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benma / visual-regexp.el

A regexp/replace command for Emacs with interactive visual feedback
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Stops working after a while #51

Closed CyberShadow closed 5 years ago

CyberShadow commented 7 years ago

Invariantly, after Emacs has been running for a few hours, visual-regexp stops displaying live previews.

I haven't tracked down what exactly causes it to break.

I'm not sure how to debug this, so here's some screenshots for now:

Working

works-1 works-2

Broken

broken-1 broken-2

benma commented 7 years ago

I also experienced this, but only very rarely and the last time was a long time ago too. so I spent only relatively little time debugging it. I hope you have better luck getting to the bottom of this.

CyberShadow commented 7 years ago

Any ideas on what to look for? Any interesting variables' states to observe?

CyberShadow commented 6 years ago

I did some research after encountering this today, and compared the states/behavior of Emacs instances with a broken and working visual-regexp. Though I did not find what initially causes visual-regexp to break, I did find how its effect makes visual-regexp stops working:

The global value of after-change-functions becomes nil.

The documentation of after-change-functions says:

If an unhandled error happens in running these functions, the variable’s value remains nil. That prevents the error from happening repeatedly and making Emacs nonfunctional.

So, it looks like visual-regexp breaks when one of the hooks in after-change-functions (possibly but not necessarily vr--after-change) runs into an error.

The workaround to fix it is to run (add-hook 'after-change-functions 'vr--after-change) again.

One permanent workaround would be to move the add-hook call to the visual-regexp interactive commands, which would also work as a small optimization by deferring adding the hook until vr-replace is ignored. (Come to think of it, that hook should actually only be set for the minibuffer, not all buffers.) I'd like to figure out what causes after-change-functions to become nil though, as that breaks the remaining hooks too.

benma commented 5 years ago

Thanks a lot for investigating. I made a commit that implements your proposed workaround:

https://github.com/benma/visual-regexp.el/commit/3e3ed81a3cbadef1f1f4cb16f9112a58641d70ca

CyberShadow commented 4 years ago

I haven't encountered this problem since your fix. Thank you!