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.

16 files changed, 175 insertions, 74 deletions

diff --git a/doc/lispref/files.texi b/doc/lispref/files.texi
index f4678ddd846..068cf054437 100644
--- a/doc/lispref/files.texi
+++ b/doc/lispref/files.texi
@@ -1567,13 +1567,16 @@ For compatibility, @var{predicate} can also be one of the symbols
 a list of one or more of these symbols.
 @end defun
 
-@defun executable-find program
+@defun executable-find program &optional remote
 This function searches for the executable file of the named
 @var{program} and returns the absolute file name of the executable,
 including its file-name extensions, if any.  It returns @code{nil} if
-the file is not found.  The functions searches in all the directories
+the file is not found.  The function searches in all the directories
 in @code{exec-path}, and tries all the file-name extensions in
 @code{exec-suffixes} (@pxref{Subprocess Creation}).
+
+If @var{remote} is non-@code{nil}, and @code{default-directory} is a
+remote directory, @var{program} is searched on the respective remote host.
 @end defun
 
 @node Changing Files
@@ -3137,8 +3140,8 @@ first, before handlers for jobs such as remote file access.
 @code{directory-file-name},
 @code{directory-files},
 @code{directory-files-and-attributes},
-@code{dired-compress-file}, @code{dired-uncache},@*
-@code{expand-file-name},
+@code{dired-compress-file}, @code{dired-uncache},
+@code{exec-path}, @code{expand-file-name},@*
 @code{file-accessible-directory-p},
 @code{file-acl},
 @code{file-attributes},
@@ -3195,7 +3198,7 @@ first, before handlers for jobs such as remote file access.
 @code{directory-files},
 @code{directory-files-and-at@discretionary{}{}{}tributes},
 @code{dired-compress-file}, @code{dired-uncache},
-@code{expand-file-name},
+@code{exec-path}, @code{expand-file-name},
 @code{file-accessible-direc@discretionary{}{}{}tory-p},
 @code{file-acl},
 @code{file-attributes},
diff --git a/doc/lispref/processes.texi b/doc/lispref/processes.texi
index 3e26f577982..f78d8485e4e 100644
--- a/doc/lispref/processes.texi
+++ b/doc/lispref/processes.texi
@@ -177,6 +177,14 @@ before starting Emacs.  Trying to modify @code{exec-path}
 independently of @env{PATH} can lead to confusing results.
 @end defopt
 
+@defun exec-path
+The function @code{exec-path} is an extension of the respective
+variable.  If @code{default-directory} indicates a remote directory,
+it returns a list of directories used for searching programs on the
+respective remote host.  In case of a local @code{default-directory},
+the function returns just the value of the variable @code{exec-path}.
+@end defun
+
 @node Shell Arguments
 @section Shell Arguments
 @cindex arguments for shell commands
diff --git a/doc/misc/tramp.texi b/doc/misc/tramp.texi
index 420fef7164c..a9de1fddc66 100644
--- a/doc/misc/tramp.texi
+++ b/doc/misc/tramp.texi
@@ -1816,9 +1816,9 @@ shell supports the login argument @samp{-l}.
 @end defopt
 
 When remote search paths are changed, local @value{tramp} caches must
-be recomputed.  To force @value{tramp} to recompute afresh, exit
-Emacs, remove the persistent file (@pxref{Connection caching}), and
-restart Emacs.
+be recomputed.  To force @value{tramp} to recompute afresh, call
+@kbd{M-x tramp-cleanup-this-connection @key{RET}} or friends
+(@pxref{Cleanup remote connections}).
 
 
 @node Remote shell setup
diff --git a/etc/NEWS b/etc/NEWS
index 632627b241d..709c446849b 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -145,6 +145,14 @@ regular expression was previously invalid, but is now accepted:
 ---
 ** The German prefix and postfix input methods now support Capital sharp S.
 
