view mercurial/parser.py @ 28164:ad11edefa7c4

localrepo: move new repo requirements into standalone function (API)

This patch extracts the code for determining requirements for a new
repo into a standalone function. By doing so, future code that will
perform an in-place repository upgrade (e.g. to generaldelta) can
examine the set of proposed new requirements and possibly take
additional actions (such as adding dotencode or fncache) when
performing the upgrade.

This patch is marked as API because _baserequirements (which was added
in b090601a80d1 so extensions could override it) has been removed and
will presumably impact whatever extension it was added for. Consumers
should be able to monkeypatch the new function to achieve the same
functionality.

The "create" argument has been dropped because the function is only
called in one location and "create" is always true in that case.

While it makes logical sense for this code to be a method so extensions
can implement a custom repo class / method to override it, this won't
actually work. This is because requirements determination occurs during
localrepository.__init__ and this is before the "reposetup"
"callback" is fired. So, the only way for extensions to customize
requirements would be to overwrite localrepo.localrepository or to
monkeypatch a function on a module during extsetup(). Since we try to
keep localrepository small, we use a standalone function. There is
probably room to offer extensions a "hook" point to alter repository
creation. But that is scope bloat.

# parser.py - simple top-down operator precedence parser for mercurial
#
# Copyright 2010 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.

# see http://effbot.org/zone/simple-top-down-parsing.htm and
# http://eli.thegreenplace.net/2010/01/02/top-down-operator-precedence-parsing/
# for background

# takes a tokenizer and elements
# tokenizer is an iterator that returns (type, value, pos) tuples
# elements is a mapping of types to binding strength, primary, prefix, infix
# and suffix actions
# an action is a tree node name, a tree label, and an optional match
# __call__(program) parses program into a labeled tree

from __future__ import absolute_import

from .i18n import _
from . import error

class parser(object):
    def __init__(self, elements, methods=None):
        self._elements = elements
        self._methods = methods
        self.current = None
    def _advance(self):
        'advance the tokenizer'
        t = self.current
        self.current = next(self._iter, None)
        return t
    def _hasnewterm(self):
        'True if next token may start new term'
        return any(self._elements[self.current[0]][1:3])
    def _match(self, m):
        'make sure the tokenizer matches an end condition'
        if self.current[0] != m:
            raise error.ParseError(_("unexpected token: %s") % self.current[0],
                                   self.current[2])
        self._advance()
    def _parseoperand(self, bind, m=None):
        'gather right-hand-side operand until an end condition or binding met'
        if m and self.current[0] == m:
            expr = None
        else:
            expr = self._parse(bind)
        if m:
            self._match(m)
        return expr
    def _parse(self, bind=0):
        token, value, pos = self._advance()
        # handle prefix rules on current token, take as primary if unambiguous
        primary, prefix = self._elements[token][1:3]
        if primary and not (prefix and self._hasnewterm()):
            expr = (primary, value)
        elif prefix:
            expr = (prefix[0], self._parseoperand(*prefix[1:]))
        else:
            raise error.ParseError(_("not a prefix: %s") % token, pos)
        # gather tokens until we meet a lower binding strength
        while bind < self._elements[self.current[0]][0]:
            token, value, pos = self._advance()
            # handle infix rules, take as suffix if unambiguous
            infix, suffix = self._elements[token][3:]
            if suffix and not (infix and self._hasnewterm()):
                expr = (suffix[0], expr)
            elif infix:
                expr = (infix[0], expr, self._parseoperand(*infix[1:]))
            else:
                raise error.ParseError(_("not an infix: %s") % token, pos)
        return expr
    def parse(self, tokeniter):
        'generate a parse tree from tokens'
        self._iter = tokeniter
        self._advance()
        res = self._parse()
        token, value, pos = self.current
        return res, pos
    def eval(self, tree):
        'recursively evaluate a parse tree using node methods'
        if not isinstance(tree, tuple):
            return tree
        return self._methods[tree[0]](*[self.eval(t) for t in tree[1:]])
    def __call__(self, tokeniter):
        'parse tokens into a parse tree and evaluate if methods given'
        t = self.parse(tokeniter)
        if self._methods:
            return self.eval(t)
        return t

def buildargsdict(trees, funcname, keys, keyvaluenode, keynode):
    """Build dict from list containing positional and keyword arguments

