Add command to replace buffer contents

Add a new command 'replace-buffer-contents' that uses the Myers diff
algorithm to non-destructively replace the accessible portion of the
current buffer.  The Myers algorithm is implemented in Gnulib.

* src/editfns.c (Freplace_buffer_contents): New command.
(set_bit, bit_is_set, buffer_chars_equal): New helper functions.
(syms_of_editfns): Define new command.

* test/src/editfns-tests.el (replace-buffer-contents-1)
(replace-buffer-contents-2): New unit tests.

* src/buffer.h (BUF_FETCH_CHAR_AS_MULTIBYTE): New helper macro.

* admin/merge-gnulib (GNULIB_MODULES): Add diffseq.h and minmax.h.

1 files changed, 31 insertions, 0 deletions

diff --git a/test/src/editfns-tests.el b/test/src/editfns-tests.el
index 3073e371933..a3ea8ab60b5 100644
--- a/test/src/editfns-tests.el
+++ b/test/src/editfns-tests.el
@@ -208,4 +208,35 @@
                  '(error "Invalid format operation %$")))
   (should (equal (format "%1$c %1$s" ?±) "± 177")))
 
+(ert-deftest replace-buffer-contents-1 ()
+  (with-temp-buffer
+    (insert #("source" 2 4 (prop 7)))
+    (let ((source (current-buffer)))
+      (with-temp-buffer
+        (insert "before dest after")
+        (let ((marker (set-marker (make-marker) 14)))
+          (save-restriction
+            (narrow-to-region 8 12)
+            (replace-buffer-contents source))
+          (should (equal (marker-buffer marker) (current-buffer)))
+          (should (equal (marker-position marker) 16)))
+        (should (equal-including-properties
+                 (buffer-string)
+                 #("before source after" 9 11 (prop 7))))
+        (should (equal (point) 9))))
+    (should (equal-including-properties
+             (buffer-string)
+             #("source" 2 4 (prop 7))))))
+
+(ert-deftest replace-buffer-contents-2 ()
+  (with-temp-buffer
+    (insert "foo bar baz qux")
+    (let ((source (current-buffer)))
+      (with-temp-buffer
+        (insert "foo BAR baz qux")
+        (replace-buffer-contents source)
+        (should (equal-including-properties
+                 (buffer-string)
+                 "foo bar baz qux"))))))
+
 ;;; editfns-tests.el ends here