221 lines
7.5 KiB
Python
221 lines
7.5 KiB
Python
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"""JsLex: a lexer for Javascript"""
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# Originally from https://bitbucket.org/ned/jslex
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import re
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class Tok:
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"""
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A specification for a token class.
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"""
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num = 0
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def __init__(self, name, regex, next=None):
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self.id = Tok.num
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Tok.num += 1
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self.name = name
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self.regex = regex
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self.next = next
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def literals(choices, prefix="", suffix=""):
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"""
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Create a regex from a space-separated list of literal `choices`.
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If provided, `prefix` and `suffix` will be attached to each choice
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individually.
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"""
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return "|".join(prefix + re.escape(c) + suffix for c in choices.split())
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class Lexer:
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"""
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A generic multi-state regex-based lexer.
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"""
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def __init__(self, states, first):
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self.regexes = {}
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self.toks = {}
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for state, rules in states.items():
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parts = []
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for tok in rules:
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groupid = "t%d" % tok.id
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self.toks[groupid] = tok
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parts.append("(?P<%s>%s)" % (groupid, tok.regex))
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self.regexes[state] = re.compile("|".join(parts), re.MULTILINE | re.VERBOSE)
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self.state = first
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def lex(self, text):
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"""
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Lexically analyze `text`.
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Yield pairs (`name`, `tokentext`).
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"""
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end = len(text)
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state = self.state
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regexes = self.regexes
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toks = self.toks
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start = 0
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while start < end:
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for match in regexes[state].finditer(text, start):
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name = match.lastgroup
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tok = toks[name]
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toktext = match.group(name)
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start += len(toktext)
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yield (tok.name, toktext)
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if tok.next:
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state = tok.next
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break
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self.state = state
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class JsLexer(Lexer):
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"""
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A Javascript lexer
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>>> lexer = JsLexer()
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>>> list(lexer.lex("a = 1"))
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[('id', 'a'), ('ws', ' '), ('punct', '='), ('ws', ' '), ('dnum', '1')]
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This doesn't properly handle non-ASCII characters in the Javascript source.
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"""
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# Because these tokens are matched as alternatives in a regex, longer
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# possibilities must appear in the list before shorter ones, for example,
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# '>>' before '>'.
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#
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# Note that we don't have to detect malformed Javascript, only properly
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# lex correct Javascript, so much of this is simplified.
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# Details of Javascript lexical structure are taken from
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# http://www.ecma-international.org/publications/files/ECMA-ST/ECMA-262.pdf
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# A useful explanation of automatic semicolon insertion is at
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# http://inimino.org/~inimino/blog/javascript_semicolons
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both_before = [
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Tok("comment", r"/\*(.|\n)*?\*/"),
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Tok("linecomment", r"//.*?$"),
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Tok("ws", r"\s+"),
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Tok("keyword", literals("""
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break case catch class const continue debugger
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default delete do else enum export extends
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finally for function if import in instanceof
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new return super switch this throw try typeof
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var void while with
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""", suffix=r"\b"), next='reg'),
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Tok("reserved", literals("null true false", suffix=r"\b"), next='div'),
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Tok("id", r"""
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([a-zA-Z_$ ]|\\u[0-9a-fA-Z]{4}) # first char
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([a-zA-Z_$0-9]|\\u[0-9a-fA-F]{4})* # rest chars
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""", next='div'),
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Tok("hnum", r"0[xX][0-9a-fA-F]+", next='div'),
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Tok("onum", r"0[0-7]+"),
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Tok("dnum", r"""
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( (0|[1-9][0-9]*) # DecimalIntegerLiteral
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\. # dot
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[0-9]* # DecimalDigits-opt
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([eE][-+]?[0-9]+)? # ExponentPart-opt
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\. # dot
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[0-9]+ # DecimalDigits
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([eE][-+]?[0-9]+)? # ExponentPart-opt
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(0|[1-9][0-9]*) # DecimalIntegerLiteral
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([eE][-+]?[0-9]+)? # ExponentPart-opt
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)
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""", next='div'),
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Tok("punct", literals("""
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>>>= === !== >>> <<= >>= <= >= == != << >> &&
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|| += -= *= %= &= |= ^=
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"""), next="reg"),
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Tok("punct", literals("++ -- ) ]"), next='div'),
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Tok("punct", literals("{ } ( [ . ; , < > + - * % & | ^ ! ~ ? : ="), next='reg'),
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Tok("string", r'"([^"\\]|(\\(.|\n)))*?"', next='div'),
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Tok("string", r"'([^'\\]|(\\(.|\n)))*?'", next='div'),
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]
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both_after = [
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Tok("other", r"."),
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]
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states = {
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# slash will mean division
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'div': both_before + [
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Tok("punct", literals("/= /"), next='reg'),
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] + both_after,
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# slash will mean regex
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'reg': both_before + [
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Tok("regex",
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r"""
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/ # opening slash
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# First character is..
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( [^*\\/[] # anything but * \ / or [
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| \\. # or an escape sequence
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| \[ # or a class, which has
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( [^\]\\] # anything but \ or ]
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| \\. # or an escape sequence
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)* # many times
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\]
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)
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# Following characters are same, except for excluding a star
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( [^\\/[] # anything but \ / or [
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| \\. # or an escape sequence
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| \[ # or a class, which has
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( [^\]\\] # anything but \ or ]
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| \\. # or an escape sequence
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)* # many times
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\]
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)* # many times
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/ # closing slash
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[a-zA-Z0-9]* # trailing flags
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""", next='div'),
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] + both_after,
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}
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def __init__(self):
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super().__init__(self.states, 'reg')
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def prepare_js_for_gettext(js):
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"""
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Convert the Javascript source `js` into something resembling C for
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xgettext.
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What actually happens is that all the regex literals are replaced with
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"REGEX".
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"""
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def escape_quotes(m):
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"""Used in a regex to properly escape double quotes."""
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s = m.group(0)
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if s == '"':
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return r'\"'
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else:
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return s
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lexer = JsLexer()
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c = []
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for name, tok in lexer.lex(js):
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if name == 'regex':
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# C doesn't grok regexes, and they aren't needed for gettext,
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# so just output a string instead.
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tok = '"REGEX"'
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elif name == 'string':
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# C doesn't have single-quoted strings, so make all strings
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# double-quoted.
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if tok.startswith("'"):
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guts = re.sub(r"\\.|.", escape_quotes, tok[1:-1])
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tok = '"' + guts + '"'
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elif name == 'id':
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# C can't deal with Unicode escapes in identifiers. We don't
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# need them for gettext anyway, so replace them with something
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# innocuous
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tok = tok.replace("\\", "U")
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c.append(tok)
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return ''.join(c)
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