Example Ruby buildpack actually uses system Ruby

[edmorley]

When I updated all usages of heroku/buildpacks:20 in this repository to instead use heroku/builder:22 the integration test for the example Ruby buildpack started failing.

After investigation, it turns out that the example Ruby buildpack is actually pretty broken at the moment.

For example, when the test runs, the image actually uses system Ruby, and so when run under heroku/builder:22 (which is based on Heroku-22, which no longer has system Ruby), the image fails at runtime.

The reason it's falling back to system Ruby seems to be due to the manual PATH definition here, since it's missing the delimiter:

libcnb.rs/examples/ruby-sample/src/layers/ruby.rs

Lines 46 to 57 in 6452900

	.chainable_insert(
	Scope::All,
	ModificationBehavior::Prepend,
	"PATH",
	context.app_dir.join(".gem/ruby/2.6.6/bin"),
	)
	.chainable_insert(
	Scope::All,
	ModificationBehavior::Prepend,
	"LD_LIBRARY_PATH",
	layer_path,
	),

This then causes a broken PATH:

$ dr --entrypoint launcher test-ruby -- bash
heroku@b4cc8af292e1:/workspace$ env
...
PATH=/workspace/.gem/ruby/2.6.6/bin/layers/libcnb-examples_ruby/ruby/bin:/layers/libcnb-examples_ruby/bundler/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
LD_LIBRARY_PATH=/layers/libcnb-examples_ruby/ruby/layers/libcnb-examples_ruby/ruby/lib

(See also buildpacks/spec#285)

I removed this manual PATH definition (which was also referencing Ruby 2.6, so completely wrong?), along with the seemingly also redundant LD_LIBRARY_CONFIG env var.

However then ran into another issue:

$ dr test-ruby
Could not find minitest-5.14.4 in any of the sources
Run `bundle install` to install missing gems.

As such, I'm going to exclude this example buildpack from the PR for heroku/builder:22 -- we'll have to fix this example buildpack first.

cc @schneems @Malax

[joshwlewis]

@edmorley looks like this was closed accidentally, due to the reference link in #399.

[edmorley]

Good spot, thank you :-)

[edmorley]

In addition to the issue mentioned in the OP here, there are multiple other problems with the Ruby CNB example in this repo:

• Fix issues with ruby-sample integration test #479
• Example Ruby buildpack uses unwrap() in non-test code #746
• Integration tests failing on main due to example Ruby CNB bundler error #755

IMO we should just delete this example, and instead:

1. Longer term add better (and simpler) examples to this repo, demonstrating concepts such as layer use, downloading a binary etc. (But nothing as complex as an example purporting to support a full language, like the current Ruby example)
2. Link to our actual CNBs for the "fully fledged CNB" example use-case

[edmorley]

Wontfix since the Ruby example has been removed in #757.