an iterable"""
    if len(args) != 1:
        # i18n: "min" is a keyword
        raise error.ParseError(_("min expects one argument"))

    iterable = evalfuncarg(context, mapping, args[0])
    try:
        x = min(pycompat.maybebytestr(iterable))
    except (TypeError, ValueError):
        # i18n: "min" is a keyword
        raise error.ParseError(_("min first argument should be an iterable"))
    return templatekw.wraphybridvalue(iterable, x, x)

@templatefunc('mod(a, b)')
def mod(context, mapping, args):
    """Calculate a mod b such that a / b + a mod b == a"""
    if not len(args) == 2:
        # i18n: "mod" is a keyword
        raise error.ParseError(_("mod expects two arguments"))

    func = lambda a, b: a % b
    return runarithmetic(context, mapping, (func, args[0], args[1]))

@templatefunc('obsfateoperations(markers)')
def obsfateoperations(context, mapping, args):
    """Compute obsfate related information based on markers (EXPERIMENTAL)"""
    if len(args) != 1:
        # i18n: "obsfateoperations" is a keyword
        raise error.ParseError(_("obsfateoperations expects one argument"))

    markers = evalfuncarg(context, mapping, args[0])

    try:
        data = obsutil.markersoperations(markers)
        return templatekw.hybridlist(data, name='operation')
    except (TypeError, KeyError):
        # i18n: "obsfateoperations" is a keyword
        errmsg = _("obsfateoperations first argument should be an iterable")
        raise error.ParseError(errmsg)

@templatefunc('obsfatedate(markers)')
def obsfatedate(context, mapping, args):
    """Compute obsfate related information based on markers (EXPERIMENTAL)"""
    if len(args) != 1:
        # i18n: "obsfatedate" is a keyword
        raise error.ParseError(_("obsfatedate expects one argument"))

    markers = evalfuncarg(context, mapping, args[0])

    try:
        data = obsutil.markersdates(markers)
        return templatekw.hybridlist(data, name='date', fmt='%d %d')
    except (TypeError, KeyError):
        # i18n: "obsfatedate" is a keyword
        errmsg = _("obsfatedate first argument should be an iterable")
        raise error.ParseError(errmsg)

@templatefunc('obsfateusers(markers)')
def obsfateusers(context, mapping, args):
    """Compute obsfate related information based on markers (EXPERIMENTAL)"""
    if len(args) != 1:
        # i18n: "obsfateusers" is a keyword
        raise error.ParseError(_("obsfateusers expects one argument"))

    markers = evalfuncarg(context, mapping, args[0])

    try:
        data = obsutil.markersusers(markers)
        return templatekw.hybridlist(data, name='user')
    except (TypeError, KeyError, ValueError):
        # i18n: "obsfateusers" is a keyword
        msg = _("obsfateusers first argument should be an iterable of "
                "obsmakers")
        raise error.ParseError(msg)

@templatefunc('obsfateverb(successors, markers)')
def obsfateverb(context, mapping, args):
    """Compute obsfate related information based on successors (EXPERIMENTAL)"""
    if len(args) != 2:
        # i18n: "obsfateverb" is a keyword
        raise error.ParseError(_("obsfateverb expects two arguments"))

    successors = evalfuncarg(context, mapping, args[0])
    markers = evalfuncarg(context, mapping, args[1])

    try:
        return obsutil.obsfateverb(successors, markers)
    except TypeError:
        # i18n: "obsfateverb" is a keyword
        errmsg = _("obsfateverb first argument should be countable")
        raise error.ParseError(errmsg)

@templatefunc('relpath(path)')
def relpath(context, mapping, args):
    """Convert a repository-absolute path into a filesystem path relative to
    the current working directory."""
    if len(args) != 1:
        # i18n: "relpath" is a keyword
        raise error.ParseError(_("relpath expects one argument"))

    repo = context.resource(mapping, 'ctx').repo()
    path = evalstring(context, mapping, args[0])
    return repo.pathto(path)

@templatefunc('revset(query[, formatargs...])')
def revset(context, mapping, args):
    """Execute a revision set query. See
    :hg:`help revset`."""
    if not len(args) > 0:
        # i18n: "revset" is a keyword
        raise error.ParseError(_("revset expects one or more arguments"))

    raw = evalstring(context, mapping, args[0])
    ctx = context.resource(mapping, 'ctx')
    repo = ctx.repo()

    def query(expr):
        m = revsetmod.match(repo.ui, expr, repo=repo)
        return m(repo)

    if len(args) > 1:
        formatargs = [evalfuncarg(context, mapping, a) for a in args[1:]]
        revs = query(revsetlang.formatspec(raw, *formatargs))
        revs = list(revs)
    else:
        cache = context.resource(mapping, 'cache')
        revsetcache = cache.setdefault("revsetcache", {})
        if raw in revsetcache:
            revs = revsetcache[raw]
        else:
            revs = query(raw)
            revs = list(revs)
            revsetcache[raw] = revs
    return templatekw.showrevslist(context, mapping, "revision", revs)

@templatefunc('rstdoc(text, style)')
def rstdoc(context, mapping, args):
    """Format reStructuredText."""
    if len(args) != 2:
        # i18n: "rstdoc" is a keyword
        raise error.ParseError(_("rstdoc expects two arguments"))

    text = evalstring(context, mapping, args[0])
    style = evalstring(context, mapping, args[1])

    return minirst.format(text, style=style, keep=['verbose'])

