templater: do not pre-evaluate generator keyword at runsymbol (issue4868)

It was introduced by e06e9fd2d99f, but the important code was removed by
a3c2d9211294. So there was no positive effect other than exhausting memory.

The problem spotted by e06e9fd2d99f is that you can't use a generator keyword
more than once. For example, in hgweb template, "{child} {child}" doesn't work
because the first "{child}" consumes the generator. But as a3c2d9211294 says,
the fix was wrong because it could overwrite a callable keyword that returns
a generator. Also the fix didn't work for a generator of generator such as
"{diff}" keyword. So, the proper fix for that problem would be to not put
a generator in a keyword table. Instead, it should be a factory of a generator.

Note that this should fix the memory issue in hgweb, but my firefox killed by
OOM in place. Be careful to not use a modern web browser to test the issue4868.

mercurial/templater.py

@@ -1,903 +1,901 b''
 # 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 i18n import _
 import os, re
 import util, config, templatefilters, templatekw, parser, error
 import revset as revsetmod
 import types
 import minirst
 
 # 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):
                     try:
                         # interpret as if it were a part of an outer string
                         data = program[s:pos].decode('string-escape')
                     except ValueError: # unbalanced escapes
                         raise error.ParseError(_("syntax error"), s)
                     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', tmpl[pos:stop].decode('string-escape')))
             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',
                            tmpl[pos:n - 1].decode('string-escape') + c))
             pos = n + 1
             continue
         if n > pos:
             parsed.append(('string', tmpl[pos:n].decode('string-escape')))
         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 compiletemplate(tmpl, context):
     parsed, pos = _parsetemplate(tmpl, 0, len(tmpl))
     return [compileexp(e, context, methods) for e in parsed]
 
 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 getfilter(exp, context):
     f = getsymbol(exp)
     if f not in context._filters:
         raise error.ParseError(_("unknown function '%s'") % f)
     return context._filters[f]
 
 def gettemplate(exp, context):
     if exp[0] == 'template':
         return [compileexp(e, context, methods) for e in exp[1]]
     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 runinteger(context, mapping, data):
     return int(data)
 
 def runstring(context, mapping, data):
     return data
 
 def runsymbol(context, mapping, key):
     v = mapping.get(key)
     if v is None:
         v = context._defaults.get(key)
     if v is None:
         try:
             v = context.process(key, mapping)
         except TemplateNotFound:
             v = ''
     if callable(v):
         return v(**mapping)
-    if isinstance(v, types.GeneratorType):
-        v = list(v)
     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):
     func, data = compileexp(exp[1], context, methods)
     filt = getfilter(exp[2], context)
     return (runfilter, (func, data, filt))
 
 def runfilter(context, mapping, data):
     func, data, filt = data
     # 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)
     try:
         return filt(thing)
     except (ValueError, AttributeError, TypeError):
         if isinstance(data, tuple):
             dt = data[1]
         else:
             dt = data
         raise util.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)
     ctmpl = gettemplate(exp[2], context)
     return (runmap, (func, data, ctmpl))
 
 def runmap(context, mapping, data):
     func, data, ctmpl = data
     d = func(context, mapping, data)
     if callable(d):
         d = d()
 
     lm = mapping.copy()
 
     for i in d:
         if isinstance(i, dict):
             lm.update(i)
             lm['originalnode'] = mapping.get('node')
             yield runtemplate(context, lm, ctmpl)
         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][0], args[0][1], 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."""
     if not (1 <= len(args) <= 2):
         # i18n: "date" is a keyword
         raise error.ParseError(_("date expects one or two arguments"))
 
     date = args[0][0](context, mapping, args[0][1])
     fmt = None
     if len(args) == 2:
         fmt = stringify(args[1][0](context, mapping, args[1][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 one, two or no arguments"))
 
     def getpatterns(i):
         if i < len(args):
             s = stringify(args[i][0](context, mapping, args[i][1])).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 = stringify(args[0][0](context, mapping, args[0][1]))
     width = 76
     initindent = ''
     hangindent = ''
     if 2 <= len(args) <= 4:
         try:
             width = int(stringify(args[1][0](context, mapping, args[1][1])))
         except ValueError:
             # i18n: "fill" is a keyword
             raise error.ParseError(_("fill expects an integer width"))
         try:
             initindent = stringify(args[2][0](context, mapping, args[2][1]))
             hangindent = stringify(args[3][0](context, mapping, args[3][1]))
         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 = int(args[1][1])
 
