Add a check for asserts on string literals

[anubh-v]

Steps

• Add yourself to CONTRIBUTORS if you are a new contributor.
• Add a ChangeLog entry describing what your PR does.
• If it's a new feature or an important bug fix, add a What's New entry in doc/whatsnew/<current release.rst>.
• Write a good description on what the PR does.

Description

This PR adds a warning for assert statements that have string literals as their first argument.
Such assert statements will never fail.

Type of Changes

	Type
✓	✨ New feature

Related Issue

Fixes #3284

[PCManticore]

Great stuff! Can you add a Changelog entry for this and some tests?

[coveralls]

Coverage decreased (-0.006%) to 89.877% when pulling 1fc127a on anubh-v:warn-assert-first-arg-is-string-literal into be87624 on PyCQA:master.

[coveralls]

Coverage increased (+0.002%) to 89.885% when pulling 8f91c81 on anubh-v:warn-assert-first-arg-is-string-literal into be87624 on PyCQA:master.

[anubh-v]

@PCManticore, is there any specific numbering to follow for the warning code? I have used W0129 for this new check, but it seems codes in the range W0110 - W0121 are also available.

[PCManticore]

@anubh-v To answer your question, the codes are usually tied to the checker, you cannot mix and match codes from one checker to another. Other than that, they should be unique so any code that's not taken should be good to go. And if your code was not unique, tests would have failed any way.

[PCManticore]

Thank you for the PR! 🎉