@templatefunc('separate(sep, args)', argspec='sep *args')
def separate(context, mapping, args):
    """Add a separator between non-empty arguments."""
    if 'sep' not in args:
        # i18n: "separate" is a keyword
        raise error.ParseError(_("separate expects at least one argument"))

    sep = evalstring(context, mapping, args['sep'])
    first = True
    for arg in args['args']:
        argstr = evalstring(context, mapping, arg)
        if not argstr:
            continue
        if first:
            first = False
        else:
            yield sep
        yield argstr

@templatefunc('shortest(node, minlength=4)')
def shortest(context, mapping, args):
    """Obtain the shortest representation of
    a node."""
    if not (1 <= len(args) <= 2):
        # i18n: "shortest" is a keyword
        raise error.ParseError(_("shortest() expects one or two arguments"))

    node = evalstring(context, mapping, args[0])

    minlength = 4
    if len(args) > 1:
        minlength = evalinteger(context, mapping, args[1],
                                # i18n: "shortest" is a keyword
                                _("shortest() expects an integer minlength"))

    # _partialmatch() of filtered changelog could take O(len(repo)) time,
    # which would be unacceptably slow. so we look for hash collision in
    # unfiltered space, which means some hashes may be slightly longer.
    cl = context.resource(mapping, 'ctx')._repo.unfiltered().changelog
    return cl.shortest(node, minlength)

@templatefunc('strip(text[, chars])')
def strip(context, mapping, args):
    """Strip characters from a string. By default,
    strips all leading and trailing whitespace."""
    if not (1 <= len(args) <= 2):
        # i18n: "strip" is a keyword
        raise error.ParseError(_("strip expects one or two arguments"))

    text = evalstring(context, mapping, args[0])
    if len(args) == 2:
        chars = evalstring(context, mapping, args[1])
        return text.strip(chars)
    return text.strip()

@templatefunc('sub(pattern, replacement, expression)')
def sub(context, mapping, args):
    """Perform text substitution
    using regular expressions."""
    if len(args) != 3:
        # i18n: "sub" is a keyword
        raise error.ParseError(_("sub expects three arguments"))

    pat = evalstring(context, mapping, args[0])
    rpl = evalstring(context, mapping, args[1])
    src = evalstring(context, mapping, args[2])
    try:
        patre = re.compile(pat)
    except re.error:
        # i18n: "sub" is a keyword
        raise error.ParseError(_("sub got an invalid pattern: %s") % pat)
    try:
        yield patre.sub(rpl, src)
    except re.error:
        # i18n: "sub" is a keyword
        raise error.ParseError(_("sub got an invalid replacement: %s") % rpl)

@templatefunc('startswith(pattern, text)')
def startswith(context, mapping, args):
    """Returns the value from the "text" argument
    if it begins with the content from the "pattern" argument."""
    if len(args) != 2:
        # i18n: "startswith" is a keyword
        raise error.ParseError(_("startswith expects two arguments"))

    patn = evalstring(context, mapping, args[0])
    text = evalstring(context, mapping, args[1])
    if text.startswith(patn):
        return text
    return ''

@templatefunc('word(number, text[, separator])')
def word(context, mapping, args):
    """Return the nth word from a string."""
    if not (2 <= len(args) <= 3):
        # i18n: "word" is a keyword
        raise error.ParseError(_("word expects two or three arguments, got %d")
                               % len(args))

    num = evalinteger(context, mapping, args[0],
                      # i18n: "word" is a keyword
                      _("word expects an integer index"))
    text = evalstring(context, mapping, args[1])
    if len(args) == 3:
        splitter = evalstring(context, mapping, args[2])
    else:
        splitter = None

    tokens = text.split(splitter)
    if num >= len(tokens) or num < -len(tokens):
        return ''
    else:
        return tokens[num]

# methods to interpret function arguments or inner expressions (e.g. {_(x)})
exprmethods = {
    "integer": lambda e, c: (runinteger, e[1]),
    "string": lambda e, c: (runstring, e[1]),
    "symbol": lambda e, c: (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

stringify = templatefilters.stringify

def _flatten(thing):
    '''yield a single stream from a possibly nested set of iterators'''
    thing = templatekw.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 = templatekw.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 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
        if defaults is None:
            defaults = {}
        if resources is None:
            resources = {}
        self._defaults = defaults
        self._resources = resources
        self._aliasmap = _aliasrules.buildmap(aliases)
        self._cache = {}  # key: (func, data)

    def symbol(self, mapping, key):
        """Resolve symbol to value or function; None if nothing found"""
        v = None
        if key not in self._resources:
            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 = None
        if key in self._resources:
            v = mapping.get(key)
        if v is None:
            v = self._resources.get(key)
        if v is None:
            raise 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 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 dict of internal data (e.g. cache), inaccessible
          from user template; may be overridden by a ``mapping`` dict.
        - ``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 resources is None:
            resources = {}
        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 = {'templ': self}
        self._resources.update(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 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 render(self, mapping):
        """Render the default unnamed template and return result as string"""
        mapping = pycompat.strkwargs(mapping)
        return stringify(self('', **mapping))

    def __call__(self, t, **mapping):
        mapping = pycompat.byteskwargs(mapping)
        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)

def loadfunction(ui, extname, registrarobj):
    """Load template function from specified registrarobj
    """
    for name, func in registrarobj._table.iteritems():
        funcs[name] = func

# tell hggettext to extract docstrings from these functions:
i18nfunctions = funcs.values()