Re: [PATCH] ob-tangle: Add flag to optionally remove files before writing

[Olivier Lischer]

Ihor Radchenko <yantar92@posteo.net> writes:

> Olivier Lischer <olivier.lischer@liolin.ch> writes:
>
>>> Thanks for the patch, but may you please explain why introducing such
>>> variable is useful?
>>
>> Sure.
>>
>> I configure all my .dotfiles in an Org mode file and tangle the
>> configuration in the right places. The tangled files are all
>> read-only to prevent accidentally editing of the "right" configuration
>> file. With the current tangling mechanism, this results in a "Permission
>> denied" error because the function writes to a read-only file. In a
>> earlier version this use case was possible because the file was
>> recreated before writing to it.
>
> Thanks for the explanation!
>
> I suggest changing your patch, setting the default value of
> `org-babel-tangle-remove-file-before-write' to 'auto.
> This will keep the current behaviour but fall back to delete + write new
> file when the tangle target is read-only.
> That will avoid feature regression.

I changed the path as you proposed.

>From a464592f622ba42732a5449d2c4db51f1975444a Mon Sep 17 00:00:00 2001
From: Olivier Lischer <olivier.lischer@liolin.ch>
Date: Tue, 23 Jan 2024 21:02:20 +0100
Subject: [PATCH] ob-tangle: Add flag to optionally remove files before writing

* lisp/ob-tangle.el: Add variable
`org-babel-tangle-remove-file-before-write'.
(org-babel-tangle): Remove file before writing when
`org-babel-tangle-remove-file-before-write' is set.

The variable `org-babel-tangle-remove-file-before-write' adds support
for the current and old behaviour of `org-babel-tangle'.

TINYCHANGE
---
 etc/ORG-NEWS      |  4 ++++
 lisp/ob-tangle.el | 14 ++++++++++----
 2 files changed, 14 insertions(+), 4 deletions(-)

diff --git a/etc/ORG-NEWS b/etc/ORG-NEWS
index f537486d4..c7c3ee264 100644
--- a/etc/ORG-NEWS
+++ b/etc/ORG-NEWS
@@ -800,6 +800,10 @@ Completion is enabled for links to man pages added using 
~org-insert-link~:
 =C-c C-l man RET emacscl TAB= to get =emacsclient=.  Of course, the ~ol-man~
 library should be loaded first.
 
+*** =ob-tangle.el=: Add flag to optionally remove files before writing
+
+When ~org-babel-tangle-remove-file-before-write~ is set to ~t~ the file is 
removed before writing.
+
 ** New functions and changes in function arguments
 *** New API functions to store data within ~org-element-cache~
 
diff --git a/lisp/ob-tangle.el b/lisp/ob-tangle.el
index 72089a9a5..64b7c2cf8 100644
--- a/lisp/ob-tangle.el
+++ b/lisp/ob-tangle.el
@@ -141,7 +141,7 @@ controlled by the :comments header argument."
   :version "24.1"
   :type 'string)
 
-(defcustom org-babel-tangle-uncomment-comments nil
+(defcustom org-babel-tangle-uncomment-comments 'auto
   "Inhibits automatic commenting and addition of trailing newline
 of tangle comments.  Use `org-babel-tangle-comment-format-beg'
 and `org-babel-tangle-comment-format-end' to customize the format
@@ -166,6 +166,12 @@ read-write permissions for the user, read-only for 
everyone else."
   :package-version '(Org . "9.6")
   :type 'integer)
 
+(defcustom org-babel-tangle-remove-file-before-write nil
+  "Prevents the deletion of an existing file before tangle"
+  :group 'org-babel-tangle
+  :package-version '(Org . "9.7")
+  :type 'boolean)
+
 (defun org-babel-find-file-noselect-refresh (file)
   "Find file ensuring that the latest changes on disk are
 represented in the file."
@@ -313,9 +319,9 @@ matching a regular expression."
                                       (compare-buffer-substrings
                                        nil nil nil
                                        tangle-buf nil nil)))))))
-                     ;; We do not erase, but overwrite previous file
-                     ;; to preserve any existing symlinks.
-                    (write-region nil nil file-name)
+                     (when (and (file-exists-p file-name) 
org-babel-tangle-remove-file-before-write)
+                       (delete-file file-name))
+                     (write-region nil nil file-name)
                     (mapc (lambda (mode) (set-file-modes file-name mode)) 
modes))
                    (push file-name path-collector))))))
         (if (equal arg '(4))
-- 
2.43.0