linters.py

# -*- coding: utf-8 -*-
"""Linters process files or lists of files for correctness."""

import io
import itertools
import json
import logging
import os
import re
import signal
import subprocess
import sys

import lint_util


# Add vendor path so we can find (our packaged versions of) flake8
_CWD = lint_util.get_real_cwd()
_parent_dir = os.path.abspath(_CWD)
_vendor_dir = os.path.join(_parent_dir, 'vendor', 'py3')
sys.path.insert(0, _vendor_dir)

import static_content_refs
import flake8.api.legacy
import flake8.formatting.default
import yaml


def _is_verbose(logger):
    """Does this logger log to stdout/stderr at the DEBUG level?"""
    # First we check if the logger itself processes anything at the
    # debug level.  If not, then the handlers won't even see it.
    if not logger.isEnabledFor(logging.DEBUG):
        return False

    for handler in getattr(logger, 'handlers', []):
        if (getattr(handler, '__class__', None) == logging.StreamHandler and
                handler.level <= logging.DEBUG and
                handler.stream in (sys.stdout, sys.stderr)):
            return True
    return False


def _has_nolint(line):
    """We can turn off linting for a line via `@Nolint` or `NoQA`.

    Unlike flake8, we care about case for NoQA.

    TODO(csilvers): return the list of error-codes that we nolint for,
    and have callers respect that.
    """
    return "@Nolint" in line or "# NoQA" in line


class Linter(object):
    """Superclass for all linters.

    When subclassing, override either process_files or process (or both,
    though if you override process_files then it doesn't matter what
    process does).
    """
    # By default, we assume all linters lint text (utf-8) files.  If a
    # linter can lint binary files, it should set CAN_BE_BINARY_FILE
    # to False.  In that case we call `process` with the raw
    # file-text, not converted to utf-8.  This only really matters for
    # python3.
    CAN_BE_BINARY_FILE = False

    def __init__(self, logger):
        self.logger = logger
        self.verbose = _is_verbose(logger)

    def _read_file(self, filename):
        """Contents of filename.

        The return type is either bytes or unicode depending on the
        value of CAN_BE_BINARY_FILE.
        """
        try:
            contents = open(filename, 'rb').read()
        except (IOError, OSError) as why:
            # Give a more useful exception mesage, that has the
            # errno-string in it.
            raise ValueError(why.args[1])

        if not self.CAN_BE_BINARY_FILE:
            contents = contents.decode('utf-8')

        return contents

    def process_files(self, files):
        """Print lint errors for a list of filenames and return error count."""
        num_errors = 0
        for f in files:
            try:
                contents = self._read_file(f)
            except Exception as why:
                self.logger.warning("SKIPPING lint of %s: %s" % (f, why))
                num_errors += 1
                continue

            num_errors += self.process(f, contents)
        return num_errors

    def process(self, file, contents):
        """Lint one file given its path and contents, returning error count."""
        raise NotImplementedError("Subclasses must override process()")

    def report(self, lint):
        """Report the output to both stdout/stderr and logfile."""
        self.logger.debug(lint)
        if not self.verbose:
            lint_util.print_(lint)


class DelegatingLinter(Linter):
    """A linter that just calls out to a binary to do its actual work."""
    def __init__(self, argv, cwd, arc_autofix_script, logger):
        """argv is the command to run (as a lint).  cwd is where to run it."""
        super(DelegatingLinter, self).__init__(logger)
        self._argv = argv
        self._cwd = cwd
        self._arc_autofix_script = arc_autofix_script

    def process_files(self, files):
        # We need to refer to all filenames relative to self._cwd.
        files = [f if os.path.isabs(f) else os.path.relpath(f, self._cwd)
                 for f in files]

        pipe = subprocess.Popen(
            self._argv + files,
            stdout=subprocess.PIPE,
            stderr=subprocess.PIPE,
            cwd=self._cwd)
        stdout, stderr = pipe.communicate()

        if stderr:
            raise RuntimeError("Unexpected stderr from linter:\n%s" % stderr)

        if stdout.strip() and self._arc_autofix_script:
            # Run through the autofix-script filter to modify each
            # lint-line to include arc fixing information.
            autofix_pipe = subprocess.Popen(
                self._arc_autofix_script,
                stdin=subprocess.PIPE,
                stdout=subprocess.PIPE,
                stderr=subprocess.PIPE,
                cwd=self._cwd)
            autofix_stdout, autofix_stderr = autofix_pipe.communicate(
                input=stdout)
            if autofix_stderr:
                raise RuntimeError("Unexpected stderr from autofixer:\n%s"
                                   % autofix_stderr)
            stdout = autofix_stdout

        lines = stdout.rstrip('\n').splitlines()
        for line in lines:
            self.report(line)
        return len(lines)


def _capture_stdout_of(fn, *args, **kwargs):
    """Call fn(*args, **kwargs) and return (fn_retval, fn_stdout_output_fp)."""
    try:
        orig_stdout = sys.stdout
        sys.stdout = io.StringIO()
        retval = fn(*args, **kwargs)
        sys.stdout.seek(0)    # so new read()/readlines() calls will return
        return (retval, sys.stdout)
    finally:
        sys.stdout = orig_stdout


class Flake8(Linter):
    """Linter for python.  process() processes one file."""
    GLOBAL_IGNORES = frozenset((
        'E266',  # too many leading '#' for block comment
        'E402',  # module level import not at top of file
        'W503',  # line break before binary operator
        'E731',  # do not assign a lambda expression
    ))

    def __init__(self, logger, propose_arc_fixes=False):
        super(Flake8, self).__init__(logger=logger)
        self._propose_arc_fixes = propose_arc_fixes
        # A map from filename of a file to lint, to the error codes that
        # we should ignore for this file.  We always ignore error codes
        # in GLOBAL_IGNORES, but each file can add more codes to ignore
        # via a `# pep8-disable` line in the file.
        self._files_to_ignored_errors = {}

    def _maybe_add_arc_fix(self, lintline, bad_line):
        """Optionally add a patch for arc lint to use for autofixing."""
        if not self._propose_arc_fixes:
            return lintline

        errcode = lintline.split(' ')[1]

