debugcommands: add debugwireproto command
We currently don't have a low-level mechanism for sending
arbitrary wire protocol commands. Having a generic and robust
mechanism for sending wire protocol commands, examining wire
data, etc would make it vastly easier to test the wire protocol
and debug server operation. This is a problem I've wanted a
solution for numerous times, especially recently as I've been
hacking on a new version of the wire protocol.
This commit establishes a `hg debugwireproto` command for sending
data to a peer.
The command invents a mini language for specifying actions to take.
This will enable a lot of flexibility for issuing commands and testing
variations for how commands are sent.
Right now, we only support low-level raw sends and receives. These
are probably the least valuable commands to intended users of this
command. But they are the most useful commands to implement to
bootstrap the feature (I've chosen to reimplement test-ssh-proto.t
using this command to prove its usefulness).
My eventual goal of `hg debugwireproto` is to allow calling wire
protocol commands with a human-friendly interface. Essentially,
people can type in a command name and arguments and
`hg debugwireproto` will figure out how to send that on the wire.
I'd love to eventually be able to save the server's raw response
to a file. This would allow us to e.g. call "getbundle" wire
protocol commands easily.
test-ssh-proto.t has been updated to use the new command in lieu
of piping directly to a server process. As part of the transition,
test behavior improved. Before, we piped all request data to the
server at once. Now, we have explicit control over the ordering of
operations. e.g. we can send one command, receive its response,
then send another command. This will allow us to more robustly
test race conditions, buffering behavior, etc.
There were some subtle changes in test behavior. For example,
previous behavior would often send trailing newlines to the server.
The new mechanism doesn't treat literal newlines specially and
requires newlines be escaped in the payload.
Because the new logging code is very low level, it is easy to
introduce race conditions in tests. For example, the number of bytes
returned by a read() may vary depending on load. This is why tests
make heavy use of "readline" for consuming data: the result of
that operation should be deterministic and not subject to race
conditions. There are still some uses of "readavailable." However,
those are only for reading from stderr. I was able to reproduce
timing issues with my system under load when using "readavailable"
globally. But if I "readline" to grab stdout, "readavailable"
appears to work deterministically for stderr. I think this is
because the server writes to stderr first. As long as the OS
delivers writes to pipes in the same order they were made, this
should work. If there are timing issues, we can introduce a
mechanism to readline from stderr.
Differential Revision: https://phab.mercurial-scm.org/D2392
# revsetlang.py - parser, tokenizer and utility for revision set language
#
# Copyright 2010 Matt Mackall <mpm@selenic.com>
#
# 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 string
from .i18n import _
from . import (
error,
node,
parser,
pycompat,
util,
)
elements = {
# token-type: binding-strength, primary, prefix, infix, suffix
"(": (21, None, ("group", 1, ")"), ("func", 1, ")"), None),
"[": (21, None, None, ("subscript", 1, "]"), None),
"#": (21, None, None, ("relation", 21), None),
"##": (20, None, None, ("_concat", 20), None),
"~": (18, None, None, ("ancestor", 18), None),
"^": (18, None, None, ("parent", 18), "parentpost"),
"-": (5, None, ("negate", 19), ("minus", 5), None),
"::": (17, "dagrangeall", ("dagrangepre", 17), ("dagrange", 17),
"dagrangepost"),
"..": (17, "dagrangeall", ("dagrangepre", 17), ("dagrange", 17),
"dagrangepost"),
":": (15, "rangeall", ("rangepre", 15), ("range", 15), "rangepost"),
"not": (10, None, ("not", 10), None, None),
"!": (10, None, ("not", 10), None, None),
"and": (5, None, None, ("and", 5), None),
"&": (5, None, None, ("and", 5), None),
"%": (5, None, None, ("only", 5), "onlypost"),
"or": (4, None, None, ("or", 4), None),
"|": (4, None, None, ("or", 4), None),
"+": (4, None, None, ("or", 4), None),
"=": (3, None, None, ("keyvalue", 3), None),
",": (2, None, None, ("list", 2), None),
")": (0, None, None, None, None),
"]": (0, None, None, None, None),
"symbol": (0, "symbol", None, None, None),
"string": (0, "string", None, None, None),
"end": (0, None, None, None, None),
}
keywords = {'and', 'or', 'not'}
symbols = {}
_quoteletters = {'"', "'"}
_simpleopletters = set(pycompat.iterbytestr("()[]#:=,-|&+!~^%"))
# default set of valid characters for the initial letter of symbols
_syminitletters = set(pycompat.iterbytestr(
string.ascii_letters.encode('ascii') +
string.digits.encode('ascii') +
'._@')) | set(map(pycompat.bytechr, xrange(128, 256)))
# default set of valid characters for non-initial letters of symbols
_symletters = _syminitletters | set(pycompat.iterbytestr('-/'))
def tokenize(program, lookup=None, syminitletters=None, symletters=None):
'''
Parse a revset statement into a stream of tokens
``syminitletters`` is the set of valid characters for the initial
letter of symbols.
