Switch from stacks to targets AKA "Stay on target" (#283)

* Bump the libcnb group across 1 directory with 3 updates

Bumps the libcnb group with 3 updates in the / directory: [libcnb](https://github.com/heroku/libcnb.rs), [libherokubuildpack](https://github.com/heroku/libcnb.rs) and [libcnb-test](https://github.com/heroku/libcnb.rs).


Updates `libcnb` from 0.17.0 to 0.19.0
- [Release notes](https://github.com/heroku/libcnb.rs/releases)
- [Changelog](https://github.com/heroku/libcnb.rs/blob/main/CHANGELOG.md)
- [Commits](heroku/libcnb.rs@v0.17.0...v0.19.0)

Updates `libherokubuildpack` from 0.17.0 to 0.21.0
- [Release notes](https://github.com/heroku/libcnb.rs/releases)
- [Changelog](https://github.com/heroku/libcnb.rs/blob/main/CHANGELOG.md)
- [Commits](heroku/libcnb.rs@v0.17.0...v0.21.0)

Updates `libcnb-test` from 0.17.0 to 0.19.0
- [Release notes](https://github.com/heroku/libcnb.rs/releases)
- [Changelog](https://github.com/heroku/libcnb.rs/blob/main/CHANGELOG.md)
- [Commits](heroku/libcnb.rs@v0.17.0...v0.19.0)

---
updated-dependencies:
- dependency-name: libcnb
  dependency-type: direct:production
  update-type: version-update:semver-minor
  dependency-group: libcnb
- dependency-name: libherokubuildpack
  dependency-type: direct:production
  update-type: version-update:semver-minor
  dependency-group: libcnb
- dependency-name: libcnb-test
  dependency-type: direct:production
  update-type: version-update:semver-minor
  dependency-group: libcnb
...

Signed-off-by: dependabot[bot] <[email protected]>

* Change to mutable layers

The layer trait interface was changed to mutable in heroku/libcnb.rs#669

* Switch from stacks to targets AKA "Stay on target"

Buildpack API 0.10 removed the concept of stacks in favor of targets heroku/libcnb.rs#773.

This commit works to upgrade applications in place by migrating metadata to support the new serialization format. This is supported by implementing TryMigrate from the `magic_migrate` crate https://docs.rs/magic_migrate/latest/magic_migrate/macro.try_migrate_link.html.

https://www.youtube.com/watch?v=NnP5iDKwuwk

* Add explicit Distro/Architecture cache messages

* Use updated magic_migrate macros

* Apply suggestions from code review

Co-authored-by: Ed Morley <[email protected]>

* Document breaking changes

* Align warning messages and error names

* Update buildpack.toml

- Add explanation for when stacks can be removed
- Move "targets" closer to "stacks" as they're logically tied together.

* Integration test for metadata migration

* Support heroku-20 and heroku-22 (only)

This buildpack does not support heroku-24 (yet) remove this stack from the TargetId struct. It also supports heroku-20 which was previously not present.

* Fix changelog

* Standardize println in integration tests

* Consistent cache clear messages

---------

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>
Co-authored-by: Ed Morley <[email protected]>

buildpacks/ruby/CHANGELOG.md

@@ -7,6 +7,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+- The buildpack now implements Buildpack API 0.10 instead of 0.9, and so requires `lifecycle` 0.17.x or newer. ([#283](https://github.com/heroku/buildpacks-ruby/pull/283/files#commit-suggestions))
+
 ## [2.1.3] - 2024-03-18
 
 ### Changed

buildpacks/ruby/Cargo.toml

@@ -16,8 +16,8 @@ glob = "0.3"
 indoc = "2"
 # libcnb has a much bigger impact on buildpack behaviour than any other dependencies,
 # so it's pinned to an exact version to isolate it from lockfile refreshes.
-libcnb = "=0.17.0"
-libherokubuildpack = { version = "=0.17.0", default-features = false, features = ["digest"] }
+libcnb = "=0.21.0"
+libherokubuildpack = { version = "=0.21.0", default-features = false, features = ["digest"] }
 rand = "0.8"
 # TODO: Consolidate on either the regex crate or the fancy-regex crate, since this repo currently uses both.
 regex = "1"
@@ -27,7 +27,8 @@ tempfile = "3"
 thiserror = "1"
 ureq = { version = "2", default-features = false, features = ["tls"] }
 url = "2"
+magic_migrate = "0.2"
+toml = "0.8"
 
 [dev-dependencies]
-libcnb-test = "=0.17.0"
-toml = "0.8"
+libcnb-test = "=0.21.0"

buildpacks/ruby/buildpack.toml

@@ -1,4 +1,4 @@
-api = "0.9"
+api = "0.10"
 
 [buildpack]
 id = "heroku/ruby"
@@ -11,11 +11,22 @@ keywords = ["ruby", "rails", "heroku"]
 [[buildpack.licenses]]
 type = "BSD-3-Clause"
 
+# This workaround can be removed once a new Pack release ships that includes:
+# https://github.com/buildpacks/pack/pull/2081
 [[stacks]]
-id = "heroku-20"
+id = "*"
 
-[[stacks]]
-id = "heroku-22"
+[[targets]]
+os = "linux"
+arch = "amd64"
+
+[[targets.distros]]
+name = "ubuntu"
+version = "20.04"
+
+[[targets.distros]]
+name = "ubuntu"
+version = "22.04"
 
 [metadata.release]
 image = { repository = "docker.io/heroku/buildpack-ruby" }

buildpacks/ruby/src/layers/bundle_download_layer.rs

@@ -1,11 +1,10 @@
+use crate::RubyBuildpack;
+use crate::RubyBuildpackError;
+use commons::gemfile_lock::ResolvedBundlerVersion;
 use commons::output::{
     fmt,
     section_log::{log_step, log_step_timed, SectionLogger},
 };
-
-use crate::RubyBuildpack;
-use crate::RubyBuildpackError;
-use commons::gemfile_lock::ResolvedBundlerVersion;
 use fun_run::{self, CommandWithName};
 use libcnb::build::BuildContext;
 use libcnb::data::layer_content_metadata::LayerTypes;
@@ -46,7 +45,7 @@ impl<'a> Layer for BundleDownloadLayer<'a> {
     }
 
     fn create(
-        &self,
+        &mut self,
         _context: &BuildContext<Self::Buildpack>,
         layer_path: &Path,
     ) -> Result<LayerResult<Self::Metadata>, RubyBuildpackError> {
@@ -106,7 +105,7 @@ impl<'a> Layer for BundleDownloadLayer<'a> {
     }
 
     fn existing_layer_strategy(
-        &self,
+        &mut self,
         _context: &BuildContext<Self::Buildpack>,
         layer_data: &LayerData<Self::Metadata>,
     ) -> Result<ExistingLayerStrategy, RubyBuildpackError> {