From 769e198ab006c5d899c4a09f99c4908c547f180d Mon Sep 17 00:00:00 2001
From: Anders Kaseorg <anders@zulip.com>
Date: Sat, 13 Jun 2020 22:01:21 -0700
Subject: [PATCH] lint: Prohibit percent formatting on literal format strings.

Signed-off-by: Anders Kaseorg <anders@zulip.com>
---
 tools/semgrep.yml | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/tools/semgrep.yml b/tools/semgrep.yml
index fbe63de40f..5f4d2eafd8 100644
--- a/tools/semgrep.yml
+++ b/tools/semgrep.yml
@@ -116,3 +116,11 @@ rules:
               ...
     severity: ERROR
     message: "Guard mutable default with read-only type (Sequence, Mapping, AbstractSet)"
+
+  - id: percent-formatting
+    languages: [python]
+    pattern-either:
+      - pattern: '"..." % ...'
+      - pattern: '("...") % ...'
+    severity: ERROR
+    message: "Prefer f-strings or .format for string formatting"