Add support for per-file ignores in config

This adds support for rules that ignore violation codes on a per-file
basis. This takes a similar functional approach to
https://github.com/snoack/flake8-per-file-ignores which allows for glob
patterns like the `--exclude` option.

Closes #156

6 files changed, 173 insertions, 5 deletions

diff --git a/src/flake8/__init__.py b/src/flake8/__init__.py
index 5f316c9..c15bf87 100644
--- a/src/flake8/__init__.py
+++ b/src/flake8/__init__.py
@@ -15,7 +15,7 @@ import sys
 LOG = logging.getLogger(__name__)
 LOG.addHandler(logging.NullHandler())
 
-__version__ = "3.6.0"
+__version__ = "3.7.0dev0"
 __version_info__ = tuple(
     int(i) for i in __version__.split(".") if i.isdigit()
 )
diff --git a/src/flake8/main/application.py b/src/flake8/main/application.py
index bd409d7..b86b3cc 100644
--- a/src/flake8/main/application.py
+++ b/src/flake8/main/application.py
@@ -65,8 +65,8 @@ class Application(object):
         self.formatter = None
         #: The :class:`flake8.plugins.notifier.Notifier` for listening plugins
         self.listener_trie = None
-        #: The :class:`flake8.style_guide.StyleGuide` built from the user's
-        #: options
+        #: The :class:`flake8.style_guide.StyleGuideManager` built from the
+        #: user's options
         self.guide = None
         #: The :class:`flake8.checker.Manager` that will handle running all of
         #: the checks selected by the user.
@@ -283,7 +283,7 @@ class Application(object):
         # type: () -> NoneType
         """Initialize our StyleGuide."""
         if self.guide is None:
-            self.guide = style_guide.StyleGuide(
+            self.guide = style_guide.StyleGuideManager(
                 self.options, self.listener_trie, self.formatter
             )
 
diff --git a/src/flake8/main/options.py b/src/flake8/main/options.py
index 73b3932..2aabab8 100644
--- a/src/flake8/main/options.py
+++ b/src/flake8/main/options.py
@@ -1,5 +1,6 @@
 """Contains the logic for all of the default options for Flake8."""
 from flake8 import defaults
+from flake8 import utils
 from flake8.main import debug
 from flake8.main import vcs
 
@@ -19,6 +20,7 @@ def register_default_options(option_manager):
     - ``--hang-closing``
     - ``--ignore``
     - ``--extend-ignore``
+    - ``--per-file-ignores``
     - ``--max-line-length``
     - ``--select``
     - ``--disable-noqa``
@@ -143,6 +145,18 @@ def register_default_options(option_manager):
     )
 
     add_option(
+        "--per-file-ignores",
+        parse_from_config=True,
+        comma_separated_list=True,
+        separator=utils.NEWLINE_SEPARATED_LIST_RE,
+        help="A pairing of filenames and violation codes that defines which "
+        "violations to ignore in a particular file. The filenames can be "
+        "specified in a manner similar to the ``--exclude`` option and the "
+        "violations work similarly to the ``--ignore`` and ``--select`` "
+        "options.",
+    )
+
+    add_option(
         "--max-line-length",
         type="int",
         metavar="n",
diff --git a/src/flake8/options/manager.py b/src/flake8/options/manager.py
index 3f4e883..7be4315 100644
--- a/src/flake8/options/manager.py
+++ b/src/flake8/options/manager.py
@@ -32,6 +32,7 @@ class Option(object):
         parse_from_config=False,
         comma_separated_list=False,
         normalize_paths=False,
+        separator=None,
     ):
         """Initialize an Option instance wrapping optparse.Option.
 
@@ -79,6 +80,8 @@ class Option(object):
         :param bool normalize_paths:
             Whether the option is expecting a path or list of paths and should
             attempt to normalize the paths to absolute paths.
+        :param separator:
+            The item that separates the "comma"-separated list.
         """
         self.short_option_name = short_option_name
         self.long_option_name = long_option_name
@@ -107,6 +110,7 @@ class Option(object):
         self.parse_from_config = parse_from_config
         self.comma_separated_list = comma_separated_list
         self.normalize_paths = normalize_paths
+        self.separator = separator or utils.COMMA_SEPARATED_LIST_RE
 
         self.config_name = None
         if parse_from_config:
diff --git a/src/flake8/style_guide.py b/src/flake8/style_guide.py
index 7565b00..42576e9 100644
--- a/src/flake8/style_guide.py
+++ b/src/flake8/style_guide.py
@@ -1,6 +1,7 @@
 """Implementation of the StyleGuide used by Flake8."""
 import collections
 import contextlib
+import copy
 import enum
 import functools
 import itertools
@@ -321,10 +322,122 @@ class DecisionEngine(object):
         return decision
 
