htmldocck.py

# Copyright 2015 The Rust Project Developers. See the COPYRIGHT
# file at the top-level directory of this distribution and at
# http://rust-lang.org/COPYRIGHT.
#
# Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
# http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
# <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
# option. This file may not be copied, modified, or distributed
# except according to those terms.

r"""
htmldocck.py is a custom checker script for Rustdoc HTML outputs.

# How and why?

The principle is simple: This script receives a path to generated HTML
documentation and a "template" script, which has a series of check
commands like `@has` or `@matches`. Each command can be used to check if
some pattern is present or not present in the particular file or in
the particular node of HTML tree. In many cases, the template script
happens to be a source code given to rustdoc.

While it indeed is possible to test in smaller portions, it has been
hard to construct tests in this fashion and major rendering errors were
discovered much later. This script is designed for making the black-box
and regression testing of Rustdoc easy. This does not preclude the needs
for unit testing, but can be used to complement related tests by quickly
showing the expected renderings.

In order to avoid one-off dependencies for this task, this script uses
a reasonably working HTML parser and the existing XPath implementation
from Python 2's standard library. Hopefully we won't render
non-well-formed HTML.

# Commands

Commands start with an `@` followed by a command name (letters and
hyphens), and zero or more arguments separated by one or more whitespace
and optionally delimited with single or double quotes. The `@` mark
cannot be preceded by a non-whitespace character. Other lines (including
every text up to the first `@`) are ignored, but it is recommended to
avoid the use of `@` in the template file.

There are a number of supported commands:

* `@has PATH` checks for the existence of given file.

  `PATH` is relative to the output directory. It can be given as `-`
  which repeats the most recently used `PATH`.

* `@has PATH PATTERN` and `@matches PATH PATTERN` checks for
  the occurrence of given `PATTERN` in the given file. Only one
  occurrence of given pattern is enough.

  For `@has`, `PATTERN` is a whitespace-normalized (every consecutive
  whitespace being replaced by one single space character) string.
  The entire file is also whitespace-normalized including newlines.

  For `@matches`, `PATTERN` is a Python-supported regular expression.
  The file remains intact but the regexp is matched with no `MULTILINE`
  and `IGNORECASE` option. You can still use a prefix `(?m)` or `(?i)`
  to override them, and `\A` and `\Z` for definitely matching
  the beginning and end of the file.

  (The same distinction goes to other variants of these commands.)

* `@has PATH XPATH PATTERN` and `@matches PATH XPATH PATTERN` checks for
  the presence of given `XPATH` in the given HTML file, and also
  the occurrence of given `PATTERN` in the matching node or attribute.
  Only one occurrence of given pattern in the match is enough.

  `PATH` should be a valid and well-formed HTML file. It does *not*
  accept arbitrary HTML5; it should have matching open and close tags
  and correct entity references at least.

  `XPATH` is an XPath expression to match. This is fairly limited:
  `tag`, `*`, `.`, `//`, `..`, `[@attr]`, `[@attr='value']`, `[tag]`,
  `[POS]` (element located in given `POS`), `[last()-POS]`, `text()`
  and `@attr` (both as the last segment) are supported. Some examples:

  - `//pre` or `.//pre` matches any element with a name `pre`.
  - `//a[@href]` matches any element with an `href` attribute.
  - `//*[@class="impl"]//code` matches any element with a name `code`,
    which is an ancestor of some element which `class` attr is `impl`.
  - `//h1[@class="fqn"]/span[1]/a[last()]/@class` matches a value of
    `class` attribute in the last `a` element (can be followed by more
    elements that are not `a`) inside the first `span` in the `h1` with
    a class of `fqn`. Note that there cannot be no additional elements
    between them due to the use of `/` instead of `//`.

  Do not try to use non-absolute paths, it won't work due to the flawed
  ElementTree implementation. The script rejects them.

  For the text matches (i.e. paths not ending with `@attr`), any
  subelements are flattened into one string; this is handy for ignoring
  highlights for example. If you want to simply check the presence of
  given node or attribute, use an empty string (`""`) as a `PATTERN`.

* `@count PATH XPATH COUNT' checks for the occurrence of given XPath
  in the given file. The number of occurrences must match the given count.

All conditions can be negated with `!`. `@!has foo/type.NoSuch.html`
checks if the given file does not exist, for example.