        # expected 2 blank lines, found 1
        if errcode == 'E302':
            return lint_util.add_arc_fix_str(lintline, bad_line, '', '\n')

        # at least two spaces before inline comment
        if errcode == 'E261':
            return lint_util.add_arc_fix_str(lintline, bad_line, '', ' ')

        # module imported but not used
        if errcode == 'F401':
            return lint_util.add_arc_fix_str(lintline, bad_line,
                                             bad_line + '\n', '')

        return lintline

    def _process_one_line(self, lintline, bad_line, ignored_rules):
        """If line is an 'error', print it and return 1.  Else return 0.

        pep8 prints all errors to stdout.  But we want to ignore some
        'errors' that are ok for us but cannot be suppressed via pep8
        flags, such as lines marked with @Nolint.  To do this, we
        intercept stdin and remove these lines.

        Arguments:
           lintline: one line of the flake8 error-output
           bad_line: the line that the lintline is referring to
           ignored_rules: a list of rules (like 'E501') that will be
              ignored

        Returns:
           1 (indicating one error) if we print the error line, 0 else.
        """
        if _has_nolint(bad_line):
            return 0

        if any(rule in lintline for rule in ignored_rules):
            return 0

        # We allow lines to be arbitrarily long if they are urls,
        # since splitting urls at 80 columns can be annoying.
        if ('E501 line too long' in lintline and
                ('http://' in bad_line or 'https://' in bad_line)):
            return 0

        # We follow python convention of allowing an unused variable
        # if it's named '_' or starts with 'unused_'.
        if ('F841 local variable' in lintline and
            ("local variable '_'" in lintline or
             "local variable 'unused_" in lintline)):
            return 0

        # It's OK to redefine variables that are unused by convention.
        if ('F812 list comprehension redefines' in lintline and
            ("redefines '_'" in lintline or
             "redefines 'unused_" in lintline)):
            return 0

        # Get rid of some warnings too.
        if 'unable to detect undefined names' in lintline:
            return 0

        # An old nolint directive that's specific to imports.
        if ('@UnusedImport' in bad_line and
                'imported but unused' in lintline):   # F401
            return 0

        # OK, looks like it's a legitimate error.
        self.report(self._maybe_add_arc_fix(lintline, bad_line))

        return 1

    def _get_file_level_nolint_rules(self, contents_lines):
        """Get a list of rules disabled at the file-level.

        This allows us to upgrade linter without having to fix all the lint
        immediately.

        We check the first three lines (three to allow for a shebang, and a
        TODO to fix the lint) for a comment that looks like:
        # pep8-disable:E101,E102,W405
        where the part following the colon is a comma-separated list of rules
        to ignore in the file.  These must all start with E or W.
        """
        for line in contents_lines[:3]:
            match = re.search(r'pep8-disable:([\S]+)', line)
            if match:
                return {rule for rule in match.group(1).split(',')}

        return set()

    def process(self, f, contents_of_f):
        """Just collect files and their file-level nolint rules.

        This is called by the default process_files(), but in our case
        it just does some pre-processing.  The actual error-detection
        is done in process2(), below.
        """
        contents_lines = contents_of_f.splitlines(True)
        self._files_to_ignored_errors[f] = (
            self.GLOBAL_IGNORES |
            self._get_file_level_nolint_rules(contents_lines)
        )
        return 0    # we cannot create any errors

    def process2(self):
        linter = self     # because we override `self` inside Reporter
        num_errors = [0]  # in a list so we can mutate it

        class Reporter(flake8.formatting.default.Default):
            def beginning(self, filename):
                self.ignored_errors = linter._files_to_ignored_errors[filename]

            def show_source(self, error):
                return error.physical_line

            def write(self, line, source):
                num_errors[0] += linter._process_one_line(
                    line.strip(), source, self.ignored_errors)

        # We do not pass in any `exclude` parameter here, because we
        # don't want to override the default excludes for the parent
        # repo.  Instead, we filter out errors we want to ignore
        # in `_process_one_line`, above.
        style_guide = flake8.api.legacy.get_style_guide()
        style_guide.init_report(Reporter)
        style_guide.check_files(self._files_to_ignored_errors.keys())

        return num_errors[0]

    def process_files(self, files):
        """Print lint errors for a list of filenames and return error count."""
        # The first line calls process() to set things up, the second
        # calls process2() to actually do the processing.
        num_errors = super(Flake8, self).process_files(files)
        num_errors += self.process2()
        return num_errors


class CustomPythonLinter(Linter):
    """A linter for generic python errors that are not caught by flake8.

    This is a linter for general (as opposed to application-specific)
    python errors that are not caught by third-party linters.  We add
    those checks here.
    """
    def _bad_super(self, line):
        # We don't want this linter to fire on this line itself!
        return ('super(type(self)' in line or      # @Nolint
                'super(self.__class__' in line)    # @Nolint

    def process(self, f, contents_of_f):
        num_errors = 0
        for (linenum_minus_1, line) in enumerate(contents_of_f.splitlines()):
            if _has_nolint(line):
                continue

            if self._bad_super(line):
                # Canonical form: <file>:<line>[:<col>]: <E|W><code> <msg>
                self.report(('%s:%s: E999 first argument to super() must be '
                             'an explicit classname, not type(self)'
                             % (f, linenum_minus_1 + 1)))
                num_errors += 1

        return num_errors


class Git(Linter):
    """Complain if the file has git merge-conflict markers in it.

