bug#28412: 26.0.50; Let save-some-buffers accept write-contents-functions

bug#28412: 26.0.50; Let save-some-buffers accept write-contents-functions

[Eric Abrahamsen]

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This is about letting `save-some-buffers' check
`write-contents-functions' before insisting on a buffer having a file to
write to.

There was a conversations about this on emacs.devel:

https://lists.gnu.org/archive/html/emacs-devel/2017-05/msg00653.html

The patch I ended up with is attached.

I'm reporting this just so the patch (and the idea) doesn't get lost. I
still think it's worth doing.


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From af4f811439785113fe2be71f499006776958755b Mon Sep 17 00:00:00 2001
From: Eric Abrahamsen <eric@ericabrahamsen.net>
Date: Thu, 25 May 2017 15:28:19 +0800
Subject: [PATCH] First whack at write-contents-functions for non-file buffers

---
 lisp/files.el | 106 +++++++++++++++++++++++++++++++---------------------------
 1 file changed, 56 insertions(+), 50 deletions(-)

diff --git a/lisp/files.el b/lisp/files.el
index 8ac1993754..c074fa7995 100644
--- a/lisp/files.el
+++ b/lisp/files.el
@@ -4943,29 +4943,14 @@ basic-save-buffer
     (if (buffer-base-buffer)
 	(set-buffer (buffer-base-buffer)))
     (if (or (buffer-modified-p)
-	    ;; handle the case when no modification has been made but
-	    ;; the file disappeared since visited
+	    ;; Handle the case when no modification has been made but
+	    ;; the file disappeared since visited.
 	    (and buffer-file-name
 		 (not (file-exists-p buffer-file-name))))
 	(let ((recent-save (recent-auto-save-p))
 	      setmodes)
-          ;; If buffer has no file name, ask user for one.
-	  (or buffer-file-name
-              (let ((filename
-                     (expand-file-name
-                      (read-file-name "File to save in: "
-                                      nil (expand-file-name (buffer-name))))))
-                (if (file-exists-p filename)
-                    (if (file-directory-p filename)
-                        ;; Signal an error if the user specified the name of an
-                        ;; existing directory.
-                        (error "%s is a directory" filename)
-                      (unless (y-or-n-p (format-message
-                                         "File `%s' exists; overwrite? "
-                                         filename))
-                        (error "Canceled"))))
-                (set-visited-file-name filename)))
-	  (or (verify-visited-file-modtime (current-buffer))
+	  (or (null buffer-file-name)
+              (verify-visited-file-modtime (current-buffer))
 	      (not (file-exists-p buffer-file-name))
 	      (yes-or-no-p
 	       (format
@@ -4977,6 +4962,7 @@ basic-save-buffer
 	    (save-excursion
 	      (and (> (point-max) (point-min))
 		   (not find-file-literally)
+                   (null buffer-read-only)
 		   (/= (char-after (1- (point-max))) ?\n)
 		   (not (and (eq selective-display t)
 			     (= (char-after (1- (point-max))) ?\r)))
@@ -4989,41 +4975,60 @@ basic-save-buffer
 		   (save-excursion
 		     (goto-char (point-max))
 		     (insert ?\n))))
-	    ;; Support VC version backups.
-	    (vc-before-save)
 	    ;; Don't let errors prevent saving the buffer.
 	    (with-demoted-errors (run-hooks 'before-save-hook))
-	    (or (run-hook-with-args-until-success 'write-contents-functions)
-		(run-hook-with-args-until-success 'local-write-file-hooks)
-		(run-hook-with-args-until-success 'write-file-functions)
-		;; If a hook returned t, file is already "written".
-		;; Otherwise, write it the usual way now.
-		(let ((dir (file-name-directory
-			    (expand-file-name buffer-file-name))))
-		  (unless (file-exists-p dir)
-		    (if (y-or-n-p
-			 (format-message
-                          "Directory `%s' does not exist; create? " dir))
-			(make-directory dir t)
-		      (error "Canceled")))
-		  (setq setmodes (basic-save-buffer-1))))
