* src/marker.c (buf_bytepos_to_charpos): Re-add the CHAR_HEAD_P assertion

This assertion was removed in 1c349c62305d432abf0fa2b6e3f5d754fe4cab79
because the assumption was invalid during set_intervals_multibyte_1.
So we change set_intervals_multibyte_1 to solve the problem in the same
way as in the rest of Fset_buffer_multibyte, which actually simplifies
the code.

* src/buffer.c (advance_to_char_boundary): Not static any more.
* src/buffer.h (advance_to_char_boundary): Add prototype.
* src/intervals.c (set_intervals_multibyte_1): Use it.

1 files changed, 4 insertions, 0 deletions

diff --git a/src/buffer.h b/src/buffer.h
index f42c3e97b97..2080a6f40b7 100644
--- a/src/buffer.h
+++ b/src/buffer.h
@@ -327,6 +327,10 @@ extern void enlarge_buffer_text (struct buffer *, ptrdiff_t);
 #define BYTE_TO_CHAR(bytepos)                   \
   (buf_bytepos_to_charpos (current_buffer, bytepos))
 
+/* For those very rare cases where you may have a "random" pointer into
+   the middle of a multibyte char, this moves to the next boundary.  */
+extern ptrdiff_t advance_to_char_boundary (ptrdiff_t byte_pos);
+
 /* Convert PTR, the address of a byte in the buffer, into a byte position.  */
 
 #define PTR_BYTE_POS(ptr) \