    git will merrily let you 'resolve' a file that still has merge
    conflict markers in it.  This lint check will hopefully catch
    that.
    """
    CAN_BE_BINARY_FILE = True

    # We don't check for ======= because it might legitimately be in
    # a file (for purposes other than as a git conflict marker).
    _MARKERS = (b'<' * 7, b'|' * 7, b'>' * 7)
    _MARKERS_RE = re.compile(br'^(%s)( |$)'
                             % b'|'.join(re.escape(m) for m in _MARKERS),
                             re.MULTILINE)

    def process(self, f, contents_of_f):
        # Ignore files that git thinks are binary; those don't ever
        # get merge conflict markers.  This is how we check, sez
        # http://stackoverflow.com/questions/6119956/how-to-determine-if-git-handles-a-file-as-binary-or-as-text:
        if b'\0' in contents_of_f[:8000]:
            return 0      # a binary file

        num_errors = 0
        for m in self._MARKERS_RE.finditer(contents_of_f):
            linenum = contents_of_f.count('\n', 0, m.start()) + 1
            self.report(('%s:%s:1: E1 git conflict marker "%s" found'
                         % (f, linenum, str(m.group(1), 'ascii'))))
            num_errors += 1
        return num_errors


class Eslint(Linter):
    """Linter for javascript.  process() processes one file.

    Arguments:
        config_path: the path of the eslintrc file
        logger: logger
        [exec_path]: the path of the eslint executable, uses khan-linter's
            copy of eslint if none is specified.
        [propose_arc_fixes]: whether or not to propose fixes to arc, defaults
            to False.
    """
    def __init__(self, config_path, logger,
                 exec_path=None,
                 propose_arc_fixes=False):
        super(Eslint, self).__init__(logger=logger)
        self._config_path = config_path
        self._exec_path = (
            exec_path or os.path.join(_CWD, 'node_modules', '.bin', 'eslint'))
        self._propose_arc_fixes = propose_arc_fixes

    def _maybe_add_arc_fix(self, lintline, bad_line):
        """Optionally add a patch for arc lint to use for autofixing."""
        if not self._propose_arc_fixes:
            return lintline

        (file_line_col, errcode, msg) = lintline.split(' ', 2)

        if errcode == 'Esemi':
            return lint_util.add_arc_fix_str(lintline, bad_line, '', ';')
        if errcode == 'Eno-extra-semi':
            return lint_util.add_arc_fix_str(lintline, bad_line, ';', '')
        if errcode == 'Ecomma-dangle':
            return lint_util.add_arc_fix_str(lintline, bad_line, '', ',')
        if errcode == 'Ecomma-spacing':
            return lint_util.add_arc_fix_str(lintline, bad_line, ',', ', ')
        if errcode == 'Espace-before-function-paren':
            return lint_util.add_arc_fix_str(lintline, bad_line,
                                             re.compile(r' +'), '')
        if errcode == 'Eprefer-const':
            return lint_util.add_arc_fix_str(lintline, bad_line,
                                             'let', 'const',
                                             search_backwards=True)

        if errcode == 'Ereact/jsx-closing-bracket-location':
            try:
                col = file_line_col.split(':')[2]
            except IndexError:
                col = None
            m = re.search(r'\(expected column (\d+)\)', msg)

            if col is not None and m is not None:
                spaces_to_add = int(m.group(1)) - int(col)
                if spaces_to_add > 0:
                    return lint_util.add_arc_fix_str(
                        lintline, bad_line, '', ' ' * spaces_to_add)
                else:
                    return lint_util.add_arc_fix_str(
                        lintline, bad_line, ' ' * -spaces_to_add, '',
                        search_backwards=True)

            # Also handle the case the \> should go on the next line
            m = re.search(r'\(expected column (\d+) on the next line\)', msg)
            if m:
                indent = int(m.group(1)) - 1
                if indent >= 0:
                    return lint_util.add_arc_fix_str(
                        lintline, bad_line, '', '\n' + ' ' * indent)

        if errcode == 'Eindent':
            m = re.search(r'Expected indentation of (\d+) space characters '
                          r'but found (\d+)',
                          msg)
            if m:
                spaces_to_add = int(m.group(1)) - int(m.group(2))
                if spaces_to_add > 0:
                    return lint_util.add_arc_fix_str(
                        lintline, bad_line, '', ' ' * spaces_to_add)
                else:
                    return lint_util.add_arc_fix_str(
                        lintline, bad_line, ' ' * -spaces_to_add, '',
                        search_backwards=True)

        if errcode in {'Ecomputed-property-spacing', 'Earray-bracket-spacing',
                       'Eobject-curly-spacing'}:
            search_backwards = 'space before' in lintline
            return lint_util.add_arc_fix_str(lintline, bad_line,
                                             re.compile(r' +'), '',
                                             search_backwards=search_backwards)

        if errcode == 'Espace-in-parens':
            try:
                col = int(file_line_col.split(':')[2]) - 2
            except IndexError:
                col = None

            if col is not None:
                paren = bad_line[col]
                search_backwards = {'(': False, ')': True}.get(paren)

                if search_backwards is not None:
                    return lint_util.add_arc_fix_str(
                        lintline, bad_line, re.compile(r' +'), '',
                        search_backwards=search_backwards)

        if errcode == 'Eprettier/prettier':
            ascii_lintline = self._ascii_prettier_string(lintline)

            insert = re.search(r'Insert `(.*?)`?$', msg)
            if insert:
                to_add = self._clean_prettier_string(insert.group(1))
                return lint_util.add_arc_fix_str(
                    ascii_lintline, bad_line, '',
                    to_add, limit_to_80=False)

            remove = re.search(r'Delete `(.*?)`?$', msg)
            if remove:
                return lint_util.add_arc_fix_str(
                    ascii_lintline, bad_line,
                    self._clean_prettier_string(remove.group(1)), '',
                    limit_to_80=False)

