Add the Publish Site workflow

[slachiewicz]

Part of codehaus-plexus/.github#58. Calls the shared workflow from codehaus-plexus/.github#62, so this site can be published from the Actions tab instead of by someone running mvn site-deploy on their laptop.

Merge codehaus-plexus/.github#65 first. Without it this would publish to the wrong branch — see below.

This repository is the odd one out

Every other site in the organisation is a project page served from gh-pages. This is the organisation page, and it is served from master:

$ gh api repos/codehaus-plexus/codehaus-plexus.github.io/pages
"source": { "branch": "master", "path": "/" }

The POM already knows that:

<!-- see https://help.github.com/articles/user-organization-and-project-pages/ -->
<scmBranch>master</scmBranch>

But the shared workflow as merged forces -Dscmpublish.scm.branch=gh-pages, which would have overridden it and pushed this site to a branch nobody serves. The build would have reported success; the only symptom would have been the site quietly never updating.

codehaus-plexus/.github#65 removes that override so the branch comes from the POM, which is where it was already correct. That is my bug from #62 — I generalised from the fourteen project sites without checking the org page. Adding this caller is what surfaced it.

The caller itself

Identical to the single-module form in codehaus-plexus/plexus-utils#334, with a comment recording why this one is different so the next person does not have to rediscover it. No multi-module input: this is a single-module build with content set to target/site.

Please dry-run it first

The workflow exposes dry-run, which builds the site and checks out the target branch without committing. Worth using here more than anywhere else, since a mistake publishes to the front page of the organisation.

I have not run it. Note also that a real run will republish the site from current source, which includes the pages converted to Markdown in #22 — so it would be worth having that reviewed first if you want the two changes to land separately.

[slachiewicz]

Updated: now passes publish-branch: master explicitly.

The dry run you triggered failed, and usefully — it showed the whole authentication approach was broken, not just the branch:

[INFO] Checking out the pub tree from scm:git:git@github.com:codehaus-plexus/...
[ERROR] ssh: Could not resolve hostname ...

maven-scm-publish-plugin ignored the https pubScmUrl the workflow passed, because the parent POM sets that parameter explicitly in <configuration> and an explicit value always wins over a -D user property. It would have failed the same way in all fifteen repositories.

codehaus-plexus/.github#66 fixes it by pushing with git directly. Merge that first, then this is ready for another dry run.