+            ;; Give `write-contents-functions' a chance to
+            ;; short-circuit the whole process.
+	    (unless (run-hook-with-args-until-success 'write-contents-functions)
+              ;; If buffer has no file name, ask user for one.
+              (or buffer-file-name
+                  (let ((filename
+                         (expand-file-name
+                          (read-file-name "File to save in: "
+                                          nil (expand-file-name (buffer-name))))))
+                    (if (file-exists-p filename)
+                        (if (file-directory-p filename)
+                            ;; Signal an error if the user specified the name of an
+                            ;; existing directory.
+                            (error "%s is a directory" filename)
+                          (unless (y-or-n-p (format-message
+                                             "File `%s' exists; overwrite? "
+                                             filename))
+                            (error "Canceled"))))
+                    (set-visited-file-name filename)))
+              ;; Support VC version backups.
+	      (vc-before-save)
+	      (or (run-hook-with-args-until-success 'local-write-file-hooks)
+	          (run-hook-with-args-until-success 'write-file-functions)
+	          ;; If a hook returned t, file is already "written".
+	          ;; Otherwise, write it the usual way now.
+	          (let ((dir (file-name-directory
+			      (expand-file-name buffer-file-name))))
+		    (unless (file-exists-p dir)
+		      (if (y-or-n-p
+		           (format-message
+                            "Directory `%s' does not exist; create? " dir))
+		          (make-directory dir t)
+		        (error "Canceled")))
+		    (setq setmodes (basic-save-buffer-1)))))
 	    ;; Now we have saved the current buffer.  Let's make sure
 	    ;; that buffer-file-coding-system is fixed to what
 	    ;; actually used for saving by binding it locally.
-	    (if save-buffer-coding-system
-		(setq save-buffer-coding-system last-coding-system-used)
-	      (setq buffer-file-coding-system last-coding-system-used))
-	    (setq buffer-file-number
-		  (nthcdr 10 (file-attributes buffer-file-name)))
-	    (if setmodes
-		(condition-case ()
-		    (progn
-		      (unless
-			  (with-demoted-errors
-			    (set-file-modes buffer-file-name (car setmodes)))
-			(set-file-extended-attributes buffer-file-name
-						      (nth 1 setmodes))))
-		  (error nil))))
+            (when buffer-file-name
+	      (if save-buffer-coding-system
+		  (setq save-buffer-coding-system last-coding-system-used)
+	        (setq buffer-file-coding-system last-coding-system-used))
+	      (setq buffer-file-number
+		    (nthcdr 10 (file-attributes buffer-file-name)))
+	      (if setmodes
+		  (condition-case ()
+		      (progn
+		        (unless
+			    (with-demoted-errors
+			        (set-file-modes buffer-file-name (car setmodes)))
+			  (set-file-extended-attributes buffer-file-name
+						        (nth 1 setmodes))))
+		    (error nil)))))
 	  ;; If the auto-save file was recent before this command,
 	  ;; delete it now.
 	  (delete-auto-save-file-if-necessary recent-save)
@@ -5255,7 +5260,8 @@ save-some-buffers
                      (and pred
                           (progn
                             (set-buffer buffer)
-                            (and buffer-offer-save (> (buffer-size) 0)))))
+                            (and buffer-offer-save (> (buffer-size) 0))))
+                     write-contents-functions)
                     (or (not (functionp pred))
                         (with-current-buffer buffer (funcall pred)))
                     (if arg
-- 
2.13.0

bug#28412: Acknowledgement (26.0.50; Let save-some-buffers accept write-contents-functions)

[Eric Abrahamsen]

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Damn, I think that was the wrong patch.

Here's the latest one.


