Fix infinite recursion under prettify-symbols-mode and linum-mode

* src/xdisp.c (get_overlay_strings_1)
(handle_single_display_spec, push_prefix_prop): Invalidate the
composition information before starting to iterate on a string.
Otherwise we might think in set_iterator_to_next that we are
delivering characters from a composition, and do all kinds of
nonsensical things, like over-step the string end.  (Bug#27761)

1 files changed, 3 insertions, 0 deletions

diff --git a/src/xdisp.c b/src/xdisp.c
index 422912e57a6..ad9b29835e7 100644
--- a/src/xdisp.c
+++ b/src/xdisp.c
@@ -5248,6 +5248,7 @@ handle_single_display_spec (struct it *it, Lisp_Object spec, Lisp_Object object,
           it->prev_stop = 0;
           it->base_level_stop = 0;
           it->string_from_display_prop_p = true;
+          it->cmp_it.id = -1;
           /* Say that we haven't consumed the characters with
              `display' property yet.  The call to pop_it in
              set_iterator_to_next will clean this up.  */
@@ -5966,6 +5967,7 @@ get_overlay_strings_1 (struct it *it, ptrdiff_t charpos, bool compute_stop_p)
       it->multibyte_p = STRING_MULTIBYTE (it->string);
       it->method = GET_FROM_STRING;
       it->from_disp_prop_p = 0;
+      it->cmp_it.id = -1;
 
       /* Force paragraph direction to be that of the parent
          buffer.  */
@@ -20506,6 +20508,7 @@ push_prefix_prop (struct it *it, Lisp_Object prop)
       it->stop_charpos = 0;
       it->prev_stop = 0;
       it->base_level_stop = 0;
+      it->cmp_it.id = -1;
 
       /* Force paragraph direction to be that of the parent
          buffer/string.  */