By default, character ``c`` is recognized as valid for initial
letter of symbols, if ``c.isalnum() or c in '._@' or ord(c) > 127``.
``symletters`` is the set of valid characters for non-initial
letters of symbols.
By default, character ``c`` is recognized as valid for non-initial
letters of symbols, if ``c.isalnum() or c in '-._/@' or ord(c) > 127``.
Check that @ is a valid unquoted token character (issue3686):
>>> list(tokenize(b"@::"))
[('symbol', '@', 0), ('::', None, 1), ('end', None, 3)]
'''
program = pycompat.bytestr(program)
if syminitletters is None:
syminitletters = _syminitletters
if symletters is None:
symletters = _symletters
if program and lookup:
# attempt to parse old-style ranges first to deal with
# things like old-tag which contain query metacharacters
parts = program.split(':', 1)
if all(lookup(sym) for sym in parts if sym):
if parts[0]:
yield ('symbol', parts[0], 0)
if len(parts) > 1:
s = len(parts[0])
yield (':', None, s)
if parts[1]:
yield ('symbol', parts[1], s + 1)
yield ('end', None, len(program))
return
pos, l = 0, len(program)
while pos < l:
c = program[pos]
if c.isspace(): # skip inter-token whitespace
pass
elif c == ':' and program[pos:pos + 2] == '::': # look ahead carefully
yield ('::', None, pos)
pos += 1 # skip ahead
elif c == '.' and program[pos:pos + 2] == '..': # look ahead carefully
yield ('..', None, pos)
pos += 1 # skip ahead
elif c == '#' and program[pos:pos + 2] == '##': # look ahead carefully
yield ('##', None, pos)
pos += 1 # skip ahead
elif c in _simpleopletters: # handle simple operators
yield (c, None, pos)
elif (c in _quoteletters or c == 'r' and
program[pos:pos + 2] in ("r'", 'r"')): # handle quoted strings
if c == 'r':
pos += 1
c = program[pos]
decode = lambda x: x
else:
decode = parser.unescapestr
pos += 1
s = pos
while pos < l: # find closing quote
d = program[pos]
if d == '\\': # skip over escaped characters
pos += 2
continue
if d == c:
yield ('string', decode(program[s:pos]), s)
break
pos += 1
else:
raise error.ParseError(_("unterminated string"), s)
# gather up a symbol/keyword
elif c in syminitletters:
s = pos
pos += 1
while pos < l: # find end of symbol
d = program[pos]
if d not in symletters:
break
if d == '.' and program[pos - 1] == '.': # special case for ..