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From 7b5f18648e3d4b2aa9a5af536a624d6518d8fdd7 Mon Sep 17 00:00:00 2001
From: Eric Abrahamsen <eric@ericabrahamsen.net>
Date: Thu, 25 May 2017 15:28:19 +0800
Subject: [PATCH] Allow write-contents-functions to short-circuit buffer saving

* lisp/files.el (basic-save-buffer): If write-contents-functions is
  non-nil, give the functions in that hook a chance to save buffer
  contents before checking if buffer is visiting a file.
  (save-some-buffers): If write-contents-functions is non nil,
  consider the buffer eligible for a save prompt.
* doc/lispref/files.texi (Saving Buffers): Mention new behavior, note
  that special-mode buffers can use this to "save" themselves.
---
 doc/lispref/files.texi |  18 +++++--
 lisp/files.el          | 136 +++++++++++++++++++++++++++----------------------
 2 files changed, 87 insertions(+), 67 deletions(-)

diff --git a/doc/lispref/files.texi b/doc/lispref/files.texi
index 2b692dbf68..a6ee0cc69c 100644
--- a/doc/lispref/files.texi
+++ b/doc/lispref/files.texi
@@ -457,15 +457,23 @@ Saving Buffers
 @defvar write-contents-functions
 This works just like @code{write-file-functions}, but it is intended
 for hooks that pertain to the buffer's contents, not to the particular
-visited file or its location.  Such hooks are usually set up by major
-modes, as buffer-local bindings for this variable.  This variable
-automatically becomes buffer-local whenever it is set; switching to a
-new major mode always resets this variable, but calling
-@code{set-visited-file-name} does not.
+visited file or its location, and can be used to create arbitrary save
+processes for buffers that aren't visiting files at all.  Such hooks
+are usually set up by major modes, as buffer-local bindings for this
+variable.  This variable automatically becomes buffer-local whenever
+it is set; switching to a new major mode always resets this variable,
+but calling @code{set-visited-file-name} does not.
 
 If any of the functions in this hook returns non-@code{nil}, the file
 is considered already written and the rest are not called and neither
 are the functions in @code{write-file-functions}.
+
+When using this hook to save buffers that are not visiting files (for
+instance, special-mode buffers), keep in mind that, if the function
+fails to save correctly and returns a @code{nil} value,
+@code{save-buffer} will go on to prompt the user for a file to save
+the buffer in.  If this is undesirable, consider having the function
+fail by raising an error.
 @end defvar
 
 @defopt before-save-hook
diff --git a/lisp/files.el b/lisp/files.el
index 8ac1993754..1f88f86b76 100644
--- a/lisp/files.el
+++ b/lisp/files.el
@@ -514,10 +514,12 @@ 'write-contents-hooks
     'write-contents-functions "22.1")
 (defvar write-contents-functions nil
   "List of functions to be called before writing out a buffer to a file.
-Only used by `save-buffer'.
-If one of them returns non-nil, the file is considered already written
-and the rest are not called and neither are the functions in
-`write-file-functions'.
+
+Only used by `save-buffer'.  If one of them returns non-nil, the
+file is considered already written and the rest are not called
+and neither are the functions in `write-file-functions'.  This
+hook can thus be used to create save behavior for buffers that
+are not visiting a file at all.
 
 This variable is meant to be used for hooks that pertain to the
 buffer's contents, not to the particular visited file; thus,
@@ -4932,9 +4934,12 @@ save-buffer-coding-system
 
