Add a new check, consider-using-join

Add a check `consider-using-in` for comparisons of a variable against
multiple values with "==" and "or"s instead of checking if the variable
is contained "in" a tuple of those values.

Close #1977

1 files changed, 13 insertions, 0 deletions

diff --git a/doc/whatsnew/2.0.rst b/doc/whatsnew/2.0.rst
index e6e57e793..946cb6cb2 100644
--- a/doc/whatsnew/2.0.rst
+++ b/doc/whatsnew/2.0.rst
@@ -16,6 +16,19 @@ Summary -- Release highlights
 New checkers
 ============
 
+* A new check was added, ``consider-using-in``.
+
+  This refactoring message is emitted when a variable is compared against multiple
+  values concatenated by ors instead of using the faster, more idiomatic "in" check.
+
+  .. code-block:: python
+
+    if variable == 1 or variable == 2 or variable == 3:  # bad
+        pass
+
+    if variable in (1, 2, 3):  # good
+        pass
+
 * A new check was added, ``consider-using-join``.
 
   This refactoring message is emitted when using a for loop over a iterable to join strings