pos -= 1
break
pos += 1
sym = program[s:pos]
if sym in keywords: # operator keywords
yield (sym, None, s)
elif '-' in sym:
# some jerk gave us foo-bar-baz, try to check if it's a symbol
if lookup and lookup(sym):
# looks like a real symbol
yield ('symbol', sym, s)
else:
# looks like an expression
parts = sym.split('-')
for p in parts[:-1]:
if p: # possible consecutive -
yield ('symbol', p, s)
s += len(p)
yield ('-', None, pos)
s += 1
if parts[-1]: # possible trailing -
yield ('symbol', parts[-1], s)
else:
yield ('symbol', sym, s)
pos -= 1
else:
raise error.ParseError(_("syntax error in revset '%s'") %
program, pos)
pos += 1
yield ('end', None, pos)
# helpers
_notset = object()
def getsymbol(x):
if x and x[0] == 'symbol':
return x[1]
raise error.ParseError(_('not a symbol'))
def getstring(x, err):
if x and (x[0] == 'string' or x[0] == 'symbol'):
return x[1]
raise error.ParseError(err)
def getinteger(x, err, default=_notset):
if not x and default is not _notset:
return default
try:
return int(getstring(x, err))
except ValueError:
raise error.ParseError(err)
def getboolean(x, err):
value = util.parsebool(getsymbol(x))
if value is not None:
return value
raise error.ParseError(err)
def getlist(x):
if not x:
return []
if x[0] == 'list':
return list(x[1:])
return [x]
def getrange(x, err):
if not x:
raise error.ParseError(err)
op = x[0]
if op == 'range':
return x[1], x[2]
elif op == 'rangepre':
return None, x[1]
elif op == 'rangepost':
return x[1], None
elif op == 'rangeall':
return None, None
raise error.ParseError(err)
def getargs(x, min, max, err):
l = getlist(x)
if len(l) < min or (max >= 0 and len(l) > max):
raise error.ParseError(err)
return l
def getargsdict(x, funcname, keys):
return parser.buildargsdict(getlist(x), funcname, parser.splitargspec(keys),
keyvaluenode='keyvalue', keynode='symbol')
# cache of {spec: raw parsed tree} built internally
_treecache = {}
def _cachedtree(spec):
# thread safe because parse() is reentrant and dict.__setitem__() is atomic
tree = _treecache.get(spec)
if tree is None:
_treecache[spec] = tree = parse(spec)
return tree
def _build(tmplspec, *repls):
"""Create raw parsed tree from a template revset statement
>>> _build(b'f(_) and _', (b'string', b'1'), (b'symbol', b'2'))
('and', ('func', ('symbol', 'f'), ('string', '1')), ('symbol', '2'))
"""
template = _cachedtree(tmplspec)
return parser.buildtree(template, ('symbol', '_'), *repls)
def _match(patspec, tree):
"""Test if a tree matches the given pattern statement; return the matches
>>> _match(b'f(_)', parse(b'f()'))
>>> _match(b'f(_)', parse(b'f(1)'))
[('func', ('symbol', 'f'), ('symbol', '1')), ('symbol', '1')]
>>> _match(b'f(_)', parse(b'f(1, 2)'))
"""
pattern = _cachedtree(patspec)
return parser.matchtree(pattern, tree, ('symbol', '_'),
{'keyvalue', 'list'})
def _matchonly(revs, bases):
return _match('ancestors(_) and not ancestors(_)', ('and', revs, bases))
def _fixops(x):
"""Rewrite raw parsed tree to resolve ambiguous syntax which cannot be
handled well by our simple top-down parser"""
if not isinstance(x, tuple):
return x
op = x[0]
if op == 'parent':
# x^:y means (x^) : y, not x ^ (:y)
# x^: means (x^) :, not x ^ (:)
post = ('parentpost', x[1])
if x[2][0] == 'dagrangepre':
return _fixops(('dagrange', post, x[2][1]))
elif x[2][0] == 'dagrangeall':
return _fixops(('dagrangepost', post))
elif x[2][0] == 'rangepre':
return _fixops(('range', post, x[2][1]))
elif x[2][0] == 'rangeall':
return _fixops(('rangepost', post))
elif op == 'or':
# make number of arguments deterministic:
# x + y + z -> (or x y z) -> (or (list x y z))
return (op, _fixops(('list',) + x[1:]))
elif op == 'subscript' and x[1][0] == 'relation':
# x#y[z] ternary
return _fixops(('relsubscript', x[1][1], x[1][2], x[2]))
return (op,) + tuple(_fixops(y) for y in x[1:])
def _analyze(x):
if x is None:
return x
op = x[0]
if op == 'minus':
return _analyze(_build('_ and not _', *x[1:]))
elif op == 'only':
return _analyze(_build('only(_, _)', *x[1:]))
elif op == 'onlypost':
return _analyze(_build('only(_)', x[1]))
elif op == 'dagrangeall':
raise error.ParseError(_("can't use '::' in this context"))
elif op == 'dagrangepre':
return _analyze(_build('ancestors(_)', x[1]))
elif op == 'dagrangepost':
return _analyze(_build('descendants(_)', x[1]))
elif op == 'negate':
s = getstring(x[1], _("can't negate that"))
return _analyze(('string', '-' + s))
elif op in ('string', 'symbol'):
return x
elif op == 'rangeall':
return (op, None)
elif op in {'or', 'not', 'rangepre', 'rangepost', 'parentpost'}:
return (op, _analyze(x[1]))
elif op == 'group':
return _analyze(x[1])
elif op in {'and', 'dagrange', 'range', 'parent', 'ancestor', 'relation',
'subscript'}:
ta = _analyze(x[1])
tb = _analyze(x[2])
return (op, ta, tb)
elif op == 'relsubscript':
ta = _analyze(x[1])
tb = _analyze(x[2])
tc = _analyze(x[3])
return (op, ta, tb, tc)
elif op == 'list':
return (op,) + tuple(_analyze(y) for y in x[1:])
elif op == 'keyvalue':
return (op, x[1], _analyze(x[2]))
elif op == 'func':
return (op, x[1], _analyze(x[2]))
raise ValueError('invalid operator %r' % op)
def analyze(x):
"""Transform raw parsed tree to evaluatable tree which can be fed to
optimize() or getset()
All pseudo operations should be mapped to real operations or functions
defined in methods or symbols table respectively.