 (defun basic-save-buffer (&optional called-interactively)
   "Save the current buffer in its visited file, if it has been modified.
-The hooks `write-contents-functions' and `write-file-functions' get a chance
-to do the job of saving; if they do not, then the buffer is saved in
-the visited file in the usual way.
+
+The hooks `write-contents-functions', `local-write-file-hooks'
+and `write-file-functions' get a chance to do the job of saving;
+if they do not, then the buffer is saved in the visited file in
+the usual way.
+
 Before and after saving the buffer, this function runs
 `before-save-hook' and `after-save-hook', respectively."
   (interactive '(called-interactively))
@@ -4943,29 +4948,14 @@ basic-save-buffer
     (if (buffer-base-buffer)
 	(set-buffer (buffer-base-buffer)))
     (if (or (buffer-modified-p)
-	    ;; handle the case when no modification has been made but
-	    ;; the file disappeared since visited
+	    ;; Handle the case when no modification has been made but
+	    ;; the file disappeared since visited.
 	    (and buffer-file-name
 		 (not (file-exists-p buffer-file-name))))
 	(let ((recent-save (recent-auto-save-p))
 	      setmodes)
-          ;; If buffer has no file name, ask user for one.
-	  (or buffer-file-name
-              (let ((filename
-                     (expand-file-name
-                      (read-file-name "File to save in: "
-                                      nil (expand-file-name (buffer-name))))))
-                (if (file-exists-p filename)
-                    (if (file-directory-p filename)
-                        ;; Signal an error if the user specified the name of an
-                        ;; existing directory.
-                        (error "%s is a directory" filename)
-                      (unless (y-or-n-p (format-message
-                                         "File `%s' exists; overwrite? "
-                                         filename))
-                        (error "Canceled"))))
-                (set-visited-file-name filename)))
-	  (or (verify-visited-file-modtime (current-buffer))
+	  (or (null buffer-file-name)
+              (verify-visited-file-modtime (current-buffer))
 	      (not (file-exists-p buffer-file-name))
 	      (yes-or-no-p
 	       (format
@@ -4977,6 +4967,7 @@ basic-save-buffer
 	    (save-excursion
 	      (and (> (point-max) (point-min))
 		   (not find-file-literally)
+                   (null buffer-read-only)
 		   (/= (char-after (1- (point-max))) ?\n)
 		   (not (and (eq selective-display t)
 			     (= (char-after (1- (point-max))) ?\r)))
@@ -4989,46 +4980,65 @@ basic-save-buffer
 		   (save-excursion
 		     (goto-char (point-max))
 		     (insert ?\n))))
-	    ;; Support VC version backups.
-	    (vc-before-save)
 	    ;; Don't let errors prevent saving the buffer.
 	    (with-demoted-errors (run-hooks 'before-save-hook))
-	    (or (run-hook-with-args-until-success 'write-contents-functions)
-		(run-hook-with-args-until-success 'local-write-file-hooks)
-		(run-hook-with-args-until-success 'write-file-functions)
-		;; If a hook returned t, file is already "written".
-		;; Otherwise, write it the usual way now.
-		(let ((dir (file-name-directory
-			    (expand-file-name buffer-file-name))))
-		  (unless (file-exists-p dir)
-		    (if (y-or-n-p
-			 (format-message
-                          "Directory `%s' does not exist; create? " dir))
-			(make-directory dir t)
-		      (error "Canceled")))
-		  (setq setmodes (basic-save-buffer-1))))
+            ;; Give `write-contents-functions' a chance to
+            ;; short-circuit the whole process.
+	    (unless (run-hook-with-args-until-success 'write-contents-functions)
+              ;; If buffer has no file name, ask user for one.
+              (or buffer-file-name
+                  (let ((filename
+                         (expand-file-name
+                          (read-file-name "File to save in: "
+                                          nil (expand-file-name (buffer-name))))))
+                    (if (file-exists-p filename)
+                        (if (file-directory-p filename)
+                            ;; Signal an error if the user specified the name of an
+                            ;; existing directory.
+                            (error "%s is a directory" filename)
+                          (unless (y-or-n-p (format-message
+                                             "File `%s' exists; overwrite? "
+                                             filename))
+                            (error "Canceled"))))
+                    (set-visited-file-name filename)))
+              ;; Support VC version backups.
+	      (vc-before-save)
+	      (or (run-hook-with-args-until-success 'local-write-file-hooks)
+	          (run-hook-with-args-until-success 'write-file-functions)
+	          ;; If a hook returned t, file is already "written".
+	          ;; Otherwise, write it the usual way now.
+	          (let ((dir (file-name-directory
+			      (expand-file-name buffer-file-name))))
+		    (unless (file-exists-p dir)
+		      (if (y-or-n-p
+		           (format-message
+                            "Directory `%s' does not exist; create? " dir))
+		          (make-directory dir t)
+		        (error "Canceled")))
+		    (setq setmodes (basic-save-buffer-1)))))
 	    ;; Now we have saved the current buffer.  Let's make sure
 	    ;; that buffer-file-coding-system is fixed to what
 	    ;; actually used for saving by binding it locally.
-	    (if save-buffer-coding-system
-		(setq save-buffer-coding-system last-coding-system-used)
-	      (setq buffer-file-coding-system last-coding-system-used))
-	    (setq buffer-file-number
-		  (nthcdr 10 (file-attributes buffer-file-name)))
-	    (if setmodes
-		(condition-case ()
-		    (progn
-		      (unless
-			  (with-demoted-errors
-			    (set-file-modes buffer-file-name (car setmodes)))
-			(set-file-extended-attributes buffer-file-name
-						      (nth 1 setmodes))))
-		  (error nil))))
-	  ;; If the auto-save file was recent before this command,
-	  ;; delete it now.
-	  (delete-auto-save-file-if-necessary recent-save)
-	  ;; Support VC `implicit' locking.
-	  (vc-after-save)
+            (when buffer-file-name
+	      (if save-buffer-coding-system
+		  (setq save-buffer-coding-system last-coding-system-used)
+	        (setq buffer-file-coding-system last-coding-system-used))
+	      (setq buffer-file-number
+		    (nthcdr 10 (file-attributes buffer-file-name)))
+	      (if setmodes
+		  (condition-case ()
+		      (progn
+		        (unless
+			    (with-demoted-errors
+			        (set-file-modes buffer-file-name (car setmodes)))
+			  (set-file-extended-attributes buffer-file-name
+						        (nth 1 setmodes))))
+		    (error nil)))
+              ;; Support VC `implicit' locking.
+	      (vc-after-save))
+            ;; If the auto-save file was recent before this command,
+	    ;; delete it now.
+	    (delete-auto-save-file-if-necessary recent-save))
 	  (run-hooks 'after-save-hook))
       (or noninteractive
           (not called-interactively)
@@ -5255,7 +5265,9 @@ save-some-buffers
                      (and pred
                           (progn
                             (set-buffer buffer)
-                            (and buffer-offer-save (> (buffer-size) 0)))))
+                            (and buffer-offer-save (> (buffer-size) 0))))
+                     (buffer-local-value
+                      'write-contents-functions buffer))
                     (or (not (functionp pred))
                         (with-current-buffer buffer (funcall pred)))
                     (if arg
-- 
2.13.0

