code review 4276059: misc/emacs: gofmt: don't clobber the current buffer on ...

misc/emacs/go-mode.el

 ;;; go-mode.el --- Major mode for the Go programming language
 
 ;;; Commentary:
 
 ;; For installation instructions, see go-mode-load.el
 
 ;;; To do:
 
 ;; * Indentation is *almost* identical to gofmt
 ;; ** We think struct literal keys are labels and outdent them
@@ skipping 482 matching lines @@
   "Reload go-mode.el and put the current buffer into Go mode.
 Useful for development work."
 
   (interactive)
   (unload-feature 'go-mode)
   (require 'go-mode)
   (go-mode))
 
 (provide 'go-mode)
 
-(defun gofmt ()
-  "Pipe the current buffer through the external tool `gofmt`."
-··
-  (interactive)
+(defun gofmt-buffer (outbuf replace errbuf)
   ;; for some reason save-excursion isn't working
   ;; probably because shell-command-on-region deletes the contents of the
   ;; region before filling in the new values
   ;; so we will save the point/mark by hand
   ;; similarly we can't use push-mark/pop-mark
   (let ((old-mark (mark t)) (old-point (point)))
     (save-restriction
       (let (deactivate-mark)
         (widen)
-        (shell-command-on-region (point-min) (point-max) "gofmt" t t shell-command-default-error-buffer)))
+        (setq exit-status (shell-command-on-region (point-min) (point-max) "gofmt"
+                                                   outbuf replace errbuf))))
     (goto-char (min old-point (point-max)))
-    (if old-mark (set-mark (min old-mark (point-max))))))
+    (if old-mark (set-mark (min old-mark (point-max)))))
+  exit-status)
+
+(defun gofmt ()
+  "Pipe the current buffer through the external tool `gofmt`."
+··
+  (interactive)
+  (gofmt-buffer t t shell-command-default-error-buffer))
+
+(defun get-empty-buffer (name)
+  "Finds or creates the buffer named name, erases it, and returns it."
+
+  (let ((buf (get-buffer-create name)))
+    (save-current-buffer
+      (set-buffer buf)
+      (erase-buffer))
+    buf))
+
+;;;###autoload
+(defun gofmt-before-save ()
+  "Add this to .emacs to run gofmt on the current buffer when saving:
+  (add-hook 'before-save-hook 'gofmt-before-save)"
+
+  (interactive)
+  (when (eq major-mode 'go-mode)

[Sameer (personal), 2011/03/19 02:01:28]

This when guard is the only bit that's specific to the hook behavior (since
before-save-hook runs in all modes, and we only want to run the rest of this on
Go files).  So we could just change all of this to:
  (defun gofmt ...the code below...)
  (defun gofmt-before-save (when (eq major-mode 'go-mode) gofmt))
Provided we're willing to change how M-x gofmt works for people now.

If we want to retain the current behavior of M-x gofmt, another option is to do:
  (defun gofmt-noclobber ...the code below...)
  (defun gofmt-before-save (when (eq major-mode 'go-mode) gofmt-noclobber))

+    (let ((outbuf (get-empty-buffer "Gofmt Output"))
+          (errbuf (get-empty-buffer "Gofmt Errors")))
+      (if (= 0 (gofmt-buffer outbuf nil errbuf))
+
+          ;; gofmt succeeded: copy outbuf into the current buffer,
+          ;; preserving the current mark and point
+          (let ((old-mark (mark t)) (old-point (point)))
+            (erase-buffer)
+            (insert-buffer-substring outbuf)
+            (goto-char (min old-point (point-max)))
+            (if old-mark (set-mark (min old-mark (point-max))))
+            (kill-buffer errbuf))
+
+        ;; gofmt failed: display the errors
+        (display-buffer errbuf))
+
+      ;; Kill outbuf, collapsing its window first if
+      ;; shell-command-on-region displayed it.
+      (delete-windows-on outbuf)
+      (kill-buffer outbuf))))