Implement command completion in remote shells. (Bug#31704)

* doc/lispref/files.texi (Locating Files): Describe optional
argument REMOTE of `executable-find'.
(Magic File Names): Add `exec-path'.

* doc/lispref/processes.texi (Subprocess Creation): Describe
function `exec-path'.

* doc/misc/tramp.texi (Remote programs): Explain refresh of search
paths by `tramp-cleanup-this-connection'.

* etc/NEWS: Mention 'exec-path' and 'executable-find'.

* lisp/files.el (exec-path): New defun.
(executable-find): Add optional argument REMOTE.

* lisp/shell.el (shell-completion-vars): Set `comint-file-name-prefix'.
(shell--command-completion-data): Use `(exec-path)'.  (Bug#31704)

* lisp/net/ange-ftp.el (exec-path):
* lisp/net/tramp.el (tramp-file-name-for-operation):
* lisp/net/tramp-adb.el (tramp-adb-file-name-handler-alist):
* lisp/net/tramp-archive.el (tramp-archive-file-name-handler-alist):
* lisp/net/tramp-gvfs.el (tramp-gvfs-file-name-handler-alist):
* lisp/net/tramp-sh.el (tramp-sh-file-name-handler-alist):
* lisp/net/tramp-smb.el (tramp-smb-file-name-handler-alist)
<exec-path>: Add handler.

* lisp/net/tramp-adb.el (tramp-adb-handle-exec-path): New defun.
(tramp-adb-maybe-open-connection): Do not set "remote-path"
connection property.

* lisp/net/tramp-compat.el (tramp-compat-exec-path): New defun.

* lisp/net/tramp-sh.el (tramp-sh-handle-exec-path): New defun.

* lisp/net/tramp.el (tramp-eshell-directory-change): Use it.

* test/lisp/net/tramp-archive-tests.el
(tramp-archive-test38-make-nearby-temp-file)
(tramp-archive-test41-file-system-info)
(tramp-archive-test43-auto-load)
(tramp-archive-test43-delay-load): Rename.

* test/lisp/net/tramp-tests.el (tramp-test34-exec-path): New test.
(tramp-test36-make-auto-save-file-name)
(tramp-test37-find-backup-file-name)
(tramp-test38-make-nearby-temp-file)
(tramp-test39-special-characters)
(tramp-test39-special-characters-with-stat)
(tramp-test39-special-characters-with-perl)
(tramp-test39-special-characters-with-ls, tramp-test40-utf8)
(tramp-test40-utf8-with-stat, tramp-test40-utf8-with-perl)
(tramp-test40-utf8-with-ls, tramp-test41-file-system-info)
(tramp-test42-asynchronous-requests, tramp-test43-auto-load)
(tramp-test43-delay-load, tramp-test43-recursive-load)
(tramp-test43-remote-load-path, tramp-test44-unload): Rename.

8 files changed, 44 insertions, 25 deletions

diff --git a/lisp/net/ange-ftp.el b/lisp/net/ange-ftp.el
index cf9667ac628..2fc7ac251ec 100644
--- a/lisp/net/ange-ftp.el
+++ b/lisp/net/ange-ftp.el
@@ -4439,6 +4439,7 @@ NEWNAME should be the name to give the new compressed or uncompressed file.")
 (put 'process-file 'ange-ftp 'ange-ftp-process-file)
 (put 'start-file-process 'ange-ftp 'ignore)
 (put 'shell-command 'ange-ftp 'ange-ftp-shell-command)
+(put 'exec-path 'ange-ftp 'ignore)
 
 ;;; Define ways of getting at unmodified Emacs primitives,
 ;;; turning off our handler.
diff --git a/lisp/net/tramp-adb.el b/lisp/net/tramp-adb.el
index df2160770b1..7cb61adde80 100644
--- a/lisp/net/tramp-adb.el
+++ b/lisp/net/tramp-adb.el
@@ -107,6 +107,7 @@ It is used for TCP/IP devices."
      . tramp-adb-handle-directory-files-and-attributes)
     (dired-compress-file . ignore)
     (dired-uncache . tramp-handle-dired-uncache)
+    (exec-path . tramp-adb-handle-exec-path)
     (expand-file-name . tramp-adb-handle-expand-file-name)
     (file-accessible-directory-p . tramp-handle-file-accessible-directory-p)
     (file-acl . ignore)
@@ -1116,6 +1117,21 @@ PRESERVE-UID-GID and PRESERVE-EXTENDED-ATTRIBUTES are completely ignored."
 	  (tramp-flush-connection-property v "process-name")
 	  (tramp-flush-connection-property v "process-buffer"))))))
 
