Improve handling of $PATH in Eshell for remote directories

* lisp/eshell/esh-util.el (eshell-path-env, eshell-parse-colon-path):
Make obsolete.
(eshell-path-env-list): New variable.
(eshell-connection-default-profile): New connection-local profile.
(eshell-get-path): Reimplement using 'eshell-path-env-list'; add
LITERAL-P argument.
(eshell-set-path): New function.

* lisp/eshell/esh-var.el (eshell-variable-aliases-list): Add entry for
$PATH.
(eshell-var-initialize): Add 'eshell-path-env-list' to
'eshell-subcommand-bindings'.

* lisp/eshell/esh-ext.el (eshell-search-path): Use 'file-name-concat'
instead of 'concat'.
(eshell/addpath): Use 'eshell-get-path' and 'eshell-set-path'.

* lisp/net/tramp-integration.el: Only apply Eshell hooks when
'eshell-path-env-list' is unbound.

* test/lisp/eshell/esh-var-tests.el
(esh-var-test/path-var/local-directory)
(esh-var-test/path-var/remote-directory, esh-var-test/path-var/set)
(esh-var-test/path-var/set-locally)
(esh-var-test/path-var-preserve-across-hosts): New tests.

* test/lisp/eshell/esh-ext-tests.el: New file.

* test/lisp/eshell/eshell-tests-helpers.el
(with-temp-eshell): Set 'eshell-last-dir-ring-file-name' to nil.
(eshell-tests-remote-accessible-p, eshell-last-input)
(eshell-last-output): New functions.
(eshell-match-output, eshell-match-output--explainer): Use
'eshell-last-input' and 'eshell-last-output'.

* doc/misc/eshell.texi (Variables): Document $PATH.

* etc/NEWS: Announce this change (bug#57556).

3 files changed, 70 insertions, 20 deletions

diff --git a/lisp/eshell/esh-ext.el b/lisp/eshell/esh-ext.el
index 98902fc6f23..d513d750d9d 100644
--- a/lisp/eshell/esh-ext.el
+++ b/lisp/eshell/esh-ext.el
@@ -77,7 +77,7 @@ but Eshell will be able to understand
     (let ((list (eshell-get-path))
           suffixes n1 n2 file)
       (while list
-        (setq n1 (concat (car list) name))
+        (setq n1 (file-name-concat (car list) name))
         (setq suffixes eshell-binary-suffixes)
         (while suffixes
           (setq n2 (concat n1 (car suffixes)))
@@ -239,17 +239,16 @@ causing the user to wonder if anything's really going on..."
      (?h "help" nil nil  "display this usage message")
      :usage "[-b] PATH
 Adds the given PATH to $PATH.")
-   (if args
-       (progn
-         (setq eshell-path-env (getenv "PATH")
-               args (mapconcat #'identity args path-separator)
-               eshell-path-env
-               (if prepend
-                   (concat args path-separator eshell-path-env)
-                 (concat eshell-path-env path-separator args)))
-         (setenv "PATH" eshell-path-env))
-     (dolist (dir (parse-colon-path (getenv "PATH")))
-       (eshell-printn dir)))))
+   (let ((path (eshell-get-path t)))
+     (if args
+         (progn
+           (setq path (if prepend
+                          (append args path)
+                        (append path args)))
+           (eshell-set-path path)
+           (string-join path (path-separator)))
+       (dolist (dir path)
+         (eshell-printn dir))))))
 
 (put 'eshell/addpath 'eshell-no-numeric-conversions t)
 (put 'eshell/addpath 'eshell-filename-arguments t)
diff --git a/lisp/eshell/esh-util.el b/lisp/eshell/esh-util.el
index 9258ca5e40e..9b464a0a137 100644
--- a/lisp/eshell/esh-util.el
+++ b/lisp/eshell/esh-util.el
@@ -249,17 +249,60 @@ trailing newlines removed.  Otherwise, this behaves as follows:
 It might be different from \(getenv \"PATH\"), when
 `default-directory' points to a remote host.")
 