++++
+** The new function 'exec-path' returns a directory list from a remote host.
+
++++
+** Function 'executable-find' supports an optional argument REMOTE.
+This triggers to search a program name on the remote host indicated by
+'default-directory'.
+
 
 * Editing Changes in Emacs 27.1
 
@@ -436,7 +444,6 @@ It can be used to set any buffer as the next one to be used by
 This means that pressing C-M-SPACE now selects the entire tree by
 default, and not just the opening element.
 
-
 ** Eshell
 
 ---
@@ -454,11 +461,15 @@ To restore the old behavior, use
 Previously eshell/kill would fail if provided a kill signal to send to the
 process.  It now accepts signals specified either by name or by its number.
 
+** Shell
+
+---
+*** Program name completion inside remote shells works now as expected.
+
 ** Pcomplete
 *** The function 'pcomplete-uniquify-list' has been renamed from
 'pcomplete-uniqify-list'.
 
-
 ** Auth-source
 
 ---
@@ -755,7 +766,6 @@ will be chosen even if you have an entry for image/* in your
 overrides all system and Emacs-provided defaults.  To get the old
 method back, set 'mailcap-prefer-mailcap-viewers' to nil.
 
-
 ** URL
 
 *** The file: handler no longer looks for index.html in directories if
@@ -763,14 +773,12 @@ you ask it for a file:///dir URL.  Since this is a low-level library,
 such decisions (if they are to be made at all) are left to
 higher-level functions.
 
-
 ** image-mode
 
 *** image-mode started using ImageMagick by default for all images
 some years back.  It now respects 'imagemagick-types-inhibit' as a way
 to disable that.
 
-
 +++
 ** The new function 'read-answer' accepts either long or short answers
 depending on the new customizable variable 'read-answer-short'.
diff --git a/lisp/files.el b/lisp/files.el
index c4a68d04407..d0804b000a6 100644
--- a/lisp/files.el
+++ b/lisp/files.el
@@ -1024,13 +1024,33 @@ customize the variable `user-emacs-directory-warning'."
                                         errtype user-emacs-directory)))))
        bestname))))
 
+(defun exec-path ()
+  "List of directories to search programs to run in remote subprocesses.
+The remote host is identified by `default-directory'.  For remote
+hosts which do not support subprocesses, this returns `nil'.
+If `default-directory' is a local directory, the value of the variable
+`exec-path' is returned."
+  (let ((handler (find-file-name-handler default-directory 'exec-path)))
+    (if handler
+        (funcall handler 'exec-path)
+      exec-path)))
 
-(defun executable-find (command)
+(defun executable-find (command &optional remote)
   "Search for COMMAND in `exec-path' and return the absolute file name.
-Return nil if COMMAND is not found anywhere in `exec-path'."
-  ;; Use 1 rather than file-executable-p to better match the behavior of
-  ;; call-process.
-  (locate-file command exec-path exec-suffixes 1))
+Return nil if COMMAND is not found anywhere in `exec-path'.  If
+REMOTE is non-nil, search on the remote host indicated by
+`default-directory' instead."
+  (if (and remote (file-remote-p default-directory))
+      (let ((res (locate-file
+                  command
+                  (mapcar
+                   (lambda (x) (concat (file-remote-p default-directory) x))
+                   (exec-path))
+                  exec-suffixes 'file-executable-p)))
+        (when (stringp res) (file-local-name res)))
+    ;; Use 1 rather than file-executable-p to better match the
+    ;; behavior of call-process.
+    (locate-file command exec-path exec-suffixes 1)))
 