bug#28412: Acknowledgement (26.0.50; Let save-some-buffers accept write-contents-functions)

[Eli Zaretskii]

> Resent-Sender: help-debbugs@gnu.org
> From: Eric Abrahamsen <eric@ericabrahamsen.net>
> Date: Sun, 10 Sep 2017 15:01:34 -0700
> 
> Here's the latest one.

Thanks.  Can we have some simple tests for this, both with and without
visiting a file?

This also needs a NEWS entry.  And please mention the bug number in
the log message.

bug#28412: Acknowledgement (26.0.50; Let save-some-buffers accept write-contents-functions)

[Eric Abrahamsen]

> Thanks.  Can we have some simple tests for this, both with and without
> visiting a file?

Is this sufficient, do you think?


(ert-deftest files-test-no-file-write-contents ()
  "Test that `write-contents-functions' permits saving a file.
Usually `basic-save-buffer' will prompt for a file name if the
current buffer has none.  It should first call the functions in
`write-contents-functions', and if one of them returns non-nil,
consider the buffer saved, without prompting for a file
name (Bug#28412)."
  (let ((read-file-name-function
         (lambda (&rest _ignore)
           (error "Prompting for file name"))))
    ;; With contents function, and no file.
    (with-temp-buffer
      (setq write-contents-functions
            (list (lambda () t)))
      (set-buffer-modified-p t)
      (should (null (save-buffer))))
    ;; With no contents function and no file.  This should reach the
    ;; `read-file-name' prompt.
    (with-temp-buffer
      (set-buffer-modified-p t)
      (should-error (save-buffer) :type 'error))
    ;; Then a buffer visiting a file: should save normally.
    (files-tests--with-temp-file temp-file-name
      (with-current-buffer (find-file-noselect temp-file-name)
        (setq write-contents-functions nil)
        (insert "p")
        (should (null (save-buffer)))
        (should (eq (buffer-size) 1))))))

bug#28412: Acknowledgement (26.0.50; Let save-some-buffers accept write-contents-functions)

[Eli Zaretskii]

> From: Eric Abrahamsen <eric@ericabrahamsen.net>
> Cc: 28412@debbugs.gnu.org
> Date: Mon, 11 Sep 2017 14:41:08 -0700
> 
> > Thanks.  Can we have some simple tests for this, both with and without
> > visiting a file?
> 
> Is this sufficient, do you think?

