Unflatten non-deterministic and panics

[cwohlman]

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Describe the bug The unflatten function is returning wrong, non-deterministic, and buggy results for me. Depending on how I run my query (same underlying data & eventual result), I will get either a panic, incorrect data, and/or different results each time I run the same query.

To Reproduce The simplest way to reproduce the issue, which seems to give some insight into the underlying problem is:

1. Load reproduction.txt
2. Run this query: { ts, foo: unflatten(this.collect) }

Changing the query to { ts, ...(unflatten(this.collect)) } results in different (incorrect) behavior.

Loading my data & intermediate queries up instead of the reproduction data above results in a panic about 50% of the time.

Expected behavior I expect the unflatten function not to carry over state from one record to the next, and for the behavior to be consistent across re-runs of the same query.

Desktop Info

• OS: Windows
• Brim Version: 0.29.0