From 79311238f16854f0b661f799398bb5cb56d084d9 Mon Sep 17 00:00:00 2001
From: Anthony Sottile <asottile@umich.edu>
Date: Fri, 10 Sep 2021 06:11:36 -0700
Subject: [PATCH] don't rewrite %-format with width+s

---
 pyupgrade/_plugins/percent_format.py  | 5 +++--
 tests/features/percent_format_test.py | 5 +++--
 2 files changed, 6 insertions(+), 4 deletions(-)

diff --git a/pyupgrade/_plugins/percent_format.py b/pyupgrade/_plugins/percent_format.py
index 8dc2c762..1b0599df 100644
--- a/pyupgrade/_plugins/percent_format.py
+++ b/pyupgrade/_plugins/percent_format.py
@@ -128,8 +128,6 @@ def _handle_part(part: PercentFormat) -> str:
             if conversion == '%':
                 return s + '%'
             parts = [s, '{']
-            if width and conversion == 's' and not conversion_flag:
-                conversion_flag = '>'
             if conversion == 's':
                 conversion = ''
             if key:
@@ -276,6 +274,9 @@ def visit_BinOp(
                 # no equivalent in format
                 if conversion in {'a', 'r'} and nontrivial_fmt:
                     break
+                # %s with None and width is not supported
+                if width and conversion == 's':
+                    break
                 # all dict substitutions must be named
                 if isinstance(node.right, ast.Dict) and not key:
                     break
diff --git a/tests/features/percent_format_test.py b/tests/features/percent_format_test.py
index 57ca3c65..0d620ce0 100644
--- a/tests/features/percent_format_test.py
+++ b/tests/features/percent_format_test.py
@@ -158,6 +158,7 @@ def test_simplify_conversion_flag(s, expected):
         '"%4%" % ()',
         # no equivalent in format specifier
         '"%.2r" % (1.25)', '"%.2a" % (1.25)',
+        pytest.param('"%8s" % (None,)', id='unsafe width-string conversion'),
         # non-string mod
         'i % 3',
         # dict format but not keyed arguments
@@ -208,8 +209,8 @@ def test_percent_format_noop_if_bug_16806():
         ('"%s" % ("%s" % ("nested",),)', '"{}".format("{}".format("nested"))'),
         ('"%s%% percent" % (15,)', '"{}% percent".format(15)'),
         ('"%3f" % (15,)', '"{:3f}".format(15)'),
-        ('"%-5s" % ("hi",)', '"{:<5}".format("hi")'),
-        ('"%9s" % (5,)', '"{:>9}".format(5)'),
+        ('"%-5f" % (5,)', '"{:<5f}".format(5)'),
+        ('"%9f" % (5,)', '"{:9f}".format(5)'),
         ('"brace {} %s" % (1,)', '"brace {{}} {}".format(1)'),
         (
             '"%s" % (\n'