[FLINK-25608][metrics] Annotate metrics classes with Public(Evolving)

[fapaul]

What is the purpose of the change

Our metrics classes are already treated as if they are public. This PR annotates the bases classes with @Public and the metrics helper exposed to the connectors with @PublicEvolving. We also fix some of our arch unit test by introducing the annotations

The change was initially required by #18302.

Brief change log

• Annotate metrics classes with public annotations

Verifying this change

• Arch unit tests still pass

Does this pull request potentially affect one of the following parts:

• Dependencies (does it add or upgrade a dependency): (yes / no)
• The public API, i.e., is any changed class annotated with @Public(Evolving): (yes / no)
• The serializers: (yes / no / don't know)
• The runtime per-record code paths (performance sensitive): (yes / no / don't know)
• Anything that affects deployment or recovery: JobManager (and its components), Checkpointing, Kubernetes/Yarn, ZooKeeper: (yes / no / don't know)
• The S3 file system connector: (yes / no / don't know)

Documentation

• Does this pull request introduce a new feature? (yes / no)
• If yes, how is the feature documented? (not applicable / docs / JavaDocs / not documented)

[fapaul]

@zentol I extracted the metrics API annotations to a separate ticket please have another look.

[flinkbot]

Thanks a lot for your contribution to the Apache Flink project. I'm the @flinkbot. I help the community
to review your pull request. We will use this comment to track the progress of the review.

Automated Checks

Last check on commit 549e1b1 (Tue Jan 11 09:44:40 UTC 2022)

Warnings:

• 1 pom.xml files were touched: Check for build and licensing issues.
• No documentation files were touched! Remember to keep the Flink docs up to date!

_{Mention the bot in a comment to re-run the automated checks.}

Review Progress

• ❓ 1. The [description] looks good.
• ❓ 2. There is [consensus] that the contribution should go into to Flink.
• ❓ 3. Needs [attention] from.
• ❓ 4. The change fits into the overall [architecture].
• ❓ 5. Overall code [quality] is good.

Please see the Pull Request Review Guide for a full explanation of the review process.

The Bot is tracking the review progress through labels. Labels are applied according to the order of the review items. For consensus, approval by a Flink committer of PMC member is required

Bot commands

The @flinkbot bot supports the following commands:

• @flinkbot approve description to approve one or more aspects (aspects: description, consensus, architecture and quality)
• @flinkbot approve all to approve all aspects
• @flinkbot approve-until architecture to approve everything until architecture
• @flinkbot attention @username1 [@username2 ..] to require somebody's attention
• @flinkbot disapprove architecture to remove an approval you gave earlier

[flinkbot]

CI report:

• 64b0798 Azure: SUCCESS

Bot commands

The @flinkbot bot supports the following commands:

• @flinkbot run azure re-run the last Azure build

[zentol]

How did you decide which classes should be public? I see that Metric and all extending interfaces are Public, yet View isn't despite being an extension for metrics.

Why are the reporter interfaces not annotated?

[fapaul]

How did you decide which classes should be public? I see that Metric and all extending interfaces are Public, yet View isn't despite being an extension for metrics.

Why are the reporter interfaces not annotated?

Good question, I mainly went through the metrics classes relevant for connectors. Do you think all classes inside the metrics-core module should be annotated?

[zentol]

Do you think all classes inside the metrics-core module should be annotated?

All interfaces + the AbstractReporter/HistogramStatistics/MetricConfig classes I think.
The remaining classes (SimpleCounter, MeterView, UnregisteredMetricsGroup) should be @Internal.

[fapaul]

I went through all the metrics classes and added the proper annotation. Thanks for your help.

[fapaul]

@zentol can you confirm this annotation?

[zentol]

yes this should be fine. While we do intend to drop it in 2.0, until then it should remain stable.

[zentol]

@flinkbot run azure