mercurial/parser.py

merge: make in-memory changes visible to external update hooks

51844b8b5017 (while 3.4 code-freeze) made all 'update' hooks run after
releasing wlock for visibility of in-memory dirstate changes. But this
breaks paired invocation of 'preupdate' and 'update' hooks.

For example, 'hg backout --merge' for TARGET revision, which isn't
parent of CURRENT, consists of steps below:

  1. update from CURRENT to TARGET
  2. commit BACKOUT revision, which backs TARGET out
  3. update from BACKOUT to CURRENT
  4. merge TARGET into CURRENT

Then, we expects hooks to run in the order below:

  - 'preupdate' on CURRENT for (1)
  - 'update'    on TARGET  for (1)
  - 'preupdate' on BACKOUT for (3)
  - 'update'    on CURRENT for (3)
  - 'preupdate' on TARGET  for (4)
  - 'update'    on CURRENT/TARGET for (4)

But hooks actually run in the order below:

  - 'preupdate' on CURRENT for (1)
  - 'preupdate' on BACKOUT for (3)
  - 'preupdate' on TARGET  for (4)
  - 'update'    on TARGET  for (1), but actually on CURRENT/TARGET
  - 'update'    on CURRENT for (3), but actually on CURRENT/TARGET
  - 'update'    on CURRENT for (4), but actually on CURRENT/TARGET

Root cause of the issue focused by 51844b8b5017 is that external
'update' hook process can't view in-memory changes (especially, of
dirstate), because they aren't written out until the end of
transaction (or wlock).

Now, hooks can be invoked just after updating, because previous
patches made in-memory changes visible to external process.

This patch may break backward compatibility from the point of view of
"scheduling hook execution", but should be reasonable because 'update'
hooks had been executed in this order before 3.4.

This patch tests "hg backout" and "hg unshelve", because the former
activates the transaction before 'update' hook invocation, but the
former doesn't.

# 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))