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, 161 insertions, 7 deletions

diff --git a/test/lisp/eshell/esh-ext-tests.el b/test/lisp/eshell/esh-ext-tests.el
new file mode 100644
index 00000000000..54191e9409e
--- /dev/null
+++ b/test/lisp/eshell/esh-ext-tests.el
@@ -0,0 +1,76 @@
+;;; esh-ext-tests.el --- esh-ext test suite  -*- lexical-binding:t -*-
+
+;; Copyright (C) 2022 Free Software Foundation, Inc.
+
+;; This file is part of GNU Emacs.
+
+;; GNU Emacs is free software: you can redistribute it and/or modify
+;; it under the terms of the GNU General Public License as published by
+;; the Free Software Foundation, either version 3 of the License, or
+;; (at your option) any later version.
+
+;; GNU Emacs is distributed in the hope that it will be useful,
+;; but WITHOUT ANY WARRANTY; without even the implied warranty of
+;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+;; GNU General Public License for more details.
+
+;; You should have received a copy of the GNU General Public License
+;; along with GNU Emacs.  If not, see <https://www.gnu.org/licenses/>.
+
+;;; Commentary:
+
+;; Tests for Eshell's external command handling.
+
+;;; Code:
+
+(require 'ert)
+(require 'esh-mode)
+(require 'esh-ext)
+(require 'eshell)
+
+(require 'eshell-tests-helpers
+         (expand-file-name "eshell-tests-helpers"
+                           (file-name-directory (or load-file-name
+                                                    default-directory))))
+
+;;; Tests:
+
+(ert-deftest esh-ext-test/addpath/end ()
+  "Test that \"addpath\" adds paths to the end of $PATH."
+  (with-temp-eshell
+   (let ((eshell-path-env-list '("/some/path" "/other/path"))
+         (expected-path (string-join '("/some/path" "/other/path" "/new/path"
+                                       "/new/path2")
+                                     (path-separator))))
+     (eshell-match-command-output "addpath /new/path /new/path2"
+                                  (concat expected-path "\n"))
+     (eshell-match-command-output "echo $PATH"
+                                  (concat expected-path "\n")))))
+
+(ert-deftest esh-ext-test/addpath/begin ()
+  "Test that \"addpath -b\" adds paths to the beginning of $PATH."
+  (with-temp-eshell
+   (let ((eshell-path-env-list '("/some/path" "/other/path"))
+         (expected-path (string-join '("/new/path" "/new/path2" "/some/path"
+                                       "/other/path")
+                                     (path-separator))))
+     (eshell-match-command-output "addpath -b /new/path /new/path2"
+                                  (concat expected-path "\n"))
+     (eshell-match-command-output "echo $PATH"
+                                  (concat expected-path "\n")))))
+
+(ert-deftest esh-ext-test/addpath/set-locally ()
+  "Test adding to the path temporarily in a subcommand."
+  (let* ((eshell-path-env-list '("/some/path" "/other/path"))
+         (original-path (string-join eshell-path-env-list (path-separator)))
+         (local-path (string-join (append eshell-path-env-list '("/new/path"))
+                                  (path-separator))))
+    (with-temp-eshell
+     (eshell-match-command-output
+      "{ addpath /new/path; env }"
+      (format "PATH=%s\n" (regexp-quote local-path)))
+     ;; After the last command, the previous $PATH value should be restored.
+     (eshell-match-command-output "echo $PATH"
+                                  (concat original-path "\n")))))
+
+;; esh-ext-tests.el ends here
diff --git a/test/lisp/eshell/esh-var-tests.el b/test/lisp/eshell/esh-var-tests.el
index a7ac52ed24a..d9b2585a327 100644
--- a/test/lisp/eshell/esh-var-tests.el
+++ b/test/lisp/eshell/esh-var-tests.el
@@ -23,6 +23,7 @@
 
 ;;; Code:
 
+(require 'tramp)
 (require 'ert)
 (require 'esh-mode)
 (require 'esh-var)
@@ -610,6 +611,65 @@ it, since the setter is nil."
    (eshell-match-command-output "echo $INSIDE_EMACS[, 1]"
                                 "eshell")))
 
