Determine the issues and PRs for a release using the GitHub APIs

[sleberknight]

Use the GitHub REST APIs to get the PRs and issues associated with a release.

This completely replaces the existing logic, which parses git commit messages to determine the issue numbers. However, this has increasingly been causing unrelated issues to be included in the generated change logs, especially when it parses commit messages from dependabot PRS. The dependabot PRs include release notes which usually includes the issue numbers and therefore can confuse the existing logic; it does not and cannot distinguish issue numbers from some other repository's release notes, and therefore includes them.

There are some issues with the GitHub APIs that will need to be handled.

1. The issues API provides a milestone query parameter, however it is the milestone number (e.g., 42) as opposed to the string (e.g., "2.4.0"). So, the REST endpoints for milestones must be used to find the milestone number, which can then be used to query for issues. Unfortunately, the milestone endpoints don't provide a way to filter on a string, so we need to query for all the open milestones and find the one we want. By limiting to open milestones, we should never need to worry about pagination.
2. The issues API defaults to finding open issues, but when doing a release, all issues should be closed. We could also use the all state and consider any open issues associated with a release to be an error.
3. We will need to handle pagination in most if not all requests.
4. The pull requests API does not provide any way to filter based on milestone, so we need to figure out a way to avoid going through every PR in a repository. For example, we might need to get the date of the previous release, and then paginate through PRs until we see one before that date.
5. When looking at PRs, we need to filter out ones that are associated with an issue, while retaining "bare" PRs that have the milestone we are releasing for. For example, PRs created by dependabot will not be associated with an issue, but they will have a milestone (which we should have assigned).

When combining the issues and PRs, we'll want to retain the existing behavior of listing from most to least recent, such that issues and PRs are listed in descending order of creation.

Update:

I think I found a much easier way to find issues an PRs for a milestone, which is to use the REST API endpoints for search, and specifically Searching issues and pull requests using Search by milestone.

And to find commit authors, we can use Compare two commits

This supersedes #26.

GitHub API references:

• REST API endpoints for pull requests
• REST API endpoints for issues
• REST API endpoints for milestones
• REST API endpoints for releases
• REST API endpoints for search
• Searching issues and pull requests
• Search by milestone
• Compare two commits

[sleberknight]

Here are some example curls:

$ curl -s -L \
  -H "Accept: application/vnd.github+json" \
  -H "Authorization: Bearer <your-token>" \
  -H "X-GitHub-Api-Version: 2022-11-28" \
  "https://api.github.com/search/issues?q=repo:kiwiproject/kiwiproject-changelog+milestone:0.11.0"

$ curl -s -L \
  -H "Accept: application/vnd.github+json" \
  -H "Authorization: Bearer <your-token>" \
  -H "X-GitHub-Api-Version: 2022-11-28" \
  "https://api.github.com/search/issues?q=repo:kiwiproject/kiwiproject-changelog+milestone:0.12.0"

[sleberknight]

You can pipe the above results into jq to get only the titles:

... | jq '.items[].title'

[sleberknight]

Notes on GitHub issue/PR responses:

• JSON object contains "total_count" of items
• contains "items" array, which contains the issue and PR objects
• issue and PR objects both contain "title", "html_url" and "number"
• issue and PR objects both contain a "labels" array
• the "labels" array contains objects
• each label object contains a "name" and a boolean "default",
• it is not clear how why a label is the "default", and in dependabot PRs there are two labels and both have "default" value of false
• probably just choose the first label and ignore "default"
• issue objects do NOT contain a "pull_request" object
• PR objects DO contain a "pull_request" object
• I don't think we actually need the "pull_request" object
• if we want to add the contributor information, I think this
  is contained in the "user" object
• the "user" object contains "login" (e.g., "sleberknight" or "dependabot[bot]")
• "user" object also contains an "html_url" which would be the link in the release notes

[sleberknight]

The structure of the response to a search for issues and PRs for a milestone has the top-level structure:

{
  "total_count": 8,
  "incomplete_results": false,
  "items": [
    { },
    { },
  ]
}

[sleberknight]

Here is example JSON for an issue/PR, with only parts we care about and everything else removed:

    {
      "html_url": "https://github.com/kiwiproject/kiwiproject-changelog/issues/174",
      "number": 174,
      "title": "Provide an \"installation\" script",
      "user": {
        "login": "sleberknight",
        "html_url": "https://github.com/sleberknight",
      },
      "labels": [
        {
          "name": "new feature",
          "default": false,
        }
      ]
    }