Fix zero-indexed column numbering

We accidentally changed column numbering from one-indexed to
zero-indexed.

docs/source/release-notes/3.0.2.rst

@@ -3,6 +3,9 @@
 
 - Fix local config file discovery.  (See also `GitLab#181`_)
 
+- Fix indexing of column numbers. We accidentally were starting column indices
+  at 0 instead of 1.
+
 
 .. links
 .. _GitLab#181:

src/flake8/formatting/base.py

@@ -139,7 +139,9 @@ class BaseFormatter(object):
         if not self.options.show_source or error.physical_line is None:
             return ''
 
-        pointer = (' ' * error.column_number) + '^'
+        # Because column numbers are 1-indexed, we need to remove one to get
+        # the proper number of space characters.
+        pointer = (' ' * (error.column_number - 1)) + '^'
         # Physical lines have a newline at the end, no need to add an extra
         # one
         return error.physical_line + pointer

src/flake8/style_guide.py

@@ -258,7 +258,9 @@ class StyleGuide(object):
         :rtype:
             int
         """
-        error = Error(code, filename, line_number, column_number, text,
+        # NOTE(sigmavirus24): Apparently we're provided with 0-indexed column
+        # numbers so we have to offset that here.
+        error = Error(code, filename, line_number, column_number + 1, text,
                       physical_line)
         error_is_selected = (self.should_report_error(error.code) is
                              Decision.Selected)

tests/unit/test_base_formatter.py

@@ -73,7 +73,7 @@ def test_show_source_updates_physical_line_appropriately(line, column):
     error = style_guide.Error('A000', 'file.py', 1, column, 'error', line)
     output = formatter.show_source(error)
     _, pointer = output.rsplit('\n', 1)
-    assert pointer.count(' ') == column
+    assert pointer.count(' ') == (column - 1)
 
 
 def test_write_uses_an_output_file():

tests/unit/test_style_guide.py

@@ -176,7 +176,7 @@ def test_handle_error_notifies_listeners(select_list, ignore_list, error_code):
                                    formatter=formatter)
 
     with mock.patch('linecache.getline', return_value=''):
-        guide.handle_error(error_code, 'stdin', 1, 1, 'error found')
+        guide.handle_error(error_code, 'stdin', 1, 0, 'error found')
     error = style_guide.Error(error_code, 'stdin', 1, 1, 'error found',
                               None)
     listener_trie.notify.assert_called_once_with(error_code, error)