 (defun load-library (library)
   "Load the Emacs Lisp library named LIBRARY.
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
diff --git a/lisp/shell.el b/lisp/shell.el
index 232186083d5..91c65ed171e 100644
--- a/lisp/shell.el
+++ b/lisp/shell.el
@@ -468,6 +468,8 @@ Shell buffers.  It implements `shell-completion-execonly' for
   (set (make-local-variable 'comint-file-name-chars) shell-file-name-chars)
   (set (make-local-variable 'comint-file-name-quote-list)
        shell-file-name-quote-list)
+  (set (make-local-variable 'comint-file-name-prefix)
+       (file-remote-p default-directory))
   (set (make-local-variable 'comint-dynamic-complete-functions)
        shell-dynamic-complete-functions)
   (setq-local comint-unquote-function #'shell--unquote-argument)
@@ -1170,9 +1172,12 @@ Returns t if successful."
          (start (if (zerop (length filename)) (point) (match-beginning 0)))
          (end (if (zerop (length filename)) (point) (match-end 0)))
          (filenondir (file-name-nondirectory filename))
-         ; why cdr? see `shell-dynamic-complete-command'
-         (path-dirs (append (cdr (reverse exec-path))
-           (if (memq system-type '(windows-nt ms-dos)) '("."))))
+         (path-dirs
+          ;; Ignore `exec-directory', the last entry in `exec-path'.
+          (append (cdr (reverse (exec-path)))
+                  (if (and (memq system-type '(windows-nt ms-dos))
+                           (not (file-remote-p default-directory)))
+                      '("."))))
          (cwd (file-name-as-directory (expand-file-name default-directory)))
          (ignored-extensions
           (and comint-completion-fignore
diff --git a/test/lisp/net/tramp-archive-tests.el b/test/lisp/net/tramp-archive-tests.el
index b327e64818b..0a8716be0d7 100644
--- a/test/lisp/net/tramp-archive-tests.el
+++ b/test/lisp/net/tramp-archive-tests.el
@@ -748,7 +748,7 @@ This tests also `file-executable-p', `file-writable-p' and `set-file-modes'."
       (tramp-archive-cleanup-hash))))
 
 ;; The functions were introduced in Emacs 26.1.
-(ert-deftest tramp-archive-test37-make-nearby-temp-file ()
+(ert-deftest tramp-archive-test38-make-nearby-temp-file ()
   "Check `make-nearby-temp-file' and `temporary-file-directory'."
   (skip-unless tramp-archive-enabled)
   ;; Since Emacs 26.1.
@@ -785,7 +785,7 @@ This tests also `file-executable-p', `file-writable-p' and `set-file-modes'."
     (delete-directory tmp-file)
     (should-not (file-exists-p tmp-file))))
 
-(ert-deftest tramp-archive-test40-file-system-info ()
+(ert-deftest tramp-archive-test41-file-system-info ()
   "Check that `file-system-info' returns proper values."
   (skip-unless tramp-archive-enabled)
   ;; Since Emacs 27.1.
@@ -802,7 +802,7 @@ This tests also `file-executable-p', `file-writable-p' and `set-file-modes'."
                  (zerop (nth 1 fsi))
                  (zerop (nth 2 fsi))))))
 
-(ert-deftest tramp-archive-test42-auto-load ()
+(ert-deftest tramp-archive-test43-auto-load ()
   "Check that `tramp-archive' autoloads properly."
   (skip-unless tramp-archive-enabled)
   ;; Autoloading tramp-archive works since Emacs 27.1.
@@ -832,7 +832,7 @@ This tests also `file-executable-p', `file-writable-p' and `set-file-modes'."
           (mapconcat 'shell-quote-argument load-path " -L ")
           (shell-quote-argument (format code file)))))))))
 
-(ert-deftest tramp-archive-test42-delay-load ()
+(ert-deftest tramp-archive-test43-delay-load ()
   "Check that `tramp-archive' is loaded lazily, only when needed."
   (skip-unless tramp-archive-enabled)
   ;; Autoloading tramp-archive works since Emacs 27.1.
diff --git a/test/lisp/net/tramp-tests.el b/test/lisp/net/tramp-tests.el
index c5cb4cb43eb..df07a8f1b89 100644
--- a/test/lisp/net/tramp-tests.el
+++ b/test/lisp/net/tramp-tests.el
@@ -33,7 +33,7 @@
 ;; remote host, set this environment variable to "/dev/null" or
 ;; whatever is appropriate on your system.
 
-;; For slow remote connections, `tramp-test41-asynchronous-requests'
+;; For slow remote connections, `tramp-test42-asynchronous-requests'
 ;; might be too heavy.  Setting $REMOTE_PARALLEL_PROCESSES to a proper
 ;; value less than 10 could help.
 