"""
return _analyze(x)
def _optimize(x):
if x is None:
return 0, x
op = x[0]
if op in ('string', 'symbol'):
return 0.5, x # single revisions are small
elif op == 'and':
wa, ta = _optimize(x[1])
wb, tb = _optimize(x[2])
w = min(wa, wb)
# (draft/secret/_notpublic() & ::x) have a fast path
m = _match('_() & ancestors(_)', ('and', ta, tb))
if m and getsymbol(m[1]) in {'draft', 'secret', '_notpublic'}:
return w, _build('_phaseandancestors(_, _)', m[1], m[2])
# (::x and not ::y)/(not ::y and ::x) have a fast path
m = _matchonly(ta, tb) or _matchonly(tb, ta)
if m:
return w, _build('only(_, _)', *m[1:])
m = _match('not _', tb)
if m:
return wa, ('difference', ta, m[1])
if wa > wb:
op = 'andsmally'
return w, (op, ta, tb)
elif op == 'or':
# fast path for machine-generated expression, that is likely to have
# lots of trivial revisions: 'a + b + c()' to '_list(a b) + c()'
ws, ts, ss = [], [], []
def flushss():
if not ss:
return
if len(ss) == 1:
w, t = ss[0]
else:
s = '\0'.join(t[1] for w, t in ss)
y = _build('_list(_)', ('string', s))
w, t = _optimize(y)
ws.append(w)
ts.append(t)
del ss[:]
for y in getlist(x[1]):
w, t = _optimize(y)
if t is not None and (t[0] == 'string' or t[0] == 'symbol'):
ss.append((w, t))
continue
flushss()
ws.append(w)
ts.append(t)
flushss()
if len(ts) == 1:
return ws[0], ts[0] # 'or' operation is fully optimized out
return max(ws), (op, ('list',) + tuple(ts))
elif op == 'not':
# Optimize not public() to _notpublic() because we have a fast version
if _match('public()', x[1]):
o = _optimize(_build('_notpublic()'))
return o[0], o[1]
else:
o = _optimize(x[1])
return o[0], (op, o[1])
elif op == 'rangeall':
return 1, x
elif op in ('rangepre', 'rangepost', 'parentpost'):
o = _optimize(x[1])
return o[0], (op, o[1])
elif op in ('dagrange', 'range'):
wa, ta = _optimize(x[1])
wb, tb = _optimize(x[2])
return wa + wb, (op, ta, tb)
elif op in ('parent', 'ancestor', 'relation', 'subscript'):
w, t = _optimize(x[1])
return w, (op, t, x[2])
elif op == 'relsubscript':
w, t = _optimize(x[1])
return w, (op, t, x[2], x[3])
elif op == 'list':
ws, ts = zip(*(_optimize(y) for y in x[1:]))
return sum(ws), (op,) + ts
elif op == 'keyvalue':
w, t = _optimize(x[2])
return w, (op, x[1], t)
elif op == 'func':
f = getsymbol(x[1])
wa, ta = _optimize(x[2])
w = getattr(symbols.get(f), '_weight', 1)
return w + wa, (op, x[1], ta)
raise ValueError('invalid operator %r' % op)
def optimize(tree):
"""Optimize evaluatable tree
All pseudo operations should be transformed beforehand.
