eshell: Introduce new buffer syntax

The new buffer syntax '#<buffer-name>' is equivalent to '#<buffer
buffer-name>'.  Remove `eshell-buffer-shorthand', as it is no longer
needed (Bug#19319).

* lisp/eshell/esh-io.el (eshell-buffer-shorthand): Remove.
(eshell-get-target): Remove shorthand-specific code.
* lisp/eshell/esh-arg.el (eshell-parse-special-reference): Parse
'#<buffer-name>'.

etc/NEWS

@@ -675,6 +675,12 @@ command line's password prompt.
 *** The new built-in command `clear' can scroll window contents out of sight.
 If provided with an optional non-nil argument, the scrollback contents will be cleared.
 
+*** New buffer syntax '#<buffer-name>', which is equivalent to
+'#<buffer buffer-name>'.  This shorthand makes interacting with
+buffers from eshell more convenient.  Custom variable
+`eshell-buffer-shorthand', which has been broken for a while, has been
+removed.
+
 ** Browse-url
 
 *** Support for the Conkeror web browser.

lisp/eshell/esh-arg.el

@@ -357,22 +357,31 @@ after are both returned."
 	  (goto-char (1+ end)))))))
 
 (defun eshell-parse-special-reference ()
-  "Parse a special syntax reference, of the form '#<type arg>'."
-  (if (and (not eshell-current-argument)
-	   (not eshell-current-quoted)
-	   (looking-at "#<\\(buffer\\|process\\)\\s-"))
-      (let ((here (point)))
-	(goto-char (match-end 0))
-	(let* ((buffer-p (string= (match-string 1) "buffer"))
-	       (end (eshell-find-delimiter ?\< ?\>)))
-	  (if (not end)
-	      (throw 'eshell-incomplete ?\<)
-	    (if (eshell-arg-delimiter (1+ end))
-		(prog1
-		    (list (if buffer-p 'get-buffer-create 'get-process)
-			  (buffer-substring-no-properties (point) end))
-		  (goto-char (1+ end)))
-	      (ignore (goto-char here))))))))
+  "Parse a special syntax reference, of the form '#<args>'.
+
+args           := `type' `whitespace' `arbitrary-args' | `arbitrary-args'
+type           := \"buffer\" or \"process\"
+arbitrary-args := any string of characters.
+
+If the form has no 'type', the syntax is parsed as if 'type' were
+\"buffer\"."
+  (when (and (not eshell-current-argument)
+             (not eshell-current-quoted)
+             (looking-at "#<\\(\\(buffer\\|process\\)\\s-\\)?"))
+    (let ((here (point)))
+      (goto-char (match-end 0)) ;; Go to the end of the match.
+      (let ((buffer-p (if (match-string 1)
+                          (string= (match-string 2) "buffer")
+                        t)) ;; buffer-p is non-nil by default.
+            (end (eshell-find-delimiter ?\< ?\>)))
+        (when (not end)
+          (throw 'eshell-incomplete ?\<))
+        (if (eshell-arg-delimiter (1+ end))
+            (prog1
+                (list (if buffer-p 'get-buffer-create 'get-process)
+                      (buffer-substring-no-properties (point) end))
+              (goto-char (1+ end)))
+          (ignore (goto-char here)))))))
 
 (defun eshell-parse-delimiter ()
   "Parse an argument delimiter, which is essentially a command operator."

lisp/eshell/esh-io.el

@@ -31,6 +31,18 @@
 ;; consistent with most shells.  Therefore, only unique features are
 ;; mentioned here.
 ;;
+;;;_* Redirect to a Buffer or Process
+;;
+;; Buffers and processes can be named with '#<buffer buffer-name>' and
+;; '#<process process-name>', respectively. As a shorthand,
+;; '#<buffer-name>' without the explicit "buffer" arg is equivalent to
+;; '#<buffer buffer-name>'.
+;;
+;;   echo hello > #<buffer *scratch*> # Overwrite '*scratch*' with 'hello'.
+;;   echo hello > #<*scratch*>        # Same as the command above.
+;;
+;;   echo hello > #<process shell> # Pipe "hello" into the shell process.
+;;
 ;;;_* Insertion
 ;;
 ;; To insert at the location of point in a buffer, use '>>>':
@@ -98,19 +110,6 @@ other buffers) ."
   :type 'integer
   :group 'eshell-io)
 
-(defcustom eshell-buffer-shorthand nil
-  "If non-nil, a symbol name can be used for a buffer in redirection.
-If nil, redirecting to a buffer requires buffer name syntax.  If this
-variable is set, redirection directly to Lisp symbols will be
-impossible.
-
-Example:
-
-  echo hello > '*scratch*  ; works if `eshell-buffer-shorthand' is t
-  echo hello > #<buffer *scratch*>  ; always works"
-  :type 'boolean
-  :group 'eshell-io)
-
 (defcustom eshell-print-queue-size 5
   "The size of the print queue, for doing buffered printing.
 This is basically a speed enhancement, to avoid blocking the Lisp code
@@ -355,21 +354,14 @@ it defaults to `insert'."
 		   (goto-char (point-max))))
 	    (point-marker))))))
 
-   ((or (bufferp target)
-	(and (boundp 'eshell-buffer-shorthand)
-	     (symbol-value 'eshell-buffer-shorthand)
-	     (symbolp target)
-	     (not (memq target '(t nil)))))
-    (let ((buf (if (bufferp target)
-		   target
-		 (get-buffer-create
-		  (symbol-name target)))))
-      (with-current-buffer buf
-	(cond ((eq mode 'overwrite)
-	       (erase-buffer))
-	      ((eq mode 'append)
-	       (goto-char (point-max))))
-	(point-marker))))
+
+   ((bufferp target)
+    (with-current-buffer target
+      (cond ((eq mode 'overwrite)
+             (erase-buffer))
+            ((eq mode 'append)
+             (goto-char (point-max))))
+      (point-marker)))
 
    ((functionp target) nil)