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From: | Jim Porter |
Subject: | bug#59469: Adding a simpler duplication of the issue |
Date: | Mon, 21 Nov 2022 20:56:16 -0800 |
On 11/21/2022 6:50 PM, Milan Zimmermann wrote:
A simpler duplication shows the issue is below.
[snip]
Same bug: After the call to non-elisp program, /usr/bin/gzip, a previously exported variable bbb (exported inside the block) is nullified.
I'm not entirely sure, but I have a suspicion that this is due to Eshell's deferred commands. Deferred commands tell Eshell to stop processing synchronously and yield to the rest of Emacs. It's a way of keeping long-running commands (e.g. external processes) from hanging the rest of Emacs.
Unfortunately, the logic to do this (see 'eshell-do-eval') was written before lexical binding was added to Emacs Lisp, and I think this is the cause of quite a few subtle bugs with Eshell command evaluation. Fixing that is bug#57635, which would leverage the generator.el internals to do this.
Of course, I could be wrong. This is reaching well past my comfort zone for Emacs Lisp, but this sure seems like an issue with 'eshell-do-eval'.
I'd certainly like to fix this one day, since it's blocking a few other things I want to do in Eshell, but I think it'll be a pretty big project.
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