[pkg/ottl] unexpected behavior of `flatten` function when handling slice attributes at top level

[bacherfl]

Component(s)

pkg/ottl

What happened?

Description

Currently, when setting the depth to 0, slices at the top level of the input of the flatten function will still be flattened.

Steps to Reproduce

Consider the following input for the flatten function:

{
  "things": [
    {
       "name": "a"
    }
  ]
}

And use the flatten function with a depth of 0:

flatten(attributes, depth=0)

Expected Result

According to the docs, there should be no flattening when the depth is set to 0, i.e. the input should be left unchanged:

{
  "things": [
    {
       "name": "a"
    }
  ]
}

Actual Result

The slice elements are flattened, regardless of the depth

{
  "things.0": {
    "name": "a"
  }
}

Collector version

v0.112.0

Environment information

Environment

OS: (e.g., "Ubuntu 20.04")
Compiler(if manually compiled): (e.g., "go 14.2")

OpenTelemetry Collector configuration

No response

Log output

No response

Additional context

No response

[github-actions]

Pinging code owners:

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

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[TylerHelmuth]

It kinda feels like a bug to let you set a depth of 0. That is the same as not calling the function.

[bacherfl]

It kinda feels like a bug to let you set a depth of 0. That is the same as not calling the function.

Yes that seemed a bit odd to me that setting the depth to 0 is a supported option. Is it possible to set this parameter dynamically as well, based on e.g. another attribute or the result of another transformation? In this case it may be justified to also support 0, even though I cannot think of a realistic use case where this might be required

[TylerHelmuth]

@bacherfl the depth parameter has to be a static value, it is not defined as a getter:

opentelemetry-collector-contrib/pkg/ottl/ottlfuncs/func_flatten.go

Line 19 in d0f4d09

Depth ottl.Optional[int64]

I think the best fix to this issue is to not allow a depth to be < 1

[bacherfl]

@bacherfl the depth parameter has to be a static value, it is not defined as a getter:

opentelemetry-collector-contrib/pkg/ottl/ottlfuncs/func_flatten.go

Line 19 in d0f4d09

Depth ottl.Optional[int64]

I think the best fix to this issue is to not allow a depth to be < 1

Got it - in this case I will adapt the PR accordingly