"""

import sys
import os.path
import re
import shlex
from collections import namedtuple
from HTMLParser import HTMLParser
from xml.etree import cElementTree as ET

# &larrb;/&rarrb; are not in HTML 4 but are in HTML 5
from htmlentitydefs import entitydefs
entitydefs['larrb'] = u'\u21e4'
entitydefs['rarrb'] = u'\u21e5'

# "void elements" (no closing tag) from the HTML Standard section 12.1.2
VOID_ELEMENTS = set(['area', 'base', 'br', 'col', 'embed', 'hr', 'img', 'input', 'keygen',
                     'link', 'menuitem', 'meta', 'param', 'source', 'track', 'wbr'])


class CustomHTMLParser(HTMLParser):
    """simplified HTML parser.

    this is possible because we are dealing with very regular HTML from
    rustdoc; we only have to deal with i) void elements and ii) empty
    attributes."""
    def __init__(self, target=None):
        HTMLParser.__init__(self)
        self.__builder = target or ET.TreeBuilder()

    def handle_starttag(self, tag, attrs):
        attrs = dict((k, v or '') for k, v in attrs)
        self.__builder.start(tag, attrs)
        if tag in VOID_ELEMENTS:
            self.__builder.end(tag)

    def handle_endtag(self, tag):
        self.__builder.end(tag)

    def handle_startendtag(self, tag, attrs):
        attrs = dict((k, v or '') for k, v in attrs)
        self.__builder.start(tag, attrs)
        self.__builder.end(tag)

    def handle_data(self, data):
        self.__builder.data(data)

    def handle_entityref(self, name):
        self.__builder.data(entitydefs[name])

    def handle_charref(self, name):
        code = int(name[1:], 16) if name.startswith(('x', 'X')) else int(name, 10)
        self.__builder.data(unichr(code).encode('utf-8'))

    def close(self):
        HTMLParser.close(self)
        return self.__builder.close()

Command = namedtuple('Command', 'negated cmd args lineno')


def concat_multi_lines(f):
    """returns a generator out of the file object, which
    - removes `\\` then `\n` then a shared prefix with the previous line then
      optional whitespace;
    - keeps a line number (starting from 0) of the first line being
      concatenated."""
    lastline = None # set to the last line when the last line has a backslash
    firstlineno = None
    catenated = ''
    for lineno, line in enumerate(f):
        line = line.rstrip('\r\n')

        # strip the common prefix from the current line if needed
        if lastline is not None:
            maxprefix = 0
            for i in xrange(min(len(line), len(lastline))):
                if line[i] != lastline[i]:
                    break
                maxprefix += 1
            line = line[maxprefix:].lstrip()

        firstlineno = firstlineno or lineno
        if line.endswith('\\'):
            lastline = line[:-1]
            catenated += line[:-1]
        else:
            yield firstlineno, catenated + line
            lastline = None
            firstlineno = None
            catenated = ''

    if lastline is not None:
        raise RuntimeError('Trailing backslash in the end of file')

LINE_PATTERN = re.compile(r'''
    (?<=(?<!\S)@)(?P<negated>!?)
    (?P<cmd>[A-Za-z]+(?:-[A-Za-z]+)*)
    (?P<args>.*)$
''', re.X)


def get_commands(template):
    with open(template, 'rUb') as f:
        for lineno, line in concat_multi_lines(f):
            m = LINE_PATTERN.search(line)
            if not m:
                continue

            negated = (m.group('negated') == '!')
            cmd = m.group('cmd')
            args = m.group('args')
            if args and not args[:1].isspace():
                raise RuntimeError('Invalid template syntax at line {}'.format(lineno+1))
            args = shlex.split(args)
            yield Command(negated=negated, cmd=cmd, args=args, lineno=lineno+1)


def _flatten(node, acc):
    if node.text:
        acc.append(node.text)
    for e in node:
        _flatten(e, acc)
        if e.tail:
            acc.append(e.tail)


def flatten(node):
    acc = []
    _flatten(node, acc)
    return ''.join(acc)


def normalize_xpath(path):
    if path.startswith('//'):
        return '.' + path # avoid warnings
    elif path.startswith('.//'):
        return path
    else:
        raise RuntimeError('Non-absolute XPath is not supported due to \
                            the implementation issue.')


