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Summary

The pack execute command is introduced to the Cloud Native Buildpacks ecosystem, providing a way to run only selected phases of the buildpack lifecycle. For the moment, only detect will be implemented, which will be invoked through pack execute detect.This feature enhances the developer experience by allowing them to quickly determine which buildpacks are relevant for their application without progressing through the entire build process. This was partially discussed in issue #681 but the issue was about implementing a dry-run flag. With further discussion with @jjbustamante, decided to go forward with this as a new pack detect command rather than a flag, and after further review it will be implemented as pack execute detect.

Definitions

Make a list of the definitions that may be useful for those reviewing. Include phrases and words that buildpack authors or other interested parties may not be familiar with.

Motivation

Enable the running of selected phases of buildpacks upon need.
Simplify and streamline the build process by providing a targeted command for buildpack detection.
Reduce build times by skipping unnecessary phases of the buildpack lifecycle.
Enable developers to quickly identify which buildpacks are applicable to their application without waiting for the entire build process to complete, or having to Ctrl+C midway through.
Lighter-weight integration testing of the build plan.

What it is

This provides a high level overview of the feature.

Define any new terminology.
Define the target persona: buildpack author, buildpack user, platform operator, platform implementor, and/or project contributor.
Explaining the feature largely in terms of examples.
If applicable, provide sample error messages, deprecation warnings, or migration guidance.
If applicable, describe the differences between teaching this to existing users and new users.

How it Works

Ideally, the user should run something like pack execute detect --path ./path/to/project --builder builder:name and it should run the analyze binary, followed by the detect binary in the lifecycle and output the logs / output of it. This also copies group.toml to a directory specified with --detect-output-dir, if the flag was enabled. The reason to run the analyze binary is to get information about the run image that may impact the outcome of detect via CNBTARGET* environment variables.

The following flags should be supported and they will work more or less like pack build.

Short	Long	type
-B	--builder	string
-b	--buildpack	strings
-r	--buildpack-registry	string
	--detect-output-dir	string
-d	--descriptor	string
	--docker-host	string
-e	--env	stringArray
	--env-file	stringArray
	--extension	strings
	--gid	int
-h	--help
	--lifecycle-image	string
	--network	string
-p	--path	string
	--post-buildpack	stringArray
	--pre-buildpack	stringArray
	--pull-policy	string
	--run-image	string
	--uid	int
	--workspace	string

Migration

This feature does not introduce any breaks to public APIs or compatibility. It provides additional functionality within the existing Cloud Native Buildpacks CLI tooling, enhancing the developer experience without requiring changes to existing workflows or configurations.

Drawbacks

Why should we not do this?

Alternatives

Initially thought of implementing this through something like pack build --detect. But after further discussion with @jjbustamante and for the following reasons, decided to do this functionality to a new command. Upon further review, this will be implemented as pack execute detect ..

The main use case of pack build is to create OCI images, and detect is just a binary in the lifecycle, so it doesn't make much sense to include it in there.
To avoid making the mostly used pack build command overly complicated.

Prior Art

This has been discussed in Issue #681 before, and looked like it was a long awaited feature and currently a few workarounds are being used to get this functionality.

Unresolved Questions

Fill after initial discussion

Spec. Changes (OPTIONAL)

Since this is a new command, the functionality of this command will have to be amended to the spec / docs.

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