@@ -4021,7 +4021,45 @@ This tests also `make-symbolic-link', `file-truename' and `add-name-to-file'."
       (put 'explicit-shell-file-name 'permanent-local nil)
       (kill-buffer "*shell*"))))
 
-(ert-deftest tramp-test34-vc-registered ()
+;; The function was introduced in Emacs 27.1.
+(ert-deftest tramp-test34-exec-path ()
+  "Check `exec-path' and `executable-find'."
+  (skip-unless (tramp--test-enabled))
+  (skip-unless (or (tramp--test-adb-p) (tramp--test-sh-p)))
+  ;; Since Emacs 27.1.
+  (skip-unless (boundp 'exec-path))
+
+  (let ((tmp-name (tramp--test-make-temp-name))
+        (default-directory tramp-test-temporary-file-directory))
+    (unwind-protect
+        (progn
+          (should (consp (with-no-warnings (exec-path))))
+          ;; Last element is the `exec-directory'.
+          (should
+           (string-equal
+            (car (last (with-no-warnings (exec-path))))
+            (file-local-name default-directory)))
+          ;; The shell "sh" shall always exist.
+          (should (executable-find "sh" 'remote))
+          ;; Since the last element in `exec-path' is the current
+          ;; directory, an executable file in that directory will be
+          ;; found.
+          (write-region "foo" nil tmp-name)
+          (should (file-exists-p tmp-name))
+          (set-file-modes tmp-name #o777)
+          (should (file-executable-p tmp-name))
+          (should
+           (string-equal
+            (executable-find (file-name-nondirectory tmp-name) 'remote)
+            (file-local-name tmp-name)))
+          (should-not
+           (executable-find
+            (concat (file-name-nondirectory tmp-name) "foo") 'remote)))
+
+      ;; Cleanup.
+      (ignore-errors (delete-file tmp-name)))))
+
+(ert-deftest tramp-test35-vc-registered ()
   "Check `vc-registered'."
   :tags '(:expensive-test)
   (skip-unless (tramp--test-enabled))
@@ -4091,7 +4129,7 @@ This tests also `make-symbolic-link', `file-truename' and `add-name-to-file'."
         ;; Cleanup.
         (ignore-errors (delete-directory tmp-name1 'recursive))))))
 
-(ert-deftest tramp-test35-make-auto-save-file-name ()
+(ert-deftest tramp-test36-make-auto-save-file-name ()
   "Check `make-auto-save-file-name'."
   (skip-unless (tramp--test-enabled))
 
@@ -4182,7 +4220,7 @@ This tests also `make-symbolic-link', `file-truename' and `add-name-to-file'."
         (ignore-errors (delete-file tmp-name1))
         (ignore-errors (delete-directory tmp-name2 'recursive))))))
 
-(ert-deftest tramp-test36-find-backup-file-name ()
+(ert-deftest tramp-test37-find-backup-file-name ()
   "Check `find-backup-file-name'."
   (skip-unless (tramp--test-enabled))
 
@@ -4293,7 +4331,7 @@ This tests also `make-symbolic-link', `file-truename' and `add-name-to-file'."
         (ignore-errors (delete-directory tmp-name2 'recursive))))))
 
 ;; The functions were introduced in Emacs 26.1.
-(ert-deftest tramp-test37-make-nearby-temp-file ()
+(ert-deftest tramp-test38-make-nearby-temp-file ()
   "Check `make-nearby-temp-file' and `temporary-file-directory'."
   (skip-unless (tramp--test-enabled))
   ;; Since Emacs 26.1.
@@ -4586,7 +4624,7 @@ This requires restrictions of file name syntax."
         (ignore-errors (delete-directory tmp-name2 'recursive))))))
 
