patch 9.0.1555: setcharsearch() does not clear last searched char properly

Problem:    setcharsearch() does not clear last searched char properly.
Solution:   Do not accept lastc_bytelen smaller than one. (closes #12398)

src/search.c

@@ -496,7 +496,7 @@ last_csearch_until(void)
 }
 
     void
-set_last_csearch(int c, char_u *s UNUSED, int len UNUSED)
+set_last_csearch(int c, char_u *s, int len)
 {
     *lastc = c;
     lastc_bytelen = len;
@@ -1789,7 +1789,7 @@ searchc(cmdarg_T *cap, int t_cmd)
     }
     else		// repeat previous search
     {
-	if (*lastc == NUL && lastc_bytelen == 1)
+	if (*lastc == NUL && lastc_bytelen <= 1)
 	    return FAIL;
 	if (dir)	// repeat in opposite direction
 	    dir = -lastcdir;
@@ -1833,7 +1833,7 @@ searchc(cmdarg_T *cap, int t_cmd)
 			return FAIL;
 		    col -= (*mb_head_off)(p, p + col - 1) + 1;
 		}
-		if (lastc_bytelen == 1)
+		if (lastc_bytelen <= 1)
 		{
 		    if (p[col] == c && stop)
 			break;

src/testdir/test_charsearch.vim

@@ -38,6 +38,8 @@ func Test_charsearch()
   " clear the character search
   call setcharsearch({'char' : ''})
   call assert_equal('', getcharsearch().char)
+  call assert_beeps('normal ;')
+  call assert_beeps('normal ,')
 
   call assert_fails("call setcharsearch([])", 'E1206:')
   enew!

src/testdir/test_charsearch_utf8.vim

@@ -13,6 +13,13 @@ func Test_search_cmds()
   call assert_equal([0, 1, 43, 0], getpos('.'))
   normal! ,
   call assert_equal([0, 1, 28, 0], getpos('.'))
+  call assert_equal('最', getcharsearch().char)
+  call setcharsearch({'char' : ''})
+  call assert_equal('', getcharsearch().char)
+  call assert_beeps('normal ;')
+  call assert_equal([0, 1, 28, 0], getpos('.'))
+  call assert_beeps('normal ,')
+  call assert_equal([0, 1, 28, 0], getpos('.'))
   bw!
 endfunc
 

src/version.c

@@ -695,6 +695,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1555,
 /**/
     1554,
 /**/