xml test output: remove legacy fallback

[rockwotj]

Boost test when writing XML files may sometimes omit the decimal point,
but still write in scientific notation as floating point seconds. To
support reading these XML files, remove the legacy fallback for these time values
where it falls back to integer milliseconds if there are no decimal points.

Fixes: #24605

[RaHorEl]

✍🏾

[travisdowns]

// This is ugly. For Historical Reasons, we have to check whether the number
// contains a decimal point or not. If it does, the number is expressed in [seconds else ms]

Hmm, pretty sure boost doesn't play this game either, e.g., if the time happens to be an integer value like 1 there will be no decimal point in the output. H/e we can work around this on the boost side too.

[rockwotj]

Yes from everywhere I have read this is supposed to always represent seconds - so maybe it's possible to just remove the millisecond fallback case?

[rockwotj]

Actually I wonder if the better route is to just remove the millisecond fallback entirely. Every tool that can write this that I have checked uses seconds for their attribute, the code hasn't changed since it was open sourced in 2015. I guess this would require an incompatible change flag. I can update the PR monday

[fmeum]

@meisterT Can you check whether Google still relies on the fallback logic?

[meisterT]

I think it's obsolete, but I will do some follow-up code archeology. Give me two more days.

[rockwotj]

Thanks @meisterT! I've proactively updated my PR in hopes the code archeology provides to confirm the fallback behavior is obsolete.

[meisterT]

Spoke too soon, sorry. Turns out it is still necessary and in more than one place :-/

The need was introduced in 2008, removed in 2009 and re-introduced in a couple of places (cargo culting I assume) in 2016+. It is non-trivial to clean these up. While I will see whether I can do that, it will take a while and Bazel for now shouldn't remove the fallback. Sorry again.

[rockwotj]

Can we add an --incompatible flag to disable them for Bazel but Blaze can keep them on?

[meisterT]

We could, but I am not sure whether it's worth the effort.