bug#47547: 28.0.50; [PATCH] Eshell cannot 'cd' in directory with 'eshell' as name

[Utkarsh Singh <utkarsh190601@gmail.com>]

Reproduce the error:

(setq eshell-cd-on-directory t) ; in-case you have changed the defaults

Invoke eshell and enter the following commands:

$ /usr/local/share/emacs/28.0.50/lisp/eshell
Read error: Is a directory, /usr/local/share/emacs/28.0.50/lisp/eshell

OR

$ mkdir /tmp/eshell
$ /tmp/eshell
Read error: Is a directory, /tmp/eshell/

So where is the problem?

Checking `eshell-interpreter-alist' value:
((eshell-visual-command-p . eshell-exec-visual)
 ((closure
   (t)
   (file _args)
    (string= (file-name-nondirectory file)
    "eshell"))
  . eshell/source)
 (#f(compiled-function
     (file args)
     #<bytecode -0x47e9576cc9960d2>)
    . eshell-dirs-substitute-cd))
    
We can see eshell is using `file-name-nondirectory' to source file which
leads to the read error.  I suggest to add one more check before
loading file from `eshell/source'. One example of such check is
`file-regular-p' check and hence I drafted this patch.

diff --git a/lisp/eshell/em-script.el b/lisp/eshell/em-script.el
index aecc48610f..6e6ae1229e 100644
--- a/lisp/eshell/em-script.el
+++ b/lisp/eshell/em-script.el
@@ -60,8 +60,9 @@ eshell-script-initialize
   "Initialize the script parsing code."
   (setq-local eshell-interpreter-alist
 	(cons (cons #'(lambda (file _args)
-                        (string= (file-name-nondirectory file)
-                                 "eshell"))
+                        (and (file-regular-p file)
+                             (string= (file-name-nondirectory file))
+                             "eshell"))
                     'eshell/source)
 	      eshell-interpreter-alist))
   (setq-local eshell-complex-commands
-- 
Utkarsh Singh
utkarshsingh.xyz