templater: expand list of parsed templates to template node

This patch eliminates a nested data structure other than the parsed tree.

  ('template', [(op, data), ..]) -> ('template', (op, data), ..)

New expanded tree can be processed by common parser functions. This change
will help implementing template aliases.

Because a (template ..) node should have at least one child node, an empty
template (template []) is mapped to (string ''). Also a trivial string
(template [(string ..)]) node is unwrapped to (string ..) at parsing phase,
instead of compiling phase.

mercurial/templater.py

@@ -1,1039 +1,1074 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 __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 _unnesttemplatelist(tree):
+    """Expand list of templates to node tuple
+
+    >>> def f(tree):
+    ...     print prettyformat(_unnesttemplatelist(tree))
+    >>> f(('template', []))
+    ('string', '')
+    >>> f(('template', [('string', 'foo')]))
+    ('string', 'foo')
+    >>> f(('template', [('string', 'foo'), ('symbol', 'rev')]))
+    (template
+      ('string', 'foo')
+      ('symbol', 'rev'))
+    >>> f(('template', [('symbol', 'rev')]))  # template(rev) -> str
+    (template
+      ('symbol', 'rev'))
+    >>> f(('template', [('template', [('string', '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 ('template', parsed)
+    return _unnesttemplatelist(('template', parsed))
+
+def prettyformat(tree):
+    return parser.prettyformat(tree, ('integer', 'string', 'symbol'))
 
 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] 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 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
+    ctmpl = [compileexp(e, context, methods) for e in exp[1:]]
     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()