[elpa] externals/org f6f26d4ce4 1/2: org-babel-tangle: Do not overwrite when contents does not change

[ELPA Syncer]

branch: externals/org
commit f6f26d4ce4622660762a3d1fabb5000455adb7b5
Author: Ihor Radchenko <yantar92@gmail.com>
Commit: Ihor Radchenko <yantar92@gmail.com>

    org-babel-tangle: Do not overwrite when contents does not change
    
    * lisp/ob-tangle.el (org-babel-tangle): Do not overwrite existing
    tangled files if their contents is exactly the same as we are going to
    write during tangle process.  This avoids unneeded disk writes and can
    speed up tangling significantly when many small files are tangled from
    a single .org source.
    
    An example of performance improvement when tangling an .org file into
    ~200 files:
    (benchmark-run 10 (org-babel-tangle))
    Before the commit (on SSD): (76.33826743 8 11.551725374)
    After the commit:           (43.628606052 4 5.751274237)
---
 lisp/ob-tangle.el | 23 ++++++++++++++++++-----
 1 file changed, 18 insertions(+), 5 deletions(-)

diff --git a/lisp/ob-tangle.el b/lisp/ob-tangle.el
index 16d938afb7..6685a15999 100644
--- a/lisp/ob-tangle.el
+++ b/lisp/ob-tangle.el
@@ -282,11 +282,24 @@ matching a regular expression."
                    lspecs)
                   (when make-dir
                     (make-directory fnd 'parents))
-                   ;; erase previous file
-                   (when (file-exists-p file-name)
-                     (delete-file file-name))
-                  (write-region nil nil file-name)
-                  (mapc (lambda (mode) (set-file-modes file-name mode)) modes)
+                   (unless
+                       (and (file-exists-p file-name)
+                            (let ((tangle-buf (current-buffer)))
+                              (with-temp-buffer
+                                (insert-file-contents file-name)
+                                (and
+                                 (equal (buffer-size)
+                                        (buffer-size tangle-buf))
+                                 (= 0
+                                    (let (case-fold-search)
+                                      (compare-buffer-substrings
+                                       nil nil nil
+                                       tangle-buf nil nil)))))))
+                     ;; erase previous file
+                     (when (file-exists-p file-name)
+                       (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))
             (org-babel-tangle-single-block 1 t)