Re: Questionable code in handling of wordend in the regexp engine in regex-emacs.c

[Alan Mackenzie <acm@muc.de>]

Hello, Eli.

On Fri, Mar 01, 2019 at 16:43:38 +0200, Eli Zaretskii wrote:
> > Date: Fri, 1 Mar 2019 14:14:48 +0000
> > From: Alan Mackenzie <acm@muc.de>
> > Cc: monnier@iro.umontreal.ca, emacs-devel@gnu.org

> > > buf_bytepos_to_charpos is not supposed to be called when the byte
> > > position is in the middle of a multibyte sequence.  We have the
> > > CHAR_HEAD_P, BYTES_BY_CHAR_HEAD, and related macros for that.

> > Thanks, I didn't know that.  Maybe we should put an assert into the code,
> > like Stefan suggested.

> We could try.

How about this, as a first approximation?



diff --git a/src/marker.c b/src/marker.c
index 36d6b10c74..9faeca49f4 100644
--- a/src/marker.c
+++ b/src/marker.c
@@ -311,7 +311,8 @@ buf_charpos_to_bytepos (struct buffer *b, ptrdiff_t charpos)
     }									\
 }
 
-/* Return the character position corresponding to BYTEPOS in B.  */
+/* Return the character position corresponding to BYTEPOS in B.
+   BYTEPOS must be at a character boundary.  */
 
 ptrdiff_t
 buf_bytepos_to_charpos (struct buffer *b, ptrdiff_t bytepos)
@@ -370,6 +371,8 @@ buf_bytepos_to_charpos (struct buffer *b, ptrdiff_t bytepos)
 	  best_below++;
 	  BUF_INC_POS (b, best_below_byte);
 	}
+      /* Check BYTEPOS was at a character boundary. */
+      eassert (best_below_byte == bytepos);
 
       /* If this position is quite far from the nearest known position,
 	 cache the correspondence by creating a marker here.
@@ -397,6 +400,8 @@ buf_bytepos_to_charpos (struct buffer *b, ptrdiff_t bytepos)
 	  best_above--;
 	  BUF_DEC_POS (b, best_above_byte);
 	}
+      /* Check BYTEPOS was at a character boundary. */
+      eassert (best_above_byte == bytepos);
 
       /* If this position is quite far from the nearest known position,
 	 cache the correspondence by creating a marker here.


-- 
Alan Mackenzie (Nuremberg, Germany).