+(defun tramp-adb-handle-exec-path ()
+  "Like `exec-path' for Tramp files."
+  (append
+   (with-parsed-tramp-file-name default-directory nil
+     (with-tramp-connection-property v "remote-path"
+       (tramp-adb-send-command v "echo \\\"$PATH\\\"")
+       (split-string
+	(with-current-buffer (tramp-get-connection-buffer v)
+	  ;; Read the expression.
+	  (goto-char (point-min))
+	  (read (current-buffer)))
+	":" 'omit)))
+   ;; The equivalent to `exec-directory'.
+   `(,(file-local-name default-directory))))
+
 (defun tramp-adb-get-device (vec)
   "Return full host name from VEC to be used in shell execution.
 E.g. a host name \"192.168.1.1#5555\" returns \"192.168.1.1:5555\"
@@ -1340,18 +1356,6 @@ connection if a previous connection has died for some reason."
 		(tramp-error
 		 vec 'file-error "Cannot switch to user `%s'" user)))
 
-	    ;; Set "remote-path" connection property.  This is needed
-	    ;; for eshell.
-	    (tramp-adb-send-command vec "echo \\\"$PATH\\\"")
-	    (tramp-set-connection-property
-	     vec "remote-path"
-	     (split-string
-	      (with-current-buffer (tramp-get-connection-buffer vec)
-		;; Read the expression.
-		(goto-char (point-min))
-		(read (current-buffer)))
-	      ":" 'omit))
-
 	    ;; Set connection-local variables.
 	    (tramp-set-connection-local-variables vec)
 
diff --git a/lisp/net/tramp-archive.el b/lisp/net/tramp-archive.el
index 42c3d40c1bb..5d7562f707e 100644
--- a/lisp/net/tramp-archive.el
+++ b/lisp/net/tramp-archive.el
@@ -220,6 +220,7 @@ It must be supported by libarchive(3).")
      . tramp-handle-directory-files-and-attributes)
     (dired-compress-file . tramp-archive-handle-not-implemented)
     (dired-uncache . tramp-archive-handle-dired-uncache)
+    (exec-path . ignore)
     ;; `expand-file-name' performed by default handler.
     (file-accessible-directory-p . tramp-handle-file-accessible-directory-p)
     (file-acl . ignore)
diff --git a/lisp/net/tramp-compat.el b/lisp/net/tramp-compat.el
index aa0c99bf9cf..9af57fb0755 100644
--- a/lisp/net/tramp-compat.el
+++ b/lisp/net/tramp-compat.el
@@ -236,6 +236,17 @@ If NAME is a remote file name, the local part of NAME is unquoted."
 (defconst tramp-compat-use-url-tramp-p (fboundp 'temporary-file-directory)
   "Whether to use url-tramp.el.")
 
