Switch to file-per-change changelog

[ysaito1001]

Motivation and Context

Implements RFC: File-per-change changelog

Description

When this PR is merged to main, it will impact developer workflow for creating a changelog entry that goes with a PR.
Prior to this, one edited CHANGELOG.next.toml to enter a changelog entry, but it often caused merge conflicts among us. With this PR, one creates a .md file (any filename stem will do) under the smithy-rs/.changelog directory. This Markdown file has the YAML front matter, and it can be created manually or via the ChangeLogger CLI (see this commit for more details).

Here are the highlights of the code changes:

• The release script has been pointed to smithy-rs/.changelog. This is pretty much what it takes to let the smithy-rs release infra switch to the new changelog mode.
• sdk-lints now disallows CHANGELOG.next.toml. It will complain if the file is present.
• The --source-to-truncate option for the changelogger's render is now optional because our internal release infra code no longer needs to specify that option (i.e. there is nothing to truncate there).
• Tests in smithy-rs-tool-common and changelogger have been updated so TOML changelog entries used in tests have been re-written to Markdown changelog entries. We want to avoid giving the false impression that TOML changelog entries are still well-supported.

Testing

• Existing tests & lints in CI
• Ran smithy-rs dry-run release and confirmed the correctness of CHANGELOG.md and SDK_CHANGELOG.next.json in the release artifacts
• Ran the internal release and confirmed CHANGELOG.md was rendered correctly in aws-sdk-rust

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[landonxjames]

Nice! Look forward to not having to merge from main to fix the CHANGELOG ever again

[github-actions]

A new generated diff is ready to view.

• No codegen difference in the AWS SDK
• No codegen difference in the Client Test
• No codegen difference in the Server Test
• No codegen difference in the Server Test Python
• No codegen difference in the Server Test Typescript

A new doc preview is ready to view.

[github-actions]

A new generated diff is ready to view.

• No codegen difference in the AWS SDK
• No codegen difference in the Client Test
• No codegen difference in the Server Test
• No codegen difference in the Server Test Python
• No codegen difference in the Server Test Typescript

A new doc preview is ready to view.

[drganjoo]

Just curious, why is the .changelog a directory and not a file? Especially since the PR description mentions that a .md file will be created. What does the changelogger tool do if multiple files are present? Also, what is the recommendation if a PR closes multiple open tickets? Should we create multiple .md files or just one and add entries to the references field list?

[drganjoo]

Thank you for making this change to the changelogger!

[github-actions]

A new generated diff is ready to view.

• No codegen difference in the AWS SDK
• No codegen difference in the Client Test
• No codegen difference in the Server Test
• No codegen difference in the Server Test Python
• No codegen difference in the Server Test Typescript

A new doc preview is ready to view.

[github-actions]

A new generated diff is ready to view.

• No codegen difference in the AWS SDK
• No codegen difference in the Client Test
• No codegen difference in the Server Test
• No codegen difference in the Server Test Python
• No codegen difference in the Server Test Typescript

A new doc preview is ready to view.

[ysaito1001]

Just curious, why is the .changelog a directory and not a file? Especially since the PR description mentions that a .md file will be created.

Not sure if I understand the question? If .changelog were a file, that'd be another version of CHANGELOG.next.toml where everyone would step on each other. The .changelog directory is a place to store individual changelog entry Markdown files by which we can avoid merge conflicts when we generate changelog entries (see RFC).

What does the changelogger tool do if multiple files are present?

As of this PR, while rendering release notes, channgelogger "folds" individual changelog entry Markdown files in the .changelog directory into what would otherwise be the contents of CHANGELOG.next.toml. But we don't have to care about that; we just need to create individual .md files under the .changelog directory.

Also, what is the recommendation if a PR closes multiple open tickets?

This won't change compared to what we've been doing for CHANGELOG.next.toml: list multiple issues in references.

Should we create multiple .md files or just one and add entries to the references field list?

Again, this is the same as today, just list multiple issues in references in a single Markdown file. If you use the changelogger CLI, then you can specify --references <issue#> (or -r <issue#>) repeatedly.