Yes, I think so.  Thanks.

bug#28412: Acknowledgement (26.0.50; Let save-some-buffers accept write-contents-functions)

[Eric Abrahamsen]

Eli Zaretskii <eliz@gnu.org> writes:

>> From: Eric Abrahamsen <eric@ericabrahamsen.net>
>> Cc: 28412@debbugs.gnu.org
>> Date: Mon, 11 Sep 2017 14:41:08 -0700
>> 
>> > Thanks.  Can we have some simple tests for this, both with and without
>> > visiting a file?
>> 
>> Is this sufficient, do you think?
>
> Yes, I think so.  Thanks.

Okay, thank you. Pushed as 9b980e2691.

bug#28412: 26.0.50; Let save-some-buffers accept write-contents-functions

[Kaushal Modi]

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Hello Eric, Eli:

I became a victim of this change because of these overlapping use-cases:

- I use ggtags.el that creates a hidden (is that the right term for that?)
buffer (starting with space) to fontify code snippets using the file's
major mode.
- The major mode I use (verilog-mode) sets write-file-functions to a
non-nil value.

So each time I quit emacs, I get a prompt to save that hidden buffer "
*Code-Fontify*" (which it didn't earlier, as intended).

Details: https://github.com/leoliu/ggtags/issues/157

I suggested calling (set-buffer-modified-p nil) in that special buffer.

But is that the best way to fix this? Or should save-some-buffers never try
to save buffers whose names begin with space?

PS: Please CC me on the replies, else I won't get those.

-- 

Kaushal Modi

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bug#28412: 26.0.50; Let save-some-buffers accept write-contents-functions

[Eli Zaretskii]

> From: Kaushal Modi <kaushal.modi@gmail.com>
> Date: Mon, 18 Sep 2017 16:16:05 +0000
> 
> - I use ggtags.el that creates a hidden (is that the right term for that?) buffer (starting with space) to fontify
> code snippets using the file's major mode.
> - The major mode I use (verilog-mode) sets write-file-functions to a non-nil value.
> 
> So each time I quit emacs, I get a prompt to save that hidden buffer " *Code-Fontify*" (which it didn't earlier, as
> intended).
> 
> Details: https://github.com/leoliu/ggtags/issues/157
> 
> I suggested calling (set-buffer-modified-p nil) in that special buffer. 
> 
> But is that the best way to fix this? Or should save-some-buffers never try to save buffers whose names begin
> with space?

Exempting buffers whose name starts with a space sounds reasonable.
Eric?

bug#28412: 26.0.50; Let save-some-buffers accept write-contents-functions

[Eric Abrahamsen]

Eli Zaretskii <eliz@gnu.org> writes:

>> From: Kaushal Modi <kaushal.modi@gmail.com>
>> Date: Mon, 18 Sep 2017 16:16:05 +0000
>> 
>> - I use ggtags.el that creates a hidden (is that the right term for that?) buffer (starting with space) to fontify
>> code snippets using the file's major mode.
>> - The major mode I use (verilog-mode) sets write-file-functions to a non-nil value.
>> 
>> So each time I quit emacs, I get a prompt to save that hidden buffer " *Code-Fontify*" (which it didn't earlier, as
>> intended).
>> 
>> Details: https://github.com/leoliu/ggtags/issues/157
>> 
>> I suggested calling (set-buffer-modified-p nil) in that special buffer. 
>> 
>> But is that the best way to fix this? Or should save-some-buffers never try to save buffers whose names begin
>> with space?
>
> Exempting buffers whose name starts with a space sounds reasonable.
> Eric?

Sounds fine to me. I'm trying to think if there's some more general
interactive-vs-non-interactive case that should be protected against,
but I can't really come up with anything. The whole point of
`save-some-buffers' is the user prompt, and this seems like a fine way
to create an exception to the prompt.

I can fix it up -- the patch should go to emacs-26, right?

