[IMPALA-3018] min(), max(), and first_value() will DCHECK on empty strings

• Type: Bug
• Status: Resolved
• Priority: Blocker
• Resolution: Fixed
• Affects Version/s: Impala 2.5.0
• Fix Version/s: Impala 2.5.0, Impala 2.7.0
• Component/s: Backend
• Labels: crash
• Target Version: Impala 2.5.0, Impala 2.7.0
• Assignee: Michael Ho
• Reporter: Skye Wanderman-Milne
• Created: 17/Feb/16 22:35
• Updated: 06/Sep/16 17:09
• Resolved: 13/Jul/16 21:05

Description

This is a very easy bug to fix, we need to remove/change the following DCHECK:

static void CopyStringVal(FunctionContext* ctx, const StringVal& src, StringVal* dst) {
  DCHECK_GT(src.len, 0); // <---- this DCHECK is wrong, should be GE
  uint8_t* copy = ctx->Allocate(src.len);
  if (UNLIKELY(copy == NULL)) {
    DCHECK(!ctx->impl()->state()->GetQueryStatus().ok());
    *dst = StringVal::null();
  } else {
    *dst = StringVal(copy, src.len);
    memcpy(dst->ptr, src.ptr, src.len);
  }

However, it appears we have very little to no test coverage on empty strings. This should also be added.