-(defun eshell-get-path ()
+(make-obsolete-variable 'eshell-path-env 'eshell-get-path "29.1")
+
+(defvar-local eshell-path-env-list nil)
+
+(connection-local-set-profile-variables
+ 'eshell-connection-default-profile
+ '((eshell-path-env-list . nil)))
+
+(connection-local-set-profiles
+ '(:application eshell)
+ 'eshell-connection-default-profile)
+
+(defun eshell-get-path (&optional literal-p)
   "Return $PATH as a list.
-Add the current directory on MS-Windows."
-  (eshell-parse-colon-path
-   (if (eshell-under-windows-p)
-       (concat "." path-separator eshell-path-env)
-     eshell-path-env)))
+If LITERAL-P is nil, return each directory of the path as a full,
+possibly-remote file name; on MS-Windows, add the current
+directory as the first directory in the path as well.
+
+If LITERAL-P is non-nil, return the local part of each directory,
+as the $PATH was actually specified."
+  (with-connection-local-application-variables 'eshell
+    (let ((remote (file-remote-p default-directory))
+          (path
+           (or eshell-path-env-list
+               ;; If not already cached, get the path from
+               ;; `exec-path', removing the last element, which is
+               ;; `exec-directory'.
+               (setq-connection-local eshell-path-env-list
+                                      (butlast (exec-path))))))
+      (when (and (not literal-p)
+                 (not remote)
+                 (eshell-under-windows-p))
+        (push "." path))
+      (if (and remote (not literal-p))
+          (mapcar (lambda (x) (file-name-concat remote x)) path)
+        path))))
+
+(defun eshell-set-path (path)
+  "Set the Eshell $PATH to PATH.
+PATH can be either a list of directories or a string of
+directories separated by `path-separator'."
+  (with-connection-local-application-variables 'eshell
+    (setq-connection-local
+     eshell-path-env-list
+     (if (listp path)
+         path
+       ;; Don't use `parse-colon-path' here, since we don't want
+       ;; the additonal translations it does on each element.
+       (split-string path (path-separator))))))
 
 (defun eshell-parse-colon-path (path-env)
   "Split string with `parse-colon-path'.
 Prepend remote identification of `default-directory', if any."
+  (declare (obsolete nil "29.1"))
   (let ((remote (file-remote-p default-directory)))
     (if remote
         (mapcar
diff --git a/lisp/eshell/esh-var.el b/lisp/eshell/esh-var.el
index caf143e1a1a..57ea42f4933 100644
--- a/lisp/eshell/esh-var.el
+++ b/lisp/eshell/esh-var.el
@@ -156,7 +156,14 @@ if they are quoted with a backslash."
     ("LINES" ,(lambda () (window-body-height nil 'remap)) t t)
     ("INSIDE_EMACS" eshell-inside-emacs t)
 
-    ;; for eshell-cmd.el
+    ;; for esh-ext.el
+    ("PATH" (,(lambda () (string-join (eshell-get-path t) (path-separator)))
+             . ,(lambda (_ value)
+                  (eshell-set-path value)
+                  value))
+     t t)
+
+    ;; for esh-cmd.el
     ("_" ,(lambda (indices quoted)
             (if (not indices)
                 (car (last eshell-last-arguments))
@@ -249,7 +256,8 @@ copied (a.k.a. \"exported\") to the environment of created subprocesses."
   (setq-local eshell-subcommand-bindings
               (append
                '((process-environment (eshell-copy-environment))
-                 (eshell-variable-aliases-list eshell-variable-aliases-list))
+                 (eshell-variable-aliases-list eshell-variable-aliases-list)
+                 (eshell-path-env-list eshell-path-env-list))
                eshell-subcommand-bindings))
 
   (setq-local eshell-special-chars-inside-quoting