+;; `exec-path' is new in Emacs 27.1.
+(eval-and-compile
+  (if (fboundp 'exec-path)
+      (defalias 'tramp-compat-exec-path 'exec-path)
+    (defun tramp-compat-exec-path ()
+      "List of directories to search programs to run in remote subprocesses."
+      (let ((handler (find-file-name-handler default-directory 'exec-path)))
+	(if handler
+	    (funcall handler 'exec-path)
+	  exec-path)))))
+
 (add-hook 'tramp-unload-hook
 	  (lambda ()
 	    (unload-feature 'tramp-loaddefs 'force)
diff --git a/lisp/net/tramp-gvfs.el b/lisp/net/tramp-gvfs.el
index 87c0c796b69..a30d7ef7138 100644
--- a/lisp/net/tramp-gvfs.el
+++ b/lisp/net/tramp-gvfs.el
@@ -536,6 +536,7 @@ It has been changed in GVFS 1.14.")
      . tramp-handle-directory-files-and-attributes)
     (dired-compress-file . ignore)
     (dired-uncache . tramp-handle-dired-uncache)
+    (exec-path . ignore)
     (expand-file-name . tramp-gvfs-handle-expand-file-name)
     (file-accessible-directory-p . tramp-handle-file-accessible-directory-p)
     (file-acl . ignore)
diff --git a/lisp/net/tramp-sh.el b/lisp/net/tramp-sh.el
index 76dae9cea5e..0b3c12333f2 100644
--- a/lisp/net/tramp-sh.el
+++ b/lisp/net/tramp-sh.el
@@ -990,6 +990,7 @@ of command line.")
      . tramp-sh-handle-directory-files-and-attributes)
     (dired-compress-file . tramp-sh-handle-dired-compress-file)
     (dired-uncache . tramp-handle-dired-uncache)
+    (exec-path . tramp-sh-handle-exec-path)
     (expand-file-name . tramp-sh-handle-expand-file-name)
     (file-accessible-directory-p . tramp-handle-file-accessible-directory-p)
     (file-acl . tramp-sh-handle-file-acl)
@@ -3083,6 +3084,13 @@ the result will be a local, non-Tramp, file name."
 	  (keyboard-quit)
 	ret))))
 
+(defun tramp-sh-handle-exec-path ()
+  "Like `exec-path' for Tramp files."
+  (append
+   (tramp-get-remote-path (tramp-dissect-file-name default-directory))
+   ;; The equivalent to `exec-directory'.
+   `(,(file-local-name default-directory))))
+
 (defun tramp-sh-handle-file-local-copy (filename)
   "Like `file-local-copy' for Tramp files."
   (with-parsed-tramp-file-name filename nil
diff --git a/lisp/net/tramp-smb.el b/lisp/net/tramp-smb.el
index 0334f052a07..335f05cfce0 100644
--- a/lisp/net/tramp-smb.el
+++ b/lisp/net/tramp-smb.el
@@ -229,6 +229,7 @@ See `tramp-actions-before-shell' for more info.")
      . tramp-handle-directory-files-and-attributes)
     (dired-compress-file . ignore)
     (dired-uncache . tramp-handle-dired-uncache)
+    (exec-path . ignore)
     (expand-file-name . tramp-smb-handle-expand-file-name)
     (file-accessible-directory-p . tramp-handle-file-accessible-directory-p)
     (file-acl . tramp-smb-handle-file-acl)
diff --git a/lisp/net/tramp.el b/lisp/net/tramp.el
index 1d6e0146c4d..d56b09a604d 100644
--- a/lisp/net/tramp.el
+++ b/lisp/net/tramp.el
@@ -2163,7 +2163,9 @@ ARGS are the arguments OPERATION has been called with."
    ((member operation
 	    '(process-file shell-command start-file-process
 	      ;; Emacs 26+ only.
-	      make-nearby-temp-file temporary-file-directory))
+	      make-nearby-temp-file temporary-file-directory
+	      ;; Emacs 27+ only.
+	      exec-path))
     default-directory)
    ;; PROC.
    ((member operation
@@ -4616,19 +4618,9 @@ Only works for Bourne-like shells."
 ;; when `default-directory' points to another host.
 (defun tramp-eshell-directory-change ()
   "Set `eshell-path-env' to $PATH of the host related to `default-directory'."
+  ;; Remove last element of `(exec-path)', which is `exec-directory'.
   (setq eshell-path-env
-	(if (tramp-tramp-file-p default-directory)
-	    (with-parsed-tramp-file-name default-directory nil
-	      (mapconcat
-	       'identity
-	       (or
-		;; When `tramp-own-remote-path' is in `tramp-remote-path',
-		;; the remote path is only set in the session cache.
-		(tramp-get-connection-property
-		 (tramp-get-connection-process v) "remote-path" nil)
-		(tramp-get-connection-property v "remote-path" nil))
-	       ":"))
-	  (getenv "PATH"))))
+	(mapconcat 'identity (butlast (tramp-compat-exec-path)) ":")))
 
 (eval-after-load "esh-util"
   '(progn