 
+class StyleGuideManager(object):
+    """Manage multiple style guides for a single run."""
+
+    def __init__(self, options, listener_trie, formatter, decider=None):
+        """Initialize our StyleGuide.
+
+        .. todo:: Add parameter documentation.
+        """
+        self.options = options
+        self.listener = listener_trie
+        self.formatter = formatter
+        self.stats = statistics.Statistics()
+        self.decider = decider or DecisionEngine(options)
+        self.style_guides = []
+        self.default_style_guide = StyleGuide(
+            options, listener_trie, formatter, decider=decider
+        )
+        self.style_guides = list(
+            itertools.chain(
+                [self.default_style_guide],
+                self.populate_style_guides_with(options),
+            )
+        )
+
+    def populate_style_guides_with(self, options):
+        """Generate style guides from the per-file-ignores option.
+
+        :param options:
+            The original options parsed from the CLI and config file.
+        :type options:
+            :class:`~optparse.Values`
+        :returns:
+            A copy of the default style guide with overridden values.
+        :rtype:
+            :class:`~flake8.style_guide.StyleGuide`
+        """
+        for value in options.per_file_ignores:
+            filename, violations_str = value.split(":")
+            violations = utils.parse_comma_separated_list(violations_str)
+            yield self.default_style_guide.copy(
+                filename=filename, extend_ignore_with=violations
+            )
+
+    def style_guide_for(self, filename):
+        """Find the StyleGuide for the filename in particular."""
+        guides = sorted(
+            (g for g in self.style_guides if g.applies_to(filename)),
+            key=lambda g: len(g.filename or ""),
+        )
+        if len(guides) > 1:
+            return guides[-1]
+        return guides[0]
+
+    @contextlib.contextmanager
+    def processing_file(self, filename):
+        """Record the fact that we're processing the file's results."""
+        guide = self.style_guide_for(filename)
+        with guide.processing_file(filename):
+            yield guide
+
+    def handle_error(
+        self,
+        code,
+        filename,
+        line_number,
+        column_number,
+        text,
+        physical_line=None,
+    ):
+        # type: (str, str, int, int, str) -> int
+        """Handle an error reported by a check.
+
+        :param str code:
+            The error code found, e.g., E123.
+        :param str filename:
+            The file in which the error was found.
+        :param int line_number:
+            The line number (where counting starts at 1) at which the error
+            occurs.
+        :param int column_number:
+            The column number (where counting starts at 1) at which the error
+            occurs.
+        :param str text:
+            The text of the error message.
+        :param str physical_line:
+            The actual physical line causing the error.
+        :returns:
+            1 if the error was reported. 0 if it was ignored. This is to allow
+            for counting of the number of errors found that were not ignored.
+        :rtype:
+            int
+        """
+        guide = self.style_guide_for(filename)
+        return guide.handle_error(
+            code, filename, line_number, column_number, text, physical_line
+        )
+
+    def add_diff_ranges(self, diffinfo):
+        """Update the StyleGuides to filter out information not in the diff.
+
+        This provides information to the underlying StyleGuides so that only
+        the errors in the line number ranges are reported.
+
+        :param dict diffinfo:
+            Dictionary mapping filenames to sets of line number ranges.
+        """
+        for guide in self.style_guides.values():
+            guide.add_diff_ranges(diffinfo)
+
+
 class StyleGuide(object):
     """Manage a Flake8 user's style guide."""
 
-    def __init__(self, options, listener_trie, formatter, decider=None):
+    def __init__(
+        self, options, listener_trie, formatter, filename=None, decider=None
+    ):
         """Initialize our StyleGuide.
 
         .. todo:: Add parameter documentation.
@@ -334,8 +447,24 @@ class StyleGuide(object):
         self.formatter = formatter
         self.stats = statistics.Statistics()
         self.decider = decider or DecisionEngine(options)
+        self.filename = filename
+        if self.filename:
+            self.filename = utils.normalize_path(self.filename)
         self._parsed_diff = {}
 
+    def __repr__(self):
+        """Make it easier to debug which StyleGuide we're using."""
+        return "<StyleGuide [{}]>".format(self.filename)
+
+    def copy(self, filename=None, extend_ignore_with=None, **kwargs):
+        """Create a copy of this style guide with different values."""
+        filename = filename or self.filename
+        options = copy.copy(self.options)
+        options.ignore.extend(extend_ignore_with or [])
+        return StyleGuide(
+            options, self.listener, self.formatter, filename=filename
+        )
+
     @contextlib.contextmanager
     def processing_file(self, filename):
         """Record the fact that we're processing the file's results."""
@@ -343,6 +472,26 @@ class StyleGuide(object):
         yield self
         self.formatter.finished(filename)
 
+    def applies_to(self, filename):
+        """Check if this StyleGuide applies to the file.
+
+        :param str filename:
+            The name of the file with violations that we're potentially
+            applying this StyleGuide to.
+        :returns:
+            True if this applies, False otherwise
+        :rtype:
+            bool
+        """
+        if self.filename is None:
+            return True
+        normalized_filename = utils.normalize_path(filename)
+        return (
+            normalized_filename == self.filename
+            or utils.fnmatch(filename, self.filename)
+            or utils.fnmatch(normalized_filename, self.filename)
+        )
+
     def should_report_error(self, code):
         # type: (str) -> Decision
         """Determine if the error code should be reported or ignored.
diff --git a/src/flake8/utils.py b/src/flake8/utils.py
index a837577..e77998d 100644
--- a/src/flake8/utils.py
+++ b/src/flake8/utils.py
@@ -11,6 +11,7 @@ import tokenize
 
 DIFF_HUNK_REGEXP = re.compile(r"^@@ -\d+(?:,\d+)? \+(\d+)(?:,(\d+))? @@.*$")
 COMMA_SEPARATED_LIST_RE = re.compile(r"[,\s]")
+NEWLINE_SEPARATED_LIST_RE = re.compile(r"[\s]")
 LOCAL_PLUGIN_LIST_RE = re.compile(r"[,\t\n\r\f\v]")