Refactor Error formatting and handling

This allows us to handle --show-source in our formatters by default.

This also adds the physical line information to the Error class instead
of passing it to is_inline_ignored. This allows us to avoid using
linecache in our formatters.

flake8/formatting/base.py

@@ -55,8 +55,9 @@ class BaseFormatter(object):
     def handle(self, error):
         """Handle an error reported by Flake8.
 
-        This defaults to calling :meth:`format` and then :meth:`write`. To
-        extend how errors are handled, override this method.
+        This defaults to calling :meth:`format`, :meth:`format_source`, and
+        then :meth:`write`. To extend how errors are handled, override this
+        method.
 
         :param error:
             This will be an instance of :class:`~flake8.style_guide.Error`.
@@ -64,7 +65,8 @@ class BaseFormatter(object):
             flake8.style_guide.Error
         """
         line = self.format(error)
-        self.write(line)
+        source = self.format_source(error)
+        self.write(line, source)
 
     def format(self, error):
         """Format an error reported by Flake8.
@@ -83,7 +85,26 @@ class BaseFormatter(object):
         raise NotImplementedError('Subclass of BaseFormatter did not implement'
                                   ' format.')
 
-    def write(self, line):
+    def format_source(self, error):
+        """Format the physical line generating the error.
+
+        :param error:
+            This will be an instance of :class:`~flake8.style_guide.Error`.
+        :returns:
+            The formatted error string if the user wants to show the source.
+            If the user does not want to show the source, this will return
+            ``None``.
+        :rtype:
+            str
+        """
+        if not self.options.show_source:
+            return None
+        pointer = (' ' * error.column_number) + '^'
+        # Physical lines have a newline at the end, no need to add an extra
+        # one
+        return error.physical_line + pointer
+
+    def write(self, line, source):
         """Write the line either to the output file or stdout.
 
         This handles deciding whether to write to a file or print to standard
@@ -94,9 +115,14 @@ class BaseFormatter(object):
             The formatted string to print or write.
         """
         if self.output_fd is not None:
-            self.output_fd.write(line + self.newline)
+            write = self.output_fd.write
+            output_func = lambda line: write(line + self.newline)
         else:
-            print(line)
+            output_func = print
+
+        output_func(line)
+        if source:
+            output_func(source)
 
     def stop(self):
         """Clean up after reporting is finished."""

flake8/style_guide.py

@@ -36,11 +36,17 @@ class Decision(enum.Enum):
     Selected = 'selected error'
 
 
-Error = collections.namedtuple('Error', ['code',
-                                         'filename',
-                                         'line_number',
-                                         'column_number',
-                                         'text'])
+Error = collections.namedtuple(
+    'Error',
+    [
+        'code',
+        'filename',
+        'line_number',
+        'column_number',
+        'text',
+        'physical_line',
+    ],
+)
 
 
 class StyleGuide(object):
@@ -157,9 +163,10 @@ class StyleGuide(object):
             LOG.debug('"%s" will be "%s"', code, decision)
         return decision
 
-    def is_inline_ignored(self, error, physical_line=None):
+    def is_inline_ignored(self, error):
         # type: (Error) -> bool
         """Determine if an comment has been added to ignore this line."""
+        physical_line = error.physical_line
         # TODO(sigmavirus24): Determine how to handle stdin with linecache
         if self.options.disable_noqa:
             return False
@@ -191,9 +198,10 @@ class StyleGuide(object):
                      physical_line=None):
         # type: (str, str, int, int, str) -> NoneType
         """Handle an error reported by a check."""
-        error = Error(code, filename, line_number, column_number, text)
+        error = Error(code, filename, line_number, column_number, text,
+                      physical_line)
         if (self.should_report_error(error.code) is Decision.Selected and
-                self.is_inline_ignored(error, physical_line) is False):
+                self.is_inline_ignored(error) is False):
             self.formatter.handle(error)
             self.listener.notify(error.code, error)
 

tests/unit/test_style_guide.py

@@ -134,7 +134,8 @@ def test_is_inline_ignored(error_code, physical_line, expected_result):
     guide = style_guide.StyleGuide(create_options(select=['E', 'W', 'F']),
                                    listener_trie=None,
                                    formatter=None)
-    error = style_guide.Error(error_code, 'filename.py', 1, 1, 'error text')
+    error = style_guide.Error(error_code, 'filename.py', 1, 1, 'error text',
+                              physical_line)
 
     with mock.patch('linecache.getline', return_value=physical_line):
         assert guide.is_inline_ignored(error) is expected_result
@@ -145,7 +146,8 @@ def test_disable_is_inline_ignored():
     guide = style_guide.StyleGuide(create_options(disable_noqa=True),
                                    listener_trie=None,
                                    formatter=None)
-    error = style_guide.Error('E121', 'filename.py', 1, 1, 'error text')
+    error = style_guide.Error('E121', 'filename.py', 1, 1, 'error text',
+                              'line')
 
     with mock.patch('linecache.getline') as getline:
         assert guide.is_inline_ignored(error) is False
@@ -171,7 +173,8 @@ def test_handle_error_notifies_listeners(select_list, ignore_list, error_code):
 
     with mock.patch('linecache.getline', return_value=''):
         guide.handle_error(error_code, 'stdin', 1, 1, 'error found')
-    error = style_guide.Error(error_code, 'stdin', 1, 1, 'error found')
+    error = style_guide.Error(error_code, 'stdin', 1, 1, 'error found',
+                              None)
     listener_trie.notify.assert_called_once_with(error_code, error)
     formatter.handle.assert_called_once_with(error)