Add an assertion to xdisp.c

* src/xdisp.c (display_mode_element): Add an assertion where
we assume that 'string' returned by decode_mode_spec is always
either a Lisp string or nil.

diff --git a/src/xdisp.c b/src/xdisp.c
index 63ca677e3620603a6365babc70420993ca7dfa35..d380645c8491f295bdf0640f3bdc5e812b28a1a5 100644 (file)
--- a/src/xdisp.c
+++ b/src/xdisp.c
@@ -24026,6 +24026,7 @@ display_mode_element (struct it *it, int depth, int field_width, int precision,
                               ? string_byte_to_char (elt, bytepos)
                               : bytepos);
                    spec = decode_mode_spec (it->w, c, field, &string);
+                   eassert (NILP (string) || STRINGP (string));
                    multibyte = !NILP (string) && STRING_MULTIBYTE (string);
 
                    switch (mode_line_target)