"Unknown build target" when using Custom setup and build-tool-depends

[martijnbastiaan]

Describe the bug
Compilation fails when some project A has a Custom setup and some project B has a build-tool-depends on an executable from project A.

To Reproduce

git clone https://github.com/martijnbastiaan/cabal-build-tool-depends-issue.git
cd cabal-build-tool-depends-issue
cabal v2-build all

Expected behavior
I would expect a custom setup that loos like:

module Main where

import Distribution.Simple (defaultMain)

main :: IO ()
main = defaultMain

to behave the same as build-type: Simple, alas, it doesn't.

Actual behavior

$ cabal v2-build all
Build profile: -w ghc-8.10.2 -O1
In order, the following will be built (use -v for more details):
 - project-a-0.1.0.0 (exe:the-exe, exe:project-a) (additional components to build)
 - project-b-0.1.0.0 (exe:project-b) (configuration changed)
setup: Unknown build target 'exe:project-a'.
There is no executable component 'project-a'.

cabal: Failed to build project-a-0.1.0.0 (which is required by exe:project-b
from project-b-0.1.0.0).

If I use a Simple build-type, it works as expected.

System information

• Ubuntu 20.04
• Cabal 3.6
• GHC 8.10