Eric

bug#28412: 26.0.50; Let save-some-buffers accept write-contents-functions

[Eli Zaretskii]

> From: Eric Abrahamsen <eric@ericabrahamsen.net>
> Cc: Kaushal Modi <kaushal.modi@gmail.com>,  28412@debbugs.gnu.org
> Date: Mon, 18 Sep 2017 11:14:35 -0700
> 
> I can fix it up -- the patch should go to emacs-26, right?

Yes, thanks.  Don't forget to mention the exception in the docs.

bug#28412: 26.0.50; Let save-some-buffers accept write-contents-functions

[Eric Abrahamsen]

On 09/18/17 22:25 PM, Eli Zaretskii wrote:
>> From: Eric Abrahamsen <eric@ericabrahamsen.net>
>> Cc: Kaushal Modi <kaushal.modi@gmail.com>,  28412@debbugs.gnu.org
>> Date: Mon, 18 Sep 2017 11:14:35 -0700
>> 
>> I can fix it up -- the patch should go to emacs-26, right?
>
> Yes, thanks.  Don't forget to mention the exception in the docs.

Okay, done.

bug#28412: 26.0.50; Let save-some-buffers accept write-contents-functions

[Eric Abrahamsen]

Eli Zaretskii <eliz@gnu.org> writes:

>> From: Kaushal Modi <kaushal.modi@gmail.com>
>> Date: Mon, 18 Sep 2017 16:16:05 +0000
>> 
>> - I use ggtags.el that creates a hidden (is that the right term for that?) buffer (starting with space) to fontify
>> code snippets using the file's major mode.
>> - The major mode I use (verilog-mode) sets write-file-functions to a non-nil value.
>> 
>> So each time I quit emacs, I get a prompt to save that hidden buffer " *Code-Fontify*" (which it didn't earlier, as
>> intended).
>> 
>> Details: https://github.com/leoliu/ggtags/issues/157
>> 
>> I suggested calling (set-buffer-modified-p nil) in that special buffer. 
>> 
>> But is that the best way to fix this? Or should save-some-buffers never try to save buffers whose names begin
>> with space?
>
> Exempting buffers whose name starts with a space sounds reasonable.
> Eric?

Also, there don't appear to be any built-in functions or regexps for
dealing with "hidden" buffers, I'm assuming:

(not (string-prefix-p " " (buffer-name buffer)))

is okay?

bug#28412: 26.0.50; Let save-some-buffers accept write-contents-functions

[Kaushal Modi]

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On Mon, Sep 18, 2017 at 3:12 PM Eric Abrahamsen <eric@ericabrahamsen.net>
wrote:

> Also, there don't appear to be any built-in functions or regexps for
> dealing with "hidden" buffers, I'm assuming:
>
> (not (string-prefix-p " " (buffer-name buffer)))
>
> is okay?
>

That crossed my mind too. So I had started looking for its existing
implementation, and found this in buff-menu.el inside list-buffers--refresh
function:

    (string= (substring name 0 1) " ")

I was wondering if that should be wrapped into a function like
buffer-internal-p (based on the many docstrings like below in buff-menu.el:
"By default, the Buffer Menu lists all buffers except those whose names
start with a space (which are for internal use)."). Having a function like
this would be better than having that logic implemented in different ways
in the emacs core.

I just don't know the best place to put this function definition. Eli?
-- 

Kaushal Modi

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bug#28412: 26.0.50; Let save-some-buffers accept write-contents-functions

[Eric Abrahamsen]

Kaushal Modi <kaushal.modi@gmail.com> writes:

> On Mon, Sep 18, 2017 at 3:12 PM Eric Abrahamsen <eric@ericabrahamsen.net> wrote:
>
>  Also, there don't appear to be any built-in functions or regexps for
>  dealing with "hidden" buffers, I'm assuming:
>
>  (not (string-prefix-p " " (buffer-name buffer)))
>
>  is okay?
>
> That crossed my mind too. So I had started looking for its existing implementation, and found this in buff-menu.el inside list-buffers--refresh function:
>
>     (string= (substring name 0 1) " ")
>
> I was wondering if that should be wrapped into a function like buffer-internal-p (based on the many docstrings like below in buff-menu.el: "By default, the Buffer Menu lists all buffers except those whose names start with a space
> (which are for internal use)."). Having a function like this would be better than having that logic implemented in different ways in the emacs core.
>
> I just don't know the best place to put this function definition. Eli?

