def readpatternfile(filepath, warn, sourceinfo=False):
    """parse a pattern file, returning a list of
    patterns. These patterns should be given to compile()
    to be validated and converted into a match function.

    trailing white space is dropped.
    the escape character is backslash.
    comments start with #.
    empty lines are skipped.

    lines can be of the following formats:

    syntax: regexp # defaults following lines to non-rooted regexps
    syntax: glob   # defaults following lines to non-rooted globs
    re:pattern     # non-rooted regular expression
    glob:pattern   # non-rooted glob
    pattern        # pattern of the current default type

    if sourceinfo is set, returns a list of tuples:
    (pattern, lineno, originalline). This is useful to debug ignore patterns.
    """

    syntaxes = {
        "re": "relre:",
        "regexp": "relre:",
        "glob": "relglob:",
        "include": "include",
        "subinclude": "subinclude",
    }
    syntax = "relre:"
    patterns = []

    fp = open(filepath, "rb")
    for lineno, line in enumerate(util.iterfile(fp), start=1):
        if "#" in line:
            global _commentre
            if not _commentre:
                _commentre = util.re.compile(br"((?:^|[^\\])(?:\\\\)*)#.*")
            # remove comments prefixed by an even number of escapes
            m = _commentre.search(line)
            if m:
                line = line[: m.end(1)]
            # fixup properly escaped comments that survived the above
            line = line.replace("\\#", "#")
        line = line.rstrip()
        if not line:
            continue

        if line.startswith("syntax:"):
            s = line[7:].strip()
            try:
                syntax = syntaxes[s]
            except KeyError:
                if warn:
                    warn(_("%s: ignoring invalid syntax '%s'\n") % (filepath, s))
            continue

        linesyntax = syntax
        for s, rels in pycompat.iteritems(syntaxes):
            if line.startswith(rels):
                linesyntax = rels
                line = line[len(rels) :]
                break
            elif line.startswith(s + ":"):
                linesyntax = rels
                line = line[len(s) + 1 :]
                break
        if sourceinfo:
            patterns.append((linesyntax + line, lineno, line))
        else:
            patterns.append(linesyntax + line)
    fp.close()
    return patterns