annotate mercurial/templater.py @ 28545:1d461ee26e1b

templater: lift parsed and compiled templates to generic data types

Before this patch, parsed and compiled templates were kept as lists. That
was inconvenient for applying transformation such as alias expansion.

This patch changes the types of the outermost objects as follows:

  stage     old             new
  --------  --------------  ------------------------------
  parsed    [(op, ..)]      ('template', [(op, ..)])
  compiled  [(func, data)]  (runtemplate, [(func, data)])

New templater.parse() function has the same signature as revset.parse()
and fileset.parse().

# 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

import os
import re
import types

from .i18n import _
from . import (
    config,
    error,
    minirst,
    parser,
    revset as revsetmod,
    templatefilters,
    templatekw,
    util,
)

# template parsing

elements = {
    # token-type: binding-strength, primary, prefix, infix, suffix
    "(": (20, None, ("group", 1, ")"), ("func", 1, ")"), None),
    ",": (2, None, None, ("list", 2), None),
    "|": (5, None, None, ("|", 5), None),
    "%": (6, None, None, ("%", 6), 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):
    pos = start
    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() or c == '-':
            s = pos
            if c == '-': # simply take negate operator as part of integer
                pos += 1
            if pos >= end or not program[pos].isdigit():
                raise error.ParseError(_("integer literal without digits"), s)
            pos += 1
            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 (r"\'", r'\"')
              or c == 'r' and program[pos:pos + 3] in (r"r\'", r'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 == '}':
            yield ('end', None, pos + 1)
            return
        else:
            raise error.ParseError(_("syntax error"), pos)
        pos += 1
    raise error.ParseError(_("unterminated template expansion"), start)

def _parsetemplate(tmpl, start, stop, quote=''):
    r"""
    >>> _parsetemplate('foo{bar}"baz', 0, 12)
    ([('string', 'foo'), ('symbol', 'bar'), ('string', '"baz')], 12)
    >>> _parsetemplate('foo{bar}"baz', 0, 12, quote='"')
    ([('string', 'foo'), ('symbol', 'bar')], 9)
    >>> _parsetemplate('foo"{bar}', 0, 9, quote='"')
    ([('string', 'foo')], 4)
    >>> _parsetemplate(r'foo\"bar"baz', 0, 12, quote='"')
    ([('string', 'foo"'), ('string', 'bar')], 9)
    >>> _parsetemplate(r'foo\\"bar', 0, 10, quote='"')
    ([('string', 'foo\\')], 6)
    """
    parsed = []
    sepchars = '{' + quote
    pos = start
    p = parser.parser(elements)
    while pos < stop:
        n = min((tmpl.find(c, pos, stop) for c in sepchars),
                key=lambda n: (n < 0, n))
        if n < 0:
            parsed.append(('string', parser.unescapestr(tmpl[pos:stop])))
            pos = stop
            break
        c = tmpl[n]
        bs = (n - pos) - len(tmpl[pos:n].rstrip('\\'))
        if bs % 2 == 1:
            # escaped (e.g. '\{', '\\\{', but not '\\{')
            parsed.append(('string', parser.unescapestr(tmpl[pos:n - 1]) + c))
            pos = n + 1
            continue
        if n > pos:
            parsed.append(('string', parser.unescapestr(tmpl[pos:n])))
        if c == quote:
            return parsed, n + 1

        parseres, pos = p.parse(tokenize(tmpl, n + 1, stop))
        parsed.append(parseres)

    if quote:
        raise error.ParseError(_("unterminated string"), start)
    return parsed, pos

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 ('template', parsed)

def compiletemplate(tmpl, context):
    """Parse and compile template string to (func, data) pair"""
    return compileexp(parse(tmpl), context, methods)

def compileexp(exp, context, curmethods):
    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] == 'template':
        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 evalfuncarg(context, mapping, arg):
    func, data = arg
    # func() may return string, generator of strings or arbitrary object such
    # as date tuple, but filter does not want generator.
    thing = func(context, mapping, data)
    if isinstance(thing, types.GeneratorType):
        thing = stringify(thing)
    return thing

def evalinteger(context, mapping, arg, err):
    v = evalfuncarg(context, mapping, arg)
    try:
        return int(v)
    except (TypeError, ValueError):
        raise error.ParseError(err)

def evalstring(context, mapping, arg):
    func, data = arg
    return stringify(func(context, mapping, data))

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)

