generate-pipeline should have a build tool plugin.

[dabrahams]

You can now have SPM plugins that generate code. Here's an example, and here it is in use.

[allevato]

Historical context: We attempted this (#416, #419) but it had to be reverted (#424) due to CI issues (and IIRC, there were SPM bugs on Windows as well that prevented the plug-in from executing properly).

But it's good to have an issue to track this, since I'd love to bring it back once those issues are resolved.

[ahoppen]

Tracked in Apple’s issue tracker as rdar://126948334