string.c: preserve coderange in rb_str_drop_bytes()

It is currently always clears the coderange.

1 files changed, 8 insertions, 1 deletions

diff --git a/string.c b/string.c
index 2012a281d6..c5ef67a6c6 100644
--- a/string.c
+++ b/string.c
@@ -4434,7 +4434,14 @@ rb_str_drop_bytes(VALUE str, long len)
 	RSTRING(str)->as.heap.len = nlen;
     }
     ptr[nlen] = 0;
-    ENC_CODERANGE_CLEAR(str);
+    if (ENC_CODERANGE(str) == ENC_CODERANGE_VALID) {
+	int n = rb_enc_precise_mbclen(ptr, ptr + nlen, STR_ENC_GET(str));
+        if (!MBCLEN_CHARFOUND_P(n))
+	    ENC_CODERANGE_SET(str, ENC_CODERANGE_BROKEN);
+    }
+    else if (ENC_CODERANGE(str) == ENC_CODERANGE_BROKEN) {
+	ENC_CODERANGE_CLEAR(str);
+    }
     return str;
 }