Split component into its own module

[jpkrohling]

From @bogdandrutu:

One question is if we want to have this package OR move everything into go.opentelemetry.io/collector/CMP (where CMP is one of receiver/processor/exporter/extension).

[codeboten]

is there an agreement on how to proceed with this split? I guess if we were to split all the type specific stuff out of component, we'd end up with some amount of repetition in the name:

import "go.opentelemetry.io/collector/exporter"

exporter.ExporterFactory
exporter.Exporter
exporter.TracesExporter

instead of what it is currently:

import "go.opentelemetry.io/collector/component"

component.ExporterFactory
component.Exporter
component.TracesExporter

It would be possible to remove some of that repetition, but I'm not sure what we would call the TracesExporter for example to make it less repetitive. I do like having the components packages separated per type to only include what's relevant in each one, and reduce the amount of code imported for each one.

@open-telemetry/collector-approvers any thoughts?

[Aneurysm9]

We could eliminate a bunch of that repetition in the per-component case, I think:

import "go.opentelemetry.io/collector/exporter"

exporter.Factory
exporter.Exporter
exporter.Traces

Not sure that there's a better name for exporter.Exporter, but url.URL exists and the world hasn't come to an end. v0v

[codeboten]

Some observations after digging into this a bit further while trying to split exporter out of component:

1. making component.Exporter an alias to exporter.Exporter causes a circular dependency since exporter.Exporter depends on component
2. this lead me down the road to split the minimum of component first and lead me to the next bump in the road
3. splitting exporter/extension from component means handling the circular dependency on Host which currently uses Extension and Exporter

Thoughts?

[dmitryax]

I don't believe we can move things from component to go.opentelemetry.io/collector/[receiver|processor|exporter|extension] at least because of component.Host. I'm not 100% sure we need to extract those parts from component, but, if we want to, maybe we can have the following packages instead:

go.opentelemetry.io/collector/component/exporter
go.opentelemetry.io/collector/component/receiver
go.opentelemetry.io/collector/component/processor
go.opentelemetry.io/collector/component/extention
go.opentelemetry.io/collector/component/host

And it's not that simple, we will also need to move other things (like component.Kind/Component) since there are interdependencies with Host.

[codeboten]

After further digging into this, the Host complication makes the split per component impractical. My plan is to keep component as a single package containing the different component types within it.

[bogdandrutu]

I made a prototype, and I think it is simple to do the split, see #6552

The main idea behind is that Host depends on "Extension" and "Exporter" interfaces which are useless anyway, they can be replaced by using Component (since they are simple renames for Component anyway), something like #6553

[dmitryax]

I submitted a follow-up issue for the split suggested by @bogdandrutu #6578