bug#59545: 29.0.50; Eshell fails to redirect output of sourced eshell file

[Jim Porter]

On 11/24/2022 7:49 AM, Milan Zimmermann wrote:
> Emacs 29 Eshell Bug: Sourcing 'redirect-echo.esh' and redirecting output
> to a file, results in the first echo string ('hello') showing in eshell,
> only the second ('there')(presumably because it is last) showing in the
> output file.

It turns out there's an even simpler way to reproduce this:

  ~ $ {echo hi; echo bye} > #<buf>
  hi  ;; Buffer "buf" now contains the string "bye".

Initially[1], I said that this was an issue with the implementation of 
'eshell-protect', but it turns out that it's actually an issue in an 
adjacent part of the Eshell I/O code. Specifically, every statement in 
Eshell gets its own set of default I/O handles, when it should actually 
inherit the handles from its parent. So in the example above, "echo hi" 
has the default I/O handles (pointing to the terminal), when its stdout 
handle should point to the buffer "buf".

Attached is a patch series to fix this, with a bunch of new tests. I 
also fixed a related issue where redirecting to /dev/null could clobber 
your other redirects. (There's *also* an issue that should be fixed for 
the release branch; I'll send that in a separate message.)

[1] https://lists.gnu.org/archive/html/emacs-devel/2022-11/msg01504.html

0001-Add-eshell-duplicate-handles-to-return-a-copy-of-fil.patch
Description: Text document

0002-Fix-handling-of-output-handles-in-nested-Eshell-form.patch
Description: Text document

0003-Simplify-handling-of-dev-null-redirection-in-Eshell.patch
Description: Text document