            replace = re.search(r'Replace `(.*?)` with `(.*?)`?$', msg)
            if replace:
                to_add = self._clean_prettier_string(replace.group(2))
                return lint_util.add_arc_fix_str(
                    ascii_lintline, bad_line,
                    self._clean_prettier_string(replace.group(1)),
                    to_add,
                    limit_to_80=False)

        return lintline

    def _ascii_prettier_string(self, prettier_string):
        return prettier_string.replace(u'·', ' ').replace(
            u'↹', '\\t').replace(u'⏎', '\\n')

    def _clean_prettier_string(self, prettier_string):
        return prettier_string.replace(u'·', ' ').replace(
            u'↹', '\t').replace(u'⏎', '\n')

    def _process_one_line(self, filename, output_line, contents_lines):
        """If line is an 'error', print it and return 1.  Else return 0.

        eslint prints all errors to stdout.  But we want to
        ignore some 'errors' that are ok for us, in particular ones
        that have been commented out with @Nolint.

        Arguments:
           filename: path to file being linted
           output_line: one line of the eslint error-output
           contents_lines: the contents of the file being linted,
              as a list of lines.

        Returns:
           1 (indicating one error) if we print the error line, 0 else.
        """
        # output_line is like:
        #   <file>:<line>:<col>: W<code> <message>
        # which is just what we need!
        bad_linenum = int(output_line.split(':', 2)[1])   # first line is '1'
        if 1 <= bad_linenum <= len(contents_lines):
            bad_line = contents_lines[bad_linenum - 1]     # convert to 0-index
        else:
            # If we can't figure out what line it's on (e.g. it's an error in
            # an empty file), try our best to report anyway.
            bad_line = ''

        # If the line has a nolint directive, ignore it.
        if _has_nolint(bad_line):
            return 0

        # Allow long lines in fixture files, which just hold test data.
        if (' Emax-len ' in output_line and
                filename.endswith(('.fixture.js', 'fixture.jsx'))):
            return 0

        # I don't know why it prints this.  Shrug.
        if 'File ignored because of your .eslintignore file' in output_line:
            return 0

        (file_line_col, errcode, msg) = output_line.split(' ', 2)

        err_type = errcode[1:]
        if err_type != "prettier/prettier":
            output_line += " (Mute with // eslint-disable-line %s)" % (
                err_type)

        self.report(self._maybe_add_arc_fix(output_line, bad_line))
        return 1

    def process(self, f, contents_of_f, eslint_lines):
        num_errors = 0
        contents_lines = contents_of_f.splitlines()  # need these for filtering
        for output_line in eslint_lines:
            num_errors += self._process_one_line(f, output_line,
                                                 contents_lines)
        return num_errors

    def _run_eslint(self, files):
        """Run eslint on the given files and returns stdout, sans header."""
        reporter_path = os.path.join(_CWD, 'eslint_reporter.js')
        assert os.path.isfile(self._exec_path), (
            "Error: eslint is missing from '%s'" % self._exec_path)

        subprocess_args = [self._exec_path, '--config', self._config_path,
                           '-f', reporter_path, '--no-color'] + files

        env = os.environ.copy()
        if 'NODE_PATH' in env:
            env['NODE_PATH'] += ':' + os.path.dirname(self._config_path)
        else:
            env['NODE_PATH'] = os.path.dirname(self._config_path)

        for _ in range(3):
            process = subprocess.Popen(
                subprocess_args,
                stdout=subprocess.PIPE,
                stderr=subprocess.PIPE,
                env=env)
            stdout, stderr = process.communicate()
            # eslint (or rather, the node process running it) is crashing
            # some small percentage of the time, for reasons we don't
            # understand.  Normally this is a segfault but sometimes it's a
            # SIGILL; I'm guessing it's jumping to some bad location.
            # (See INFRA-1000.)  Until we figure out how to fix
            # this, if we see a segfault, just retry a couple of times.
            # TODO(benkraft): If the segfault ever gets fixed, remove this
            # retry logic.
            if -process.returncode not in (signal.SIGSEGV, signal.SIGILL):
                break

        stdout, stderr = stdout.decode('utf-8'), stderr.decode('utf-8')

        # eslint prints out a warning about browserslist to stderr even
        # though it's just a warning.
        if stderr and not stderr.startswith("Browserslist:"):
            raise RuntimeError(
                "Unexpected stderr from linter (exited %s):\n%s\nstdout:\n%s"
                % (process.returncode, stderr, stdout))

        # Check for the "Lint results:" message outputted as the first line of
        # eslint_reporter.js. This helps us distinguish between two "failure"
        # cases: ESLint successfully linting but yielding errors, and ESLint
        # crashing.
        if not stdout.strip():
            raise RuntimeError("Expected stdout from linter (exited %s), "
                               "got none." % process.returncode)
        stdout_lines = stdout.splitlines()
        if stdout_lines[0].strip() != 'Lint results:':
            raise RuntimeError("Unexpected stdout from linter (exited %s):\n%s"
                               % (process.returncode, stdout))
        return stdout_lines[1:]

    def lint_files(self, files):
        """Execute a linter on a list of files and return the stdout for each.