    Invalid keywords or too many positional arguments are rejected, but
    missing arguments are just omitted.
    """
    if len(trees) > len(keys):
        raise error.ParseError(_("%(func)s takes at most %(nargs)d arguments")
                               % {'func': funcname, 'nargs': len(keys)})
    args = {}
    # consume positional arguments
    for k, x in zip(keys, trees):
        if x[0] == keyvaluenode:
            break
        args[k] = x
    # remainder should be keyword arguments
    for x in trees[len(args):]:
        if x[0] != keyvaluenode or x[1][0] != keynode:
            raise error.ParseError(_("%(func)s got an invalid argument")
                                   % {'func': funcname})
        k = x[1][1]
        if k not in keys:
            raise error.ParseError(_("%(func)s got an unexpected keyword "
                                     "argument '%(key)s'")
                                   % {'func': funcname, 'key': k})
        if k in args:
            raise error.ParseError(_("%(func)s got multiple values for keyword "
                                     "argument '%(key)s'")
                                   % {'func': funcname, 'key': k})
        args[k] = x[2]
    return args

def unescapestr(s):
    try:
        return s.decode("string_escape")
    except ValueError as e:
        # mangle Python's exception into our format
        raise error.ParseError(str(e).lower())

def _prettyformat(tree, leafnodes, level, lines):
    if not isinstance(tree, tuple) or tree[0] in leafnodes:
        lines.append((level, str(tree)))
    else:
        lines.append((level, '(%s' % tree[0]))
        for s in tree[1:]:
            _prettyformat(s, leafnodes, level + 1, lines)
        lines[-1:] = [(lines[-1][0], lines[-1][1] + ')')]

def prettyformat(tree, leafnodes):
    lines = []
    _prettyformat(tree, leafnodes, 0, lines)
    output = '\n'.join(('  ' * l + s) for l, s in lines)
    return output

def simplifyinfixops(tree, targetnodes):
    """Flatten chained infix operations to reduce usage of Python stack

    >>> def f(tree):
    ...     print prettyformat(simplifyinfixops(tree, ('or',)), ('symbol',))
    >>> f(('or',
    ...     ('or',
    ...       ('symbol', '1'),
    ...       ('symbol', '2')),
    ...     ('symbol', '3')))
    (or
      ('symbol', '1')
      ('symbol', '2')
      ('symbol', '3'))
    >>> f(('func',
    ...     ('symbol', 'p1'),
    ...     ('or',
    ...       ('or',
    ...         ('func',
    ...           ('symbol', 'sort'),
    ...           ('list',
    ...             ('or',
    ...               ('or',
    ...                 ('symbol', '1'),
    ...                 ('symbol', '2')),
    ...               ('symbol', '3')),
    ...             ('negate',
    ...               ('symbol', 'rev')))),
    ...         ('and',
    ...           ('symbol', '4'),
    ...           ('group',
    ...             ('or',
    ...               ('or',
    ...                 ('symbol', '5'),
    ...                 ('symbol', '6')),
    ...               ('symbol', '7'))))),
    ...       ('symbol', '8'))))
    (func
      ('symbol', 'p1')
      (or
        (func
          ('symbol', 'sort')
          (list
            (or
              ('symbol', '1')
              ('symbol', '2')
              ('symbol', '3'))
            (negate
              ('symbol', 'rev'))))
        (and
          ('symbol', '4')
          (group
            (or
              ('symbol', '5')
              ('symbol', '6')
              ('symbol', '7'))))
        ('symbol', '8')))
    """
    if not isinstance(tree, tuple):
        return tree
    op = tree[0]
    if op not in targetnodes:
        return (op,) + tuple(simplifyinfixops(x, targetnodes) for x in tree[1:])

    # walk down left nodes taking each right node. no recursion to left nodes
    # because infix operators are left-associative, i.e. left tree is deep.
    # e.g. '1 + 2 + 3' -> (+ (+ 1 2) 3) -> (+ 1 2 3)
    simplified = []
    x = tree
    while x[0] == op:
        l, r = x[1:]
        simplified.append(simplifyinfixops(r, targetnodes))
        x = l
    simplified.append(simplifyinfixops(x, targetnodes))
    simplified.append(op)
    return tuple(reversed(simplified))