Let isort decide which config to use

isort will look for a configuration in pyproject.toml
when the TOML library is available.

flake8-isort has its own mechanism to look up an appropriate
configuration file and will pass its path on to isort.
Right now, flake8-isort doesn't consider pyproject.toml files as
configuration file candidates and will raise an error if there's
no other configuration file than the pyproject.toml.

Luckily, there's the parameter `--no-isort-config` to make flake8-isort
not stall when it cannot find a config file.
In this case, isort will not be instructed to look for a specific
configuration file by flake8-isort but instead look for it itself
(beginning from either the currently linted file path
or the current working directory).

This is great because it means that we can rely on isort
to figure out which config to use
and linting behavior between both libraries will be exactly the same.
The search for a configuration file can be removed from flake8-isort
and we get Pyproject.toml support for free.
The `--no-isort-config` option can be removed as well
because from now on it will always be the burden of isort
to figure out which config to use.

Related to gforcada#71
Closes gforcada#78

flake8_isort.py

@@ -1,17 +1,8 @@
 # -*- coding: utf-8 -*-
 from difflib import Differ
 from isort import SortImports
-from os.path import expanduser
 from testfixtures import OutputCapture
 
-import os
-
-
-try:
-    from configparser import ConfigParser as SafeConfigParser
-except ImportError:
-    from ConfigParser import SafeConfigParser
-
 
 class Flake8Isort(object):
     name = 'flake8_isort'
@@ -32,7 +23,6 @@ class Flake8Isort(object):
         'I005 isort found an unexpected missing import'
     )
 
-    config_file = None
     show_traceback = False
     stdin_display_name = None
 
@@ -43,12 +33,6 @@ def __init__(self, tree, filename, lines, search_current=True):
 
     @classmethod
     def add_options(cls, parser):
-        parser.add_option(
-            '--no-isort-config',
-            action='store_true',
-            parse_from_config=True,
-            help='Do not require explicit configuration to be found'
-        )
 
         parser.add_option(
             '--isort-show-traceback',
@@ -59,93 +43,27 @@ def add_options(cls, parser):
 
     @classmethod
     def parse_options(cls, options):
-        if options.no_isort_config is None:
-            cls.config_file = True
-        else:
-            cls.config_file = False
-
         cls.stdin_display_name = options.stdin_display_name
         cls.show_traceback = options.isort_show_traceback
 