        Arguments:
            exec_path: A path to the linter's executable
            files: A list of filenames
            extra_flags: (optional) A list of commandline flags to include in
                         the subprocess call

        Returns:
            dict of {f: stdout_lines} from filename to stdout as an array of
            stdout lines only containing files that had output; if there are
            no lint errors, an empty dict.
        """
        stdout_lines = []
        # We need to keep sum(|files|) less than about 250k for OS X's
        # commandline limit.  2000 files at a time should do that.
        for i in range(0, len(files), 2000):
            stdout_lines.extend(self._run_eslint(files[i:i + 2000]))

        # eslint_reporter specifies that errors are reported on
        # individual lines starting with "filename:line:col".  It
        # converts all filenames to an absolute path; we convert them
        # back to relpaths here.
        lint_lines = []
        for line in stdout_lines:
            parts = line.split(':', 1)
            if len(parts) != 2:
                raise RuntimeError("Unexpected stdout from linter:\n%s" %
                                   stdout_lines)
            lint_lines.append('%s:%s' % (os.path.relpath(parts[0]), parts[1]))

        get_filename = lambda line: line.split(':', 1)[0]
        lines = sorted(lint_lines, key=get_filename)
        output = {}
        for filename, flines in itertools.groupby(lines, get_filename):
            output[filename] = list(flines)

        return output

    def process_files(self, files):
        """Lint a series of files, and self.process() each with an error."""
        num_errors = 0
        file_to_lint_output = self.lint_files(files)
        for filename in files:
            if filename in file_to_lint_output:
                lintlines = file_to_lint_output[filename]
                try:
                    contents = self._read_file(filename)
                except Exception as why:
                    self.logger.warning("SKIPPING lint of %s: %s"
                                        % (filename, why))
                    num_errors += 1
                    continue
                num_errors += self.process(filename, contents, lintlines)
        return num_errors


def _indent_of(s):
    """Return the prefix of s that is whitespace."""
    return s[:len(s) - len(s.lstrip(" \t"))]


class GraphqlSchemaLint(Linter):
    """Linter for graphql SDL (schema) files.  process() processes one file."""
    def __init__(self, config_path, logger, propose_arc_fixes=False):
        super(GraphqlSchemaLint, self).__init__(logger=logger)
        self._config_path = config_path
        self._propose_arc_fixes = propose_arc_fixes

    def _maybe_add_arc_fix(self, lintline, bad_line,
                           line_before_bad_line, line_after_bad_line):
        """Optionally add a patch for arc lint to use for autofixing."""
        if not self._propose_arc_fixes:
            return lintline

        if 'should have a blank line before it' in lintline:
            return lint_util.add_arc_fix_str(
                lintline, bad_line, re.compile(r'^'), '\n',
                search_backwards=True, limit_to_80=False)

        if 'should use triple-quotes' in lintline:
            return lint_util.add_arc_fix_str(
                lintline, bad_line, '"', '"""', limit_to_80=False)

        if 'should not include a blank line' in lintline:
            return lint_util.add_arc_fix_str(
                lintline, bad_line, bad_line + '\n', '', limit_to_80=False)

        if 'should not put the leading triple-quote on its own line' in (
                lintline):
            # We also want to get rid of the indentation on the subsequent
            # line.
            return lint_util.add_arc_fix_str(
                lintline, bad_line,
                '"""\n%s' % _indent_of(line_after_bad_line), '"""',
                limit_to_80=False)

        if 'should put the leading triple-quote on its own line' in lintline:
            # We need to indent the new line that we add.  We use as much
            # indentation as bad_line has.
            return lint_util.add_arc_fix_str(
                lintline, bad_line, '"""', '"""\n%s' % _indent_of(bad_line),
                limit_to_80=False)

        if 'should not put the trailing triple-quote on its own line' in (
                lintline):
            # We need to get rid of the newline on the previous line,
            # plus the leading whitespace on this line.  That means,
            # from arc's point of view, the line being edited is
            # actually the *previous* line, so we need to munge lintline.
            (location, rest) = lintline.split(' ', 1)
            (fname, line, col, loc_rest) = location.split(':', 3)
            lintline = '%s:%s:%s:%s %s' % (fname, int(line) - 1, 1, loc_rest,
                                           rest)
            return lint_util.add_arc_fix_str(
                lintline, line_before_bad_line,
                '\n%s' % _indent_of(bad_line), '', limit_to_80=False)

        if 'should put the trailing triple-quote on its own line' in lintline:
            # We need to indent the new line same as bad_line.
            return lint_util.add_arc_fix_str(
                lintline, bad_line, '"""', '\n%s"""' % _indent_of(bad_line),
                limit_to_80=False)

        return lintline

    def _process_one_line(self, filename, output_line, contents_lines):
        """If line is no-linted, return 0.  Else, print it and return 1.

        Arguments:
           filename: path to file being linted
           output_line: one line of the eslint error-output
           contents_lines: the contents of the file being linted,
              as a list of lines.

        Returns:
           1 (indicating one error) if we print the error line, 0 else.
        """
        # output_line is like:
        #   stdin:<line>:<col> <message>
        # which is almost what we need!  We need to add a `:` and an error
        # code.  For now we use a generic one.
        # TODO(csilvers): rewrite the linter to use error codes everywhere,
        #                 so we don't have to parse error text.
        (_, bad_linenum, col_and_msg) = output_line.split(':', 2)
        (bad_colnum, msg) = col_and_msg.split(' ', 1)

        output_line = ('%s:%s:%s: Eschema %s'
                       % (filename, bad_linenum, bad_colnum, msg))

        bad_linenum = int(bad_linenum)
        if 1 <= bad_linenum <= len(contents_lines):
            bad_line = contents_lines[bad_linenum - 1]     # convert to 0-index
        else:
            # If we can't figure out what line it's on (e.g. it's an error in
            # an empty file), try our best to report anyway.
            bad_line = ''

        if 1 <= bad_linenum - 1 <= len(contents_lines):
            line_before_bad_line = contents_lines[bad_linenum - 2]
        else:
            line_before_bad_line = ''
        if 1 <= bad_linenum + 1 <= len(contents_lines):
            line_after_bad_line = contents_lines[bad_linenum]
        else:
            line_after_bad_line = ''

