parser: reorder alias expansion routine to return early

I think it improves readability to move trivial cases first, and unindent
blocks.

mercurial/parser.py

@@ -1,544 +1,542 b''
 # 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))
 
 def parseerrordetail(inst):
     """Compose error message from specified ParseError object
     """
     if len(inst.args) > 1:
         return _('at %s: %s') % (inst.args[1], inst.args[0])
     else:
         return inst.args[0]
 
 class alias(object):
     """Parsed result of alias"""
 
     def __init__(self, name, tree, args, err, replacement):
         self.name = name
         self.tree = tree
         self.args = args
         self.error = err
         self.replacement = replacement
         # whether own `error` information is already shown or not.
         # this avoids showing same warning multiple times at each `findaliases`.
         self.warned = False
 
 class basealiasrules(object):
     """Parsing and expansion rule set of aliases
 
     This is a helper for fileset/revset/template aliases. A concrete rule set
     should be made by sub-classing this and implementing class/static methods.
 
     It supports alias expansion of symbol and funciton-call styles::
 
         # decl = defn
         h = heads(default)
         b($1) = ancestors($1) - ancestors(default)
     """
     # typically a config section, which will be included in error messages
     _section = None
     # tags of symbol and function nodes
     _symbolnode = 'symbol'
     _funcnode = 'func'
 
     def __new__(cls):
         raise TypeError("'%s' is not instantiatable" % cls.__name__)
 
     @staticmethod
     def _parse(spec):
         """Parse an alias name, arguments and definition"""
         raise NotImplementedError
 
     @staticmethod
     def _getlist(tree):
         """Extract a list of arguments from parsed tree"""
         raise NotImplementedError
 
     @classmethod
     def _builddecl(cls, decl):
         """Parse an alias declaration into ``(name, tree, args, errorstr)``
 
         This function analyzes the parsed tree. The parsing rule is provided
         by ``_parse()``.
 
         - ``name``: of declared alias (may be ``decl`` itself at error)
         - ``tree``: parse result (or ``None`` at error)
         - ``args``: list of argument names (or None for symbol declaration)
         - ``errorstr``: detail about detected error (or None)
 
         >>> sym = lambda x: ('symbol', x)
         >>> symlist = lambda *xs: ('list',) + tuple(sym(x) for x in xs)
         >>> func = lambda n, a: ('func', sym(n), a)
         >>> parsemap = {
         ...     'foo': sym('foo'),
         ...     '$foo': sym('$foo'),
         ...     'foo::bar': ('dagrange', sym('foo'), sym('bar')),
         ...     'foo()': func('foo', None),
         ...     '$foo()': func('$foo', None),
         ...     'foo($1, $2)': func('foo', symlist('$1', '$2')),
         ...     'foo(bar_bar, baz.baz)':
         ...         func('foo', symlist('bar_bar', 'baz.baz')),
         ...     'foo(bar($1, $2))':
         ...         func('foo', func('bar', symlist('$1', '$2'))),
         ...     'foo($1, $2, nested($1, $2))':
         ...         func('foo', (symlist('$1', '$2') +
         ...                      (func('nested', symlist('$1', '$2')),))),
         ...     'foo("bar")': func('foo', ('string', 'bar')),
         ...     'foo($1, $2': error.ParseError('unexpected token: end', 10),
         ...     'foo("bar': error.ParseError('unterminated string', 5),
         ...     'foo($1, $2, $1)': func('foo', symlist('$1', '$2', '$1')),
         ... }
         >>> def parse(expr):
         ...     x = parsemap[expr]
         ...     if isinstance(x, Exception):
         ...         raise x
         ...     return x
         >>> def getlist(tree):
         ...     if not tree:
         ...         return []
         ...     if tree[0] == 'list':
         ...         return list(tree[1:])
         ...     return [tree]
         >>> class aliasrules(basealiasrules):
         ...     _parse = staticmethod(parse)
         ...     _getlist = staticmethod(getlist)
         >>> builddecl = aliasrules._builddecl
         >>> builddecl('foo')
         ('foo', ('symbol', 'foo'), None, None)
         >>> builddecl('$foo')
         ('$foo', None, None, "'$' not for alias arguments")
         >>> builddecl('foo::bar')
         ('foo::bar', None, None, 'invalid format')
         >>> builddecl('foo()')
         ('foo', ('func', ('symbol', 'foo')), [], None)
         >>> builddecl('$foo()')
         ('$foo()', None, None, "'$' not for alias arguments")
         >>> builddecl('foo($1, $2)')
         ('foo', ('func', ('symbol', 'foo')), ['$1', '$2'], None)
         >>> builddecl('foo(bar_bar, baz.baz)')
         ('foo', ('func', ('symbol', 'foo')), ['bar_bar', 'baz.baz'], None)
         >>> builddecl('foo($1, $2, nested($1, $2))')
         ('foo($1, $2, nested($1, $2))', None, None, 'invalid argument list')
         >>> builddecl('foo(bar($1, $2))')
         ('foo(bar($1, $2))', None, None, 'invalid argument list')
         >>> builddecl('foo("bar")')
         ('foo("bar")', None, None, 'invalid argument list')
         >>> builddecl('foo($1, $2')
         ('foo($1, $2', None, None, 'at 10: unexpected token: end')
         >>> builddecl('foo("bar')
         ('foo("bar', None, None, 'at 5: unterminated string')
         >>> builddecl('foo($1, $2, $1)')
         ('foo', None, None, 'argument names collide with each other')
         """
         try:
             tree = cls._parse(decl)
         except error.ParseError as inst:
             return (decl, None, None, parseerrordetail(inst))
 
