[Emacs-diffs] master f3b24e9: Add assertion to STRING_SET_CHARS

[Eli Zaretskii]

branch: master
commit f3b24e90dc9fad355102e1fdf2828ca33d447a07
Author: Eli Zaretskii <address@hidden>
Commit: Eli Zaretskii <address@hidden>

    Add assertion to STRING_SET_CHARS
    
    * src/lisp.h (STRING_SET_CHARS): Add an assertion and commentary
    to prevent incorrect usage.  For details, see this discussion:
    http://lists.gnu.org/archive/html/emacs-devel/2017-04/msg00412.html.
---
 src/lisp.h | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/src/lisp.h b/src/lisp.h
index 678e261..e0bad58 100644
--- a/src/lisp.h
+++ b/src/lisp.h
@@ -1369,6 +1369,10 @@ SBYTES (Lisp_Object string)
 INLINE void
 STRING_SET_CHARS (Lisp_Object string, ptrdiff_t newsize)
 {
+  /* This function cannot change the size of data allocated for the
+     string when it was created.  */
+  eassert ((STRING_MULTIBYTE (string) && newsize <= SBYTES (string))
+          || (!STRING_MULTIBYTE (string) && newsize == SCHARS (string)));
   XSTRING (string)->size = newsize;
 }