Parity: `Could not find target named 'exec2'` failure when building sample package (SwiftBuild)

[bkhouri]

Running the swift run swift-build --package-path Fixtures/Miscellaneous/MultipleExecutables --target exec2 fails with an unexpected error message.

❯ swift run swift-build --package-path Fixtures/Miscellaneous/MultipleExecutables --target exec2 --build-system swiftbuild
Building for debugging...
[1/1] Write swift-version--68B999B8113CC7E.txt
Build of product 'swift-build' complete! (0.35s)
error: Could not find target named 'exec2'
error: The operation couldn’t be completed. (TSCUtility.Diagnostics error 0.)

Observed on branch main (commit ID ec2a626d905c74d71745912ac83ae55ddb179844).

[bkhouri]

There is a sample package in the Swift Package manager that is used for tests Fixtures/Miscellaneous/MultipleExecutables. This package defined 3 targets and three products. The products are a 1:1 mapping to the targets, which there is 1 library and 2 targets, that have a main.swift, which makes them executables.

With the native build system, swift build --target <name> allows the user to specify executable targets. However, with SwiftBuild, the executable target do not appear as a node in the PIF - though the associated product does build correctly as it contains the executable target information. So a user running swift build --target <name> --build-system swiftbuild will be presented with an error.

There are a few solutions:

1. Clearly document this as a behaviour difference between the native and SwiftBuild - the users can always execute --product isntead of --target
2. Have SwiftPM try to build the most suitable product if the target does not exist. Then, how do we handle the case if there are multiple suitable products for a given target?
3. Modify the PIF so a node exists for the executable target, and modify the product target to depend on said node.

Thoughts/question/concerns?