"""
_weight, newtree = _optimize(tree)
return newtree
# the set of valid characters for the initial letter of symbols in
# alias declarations and definitions
_aliassyminitletters = _syminitletters | {'$'}
def _parsewith(spec, lookup=None, syminitletters=None):
"""Generate a parse tree of given spec with given tokenizing options
>>> _parsewith(b'foo($1)', syminitletters=_aliassyminitletters)
('func', ('symbol', 'foo'), ('symbol', '$1'))
>>> _parsewith(b'$1')
Traceback (most recent call last):
...
ParseError: ("syntax error in revset '$1'", 0)
>>> _parsewith(b'foo bar')
Traceback (most recent call last):
...
ParseError: ('invalid token', 4)
"""
p = parser.parser(elements)
tree, pos = p.parse(tokenize(spec, lookup=lookup,
syminitletters=syminitletters))
if pos != len(spec):
raise error.ParseError(_('invalid token'), pos)
return _fixops(parser.simplifyinfixops(tree, ('list', 'or')))
class _aliasrules(parser.basealiasrules):
"""Parsing and expansion rule set of revset aliases"""
_section = _('revset alias')
@staticmethod
def _parse(spec):
"""Parse alias declaration/definition ``spec``
This allows symbol names to use also ``$`` as an initial letter
(for backward compatibility), and callers of this function should
examine whether ``$`` is used also for unexpected symbols or not.
"""
return _parsewith(spec, syminitletters=_aliassyminitletters)
@staticmethod
def _trygetfunc(tree):
if tree[0] == 'func' and tree[1][0] == 'symbol':
return tree[1][1], getlist(tree[2])
def expandaliases(tree, aliases, warn=None):
"""Expand aliases in a tree, aliases is a list of (name, value) tuples"""
aliases = _aliasrules.buildmap(aliases)
tree = _aliasrules.expand(aliases, tree)
# warn about problematic (but not referred) aliases
if warn is not None:
for name, alias in sorted(aliases.iteritems()):
if alias.error and not alias.warned:
warn(_('warning: %s\n') % (alias.error))
alias.warned = True
return tree
def foldconcat(tree):
"""Fold elements to be concatenated by `##`
"""
if not isinstance(tree, tuple) or tree[0] in ('string', 'symbol'):
return tree
if tree[0] == '_concat':
pending = [tree]
l = []
while pending:
e = pending.pop()
if e[0] == '_concat':
pending.extend(reversed(e[1:]))
elif e[0] in ('string', 'symbol'):
l.append(e[1])
else:
msg = _("\"##\" can't concatenate \"%s\" element") % (e[0])
raise error.ParseError(msg)
return ('string', ''.join(l))
else:
return tuple(foldconcat(t) for t in tree)
def parse(spec, lookup=None):
return _parsewith(spec, lookup=lookup)
def _quote(s):
r"""Quote a value in order to make it safe for the revset engine.
>>> _quote(b'asdf')
"'asdf'"
>>> _quote(b"asdf'\"")
'\'asdf\\\'"\''
>>> _quote(b'asdf\'')
"'asdf\\''"
>>> _quote(1)
"'1'"
"""
return "'%s'" % util.escapestr(pycompat.bytestr(s))
def _formatargtype(c, arg):
if c == 'd':
return '%d' % int(arg)
elif c == 's':
return _quote(arg)
elif c == 'r':
parse(arg) # make sure syntax errors are confined
return '(%s)' % arg
elif c == 'n':
return _quote(node.hex(arg))
elif c == 'b':
try:
return _quote(arg.branch())
except AttributeError:
raise TypeError
raise error.ParseError(_('unexpected revspec format character %s') % c)
def _formatlistexp(s, t):
l = len(s)
if l == 0:
return "_list('')"
elif l == 1:
return _formatargtype(t, s[0])
elif t == 'd':
return "_intlist('%s')" % "\0".join('%d' % int(a) for a in s)
elif t == 's':
return "_list(%s)" % _quote("\0".join(s))
elif t == 'n':
return "_hexlist('%s')" % "\0".join(node.hex(a) for a in s)
elif t == 'b':
try:
return "_list('%s')" % "\0".join(a.branch() for a in s)
except AttributeError:
raise TypeError
m = l // 2
return '(%s or %s)' % (_formatlistexp(s[:m], t), _formatlistexp(s[m:], t))
def _formatparamexp(args, t):
return ', '.join(_formatargtype(t, a) for a in args)
_formatlistfuncs = {
'l': _formatlistexp,
'p': _formatparamexp,
}
def formatspec(expr, *args):
'''
This is a convenience function for using revsets internally, and
escapes arguments appropriately. Aliases are intentionally ignored
so that intended expression behavior isn't accidentally subverted.