It might be nice to have something like:

(defsubst buffer-internal-p (buf)
  (eq (aref (buffer-name buf) 0) ?\s))

bug#28412: 26.0.50; Let save-some-buffers accept write-contents-functions

[Kaushal Modi]

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On Mon, Sep 18, 2017 at 4:53 PM Eric Abrahamsen <eric@ericabrahamsen.net>
wrote:

>
> It might be nice to have something like:
>
> (defsubst buffer-internal-p (buf)
>   (eq (aref (buffer-name buf) 0) ?\s))
>

Yup. I also see this in the "(emacs) Undo" Info node:

   Some specialized buffers do not make undo records.  Buffers whose
names start with spaces never do; these buffers are used internally by
Emacs to hold text that users don’t normally look at or edit.

But I cannot find the code that implements that.

It would be nice to have these places to use the same defsubst.

Btw I confirm the fix. Thanks!
-- 

Kaushal Modi

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bug#28412: 26.0.50; Let save-some-buffers accept write-contents-functions

[Eli Zaretskii]

> From: Kaushal Modi <kaushal.modi@gmail.com>
> Date: Mon, 18 Sep 2017 21:48:15 +0000
> Cc: Eli Zaretskii <eliz@gnu.org>, 28412@debbugs.gnu.org
> 
> Yup. I also see this in the "(emacs) Undo" Info node:
> 
> Some specialized buffers do not make undo records. Buffers whose
> names start with spaces never do; these buffers are used internally by
> Emacs to hold text that users don’t normally look at or edit.
> 
> But I cannot find the code that implements that.

It's in get-buffer-create:

  bset_undo_list (b, SREF (name, 0) != ' ' ? Qnil : Qt);

bug#28412: 26.0.50; Let save-some-buffers accept write-contents-functions

[Kaushal Modi]

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To close the loop:

A better fix (I confirm this iteration of the fix too -- fix for the ggtags
issue[3]) for this was later applied in commit 3d3778d8[1]. See this
emacs-devel thread[2] for discussion that arrived to this conclusion.

[1]:
http://git.savannah.gnu.org/cgit/emacs.git/commit/?h=emacs-26&id=3d3778d82a87139ef50a24146f5bad2a57a82094
[2]: http://lists.gnu.org/archive/html/emacs-devel/2017-09/msg00858.html
[3]: https://github.com/leoliu/ggtags/issues/157

-- 

Kaushal Modi

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bug#28412: 26.0.50; Let save-some-buffers accept write-contents-functions

[Eric Abrahamsen]

closing

bug#28412: 26.0.50; Let save-some-buffers accept write-contents-functions

[Eli Zaretskii]

> From: Kaushal Modi <kaushal.modi@gmail.com>
> Date: Mon, 18 Sep 2017 19:23:10 +0000
> Cc: 28412@debbugs.gnu.org
> 
> (string= (substring name 0 1) " ")
> 
> I was wondering if that should be wrapped into a function like buffer-internal-p (based on the many docstrings
> like below in buff-menu.el: "By default, the Buffer Menu lists all buffers except those whose names start with a
> space (which are for internal use)."). Having a function like this would be better than having that logic
> implemented in different ways in the emacs core.
> 
> I just don't know the best place to put this function definition. Eli?

I'm not sure such a simple test should be canonicalized.

bug#28412: 26.0.50; Let save-some-buffers accept write-contents-functions

[Eli Zaretskii]

> From: Eric Abrahamsen <eric@ericabrahamsen.net>
> Cc: Kaushal Modi <kaushal.modi@gmail.com>,  28412@debbugs.gnu.org
> Date: Mon, 18 Sep 2017 12:12:01 -0700
> 
> Also, there don't appear to be any built-in functions or regexps for
> dealing with "hidden" buffers, I'm assuming:
> 
> (not (string-prefix-p " " (buffer-name buffer)))
> 
> is okay?

Yes, but I think aref would be simpler (and probably faster).