class CachedFiles(object):
    def __init__(self, root):
        self.root = root
        self.files = {}
        self.trees = {}
        self.last_path = None

    def resolve_path(self, path):
        if path != '-':
            path = os.path.normpath(path)
            self.last_path = path
            return path
        elif self.last_path is None:
            raise RuntimeError('Tried to use the previous path in the first command')
        else:
            return self.last_path

    def get_file(self, path):
        path = self.resolve_path(path)
        try:
            return self.files[path]
        except KeyError:
            try:
                with open(os.path.join(self.root, path)) as f:
                    data = f.read()
            except Exception as e:
                raise RuntimeError('Cannot open file {!r}: {}'.format(path, e))
            else:
                self.files[path] = data
                return data

    def get_tree(self, path):
        path = self.resolve_path(path)
        try:
            return self.trees[path]
        except KeyError:
            try:
                f = open(os.path.join(self.root, path))
            except Exception as e:
                raise RuntimeError('Cannot open file {!r}: {}'.format(path, e))
            try:
                with f:
                    tree = ET.parse(f, CustomHTMLParser())
            except Exception as e:
                raise RuntimeError('Cannot parse an HTML file {!r}: {}'.format(path, e))
            else:
                self.trees[path] = tree
                return self.trees[path]


def check_string(data, pat, regexp):
    if not pat:
        return True # special case a presence testing
    elif regexp:
        return re.search(pat, data) is not None
    else:
        data = ' '.join(data.split())
        pat = ' '.join(pat.split())
        return pat in data


def check_tree_attr(tree, path, attr, pat, regexp):
    path = normalize_xpath(path)
    ret = False
    for e in tree.findall(path):
        try:
            value = e.attrib[attr]
        except KeyError:
            continue
        else:
            ret = check_string(value, pat, regexp)
            if ret:
                break
    return ret


def check_tree_text(tree, path, pat, regexp):
    path = normalize_xpath(path)
    ret = False
    for e in tree.findall(path):
        try:
            value = flatten(e)
        except KeyError:
            continue
        else:
            ret = check_string(value, pat, regexp)
            if ret:
                break
    return ret


def check_tree_count(tree, path, count):
    path = normalize_xpath(path)
    return len(tree.findall(path)) == count


def check(target, commands):
    cache = CachedFiles(target)
    for c in commands:
        if c.cmd == 'has' or c.cmd == 'matches': # string test
            regexp = (c.cmd == 'matches')
            if len(c.args) == 1 and not regexp: # @has <path> = file existence
                try:
                    cache.get_file(c.args[0])
                    ret = True
                except RuntimeError:
                    ret = False
            elif len(c.args) == 2: # @has/matches <path> <pat> = string test
                ret = check_string(cache.get_file(c.args[0]), c.args[1], regexp)
            elif len(c.args) == 3: # @has/matches <path> <pat> <match> = XML tree test
                tree = cache.get_tree(c.args[0])
                pat, sep, attr = c.args[1].partition('/@')
                if sep: # attribute
                    ret = check_tree_attr(cache.get_tree(c.args[0]), pat, attr, c.args[2], regexp)
                else: # normalized text
                    pat = c.args[1]
                    if pat.endswith('/text()'):
                        pat = pat[:-7]
                    ret = check_tree_text(cache.get_tree(c.args[0]), pat, c.args[2], regexp)
            else:
                raise RuntimeError('Invalid number of @{} arguments \
                                    at line {}'.format(c.cmd, c.lineno))

        elif c.cmd == 'count': # count test
            if len(c.args) == 3: # @count <path> <pat> <count> = count test
                ret = check_tree_count(cache.get_tree(c.args[0]), c.args[1], int(c.args[2]))
            else:
                raise RuntimeError('Invalid number of @{} arguments \
                                    at line {}'.format(c.cmd, c.lineno))

        elif c.cmd == 'valid-html':
            raise RuntimeError('Unimplemented @valid-html at line {}'.format(c.lineno))

        elif c.cmd == 'valid-links':
            raise RuntimeError('Unimplemented @valid-links at line {}'.format(c.lineno))

        else:
            raise RuntimeError('Unrecognized @{} at line {}'.format(c.cmd, c.lineno))

        if ret == c.negated:
            raise RuntimeError('@{}{} check failed at line {}'.format('!' if c.negated else '',
                                                                      c.cmd, c.lineno))

if __name__ == '__main__':
    if len(sys.argv) < 3:
        print >>sys.stderr, 'Usage: {} <doc dir> <template>'.format(sys.argv[0])
        raise SystemExit(1)
    else:
        check(sys.argv[1], get_commands(sys.argv[2]))