        # If the line has a nolint directive, ignore it.
        if _has_nolint(bad_line):
            return 0

        self.report(self._maybe_add_arc_fix(
            output_line, bad_line, line_before_bad_line, line_after_bad_line))
        return 1

    def _run_linter(self, contents_of_f):
        # In theory we can process all the schema files in one call to
        # the linter, but in practice we run afoul of the fact that
        # graphql-schema-linter is not federation-aware.  As a result,
        # when parsing multiple schema files it keeps complaining
        # about things like `Query is defined twice` (same for all
        # @external fields).  I'm hopeful that processing files one at
        # a time, there won't be any duplicate definitions.
        p = subprocess.Popen(
            [os.path.join(_CWD, 'node_modules/.bin/graphql-schema-linter'),
             '--config-directory=%s' % os.path.dirname(self._config_path),
             '--format=compact',
             '--stdin',
             ],
            stdin=subprocess.PIPE,
            stdout=subprocess.PIPE,
            stderr=subprocess.PIPE)

        (stdout, stderr) = p.communicate(input=contents_of_f.encode('utf-8'))
        (stdout, stderr) = (stdout.decode('utf-8'), stderr.decode('utf-8'))

        if stderr:
            raise RuntimeError(
                "Unexpected output from linter (rc %s):\n"
                "stderr:\n%s\nstdout:\n%s"
                % (p.returncode, stderr, stdout))

        return stdout

    def process(self, f, contents_of_f):
        num_lines = contents_of_f.count('\n')

        # It's likely the schema we're linting references types
        # defined in other schema files.  The linter needs those types
        # to be defined in order to be able to parse.  We append those
        # definitions to the end of our file-to-lint, but ignore any
        # lint errors in them (since the user didn't ask to lint those
        # types).  That's why we calculated num_lines above.
        #
        # Ideally, we'd just append the entire composed schema (well,
        # excepting the file we're linting), which is guaranteed to
        # define all the types we use.  But that runs into problems
        # with `@extends`; see
        #    https://github.com/cjoudrey/graphql-schema-linter/issues/210
        #
        # So instead we take a two-pronged approach:
        # 1) We find the `gqlgen.yml` file that belongs to this service and
        #   parse it to find out all the other schema files the service depends
        #   on. This matches what gqlgen does, and will not have the @extends
        #   problem since it's only for a single backend.
        # 2) We then try to run the linter and catch all "undefined
        #    type" errors.  We then add fake definitions for those
        #    types, and re-run the linter.
        # The only external symbols it's really important we define
        # correctly are interfaces, since our linter needs to know
        # what fields an interface defines.  Hopefully we never
        # extend an interface defined in a different service!

        # But first, let's define the directives that graphql uses.
        contents_of_f += """
        scalar _FieldSet
        directive @external on FIELD_DEFINITION
        directive @requires(fields: _FieldSet!) on FIELD_DEFINITION
        directive @provides(fields: _FieldSet!) on FIELD_DEFINITION
        directive @key(fields: _FieldSet!) on OBJECT | INTERFACE
        directive @extends on OBJECT | INTERFACE
        """
        # All schema files should live at the top level of a service, so we can
        # look for the current gqlgen.yml
        service_root = os.path.dirname(f)
        gqlgen_path = os.path.join(service_root, "gqlgen.yml")

        try:
            gqlgen_contents = yaml.safe_load(self._read_file(gqlgen_path))
            schema_files = [
                os.path.join(service_root, schema_file)
                for schema_file in gqlgen_contents["schema"]]
        except Exception:
            # If the gqlgen.yml file doesn't exist (for shared schemas) we
            # assume there are no related files we need.
            schema_files = []

        for other_f in schema_files:
            if other_f == f:
                continue
            # TODO(csilvers): cache these.
            try:
                contents_of_other_f = self._read_file(other_f)
                contents_of_f += '\n' + contents_of_other_f + '\n'
            except Exception:
                # We'll just fall back to the "define fake types".
                continue

        # The linter also complains if a schema file doesn't
        # have a (not-extending) Query, which is fine in
        # federation-land.  We add one if need be.
        if (contents_of_f.count("type Query") ==
                contents_of_f.count("extend type Query")):
            contents_of_f += '\ntype Query { dummyForLinting: String }\n'

        # We likewise need to add in a `@migrate` directive if one hasn't been
        # added for us, since we use this directive.
        # TODO(dhruv): Remove this section once D62244 lands and a few days
        # have gone by to allow folks to update old branches, definitely by
        # 2020/04/27.
        migrate_def = """
        directive @migrate(from: String!, state: String!) on FIELD_DEFINITION
        """
        if (contents_of_f.count("directive @migrate") == 0):
            contents_of_f += migrate_def

        stdout = self._run_linter(contents_of_f)
        num_errors = 0

        if not stdout.strip():
            # There are no errors to report. Return early to avoid all of the
            # text manipulation below.
            return num_errors

        # Remove descriptions and comments so that when we search for unknown
        # types in the schema we don't match free-form text that happens to
        # match the schema text we're looking for.
        #
        # Note that the removal of `#` comments isn't entirely correct since
        # `#` can appear inside a string, but the following regex is good
        # enough for our purposes.
        contents_without_comments = re.sub(
            r'""".*?"""', "", contents_of_f, flags=re.DOTALL)
        contents_without_comments = re.sub(
            r'#.*', '', contents_without_comments)