 (defun tramp--test-special-characters ()
-  "Perform the test in `tramp-test38-special-characters*'."
+  "Perform the test in `tramp-test39-special-characters*'."
   ;; Newlines, slashes and backslashes in file names are not
   ;; supported.  So we don't test.  And we don't test the tab
   ;; character on Windows or Cygwin, because the backslash is
@@ -4634,7 +4672,7 @@ This requires restrictions of file name syntax."
                files (list (mapconcat 'identity files ""))))))
 
 ;; These tests are inspired by Bug#17238.
-(ert-deftest tramp-test38-special-characters ()
+(ert-deftest tramp-test39-special-characters ()
   "Check special characters in file names."
   (skip-unless (tramp--test-enabled))
   (skip-unless (not (tramp--test-rsync-p)))
@@ -4642,7 +4680,7 @@ This requires restrictions of file name syntax."
 
   (tramp--test-special-characters))
 
-(ert-deftest tramp-test38-special-characters-with-stat ()
+(ert-deftest tramp-test39-special-characters-with-stat ()
   "Check special characters in file names.
 Use the `stat' command."
   :tags '(:expensive-test)
@@ -4660,7 +4698,7 @@ Use the `stat' command."
           tramp-connection-properties)))
     (tramp--test-special-characters)))
 
-(ert-deftest tramp-test38-special-characters-with-perl ()
+(ert-deftest tramp-test39-special-characters-with-perl ()
   "Check special characters in file names.
 Use the `perl' command."
   :tags '(:expensive-test)
@@ -4681,7 +4719,7 @@ Use the `perl' command."
           tramp-connection-properties)))
     (tramp--test-special-characters)))
 
-(ert-deftest tramp-test38-special-characters-with-ls ()
+(ert-deftest tramp-test39-special-characters-with-ls ()
   "Check special characters in file names.
 Use the `ls' command."
   :tags '(:expensive-test)
@@ -4704,7 +4742,7 @@ Use the `ls' command."
     (tramp--test-special-characters)))
 
 (defun tramp--test-utf8 ()
-  "Perform the test in `tramp-test39-utf8*'."
+  "Perform the test in `tramp-test40-utf8*'."
   (let* ((utf8 (if (and (eq system-type 'darwin)
                         (memq 'utf-8-hfs (coding-system-list)))
                    'utf-8-hfs 'utf-8))
@@ -4739,7 +4777,7 @@ Use the `ls' command."
              (replace-regexp-in-string "[\t\n/.?]" "" x)))
           language-info-alist)))))))
 
-(ert-deftest tramp-test39-utf8 ()
+(ert-deftest tramp-test40-utf8 ()
   "Check UTF8 encoding in file names and file contents."
   (skip-unless (tramp--test-enabled))
   (skip-unless (not (tramp--test-docker-p)))
@@ -4749,7 +4787,7 @@ Use the `ls' command."
 
   (tramp--test-utf8))
 
-(ert-deftest tramp-test39-utf8-with-stat ()
+(ert-deftest tramp-test40-utf8-with-stat ()
   "Check UTF8 encoding in file names and file contents.
 Use the `stat' command."
   :tags '(:expensive-test)
@@ -4769,7 +4807,7 @@ Use the `stat' command."
           tramp-connection-properties)))
     (tramp--test-utf8)))
 
-(ert-deftest tramp-test39-utf8-with-perl ()
+(ert-deftest tramp-test40-utf8-with-perl ()
   "Check UTF8 encoding in file names and file contents.
 Use the `perl' command."
   :tags '(:expensive-test)
@@ -4792,7 +4830,7 @@ Use the `perl' command."
           tramp-connection-properties)))
     (tramp--test-utf8)))
 
-(ert-deftest tramp-test39-utf8-with-ls ()
+(ert-deftest tramp-test40-utf8-with-ls ()
   "Check UTF8 encoding in file names and file contents.
 Use the `ls' command."
   :tags '(:expensive-test)
@@ -4815,7 +4853,7 @@ Use the `ls' command."
           tramp-connection-properties)))
     (tramp--test-utf8)))
 
