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, 9 insertions, 0 deletions

diff --git a/src/buffer.h b/src/buffer.h
index a2bdc4e7294..be270fe4823 100644
--- a/src/buffer.h
+++ b/src/buffer.h
@@ -412,6 +412,15 @@ extern void enlarge_buffer_text (struct buffer *, ptrdiff_t);
    ? BUF_FETCH_MULTIBYTE_CHAR ((buf), (pos))    \
    : BUF_FETCH_BYTE ((buf), (pos)))
 
+/* Return character at byte position POS in buffer BUF.  If BUF is
+   unibyte and the character is not ASCII, make the returning
+   character multibyte.  */
+
+#define BUF_FETCH_CHAR_AS_MULTIBYTE(buf, pos)           \
+  (! NILP (BVAR ((buf), enable_multibyte_characters))   \
+   ? BUF_FETCH_MULTIBYTE_CHAR ((buf), (pos))            \
+   : UNIBYTE_TO_CHAR (BUF_FETCH_BYTE ((buf), (pos))))
+
 /* Return the byte at byte position N in buffer BUF.   */
 
 #define BUF_FETCH_BYTE(buf, n) \