     def run(self):
-        settings_file = self.search_isort_config()
-        if self.config_file and not settings_file:
-            yield 0, 0, self.no_config_msg, type(self)
+        if self.filename is not self.stdin_display_name:
+            file_path = self.filename
         else:
-            if self.filename is not self.stdin_display_name:
-                file_path = self.filename
-            else:
-                file_path = None
-            with OutputCapture() as buffer:
-                sort_result = SortImports(
-                    file_path=file_path,
-                    file_contents=''.join(self.lines),
-                    check=True,
-                    settings_path=settings_file,
-                    show_diff=True,
-                )
-            traceback = self._format_isort_output(buffer)
-
-            for line_num, message in self.sortimports_linenum_msg(sort_result):
-                if self.show_traceback:
-                    message += traceback
-                yield line_num, 0, message, type(self)
-
-    def search_isort_config(self):
-        # type: () -> Optional[str]  # noqa: F821
-        """Search for isort configuration all the way up to the root folder
-
-        Looks for ``.isort.cfg``, ``.editorconfig`` or ``[isort]`` section in
-        ``setup.cfg``, ``tox.ini``, or ``.flake8`` config files.
-        """
-        full_path = os.path.abspath(self.filename)
-        split_path = (os.path.dirname(full_path), True)
-        while split_path[1]:
-            config_on_file = self._search_config_on_path(split_path[0])
-            if config_on_file:
-                return config_on_file
-            split_path = os.path.split(split_path[0])
-
-        if self.search_current:
-            return self.search_isort_config_at_current()
-
-        # last attempt, check home folder
-        home = expanduser('~')
-        config_on_home = self._search_config_on_path(home)
-        if config_on_home:
-            return config_on_home
-
-        return None
-
-    def search_isort_config_at_current(self):
-        # type: () -> Optional[str]  # noqa: F821
-        """Search for isort configuration at current directory"""
-        return self._search_config_on_path(os.path.realpath('.'))
-
-    def _search_config_on_path(self, path):
-        # type: (str) -> Optional[str]  # noqa: F821
-        """Search for isort configuration files at the specifed path.
-
-        Args:
-            path: The path to search for config files on.
-
-        Return:
-            str: the isort config if found otherwise, None
-        """
-        for config_file in ('.isort.cfg', '.editorconfig'):
-            config_file_path = os.path.join(path, config_file)
-            if os.path.isfile(config_file_path):
-                return config_file_path
-
-        # Check for '[isort]' section in other configuration files.
-        for config_file in ('tox.ini', 'setup.cfg', '.flake8'):
-            config_file_path = os.path.join(path, config_file)
-            config = SafeConfigParser()
-            config.read(config_file_path)
-            if 'isort' in config.sections():
-                return config_file_path
-
-        return None
+            file_path = None
+        with OutputCapture() as buffer:
+            sort_result = SortImports(
+                file_path=file_path,
+                file_contents=''.join(self.lines),
+                check=True,
+                show_diff=True,
+            )
+        traceback = self._format_isort_output(buffer)
+
+        for line_num, message in self.sortimports_linenum_msg(sort_result):
+            if self.show_traceback:
+                message += traceback
+            yield line_num, 0, message, type(self)
 
     def sortimports_linenum_msg(self, sort_result):
         """Parses isort.SortImports for line number changes and message

run_tests.py

@@ -225,8 +225,7 @@ def test_isortcfg_found(self):
 
     def test_isortcfg_not_found(self):
         (file_path, lines) = self._given_a_file_in_test_dir(
-            'from sys import pid\n'
-            'import threading',
+            'from sys import pid, path',
             isort_config='force_single_line=True'
         )
         # remove the .isort.cfg file
@@ -239,33 +238,9 @@ def test_isortcfg_not_found(self):
             checker.config_file = True
             ret = list(checker.run())
             self.assertEqual(len(ret), 1)
-            self.assertEqual(ret[0][0], 0)
+            self.assertEqual(ret[0][0], 1)
             self.assertEqual(ret[0][1], 0)
-            self.assertTrue(ret[0][2].startswith('I002 '))
-
-    def test_default_option(self):
-        """By default a config file (.isort.cfg) is expected"""
-        (file_path, lines) = self._given_a_file_in_test_dir(
-            'from sys import pid\n'
-            'import threading\n',
-            isort_config='force_single_line=True'
-        )
-        with OutputCapture():
-            app = application.Application()
-            app.run([file_path, ])
-            self.assertTrue(Flake8Isort.config_file)
-
-    def test_config_file(self):
-        """Check that one can force to not look for a config file"""
-        (file_path, lines) = self._given_a_file_in_test_dir(
-            'from sys import pid\n'
-            'import threading\n',
-            isort_config='force_single_line=True'
-        )
-        with OutputCapture():
-            app = application.Application()
-            app.run(['--no-isort-config', file_path, ])
-            self.assertFalse(Flake8Isort.config_file)
+            self.assertTrue(ret[0][2].startswith('I001 '))
 
     def test_isort_formatted_output(self):
         options = collections.namedtuple(
@@ -294,7 +269,6 @@ def test_isort_formatted_output(self):
             self.assertEqual(ret[0][1], 0)
             self.assertIn(diff, ret[0][2])
 
-    @unittest.expectedFailure
     def test_isort_uses_pyproject_toml_if_available(self):
         (file_path, lines) = self._given_a_file_in_test_dir(
             'import os\n'