-(ert-deftest tramp-test40-file-system-info ()
+(ert-deftest tramp-test41-file-system-info ()
   "Check that `file-system-info' returns proper values."
   (skip-unless (tramp--test-enabled))
   ;; Since Emacs 27.1.
@@ -4837,7 +4875,7 @@ Use the `ls' command."
   (ert-fail (format "`%s' timed out" (ert-test-name (ert-running-test)))))
 
 ;; This test is inspired by Bug#16928.
-(ert-deftest tramp-test41-asynchronous-requests ()
+(ert-deftest tramp-test42-asynchronous-requests ()
   "Check parallel asynchronous requests.
 Such requests could arrive from timers, process filters and
 process sentinels.  They shall not disturb each other."
@@ -5012,7 +5050,7 @@ process sentinels.  They shall not disturb each other."
         (ignore-errors (delete-directory tmp-name 'recursive)))))))
 
 ;; This test is inspired by Bug#29163.
-(ert-deftest tramp-test42-auto-load ()
+(ert-deftest tramp-test43-auto-load ()
   "Check that Tramp autoloads properly."
   (let ((default-directory (expand-file-name temporary-file-directory))
         (code
@@ -5030,7 +5068,7 @@ process sentinels.  They shall not disturb each other."
         (mapconcat 'shell-quote-argument load-path " -L ")
         (shell-quote-argument code)))))))
 
-(ert-deftest tramp-test42-delay-load ()
+(ert-deftest tramp-test43-delay-load ()
   "Check that Tramp is loaded lazily, only when needed."
   ;; The autoloaded Tramp objects are different since Emacs 26.1.  We
   ;; cannot test older Emacsen, therefore.
@@ -5063,7 +5101,7 @@ process sentinels.  They shall not disturb each other."
           (mapconcat 'shell-quote-argument load-path " -L ")
           (shell-quote-argument (format code tm)))))))))
 
-(ert-deftest tramp-test42-recursive-load ()
+(ert-deftest tramp-test43-recursive-load ()
   "Check that Tramp does not fail due to recursive load."
   (skip-unless (tramp--test-enabled))
 
@@ -5087,7 +5125,7 @@ process sentinels.  They shall not disturb each other."
           (mapconcat 'shell-quote-argument load-path " -L ")
           (shell-quote-argument code))))))))
 
-(ert-deftest tramp-test42-remote-load-path ()
+(ert-deftest tramp-test43-remote-load-path ()
   "Check that Tramp autoloads its packages with remote `load-path'."
   ;; The autoloaded Tramp objects are different since Emacs 26.1.  We
   ;; cannot test older Emacsen, therefore.
@@ -5115,7 +5153,7 @@ process sentinels.  They shall not disturb each other."
         (mapconcat 'shell-quote-argument load-path " -L ")
         (shell-quote-argument code)))))))
 
-(ert-deftest tramp-test43-unload ()
+(ert-deftest tramp-test44-unload ()
   "Check that Tramp and its subpackages unload completely.
 Since it unloads Tramp, it shall be the last test to run."
   :tags '(:expensive-test)
@@ -5176,14 +5214,14 @@ Since it unloads Tramp, it shall be the last test to run."
 ;; * file-name-case-insensitive-p
 
 ;; * Work on skipped tests.  Make a comment, when it is impossible.
-;; * Revisit expensive tests, once problems in tramp-error are solved.
+;; * Revisit expensive tests, once problems in `tramp-error' are solved.
 ;; * Fix `tramp-test05-expand-file-name-relative' in `expand-file-name'.
 ;; * Fix `tramp-test06-directory-file-name' for `ftp'.
 ;; * Investigate, why `tramp-test11-copy-file' and `tramp-test12-rename-file'
 ;;   do not work properly for `owncloud'.
 ;; * Fix `tramp-test29-start-file-process' on MS Windows (`process-send-eof'?).
 ;; * Fix `tramp-test30-interrupt-process', timeout doesn't work reliably.
-;; * Fix Bug#16928 in `tramp-test41-asynchronous-requests'.
+;; * Fix Bug#16928 in `tramp-test42-asynchronous-requests'.
 
 (provide 'tramp-tests)
 ;;; tramp-tests.el ends here