Add version control tools to the heroku-16/18 build images

[jmorrell]

I'm mainly opening this to prompt discussion and learn.

After a recent discussion with @freeformz slack link I found that the go buildpack needs to install mercurial and bazaar version control tools to support go.mod apps.

Relevant PR: heroku/heroku-buildpack-go#345

These seem like tools that should be in the build stack image. Is there a reason they are not there? Has there been previous discussion around this? (search is not bringing things up)

[freeformz]

Adding this to the build images would allow me to remove stuff from the go buildpack and generally make things easier for a few customers. So I'm +1000 on this.

[freeformz]

Related to this heroku/heroku-buildpack-go#345

[jmorrell]

Note: I've not tested this and am mainly interested in learning if there are any blockers / objections. CI is currently failing, but I will do due diligence on the PR if there aren't any.

[freeformz]

I fixed the build errors and at least one more.

[edmorley]

The Postgres key error fix has been split out to #143 - could you rebase on top of master and remove that change? (The key has been replaced rather than a second added; which is why it's not showing any conflicts)

[edmorley]

These seem like tools that should be in the build stack image. Is there a reason they are not there? Has there been previous discussion around this? (search is not bringing things up)

I like the idea of adding these packages. I don't remember seeing any discussion about them on this repo before.

In general I think the possible reasons for not adding a new package are:

• that it increases the build/runtime image sizes too much - however this PR only results in a 40MB increase for heroku-16-build and 20MB for heroku-18-build (and none for the runtime image), so a non-issue
• that it allows for anti-patterns (for example including the sqlite headers makes it easier for apps to inadvertently use ephemeral dyno storage for ORM backends) - but I don't think that applies here
• that it might be incompatible with existing buildpacks/apps

Regarding the last point - I'm presuming the Go buildpack will happily continue to use the vendored binaries in preference to the new ones in the stack image, so therefore not an issue?

[jmorrell]

@edmorley rebased 👍

[edmorley]

Thank you for the changes - looks good to me 👍

[edmorley]

This has been released to staging, if you'd like to test there? :-)

[edmorley]

The changes here are now in production.

[edmorley]

Unfortunately today's stack image update had to be rolled back (due other dependency updates from upstream), so the VCS tools won't be available in production for a bit longer.