bug#74550: eshell cannot set the environment variable PATH on Windows

[Siyuan Chen <chansey97@gmail.com>]

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Dear Jim,

It works, thanks.

However, this seems to be a global setting only. Is there any equivalent of
with-environment-variables for exec-path?

For example, with regular shell, I can do something like:

```
(defun shell1 ()
  (interactive)
  (let ((explicit-shell-file-name "cmdproxy")
        (current-prefix-arg 4))
    (with-environment-variables (("PATH" (concat "C:/env1" path-separator
(getenv "PATH"))))
      (call-interactively 'shell))
    ))

(defun shell2 ()
  (interactive)
  (let ((explicit-shell-file-name "cmdproxy")
        (current-prefix-arg 4))
    (with-environment-variables (("PATH" (concat "C:/env2" path-separator
(getenv "PATH"))))
      (call-interactively 'shell))
    ))
```

to create two *shell* buffers with different PATH "C:/env1" and "C:/env2".

How to do the same thing in eshell?

I have tried with the following code but it doesn't work as expected.

 ```
 (defun eshell1()
  (interactive)
  (let ((exec-path (cons "C:/env1" (copy-sequence exec-path)))
        (current-prefix-arg "new"))
    (call-interactively 'eshell)))
 ```

 ```
 (defun eshell2()
  (interactive)
  (let ((exec-path (cons "C:/env2" (copy-sequence exec-path)))
        (current-prefix-arg "new"))
    (call-interactively 'eshell)))
 ```

M-x eshell1 and echo $PATH

M-x eshell2 and echo $PATH

The result is that the eshell1 buffer can show C:/env1, but eshell2 can not.

Thanks.

Best regards,
Siyuan Chen

On Wed, Nov 27, 2024 at 5:14 AM Jim Porter <jporterbugs@gmail.com> wrote:

> On 11/26/2024 12:38 PM, Siyuan Chen wrote:
> > Reproduce steps:
> >
> > 1. Emacs -Q
> >
> > 2. M-x eval-expression `(setenv "PATH" (concat "C:/env" path-separator
> > (getenv "PATH")))`
> >
> > 3. M-x eshell
> >
> > 4. In the *eshell* window, type `echo $PATH`, but the path "C:/env"
> > doesn't show in the result.
>
> Thanks for the bug report. This is an intentionally-incompatible change
> in Eshell to improve behavior with remote systems via Tramp. Here's the
> relevant section from the Emacs 29 NEWS:
>
> > *** Eshell's PATH is now derived from 'exec-path'.
> > For consistency with remote connections, Eshell now uses 'exec-path'
> > to determine the execution path on the local or remote system, instead
> > of using the PATH environment variable directly.
>
> So instead, you want to do something like '(push "C:/env" exec-path)' in
> order to update the PATH in a way where Eshell sees it.
>
>

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