         if tree[0] == cls._symbolnode:
             # "name = ...." style
             name = tree[1]
             if name.startswith('$'):
                 return (decl, None, None, _("'$' not for alias arguments"))
             return (name, tree, None, None)
 
         if tree[0] == cls._funcnode and tree[1][0] == cls._symbolnode:
             # "name(arg, ....) = ...." style
             name = tree[1][1]
             if name.startswith('$'):
                 return (decl, None, None, _("'$' not for alias arguments"))
             args = []
             for arg in cls._getlist(tree[2]):
                 if arg[0] != cls._symbolnode:
                     return (decl, None, None, _("invalid argument list"))
                 args.append(arg[1])
             if len(args) != len(set(args)):
                 return (name, None, None,
                         _("argument names collide with each other"))
             return (name, tree[:2], args, None)
 
         return (decl, None, None, _("invalid format"))
 
     @classmethod
     def _relabelargs(cls, tree, args):
         """Mark alias arguments as ``_aliasarg``"""
         if not isinstance(tree, tuple):
             return tree
         op = tree[0]
         if op != cls._symbolnode:
             return (op,) + tuple(cls._relabelargs(x, args) for x in tree[1:])
 
         assert len(tree) == 2
         sym = tree[1]
         if sym in args:
             op = '_aliasarg'
         elif sym.startswith('$'):
             raise error.ParseError(_("'$' not for alias arguments"))
         return (op, sym)
 
     @classmethod
     def _builddefn(cls, defn, args):
         """Parse an alias definition into a tree and marks substitutions
 
         This function marks alias argument references as ``_aliasarg``. The
         parsing rule is provided by ``_parse()``.
 
         ``args`` is a list of alias argument names, or None if the alias
         is declared as a symbol.
 
         >>> parsemap = {
         ...     '$1 or foo': ('or', ('symbol', '$1'), ('symbol', 'foo')),
         ...     '$1 or $bar': ('or', ('symbol', '$1'), ('symbol', '$bar')),
         ...     '$10 or baz': ('or', ('symbol', '$10'), ('symbol', 'baz')),
         ...     '"$1" or "foo"': ('or', ('string', '$1'), ('string', 'foo')),
         ... }
         >>> class aliasrules(basealiasrules):
         ...     _parse = staticmethod(parsemap.__getitem__)
         ...     _getlist = staticmethod(lambda x: [])
         >>> builddefn = aliasrules._builddefn
         >>> def pprint(tree):
         ...     print prettyformat(tree, ('_aliasarg', 'string', 'symbol'))
         >>> args = ['$1', '$2', 'foo']
         >>> pprint(builddefn('$1 or foo', args))
         (or
           ('_aliasarg', '$1')
           ('_aliasarg', 'foo'))
         >>> try:
         ...     builddefn('$1 or $bar', args)
         ... except error.ParseError as inst:
         ...     print parseerrordetail(inst)
         '$' not for alias arguments
         >>> args = ['$1', '$10', 'foo']
         >>> pprint(builddefn('$10 or baz', args))
         (or
           ('_aliasarg', '$10')
           ('symbol', 'baz'))
         >>> pprint(builddefn('"$1" or "foo"', args))
         (or
           ('string', '$1')
           ('string', 'foo'))
         """
         tree = cls._parse(defn)
         if args:
             args = set(args)
         else:
             args = set()
         return cls._relabelargs(tree, args)
 