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 = mapping.get(key)
    if v is None:
        v = context._defaults.get(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):
        return v(**mapping)
    return v

def buildtemplate(exp, context):
    ctmpl = [compileexp(e, context, methods) for e in exp[1]]
    if len(ctmpl) == 1:
        return ctmpl[0]  # fast path for string with no template fragment
    return (runtemplate, ctmpl)

def runtemplate(context, mapping, template):
    for func, data in template:
        yield func(context, mapping, data)

def buildfilter(exp, context):
    arg = compileexp(exp[1], context, methods)
    n = getsymbol(exp[2])
    if n in context._filters:
        filt = context._filters[n]
        return (runfilter, (arg, filt))
    if n in funcs:
        f = funcs[n]
        return (f, [arg])
    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):
        if isinstance(arg[1], tuple):
            dt = arg[1][1]
        else:
            dt = arg[1]
        raise error.Abort(_("template filter '%s' is not compatible with "
                           "keyword '%s'") % (filt.func_name, dt))

def buildmap(exp, context):
    func, data = compileexp(exp[1], context, methods)
    tfunc, tdata = gettemplate(exp[2], context)
    return (runmap, (func, data, tfunc, tdata))

def runmap(context, mapping, data):
    func, data, tfunc, tdata = data
    d = func(context, mapping, data)
    if util.safehasattr(d, 'itermaps'):
        diter = d.itermaps()
    else:
        try:
            diter = iter(d)
        except TypeError:
            if func is runsymbol:
                raise error.ParseError(_("keyword '%s' is not iterable") % data)
            else:
                raise error.ParseError(_("%r is not iterable") % d)

    for i in diter:
        lm = mapping.copy()
        if isinstance(i, dict):
            lm.update(i)
            lm['originalnode'] = mapping.get('node')
            yield tfunc(context, lm, tdata)
        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 i

def buildfunc(exp, context):
    n = getsymbol(exp[1])
    args = [compileexp(x, context, exprmethods) for x in getlist(exp[2])]
    if n in funcs:
        f = funcs[n]
        return (f, args)
    if n in context._filters:
        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 date(context, mapping, args):
    """:date(date[, fmt]): 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 util.datestr(date)
        else:
            return util.datestr(date, fmt)
    except (TypeError, ValueError):
        # i18n: "date" is a keyword
        raise error.ParseError(_("date expects a date information"))

def diff(context, mapping, args):
    """:diff([includepattern [, excludepattern]]): 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 = mapping['ctx']
    chunks = ctx.diff(match=ctx.match([], getpatterns(0), getpatterns(1)))

    return ''.join(chunks)

def fill(context, mapping, args):
    """:fill(text[, width[, initialident[, hangindent]]]): 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)

def pad(context, mapping, args):
    """:pad(text, width[, fillchar=' '[, right=False]]): Pad text with a
    fill character."""
    if not (2 <= len(args) <= 4):
        # i18n: "pad" is a keyword
        raise error.ParseError(_("pad() expects two to four arguments"))

    width = evalinteger(context, mapping, args[1],
                        # i18n: "pad" is a keyword
                        _("pad() expects an integer width"))

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

    right = False
    fillchar = ' '
    if len(args) > 2:
        fillchar = evalstring(context, mapping, args[2])
    if len(args) > 3:
        right = util.parsebool(args[3][1])

    if right:
        return text.rjust(width, fillchar)
    else:
        return text.ljust(width, fillchar)

def indent(context, mapping, args):
    """:indent(text, indentchars[, firstline]): 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)

def get(context, mapping, args):
    """:get(dict, key): 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 dictarg.get(key)

def if_(context, mapping, args):
    """:if(expr, then[, else]): 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 = evalstring(context, mapping, args[0])
    if test:
        yield args[1][0](context, mapping, args[1][1])
    elif len(args) == 3:
        yield args[2][0](context, mapping, args[2][1])

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

    item = evalstring(context, mapping, args[0])
    items = evalfuncarg(context, mapping, args[1])

    if item in items:
        yield args[2][0](context, mapping, args[2][1])
    elif len(args) == 4:
        yield args[3][0](context, mapping, args[3][1])

def ifeq(context, mapping, args):
    """:ifeq(expr1, expr2, then[, else]): 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 args[2][0](context, mapping, args[2][1])
    elif len(args) == 4:
        yield args[3][0](context, mapping, args[3][1])

def join(context, mapping, args):
    """:join(list, sep): 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"))

    joinset = args[0][0](context, mapping, args[0][1])
    if util.safehasattr(joinset, 'itermaps'):
        jf = joinset.joinfmt
        joinset = [jf(x) for x in joinset.itermaps()]

    joiner = " "
    if len(args) > 1:
        joiner = evalstring(context, mapping, args[1])

    first = True
    for x in joinset:
        if first:
            first = False
        else:
            yield joiner
        yield x

def label(context, mapping, args):
    """:label(label, expr): 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 = 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)

def latesttag(context, mapping, args):
    """:latesttag([pattern]): The global tags matching the given pattern on the
    most recent globally tagged ancestor of this changeset."""
    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(pattern, **mapping)

def localdate(context, mapping, args):
    """:localdate(date[, tz]): 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 = util.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, str):
            tzoffset = util.parsetimezone(tz)
        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 = util.makedate()[1]
    return (date[0], tzoffset)

def revset(context, mapping, args):
    """:revset(query[, formatargs...]): 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 = mapping['ctx']
    repo = ctx.repo()

