Improve warning message

https://github.com/ruby/ruby/pull/2637#discussion_r341812475

1 files changed, 2 insertions, 2 deletions

diff --git a/re.c b/re.c
index 6b8eda4df8..34880a849c 100644
--- a/re.c
+++ b/re.c
@@ -3324,7 +3324,7 @@ rb_reg_match_m(int argc, VALUE *argv, VALUE re)
     }
 
     if (NIL_P(str)) {
-        rb_warn("given argument is nil");
+        rb_warn("given argument is nil; this will raise a TypeError in the next release");
     }
     pos = reg_match_pos(re, &str, pos);
     if (pos < 0) {
@@ -3372,7 +3372,7 @@ rb_reg_match_p(VALUE re, VALUE str, long pos)
     int tmpreg;
 
     if (NIL_P(str)) {
-        rb_warn("given argument is nil");
+        rb_warn("given argument is nil; this will raise a TypeError in the next release");
         return Qfalse;
     }
     str = SYMBOL_P(str) ? rb_sym2str(str) : StringValue(str);