+(ert-deftest esh-var-test/path-var/local-directory ()
+  "Test using $PATH in a local directory."
+  (let ((expected-path (string-join (eshell-get-path t) (path-separator))))
+    (with-temp-eshell
+     (eshell-match-command-output "echo $PATH" (regexp-quote expected-path)))))
+
+(ert-deftest esh-var-test/path-var/remote-directory ()
+  "Test using $PATH in a remote directory."
+  (skip-unless (eshell-tests-remote-accessible-p))
+  (let* ((default-directory ert-remote-temporary-file-directory)
+         (expected-path (string-join (eshell-get-path t) (path-separator))))
+    (with-temp-eshell
+     (eshell-match-command-output "echo $PATH" (regexp-quote expected-path)))))
+
+(ert-deftest esh-var-test/path-var/set ()
+  "Test setting $PATH."
+  (let* ((path-to-set-list '("/some/path" "/other/path"))
+         (path-to-set (string-join path-to-set-list (path-separator))))
+    (with-temp-eshell
+     (eshell-match-command-output (concat "set PATH " path-to-set)
+                                  (concat path-to-set "\n"))
+     (eshell-match-command-output "echo $PATH" (concat path-to-set "\n"))
+     (should (equal (eshell-get-path t) path-to-set-list)))))
+
+(ert-deftest esh-var-test/path-var/set-locally ()
+  "Test setting $PATH temporarily for a single command."
+  (let* ((path-to-set-list '("/some/path" "/other/path"))
+         (path-to-set (string-join path-to-set-list (path-separator))))
+    (with-temp-eshell
+     (eshell-match-command-output (concat "set PATH " path-to-set)
+                                  (concat path-to-set "\n"))
+     (eshell-match-command-output "PATH=/local/path env"
+                                  "PATH=/local/path\n")
+     ;; After the last command, the previous $PATH value should be restored.
+     (eshell-match-command-output "echo $PATH" (concat path-to-set "\n"))
+     (should (equal (eshell-get-path t) path-to-set-list)))))
+
+(ert-deftest esh-var-test/path-var/preserve-across-hosts ()
+  "Test that $PATH can be set independently on multiple hosts."
+  (let ((local-directory default-directory)
+        local-path remote-path)
+    (with-temp-eshell
+     ;; Set the $PATH on localhost.
+     (eshell-insert-command "set PATH /local/path")
+     (setq local-path (eshell-last-output))
+     ;; `cd' to a remote host and set the $PATH there too.
+     (eshell-insert-command
+      (format "cd %s" ert-remote-temporary-file-directory))
+     (eshell-insert-command "set PATH /remote/path")
+     (setq remote-path (eshell-last-output))
+     ;; Return to localhost and check that $PATH is the value we set
+     ;; originally.
+     (eshell-insert-command (format "cd %s" local-directory))
+     (eshell-match-command-output "echo $PATH" (regexp-quote local-path))
+     ;; ... and do the same for the remote host.
+     (eshell-insert-command
+      (format "cd %s" ert-remote-temporary-file-directory))
+     (eshell-match-command-output "echo $PATH" (regexp-quote remote-path)))))
+
 (ert-deftest esh-var-test/last-status-var-lisp-command ()
   "Test using the \"last exit status\" ($?) variable with a Lisp command"
   (with-temp-eshell
diff --git a/test/lisp/eshell/eshell-tests-helpers.el b/test/lisp/eshell/eshell-tests-helpers.el
index e713e162ad0..1d9674070c0 100644
--- a/test/lisp/eshell/eshell-tests-helpers.el
+++ b/test/lisp/eshell/eshell-tests-helpers.el
@@ -31,11 +31,22 @@
 (require 'eshell)
 
 (defvar eshell-history-file-name nil)
+(defvar eshell-last-dir-ring-file-name nil)
 
 (defvar eshell-test--max-subprocess-time 5
   "The maximum amount of time to wait for a subprocess to finish, in seconds.
 See `eshell-wait-for-subprocess'.")
 
+(defun eshell-tests-remote-accessible-p ()
+  "Return if a test involving remote files can proceed.
+If using this function, be sure to load `tramp' near the
+beginning of the test file."
+  (ignore-errors
+    (and
+     (file-remote-p ert-remote-temporary-file-directory)
+     (file-directory-p ert-remote-temporary-file-directory)
+     (file-writable-p ert-remote-temporary-file-directory))))
+
 (defmacro with-temp-eshell (&rest body)
   "Evaluate BODY in a temporary Eshell buffer."
   `(save-current-buffer
@@ -44,6 +55,7 @@ See `eshell-wait-for-subprocess'.")
               ;; back on $HISTFILE.
               (process-environment (cons "HISTFILE" process-environment))
               (eshell-history-file-name nil)
+              (eshell-last-dir-ring-file-name nil)
               (eshell-buffer (eshell t)))
          (unwind-protect
              (with-current-buffer eshell-buffer
@@ -83,19 +95,25 @@ After inserting, call FUNC.  If FUNC is nil, instead call
   (insert-and-inherit command)
   (funcall (or func 'eshell-send-input)))
 
+(defun eshell-last-input ()
+  "Return the input of the last Eshell command."
+  (buffer-substring-no-properties
+   eshell-last-input-start eshell-last-input-end))
+
+(defun eshell-last-output ()
+  "Return the output of the last Eshell command."
+  (buffer-substring-no-properties
+   (eshell-beginning-of-output) (eshell-end-of-output)))
+
 (defun eshell-match-output (regexp)
   "Test whether the output of the last command matches REGEXP."
-  (string-match-p
-    regexp (buffer-substring-no-properties
-            (eshell-beginning-of-output) (eshell-end-of-output))))
+  (string-match-p regexp (eshell-last-output)))
 
 (defun eshell-match-output--explainer (regexp)
   "Explain the result of `eshell-match-output'."
   `(mismatched-output
-    (command ,(buffer-substring-no-properties
-               eshell-last-input-start eshell-last-input-end))
-    (output ,(buffer-substring-no-properties
-              (eshell-beginning-of-output) (eshell-end-of-output)))
+    (command ,(eshell-last-input))
+    (output ,(eshell-last-output))
     (regexp ,regexp)))
 
 (put 'eshell-match-output 'ert-explainer #'eshell-match-output--explainer)