     text = stringify(args[0][0](context, mapping, args[0][1]))
 
     right = False
     fillchar = ' '
     if len(args) > 2:
         fillchar = stringify(args[2][0](context, mapping, args[2][1]))
     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 = stringify(args[0][0](context, mapping, args[0][1]))
     indent = stringify(args[1][0](context, mapping, args[1][1]))
 
     if len(args) == 3:
         firstline = stringify(args[2][0](context, mapping, args[2][1]))
     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 type."""
     if len(args) != 2:
         # i18n: "get" is a keyword
         raise error.ParseError(_("get() expects two arguments"))
 
     dictarg = args[0][0](context, mapping, args[0][1])
     if not util.safehasattr(dictarg, 'get'):
         # i18n: "get" is a keyword
         raise error.ParseError(_("get() expects a dict as first argument"))
 
     key = args[1][0](context, mapping, args[1][1])
     yield 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 = stringify(args[0][0](context, mapping, args[0][1]))
     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 = stringify(args[0][0](context, mapping, args[0][1]))
     items = args[1][0](context, mapping, args[1][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 = stringify(args[0][0](context, mapping, args[0][1]))
     match = stringify(args[1][0](context, mapping, args[1][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 callable(joinset):
         jf = joinset.joinfmt
         joinset = [jf(x) for x in joinset()]
 
     joiner = " "
     if len(args) > 1:
         joiner = stringify(args[1][0](context, mapping, args[1][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"))
 
     # ignore args[0] (the label string) since this is supposed to be a a no-op
     yield args[1][0](context, mapping, args[1][1])
 
 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 = stringify(args[0][0](context, mapping, args[0][1]))
     ctx = mapping['ctx']
     repo = ctx.repo()
 
     def query(expr):
         m = revsetmod.match(repo.ui, expr)
         return m(repo)
 
     if len(args) > 1:
         formatargs = list([a[0](context, mapping, a[1]) for a in args[1:]])
         revs = query(revsetmod.formatspec(raw, *formatargs))
         revs = list([str(r) for r in revs])
     else:
         revsetcache = mapping['cache'].setdefault("revsetcache", {})
         if raw in revsetcache:
             revs = revsetcache[raw]
         else:
             revs = query(raw)
             revs = list([str(r) for r in revs])
             revsetcache[raw] = revs
 
     return templatekw.showlist("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 = stringify(args[0][0](context, mapping, args[0][1]))
     style = stringify(args[1][0](context, mapping, args[1][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 = stringify(args[0][0](context, mapping, args[0][1]))
 
     minlength = 4
     if len(args) > 1:
         minlength = int(args[1][1])
 
     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."""
     if not (1 <= len(args) <= 2):
         # i18n: "strip" is a keyword
         raise error.ParseError(_("strip expects one or two arguments"))
 
     text = stringify(args[0][0](context, mapping, args[0][1]))
     if len(args) == 2:
         chars = stringify(args[1][0](context, mapping, args[1][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 = stringify(args[0][0](context, mapping, args[0][1]))
     rpl = stringify(args[1][0](context, mapping, args[1][1]))
     src = stringify(args[2][0](context, mapping, args[2][1]))
     yield re.sub(pat, rpl, src)
 
 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 = stringify(args[0][0](context, mapping, args[0][1]))
     text = stringify(args[1][0](context, mapping, args[1][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))
 
     try:
         num = int(stringify(args[0][0](context, mapping, args[0][1])))
     except ValueError:
         # i18n: "word" is a keyword
         raise error.ParseError(_("word expects an integer index"))
     text = stringify(args[1][0](context, mapping, args[1][1]))
     if len(args) == 3:
         splitter = stringify(args[2][0](context, mapping, args[2][1]))
     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,
     "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={}, defaults={}):
         self._loader = loader
         self._filters = filters
         self._defaults = defaults
         self._cache = {}
 
     def _load(self, t):
         '''load, parse, and cache a template'''
         if t not in self._cache:
             self._cache[t] = compiletemplate(self._loader(t), self)
         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.'''
         return _flatten(runtemplate(self, mapping, self._load(t)))
 
 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[0] == "map-cmdline":
             stylelist.append(split[1])
     return ", ".join(sorted(stylelist))
 
 class TemplateNotFound(util.Abort):
     pass
 
 class templater(object):
 
     def __init__(self, mapfile, filters={}, defaults={}, cache={},
                  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.'''
         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 util.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()