     @classmethod
     def build(cls, decl, defn):
         """Parse an alias declaration and definition into an alias object"""
         repl = efmt = None
         name, tree, args, err = cls._builddecl(decl)
         if err:
             efmt = _('failed to parse the declaration of %(section)s '
                      '"%(name)s": %(error)s')
         else:
             try:
                 repl = cls._builddefn(defn, args)
             except error.ParseError as inst:
                 err = parseerrordetail(inst)
                 efmt = _('failed to parse the definition of %(section)s '
                          '"%(name)s": %(error)s')
         if err:
             err = efmt % {'section': cls._section, 'name': name, 'error': err}
         return alias(name, tree, args, err, repl)
 
     @classmethod
     def buildmap(cls, items):
         """Parse a list of alias (name, replacement) pairs into a dict of
         alias objects"""
         aliases = {}
         for decl, defn in items:
             a = cls.build(decl, defn)
             aliases[a.name] = a
         return aliases
 
     @classmethod
     def _getalias(cls, aliases, tree):
         """If tree looks like an unexpanded alias, return it. Return None
         otherwise.
         """
         if not isinstance(tree, tuple):
             return None
         if tree[0] == cls._symbolnode:
             name = tree[1]
             a = aliases.get(name)
             if a and a.args is None and a.tree == tree:
                 return a
         if tree[0] == cls._funcnode and tree[1][0] == cls._symbolnode:
             name = tree[1][1]
             a = aliases.get(name)
             if a and a.args is not None and a.tree == tree[:2]:
                 return a
         return None
 
     @classmethod
     def _expandargs(cls, tree, args):
         """Replace _aliasarg instances with the substitution value of the
         same name in args, recursively.
         """
         if not isinstance(tree, tuple):
             return tree
         if tree[0] == '_aliasarg':
             sym = tree[1]
             return args[sym]
         return tuple(cls._expandargs(t, args) for t in tree)
 
     @classmethod
     def _expand(cls, aliases, tree, expanding, cache):
         if not isinstance(tree, tuple):
             return tree
         a = cls._getalias(aliases, tree)
-        if a is not None:
-            if a.error:
-                raise error.Abort(a.error)
-            if a in expanding:
-                raise error.ParseError(_('infinite expansion of %(section)s '
-                                         '"%(name)s" detected')
-                                       % {'section': cls._section,
-                                          'name': a.name})
-            expanding.append(a)
-            if a.name not in cache:
-                cache[a.name] = cls._expand(aliases, a.replacement, expanding,
-                                            cache)
-            result = cache[a.name]
-            expanding.pop()
-            if a.args is not None:
-                l = cls._getlist(tree[2])
-                if len(l) != len(a.args):
-                    raise error.ParseError(_('invalid number of arguments: %d')
-                                           % len(l))
-                l = [cls._expand(aliases, t, [], cache) for t in l]
-                result = cls._expandargs(result, dict(zip(a.args, l)))
-        else:
-            result = tuple(cls._expand(aliases, t, expanding, cache)
-                           for t in tree)
-        return result
+        if a is None:
+            return tuple(cls._expand(aliases, t, expanding, cache)
+                         for t in tree)
+        if a.error:
+            raise error.Abort(a.error)
+        if a in expanding:
+            raise error.ParseError(_('infinite expansion of %(section)s '
+                                     '"%(name)s" detected')
+                                   % {'section': cls._section, 'name': a.name})
+        expanding.append(a)
+        if a.name not in cache:
+            cache[a.name] = cls._expand(aliases, a.replacement, expanding,
+                                        cache)
+        result = cache[a.name]
+        expanding.pop()
+        if a.args is None:
+            return result
+        l = cls._getlist(tree[2])
+        if len(l) != len(a.args):
+            raise error.ParseError(_('invalid number of arguments: %d')
+                                   % len(l))
+        l = [cls._expand(aliases, t, [], cache) for t in l]
+        return cls._expandargs(result, dict(zip(a.args, l)))
 
     @classmethod
     def expand(cls, aliases, tree):
         """Expand aliases in tree, recursively.
 
         'aliases' is a dictionary mapping user defined aliases to alias objects.
         """
         return cls._expand(aliases, tree, [], {})