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

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

    return templatekw.showrevslist("revision", revs, **mapping)

def rstdoc(context, mapping, args):
    """:rstdoc(text, style): 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'])

def shortest(context, mapping, args):
    """:shortest(node, minlength=4): 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"))

    cl = mapping['ctx']._repo.changelog
    def isvalid(test):
        try:
            try:
                cl.index.partialmatch(test)
            except AttributeError:
                # Pure mercurial doesn't support partialmatch on the index.
                # Fallback to the slow way.
                if cl._partialmatch(test) is None:
                    return False

            try:
                i = int(test)
                # if we are a pure int, then starting with zero will not be
                # confused as a rev; or, obviously, if the int is larger than
                # the value of the tip rev
                if test[0] == '0' or i > len(cl):
                    return True
                return False
            except ValueError:
                return True
        except error.RevlogError:
            return False

    shortest = node
    startlength = max(6, minlength)
    length = startlength
    while True:
        test = node[:length]
        if isvalid(test):
            shortest = test
            if length == minlength or length > startlength:
                return shortest
            length -= 1
        else:
            length += 1
            if len(shortest) <= length:
                return shortest

def strip(context, mapping, args):
    """:strip(text[, chars]): 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()

def sub(context, mapping, args):
    """:sub(pattern, replacement, expression): 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)

def startswith(context, mapping, args):
    """:startswith(pattern, text): 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 ''


def word(context, mapping, args):
    """:word(number, text[, separator]): 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,
    }

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

funcs = {
    "date": date,
    "diff": diff,
    "fill": fill,
    "get": get,
    "if": if_,
    "ifcontains": ifcontains,
    "ifeq": ifeq,
    "indent": indent,
    "join": join,
    "label": label,
    "latesttag": latesttag,
    "localdate": localdate,
    "pad": pad,
    "revset": revset,
    "rstdoc": rstdoc,
    "shortest": shortest,
    "startswith": startswith,
    "strip": strip,
    "sub": sub,
    "word": word,
}

# template engine

stringify = templatefilters.stringify

def _flatten(thing):
    '''yield a single stream from a possibly nested set of iterators'''
    if isinstance(thing, str):
        yield thing
    elif not util.safehasattr(thing, '__iter__'):
        if thing is not None:
            yield str(thing)
    else:
        for i in thing:
            if isinstance(i, str):
                yield i
            elif not util.safehasattr(i, '__iter__'):
                if i is not None:
                    yield str(i)
            elif i is not None:
                for j in _flatten(i):
                    yield j

def unquotestring(s):
    '''unwrap quotes'''
    if len(s) < 2 or s[0] != s[-1]:
        raise SyntaxError(_('unmatched quotes'))
    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):
        self._loader = loader
        if filters is None:
            filters = {}
        self._filters = filters
        if defaults is None:
            defaults = {}
        self._defaults = defaults
        self._cache = {}  # key: (func, data)

    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:
                self._cache[t] = compiletemplate(self._loader(t), self)
            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))

class TemplateNotFound(error.Abort):
    pass

class templater(object):

    def __init__(self, mapfile, filters=None, defaults=None, cache=None,
                 minchunk=1024, maxchunk=65536):
        '''set up template engine.
        mapfile is name of file to read map definitions from.
        filters is dict of functions. each transforms a value into another.
        defaults is dict of default map definitions.'''
        if filters is None:
            filters = {}
        if defaults is None:
            defaults = {}
        if cache is None:
            cache = {}
        self.mapfile = mapfile or 'template'
        self.cache = cache.copy()
        self.map = {}
        if mapfile:
            self.base = os.path.dirname(mapfile)
        else:
            self.base = ''
        self.filters = templatefilters.filters.copy()
        self.filters.update(filters)
        self.defaults = defaults
        self.minchunk, self.maxchunk = minchunk, maxchunk
        self.ecache = {}

        if not mapfile:
            return
        if not os.path.exists(mapfile):
            raise error.Abort(_("style '%s' not found") % mapfile,
                             hint=_("available styles: %s") % stylelist())

        conf = config.config(includepaths=templatepaths())
        conf.read(mapfile)

        for key, val in conf[''].items():
            if not val:
                raise SyntaxError(_('%s: missing value') % conf.source('', key))
            if val[0] in "'\"":
                try:
                    self.cache[key] = unquotestring(val)
                except SyntaxError as inst:
                    raise SyntaxError('%s: %s' %
                                      (conf.source('', key), inst.args[0]))
            else:
                val = 'default', val
                if ':' in val[1]:
                    val = val[1].split(':', 1)
                self.map[key] = val[0], os.path.join(self.base, val[1])

    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:
                raise IOError(inst.args[0], _('template file %s: %s') %
                              (self.map[t][1], inst.args[1]))
        return self.cache[t]

    def __call__(self, t, **mapping):
        ttype = t in self.map and self.map[t][0] or 'default'
        if ttype not in self.ecache:
            self.ecache[ttype] = engines[ttype](self.load,
                                                 self.filters, self.defaults)
        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, str):
        paths = [paths]

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

    for style in styles:
        # only plain name is allowed to honor template paths
        if (not style
            or style in (os.curdir, os.pardir)
            or os.sep in style
            or os.altsep and os.altsep 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)

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