fix derivative preserving fields from wrong point in stream

[phemmer]

#1333 changed the derivative node to add the derivative to the current point instead of the previous one. However due to a typo in the code, for stream nodes, it effectively resulted the emitted point containing the values of the previous point, the timestamp of the current point, and the derivative of the current point.

When using batch, the result was as it's supposed to be (values, timestamp, and derivative all from the current point). The batch code had the same typo, it worked because of ordering of the code.

Unfortunately there were no tests that would have caught the behavior, so I added some.

Required for all non-trivial PRs

• Rebased/mergable
• Tests pass
• CHANGELOG.md updated
• Sign CLA (if not already signed)

[nathanielc]

@phemmer Thanks! I'll take a look at this tomorrow.

[nathanielc]

@desa Can you review this as well?

In summary the issue was we carried forward the other fields from the previous point instead of the current point, which is odd since the time is of the current point as well as the derivative result.

Makes sense why we didn't catch it first as it is not the most common use case but glad we now have tests for it ❤️.

[nathanielc]

@phemmer We are planning to release a version 1.3.1 with this fix. Can you change the PR to target the v1.3 branch? Thanks

[phemmer]

branch changed.

[desa]

LGTM 👍

[desa]

@phemmer can you rebase onto v1.3 and drop the other commits?

[phemmer]

Whoops. Didn't notice that after I switched the branch. Done.
Should I also add a note to the CHANGELOG?

[nathanielc]

@phemmer

Should I also add a note to the CHANGELOG?

Yes please, I added a 1.3.1 section.

[phemmer]

done