[pkg/ottl] Add math expressions support to slices dynamic indexing

[edmocosta]

Component(s)

pkg/ottl

Is your feature request related to a problem? Please describe.

OTTL supports indexing maps and slices with dynamic values (#36644), allowing statements to access elements using any ottl.mathExprLiteral literal (Int, String, Converter, Path), which is great.

Maybe, It would be useful to extend the slice indexing support with math expressions, so we would be able to also access elements that needs some kind of computation. For example, to get the last slice's element, we can currently use:

log_statements:
 - context: log
   statements:
    - set(cache["last"], Len(attributes["array.attribute"]) - 1)
    - set(attributes["new"], attributes["array.attribute"][cache["last"]])

With math expression support, we could avoid using the cache and express the above statements as:

log_statements:
 - context: log
   statements:
    - set(attributes["new"], attributes["array.attribute"][Len(attributes["array.attribute"]) - 1)])

Describe the solution you'd like

--

Describe alternatives you've considered

Using cache, which also seems reasonable.

Additional context

No response

[github-actions]

Pinging code owners:

• pkg/ottl: @TylerHelmuth @kentquirk @bogdandrutu @evan-bradley @edmocosta

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[odubajDT]

Hey, I would like to look at this if it gets accepted

[TylerHelmuth]

I support this idea

[odubajDT]

@edmocosta @TylerHelmuth created a draft PR with a working version.

Will add some more tests in the next days before marking it ready for review. If you have time, you can have a first look and also if you have ideas for statements you would like to have in E2E tests, it will be appreciated!