        # Now find undefined types and add them in.
        new_type_re = re.compile(
            r'(?:Unknown type|Cannot extend type) "([^"]*)"')
        added_types = set()
        for output_line in stdout.splitlines():
            m = new_type_re.search(output_line)
            if m and m.group(1) not in added_types:
                new_type = m.group(1)
                if (' implements %s ' % new_type) in contents_without_comments:
                    # e.g. "type Foo implements InterfaceInOtherFile { ... }"
                    # TODO(csilvers): It's unlikely Foo defines dummyForLinting
                    # so this will give an opaque error.  What should we do??
                    contents_of_f += (
                        '\ninterface %s { dummyForLinting: String }\n'
                        % new_type)
                elif (('%s)' % new_type) in contents_without_comments or
                      ('%s,' % new_type) in contents_without_comments):
                    # e.g. "myvar(param: InputInOtherFile): String"
                    contents_of_f += (
                        '\ninput %s { dummyForLinting: String }\n' % new_type)
                else:
                    # e.g. "myvar: TypeInOtherFile"
                    contents_of_f += (
                        '\ntype %s { dummyForLinting: String }\n' % new_type)
                added_types.add(new_type)
        if added_types:
            stdout = self._run_linter(contents_of_f)

        contents_lines = contents_of_f.splitlines()  # need these for filtering
        for output_line in stdout.splitlines():
            if not output_line:
                continue

            invalid_schema = 'invalid-graphql-schema' in output_line

            # Skip lint errors for the "fake" text we added. The one exception
            # is a schema validation error, which aborts the entire lint if it
            # occurs. We report those.
            (_, bad_linenum, _) = output_line.split(':', 2)
            if int(bad_linenum) > num_lines and not invalid_schema:
                continue

            num_errors += self._process_one_line(f, output_line,
                                                 contents_lines)

        return num_errors


class LessHint(Linter):
    """Linter for less."""
    def _process_one_line(self, filename, output_line, contents_lines):
        # output_line is like:
        #   <file>:<line>:<col>: W<code> <message>
        bad_linenum = int(output_line.split(':', 2)[1])   # first line is '1'
        if bad_linenum <= len(contents_lines):
            bad_line = contents_lines[bad_linenum - 1]     # convert to 0-index
            # If the line has a nolint directive, ignore it.
            if _has_nolint(bad_line):
                return 0

        self.report(output_line)
        return 1

    def process(self, f, contents_of_f, lesshint_lines):
        num_errors = 0
        contents_lines = contents_of_f.splitlines()  # need these for filtering
        for output_line in lesshint_lines:
            num_errors += self._process_one_line(f, output_line,
                                                 contents_lines)
        return num_errors

    def lint_files(self, files):
        """Execute a linter on a list of files and return the stdout for each.

        Returns:
            dict of {f: stdout_lines} from filename to stdout as an array of
            stdout lines only containing files that had output; if there are
            no lint errors, an empty dict.
        """
        exec_path = os.path.join(_CWD, 'node_modules', '.bin', 'lesshint')
        reporter_path = os.path.join(_CWD, 'lesshint_reporter.js')
        assert os.path.isfile(exec_path), (
            "Vendoring error: lesshint is missing from '%s'" % exec_path)

        subprocess_args = [exec_path, '--reporter', reporter_path] + files

        pipe = subprocess.Popen(
            subprocess_args,
            stdout=subprocess.PIPE,
            stderr=subprocess.PIPE)
        stdout, stderr = pipe.communicate()

        if stderr:
            raise RuntimeError("Unexpected stderr from lesshint:\n%s" % stderr)

        output = {}

        # lesshint_reporter specifies that errors are reported on individual
        # lines starting with "filename:line:col"
        get_filename = lambda line: line.split(':', 1)[0]
        lines = sorted(stdout.splitlines(), key=get_filename)
        for filename, flines in itertools.groupby(lines, get_filename):
            output[filename] = list(flines)

        return output

    def process_files(self, files):
        """Lint a series of files, and self.process() each with an error."""
        num_errors = 0
        file_to_lint_output = self.lint_files(files)
        for filename in files:
            if filename in file_to_lint_output:
                lintlines = file_to_lint_output[filename]
                try:
                    contents = self._read_file(filename)
                except Exception as why:
                    self.logger.warning("SKIPPING lint of %s: %s"
                                        % (filename, why))
                    num_errors += 1
                    continue
                num_errors += self.process(filename, contents, lintlines)
        return num_errors


class HtmlLinter(Linter):
    """Linter for html.  process() processes one file.

    The main thing we look for with html is that the static images
    are properly escaped using the |static_url filter.  This is
    applied only to files in the 'templates' directory.
    """
    def process(self, f, contents_of_f):
        if ('templates' + os.sep) in f:
            # s_c_r.lint_one_file() happily ignores @Nolint lines for us.
            errors = static_content_refs.lint_one_file(f, contents_of_f)
            for (fname, linenum, colnum, unused_endcol, msg) in errors:
                # Canonical form: <file>:<line>[:<col>]: <E|W><code> <msg>
                self.report('%s:%s:%s: E=static_url= %s'
                            % (fname, linenum, colnum, msg))
            return len(errors)
        else:
            return 0


class YamlLinter(Linter):
    """Linter for .yaml files.  process() processes one file.

    We just make sure the file has no syntax errors, and can be successfully
    loaded.
    """
    def process(self, f, contents_of_f):
        try:
            # We allow multiple documents within the same YAML file.
            # Since safe_load_all returns a generator, we have to make sure it
            # is properly unrolled.
            list(yaml.safe_load_all(contents_of_f))
            return 0
        except yaml.parser.ParserError as e:
            self.report(('%s:%s:%s: E=yaml= Error parsing yaml: %s %s'
                         % (f,
                            e.problem_mark.line + 1,  # yaml.Mark is 0-indexed
                            1,
                            e.problem, e.context)))
            return 1


class KtLint(Linter):
    """Linter for kotlin, using the vendored copy of `ktlint`.

    TODO(colin): add autofixing using `ktlint -F`
    """

    def _is_not_skipped(self, file, lint_err_lines):
        """For each lint error in the given file check if it's nolinted.

