Can a dependency be a TARGET?

[philderbeast]

This function shows every single single component in elaboratedPlanToExecute. This does not correspond to the list of available targets.

E.g.

✦ ~/code/cabal branchless/09946f1d1fa1217f4480d9ac919e2b264b5a3ecb*
λ $(cabal list-bin cabal) target
...
 - uuid-types:lib
 - vector-algorithms:lib
 - vector-binary-instances:lib
 - vector-stream:lib
 - vector-th-unbox:lib
 - vector:lib
 - wherefrom-compat:lib
 - witherable:lib
 - zinza:lib
 - zlib:lib

✦ ~/code/cabal branchless/09946f1d1fa1217f4480d9ac919e2b264b5a3ecb* 10s
λ $(cabal list-bin cabal) build zlib:lib
Warning: this is a debug build of cabal-install with assertions enabled.
Error: [Cabal-7130]
Internal error in target matching: could not make an unambiguous fully qualified target
selector for 'zlib:lib'. We made the target 'zlib:lib' (unknown-component) that was expected
to be unambiguous but matches the following targets:
'zlib:lib', matching:
  - zlib:lib (unknown-component)
  - :pkg:zlib:lib:zlib:file:lib (unknown-file)

Note: Cabal expects to be able to make a single fully qualified name for a target or provide
a more specific error. Our failure to do so is a bug in cabal.
Tracking issue: https://github.com/haskell/cabal/issues/8684

Hint: this may be caused by trying to build a package that exists in the project directory but
is missing from the 'packages' stanza in your cabal project file.

Originally posted by @andreabedini in #9744 (comment)

I added a printPlanTargetForms that would print zlib:lib as if it was a target. With the above command snippet, @andreabedini shows that this is not a target. I did a little more exploration around this and found that while zlib:lib and zlib:lib:zlib are rejected as targets (to the build command for example), the package name by itself is not rejected in the same way.

$ cabal clean

$ cabal build zlib:lib
...
Error: [Cabal-7130] (as above)
...

$ cabal build zlib:lib:zlib
...
Error: [Cabal-7130]
Internal error in target matching: could not make an unambiguous fully qualified target
selector for 'zlib:lib:zlib'. We made the target 'zlib:lib:zlib' (unknown-component) that was
expected to be unambiguous but matches the following targets:
'zlib:lib:zlib', matching:
  - zlib:lib:zlib (unknown-component)
  - zlib:lib:zlib (unknown-file)
':pkg:zlib:lib:zlib', matching:
  - zlib:lib:zlib (unknown-component)
...

$ cabal build zlib
...
Resolving dependencies...
Up to date

We can cabal build all --only-dependencies and this will:

Install only the dependencies necessary to build the given packages.

SOURCE: cabal users guide - phase control

If it is possible to build only dependencies then is it possible to build only a single dependency? If so, where do I go looking for the build artifacts?

What is cabal actually doing with cabal build zlib? Is zlib a target?

$ cabal build --help
Compile targets within the project.

Usage: cabal build [TARGETS] [FLAGS]