pack build should support --extension

[natalieparellano]

Description

Today you can run pack build --buildpack to dynamically add buildpacks to the builder and modify the order. It should be possible to add extensions in the same way.

Proposed solution

• --extensions should always come first
• There is a separate order for extensions (order-extensions in order.toml) so we'll need to take that into account
• This should be blocked on pack should support pack extension * commands #1470 (support for pack extension package) as --extension can accept a package input - we can make a separate issue for extension packages

Additional context

• This feature should be documented somewhere

[edithwuly]

Hi @natalieparellano, I would like to have a try at this issue.

[natalieparellano]

That is awesome @edithwuly! I can assign the issue to you if you like. In case it's helpful, here are a few relevant places in the code:

• pack/pkg/client/build.go

  Line 133 in 0a19002

  Buildpacks []string

  - Buildpacks holds additional buildpacks from --buildpack; we'll likely want to make an Extensions

• pack/internal/commands/build.go

  Line 161 in 0a19002

  Buildpacks: buildpacks,

  - where we read in the build options

• pack/pkg/client/build.go

  Line 751 in 0a19002

  func (c *Client) processBuildpacks(ctx context.Context, builderImage imgutil.Image, builderBPs []dist.ModuleInfo, builderOrder dist.Order, stackID string, opts BuildOptions) (fetchedBPs []buildpack.BuildModule, order dist.Order, err error) {

  - where we download the additional buildpacks; we can likely re-use some of this function for extensions; however the project descriptor part is not relevant and instead of appending to bldr.Order(), we want to append to bldr.OrderExtensions()

Please don't hesitate to reach out if you have any questions!

[edithwuly]

Thanks @natalieparellano! It will be great if you could assign this issue to me. And the places you share are exactly what I'm looking for. I will let you know as soon as there is progress.

[jjbustamante]

Thanks a lot for helping us with this @edithwuly!

[edithwuly]

Hi @natalieparellano, I have looking into the code and have some idea about what to do.

• pack/pkg/client/build.go

  Line 133 in 6219ee5

  Buildpacks []string

  • I'm going to create a field Extensions to hold additional extensions from --extension

• pack/pkg/client/build.go

  Line 751 in 6219ee5

  func (c *Client) processBuildpacks(ctx context.Context, builderImage imgutil.Image, builderBPs []dist.ModuleInfo, builderOrder dist.Order, stackID string, opts BuildOptions) (fetchedBPs []buildpack.BuildModule, order dist.Order, err error) {

  • I'm going to create a function processExtensions() to fetch and order extensions. I believe I can re-use some code of processBuildpacks(). And I notice there are many conditions considered in processBuildpacks() like locatorType and opts.PreBuildpacks. Is there any condition I need to consider when processing extensions?

• pack/pkg/client/build.go

  Line 942 in 6219ee5

  func (c *Client) createEphemeralBuilder(rawBuilderImage imgutil.Image, env map[string]string, order dist.Order, buildpacks []buildpack.BuildModule) (*builder.Builder, error) {

  • I'm going to pass the fetched extensions and order to createEphemeralBuilder(), and add them to the builder by invoking bldr.AddExtension() and bldr.SetOrderExtensions()

Is there anything wrong or missed?

[natalieparellano]

@edithwuly that looks right to me! For processExtensions(), all LocatorType values are valid for extensions also, except for RegistryLocator. You don't need to worry about opts.PreBuildpacks, because there isn't an equivalent concept for extensions.

[edithwuly]

@natalieparellano sounds great! Thanks for your help! I'm working on it.

[edithwuly]

Hi @natalieparellano! I have completed a simple version and proposed a PR. Please help me review, thanks!

Besides, when developing, I have some questions:

• About the order of extensions. I'm not sure whether the added extensions should be placed at first, and I just re-used prependBuildpackToOrder() since there is no pre or post concept for extensions.
• I handle RegistryLocator in processExtensions() and re-used fetchBuildpack() to fetch extensions by just adding ModuleKind value in DownloadOptions structure. Is there any conditions I didn't consider?
• Should I do some unit tests or end-to-end tests? I have tested this version for tutorial case on Buildpack official website. Maybe you can help me get more test cases!

[natalieparellano]

@edithwuly thank you so much for the PR! I'll look this over tomorrow :)