        Args:
            lint_err_lines: a list of (line (0-indexed), message) tuples
        Returns:
            a list of booleans, one per input, True if that lint error has
            not been skipped via `@Nolint`.
        """
        with open(file) as f:
            lines = f.readlines()
            line_count = len(lines) - 1
            # Cap the indexing at the max number of lines in the file
            return [not _has_nolint(lines[min(lint_err[0], line_count)])
                    for lint_err in lint_err_lines]

    def process_files(self, files):
        exec_path = os.path.abspath(os.path.join(_CWD, 'vendor', 'ktlint'))
        assert os.path.isfile(exec_path), (
            "Vendoring error: ktlint is missing from '%s'" % exec_path)

        version_info_pipe = subprocess.Popen(
            ['java', '-version'],
            stdout=subprocess.PIPE,
            stderr=subprocess.PIPE)
        # Apparently java version info is printed to stderr...
        _, version_info = version_info_pipe.communicate()
        version_re = r'\w+ version "(\d\.\d)'
        matchobj = re.search(version_re, version_info.decode('utf-8'))
        assert matchobj is not None, (
            "Unable to determine version of java for running ktlint.")
        version = matchobj.group(1)

        # Between java 8 and java 9, java changed its version numbering scheme
        # to go from 1.x.y to x.y.
        if version == '1.8':
            ktlint_command = [exec_path] + files
        else:
            raise AssertionError('Unsupported version of java, %s' % version)

        pipe = subprocess.Popen(
            ktlint_command,
            stdout=subprocess.PIPE,
            stderr=subprocess.PIPE)

        stdout, stderr = pipe.communicate()
        stdout, stderr = stdout.decode('utf-8'), stderr.decode('utf-8')

        if stderr:
            raise RuntimeError("Unexpected stderr from linter:\n%s" % stderr)

        num_errors = 0
        lint_by_file = {}
        for line in stdout.splitlines():
            # Lint line format is file:line:col:message
            # Message could contain ':' so only split up to 3 times
            parts = line.split(':', 3)
            if len(parts) != 4:
                raise RuntimeError("Unexpected stdout from linter:\n%s" %
                                   stdout)
            file, line_number, _, _ = parts

            lint_by_file.setdefault(file, [])
            lint_by_file[file].append((int(line_number) - 1, line))

        for file, lint in lint_by_file.items():
            for _, lint_err in itertools.compress(
                    lint, self._is_not_skipped(file, lint)):
                self.report(lint_err)
                num_errors += 1

        return num_errors


class GoLint(Linter):
    """Linter for Go, using the golangci-lint

    golangci-lint can enable multiple go linters, for instance `gofmt`,
    `golint` with their individual options.
    we use .golangci.yml, the config file, in each go git repo to
    config golangci.
    """
    def process_files(self, files):
        exec_path = os.path.abspath(os.path.join(
            _CWD, 'vendor', 'github.com', 'golangci', 'golangci-lint',
            'cmd', 'golangci-lint', 'main.go'))
        output_path = os.path.abspath(os.path.join(
            _CWD, 'bin', 'golangci-lint'))

        assert os.path.isfile(exec_path), (
            "Vendoring error: golangci-lint is missing from '%s'" % exec_path)

        # We can't just use go run, because we need to run the build in
        # khan-linter's go module, but the files under lint, and the caller's
        # working directory, may be in another go module.  So instead we build
        # in khan-linter, and then call the binary in caller's cwd.
        # TODO(benkraft): Only run `go build` if anything in the repo has
        # changed.  (Not a big deal, since it's pretty fast.)
        subprocess.check_call(['go', 'build', '-o', output_path, exec_path],
                              cwd=_CWD)

        # HACK: Sadly, while golangci-lint can accept files as arguments, it
        # doesn't handle them in a first-class way: among other things, they
        # must all be in the same package.  So we pass all the directories we
        # care about, and let golangci-lint lint the whole package (it would
        # probably need to compile the whole package anyway, so it's not a big
        # loss), and then discard the errors that aren't for files we asked
        # about.
        dirs = sorted({os.path.abspath(os.path.dirname(f)) for f in files})
        process = subprocess.Popen(
            ['xargs', '-0', output_path, 'run', '--out-format=json'],
            stdin=subprocess.PIPE,
            stdout=subprocess.PIPE,
            stderr=subprocess.PIPE)

        stdout, stderr = process.communicate(input='\0'.join(dirs))
        stdout, stderr = stdout.decode('utf-8'), stderr.decode('utf-8')

        # golangci-lint seems to exit 123 on errors, even if you tell it not to
        # (with --issues-exit-code).  So we just check stderr to see if
        # anything crashed.
        if stderr:
            raise RuntimeError("Unexpected stderr from linter:\n%s" % stderr)

        results = json.loads(stdout)
        num_errors = 0
        for issue in results['Issues'] or []:
            # The format doesn't seem to be documented, but here's a sample
            # issue:
            # {
            #   "FromLinter": "lll",
            #   "Text": "line is 111 characters",
            #   "SourceLines": ["<elided>"],
            #   "Replacement": null,
            #   "Pos": {
            #     "Filename": "resolver.go",
            #     "Offset": 0,
            #     "Line": 95,
            #     "Column": 0
            #   }
            # }
            # TODO(benkraft): If the linter provides a suggested replacement,
            # report that to arc.
            # TODO(benkraft): If we want to support @Nolint in go linters, add
            # a check for _has_nolint using issue["SourceLines] here.
            filename = issue["Pos"]["Filename"]
            if filename not in files:
                continue  # not a file we wanted to lint (see HACK above)

            lineno = issue["Pos"]["Line"]
            colno = issue["Pos"]["Column"]
            postext = "%s:%s" % (lineno, colno) if colno else str(lineno)
            # Format like golangci-lint's default text output
            msg = "%s:%s: E%s %s" % (
                filename, postext, issue["FromLinter"], issue["Text"])

            num_errors += 1
            self.report(msg)

        return num_errors