git blame lied to me: the 2020 bug fix hiding behind a 2023 refactor

Shyam — Sat, 24 Oct 2026 07:39:18 +0000

This line is in Flask's app.py:

self_ref = weakref.ref(self)

Looks over-engineered. Why not just self?

git blame says 2023

$ git blame -w -M -C -C -C -L355,355 src/flask/app.py
0ec7f713 (pgjones 2023-06-11)  self_ref = weakref.ref(self)

"Split the App and Blueprint into Sansio and IO parts." That commit only moved code. Blame tells you who last touched a line, not why it exists.

The real reason is from 2020

$ git log -S"weakref.ref(self)" --oneline
0ec7f713 Split the App and Blueprint into Sansio and IO parts
8efea0cc Break reference cycle created by default in Flask instances.

The weakref stops a memory leak (#3761). "Simplify" it and the leak is back. You'd only find this if you already suspected a story.

So I built Blot

Blot is a pre-commit hook that has read your git history. It warns when a commit:

removes a fix: edits a line a bug fix added
re-adds a bug: brings back a line a fix removed
forgets a related file: changes A but not B, when they always change together

Or ask about any line. It skips commits that only moved code:

$ blot why src/flask/app.py:355
  explained by  8efea0cc  2020-10-03  Break reference cycle ...  [bug fix]
  traced past   0ec7f713  2023-06-11  Split the App and Blueprint ...  [refactor]

Local, no AI, no account. Warns, never blocks.

Staying quiet was the hard part

My first version gave Django 26 warnings per 10 commits. So I replayed the last 500 commits of 5 repos, read every warning, and turned each noise pattern into a rule.

Repo	Before	After
Flask	1.96	0.10
Express	1.00	0.18
Django	26.30	1.29

The replays also found real moments, like Express reverting the CVE-2024-51999 security patch. Blot flagged it.

Try it

pip install blot-git
blot index
blot install-hook

Sym-jay / Blot

A pre-commit check that has read your project's history. Sora the slime warns when a change removes a fix, re-adds a fixed bug, or forgets a file that always changes too.

Blot

A pre-commit check that has read your project's history.

Meet Sora, the slime who remembers every fix.

Don't take down a fence until you know why it was put up.

Blot warns you before you commit when your change:

removes a fix: deletes or edits code that was added to fix a bug
re-adds a bug: brings back a line that a bug fix deliberately removed
forgets a related file: changes A but not B, when the two almost always change together

It runs locally, needs no account or AI, and stays quiet unless the history gives it a real reason to speak.

A real run on Flask. Plain git blame points to a 2023 commit that only moved this line; Blot traces past it to the 2020 fix that explains it. (Regenerate with python assets/demo/make_demo.py.)

Status: pre-alpha. Milestones M1 and M2 are…

View on GitHub

Pre-alpha. If it cries wolf on your repo, open an issue; that's exactly the feedback I need.

Built with help from Claude (of course, phew); every number here is from a real run.

DEV Community: Shyam