New electric forward slash Eshell module

* lisp/eshell/em-elecslash.el: New file.
* etc/NEWS:
* doc/misc/eshell.texi (Electric forward slash): Document the module.
(Make / electric): Retitle to "Make / more electric", update, add
"@noindent", and standardize terminology.

1 files changed, 120 insertions, 0 deletions

diff --git a/lisp/eshell/em-elecslash.el b/lisp/eshell/em-elecslash.el
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+++ b/lisp/eshell/em-elecslash.el
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+;;; em-elecslash.el --- electric forward slashes  -*- lexical-binding:t -*-
+
+;; Copyright (C) 2022 Free Software Foundation, Inc.
+
+;; Author: Sean Whitton <spwhitton@spwhitton.name>
+
+;; 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:
+
+;; Electric forward slash in remote Eshells.
+
+;;; Code:
+
+(require 'tramp)
+(require 'thingatpt)
+(require 'esh-cmd)
+(require 'esh-ext)
+(require 'esh-mode)
+
+;; This makes us an option when customizing `eshell-modules-list'.
+;;;###autoload
+(progn
+(defgroup eshell-elecslash nil
+  "Electric forward slash in remote Eshells.
+
+This module helps with supplying absolute file name arguments to
+remote commands.  After enabling it, typing a forward slash as
+the first character of a command line argument will automatically
+insert the Tramp prefix, /method:host:.  The automatic insertion
+applies only when `default-directory' is remote and the command
+is a Lisp function.
+
+The result is that in most cases of supplying absolute file name
+arguments to commands you should see the Tramp prefix inserted
+automatically only when that's what you'd reasonably expect.
+This frees you from having to keep track of whether commands are
+Lisp functions or external when typing command line arguments."
+  :tag "Electric forward slash"
+  :group 'eshell-module))
+
+;;; Functions:
+
+(defun eshell-elecslash-initialize () ;Called from `eshell-mode' via intern-soft!
+  "Initialize remote Eshell electric forward slash support."
+  (add-hook 'post-self-insert-hook
+            #'eshell-electric-forward-slash nil t))
+
+(defun eshell-electric-forward-slash ()
+  "Implementation of electric forward slash in remote Eshells.
+
+Initializing the `eshell-elecslash' module adds this function to
+`post-self-insert-hook'.  Typing / or ~/ as the first character
+of a command line argument automatically inserts the Tramp prefix
+in the case that `default-directory' is remote and the command is
+a Lisp function.  Typing a second forward slash undoes the
+insertion."
+  (when (eq ?/ (char-before))
+    (delete-char -1)
+    (let ((tilde-before (eq ?~ (char-before)))
+          (command (save-excursion
+                     (eshell-bol)
+                     (skip-syntax-forward " ")
+                     (thing-at-point 'sexp))))
+      (if (and (file-remote-p default-directory)
+               ;; We can't formally parse the input.  But if there is
+               ;; one of these operators behind us, then looking at
+               ;; the first command would not be sensible.  So be
+               ;; conservative: don't insert the Tramp prefix if there
+               ;; are any of these operators behind us.
+               (not (looking-back (regexp-opt '("&&" "|" ";"))
+                                  eshell-last-output-end))
+	       (or (= (point) eshell-last-output-end)
+		   (and tilde-before
+                        (= (1- (point)) eshell-last-output-end))
+		   (and (or tilde-before
+                            (eq ?\s (char-syntax (char-before))))
+		        (or (eshell-find-alias-function command)
+			    (and (fboundp (intern-soft command))
+			         (or eshell-prefer-lisp-functions
+				     (not (eshell-search-path command))))))))
+	  (let ((map (make-sparse-keymap))
+	        (start (if tilde-before (1- (point)) (point)))
+                (localname
+                 (tramp-file-name-localname
+                  (tramp-dissect-file-name default-directory))))
+	    (when tilde-before (delete-char -1))
+	    (insert
+             (substring default-directory 0
+                        (string-search localname default-directory)))
+	    (unless tilde-before (insert "/"))
+	    ;; Typing a second slash undoes the insertion, for when
+	    ;; you really do want to type a local absolute file name.
+	    (define-key map "/" (lambda ()
+				  (interactive)
+				  (delete-region start (point))
+				  (insert (if tilde-before "~/" "/"))))
+	    (set-transient-map map))
+        (insert "/")))))
+
+(provide 'em-elecslash)
+
+;; Local Variables:
+;; generated-autoload-file: "esh-groups.el"
+;; End:
+
+;;; esh-elecslash.el ends here