Fixed varint length when buffer is reallocated.

tests/conformance_upb_failures.txt

@@ -12,10 +12,4 @@ Required.ProtobufInput.RepeatedScalarSelectsLast.FIXED32.ProtobufOutput
 Required.ProtobufInput.RepeatedScalarSelectsLast.FIXED64.ProtobufOutput
 Required.ProtobufInput.RepeatedScalarSelectsLast.UINT64.ProtobufOutput
 Required.ProtobufInput.ValidDataRepeated.BOOL.ProtobufOutput
-Required.ProtobufInput.ValidDataRepeated.INT32.ProtobufOutput
-Required.ProtobufInput.ValidDataRepeated.INT64.ProtobufOutput
-Required.ProtobufInput.ValidDataRepeated.SINT32.ProtobufOutput
-Required.ProtobufInput.ValidDataRepeated.SINT64.ProtobufOutput
-Required.ProtobufInput.ValidDataRepeated.UINT32.ProtobufOutput
-Required.ProtobufInput.ValidDataRepeated.UINT64.ProtobufOutput
 Required.ProtobufInput.ValidDataScalar.BOOL.ProtobufOutput

upb/encode.c

@@ -167,12 +167,12 @@ static bool upb_encode_array(upb_encstate *e, const char *field_mem,
 #define VARINT_CASE(ctype, encode) { \
   ctype *start = arr->data; \
   ctype *ptr = start + arr->len; \
-  char *buf_ptr = e->ptr; \
+  size_t pre_len = e->limit - e->ptr; \
   do { \
     ptr--; \
     CHK(upb_put_varint(e, encode)); \
   } while (ptr != start); \
-  CHK(upb_put_varint(e, buf_ptr - e->ptr)); \
+  CHK(upb_put_varint(e, e->limit - e->ptr - pre_len)); \
 } \
 break; \
 do { ; } while(0)