From 57e82688df3f36d023352e3d12435f36f51ee9ac Mon Sep 17 00:00:00 2001
From: Ian Cordasco <graffatcolmingov@gmail.com>
Date: Sat, 9 Jul 2016 20:21:26 -0500
Subject: [PATCH 1/2] Handle errors reported in empty files

Some plugins (e.g., flake8-future-import) report errors for empty
files. Those plugins default to reporting the line number as 1 which
caused earlier versions of Flake8 3.0 beta to crash on an IndexError

Closes #157
---
 src/flake8/formatting/base.py | 5 +++--
 src/flake8/processor.py       | 8 +++++++-
 2 files changed, 10 insertions(+), 3 deletions(-)

diff --git a/src/flake8/formatting/base.py b/src/flake8/formatting/base.py
index 4fda6f4..7c2e4b5 100644
--- a/src/flake8/formatting/base.py
+++ b/src/flake8/formatting/base.py
@@ -123,8 +123,9 @@ class BaseFormatter(object):
         :rtype:
             str
         """
-        if not self.options.show_source:
-            return None
+        if not self.options.show_source or error.physical_line is None:
+            return ''
+
         pointer = (' ' * error.column_number) + '^'
         # Physical lines have a newline at the end, no need to add an extra
         # one
diff --git a/src/flake8/processor.py b/src/flake8/processor.py
index 1824ed1..76c5512 100644
--- a/src/flake8/processor.py
+++ b/src/flake8/processor.py
@@ -250,7 +250,13 @@ class FileProcessor(object):
 
     def line_for(self, line_number):
         """Retrieve the physical line at the specified line number."""
-        return self.lines[line_number - 1]
+        adjusted_line_number = line_number - 1
+        # NOTE(sigmavirus24): Some plugins choose to report errors for empty
+        # files on Line 1. In those casese, we shouldn't bother trying to
+        # retrieve a physical line (since none exist).
+        if 0 <= adjusted_line_number < len(self.lines):
+            return self.lines[adjusted_line_number]
+        return None
 
     def next_line(self):
         """Get the next line from the list."""

From e977c6671a470d431ffe869069d95692e846d261 Mon Sep 17 00:00:00 2001
From: Ian Cordasco <graffatcolmingov@gmail.com>
Date: Sat, 9 Jul 2016 20:26:08 -0500
Subject: [PATCH 2/2] Update tests for errors with no physical line

---
 tests/unit/test_base_formatter.py | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/tests/unit/test_base_formatter.py b/tests/unit/test_base_formatter.py
index dc4a95c..f148806 100644
--- a/tests/unit/test_base_formatter.py
+++ b/tests/unit/test_base_formatter.py
@@ -51,7 +51,15 @@ def test_show_source_returns_nothing_when_not_showing_source():
     formatter = base.BaseFormatter(options(show_source=False))
     assert formatter.show_source(
         style_guide.Error('A000', 'file.py', 1, 1, 'error text', 'line')
-    ) is None
+    ) is ''
+
+
+def test_show_source_returns_nothing_when_there_is_source():
+    """Ensure we return nothing when there is no line."""
+    formatter = base.BaseFormatter(options(show_source=True))
+    assert formatter.show_source(
+        style_guide.Error('A000', 'file.py', 1, 1, 'error text', None)
+    ) is ''
 
 
 @pytest.mark.parametrize('line, column', [