Supported arguments:
%r = revset expression, parenthesized
%d = int(arg), no quoting
%s = string(arg), escaped and single-quoted
%b = arg.branch(), escaped and single-quoted
%n = hex(arg), single-quoted
%% = a literal '%'
Prefixing the type with 'l' specifies a parenthesized list of that type,
and 'p' specifies a list of function parameters of that type.
>>> formatspec(b'%r:: and %lr', b'10 or 11', (b"this()", b"that()"))
'(10 or 11):: and ((this()) or (that()))'
>>> formatspec(b'%d:: and not %d::', 10, 20)
'10:: and not 20::'
>>> formatspec(b'%ld or %ld', [], [1])
"_list('') or 1"
>>> formatspec(b'keyword(%s)', b'foo\\xe9')
"keyword('foo\\\\xe9')"
>>> b = lambda: b'default'
>>> b.branch = b
>>> formatspec(b'branch(%b)', b)
"branch('default')"
>>> formatspec(b'root(%ls)', [b'a', b'b', b'c', b'd'])
"root(_list('a\\\\x00b\\\\x00c\\\\x00d'))"
>>> formatspec(b'sort(%r, %ps)', b':', [b'desc', b'user'])
"sort((:), 'desc', 'user')"
>>> formatspec(b'%ls', [b'a', b"'"])
"_list('a\\\\x00\\\\'')"
'''
expr = pycompat.bytestr(expr)
argiter = iter(args)
ret = []
pos = 0
while pos < len(expr):
q = expr.find('%', pos)
if q < 0:
ret.append(expr[pos:])
break
ret.append(expr[pos:q])
pos = q + 1
try:
d = expr[pos]
except IndexError:
raise error.ParseError(_('incomplete revspec format character'))
if d == '%':
ret.append(d)
pos += 1
continue
try:
arg = next(argiter)
except StopIteration:
raise error.ParseError(_('missing argument for revspec'))
f = _formatlistfuncs.get(d)
if f:
# a list of some type
pos += 1
try:
d = expr[pos]
except IndexError:
raise error.ParseError(_('incomplete revspec format character'))
try:
ret.append(f(list(arg), d))
except (TypeError, ValueError):
raise error.ParseError(_('invalid argument for revspec'))
else:
try:
ret.append(_formatargtype(d, arg))
except (TypeError, ValueError):
raise error.ParseError(_('invalid argument for revspec'))
pos += 1
try:
next(argiter)
raise error.ParseError(_('too many revspec arguments specified'))
except StopIteration:
pass
return ''.join(ret)
def prettyformat(tree):
return parser.prettyformat(tree, ('string', 'symbol'))
def depth(tree):
if isinstance(tree, tuple):
return max(map(depth, tree)) + 1
else:
return 0
def funcsused(tree):
if not isinstance(tree, tuple) or tree[0] in ('string', 'symbol'):
return set()
else:
funcs = set()
for s in tree[1:]:
funcs |= funcsused(s)
if tree[0] == 'func':
funcs.add(tree[1][1])
return funcs
_hashre = util.re.compile('[0-9a-fA-F]{1,40}$')
def _ishashlikesymbol(symbol):
"""returns true if the symbol looks like a hash"""
return _hashre.match(symbol)
def gethashlikesymbols(tree):
"""returns the list of symbols of the tree that look like hashes
>>> gethashlikesymbols(parse(b'3::abe3ff'))
['3', 'abe3ff']
>>> gethashlikesymbols(parse(b'precursors(.)'))
[]
>>> gethashlikesymbols(parse(b'precursors(34)'))
['34']
>>> gethashlikesymbols(parse(b'abe3ffZ'))
[]
"""
if not tree:
return []
if tree[0] == "symbol":
if _ishashlikesymbol(tree[1]):
return [tree[1]]
elif len(tree) >= 3:
results = []
for subtree in tree[1:]:
results += gethashlikesymbols(subtree)
return results
return []