Force cabal to use a build plan where exe:cabal-plan is enabled

[fendor]

For some reason, cabal v2-install cabal-plan installs the library on macos instead of the executable, causing CI failures such as: https://github.com/haskell/cabal/pull/7477/checks?check_run_id=3170346447

Logs from CI:

  cd $(mktemp -d)
  cabal v2-install cabal-plan --constraint='cabal-plan ^>=0.6.2.0' --constraint='aeson +fast'
  shell: /bin/bash -e {0}
Resolving dependencies...
Build profile: -w ghc-8.8.3 -O1
In order, the following will be built (use -v for more details):
 - base-compat-0.11.2 (lib) (requires download & build)
 - base-orphans-0.8.4 (lib) (requires download & build)
 - base16-bytestring-0.1.1.7 (lib) (requires download & build)
 - dlist-1.0 (lib) (requires download & build)
 - hashable-1.3.2.0 (lib) (requires download & build)
 - indexed-traversable-0.1.1 (lib) (requires download & build)
 - integer-logarithms-1.0.3.1 (lib) (requires download & build)
 - primitive-0.7.1.0 (lib) (requires download & build)
 - splitmix-0.1.0.3 (lib) (requires download & build)
 - tagged-0.8.6.1 (lib) (requires download & build)
 - th-abstraction-0.4.2.0 (lib) (requires download & build)
 - transformers-compat-0.7 (lib) (requires download & build)
 - base-compat-batteries-0.11.2 (lib) (requires download & build)
 - time-compat-1.9.6 (lib) (requires download & build)
 - unordered-containers-0.2.14.0 (lib) (requires download & build)
 - data-fix-0.3.1 (lib) (requires download & build)
 - vector-0.12.3.0 (lib) (requires download & build)
 - scientific-0.3.7.0 (lib) (requires download & build)
 - random-1.2.0 (lib) (requires download & build)
 - distributive-0.6.2.1 (lib) (requires download & build)
 - attoparsec-0.14.1 (lib) (requires download & build)
 - uuid-types-1.0.5 (lib) (requires download & build)
 - comonad-5.0.8 (lib) (requires download & build)
 - bifunctors-5.5.11 (lib) (requires download & build)
 - assoc-1.0.2 (lib) (requires download & build)
 - these-1.1.1.1 (lib) (requires download & build)
 - strict-0.4.0.1 (lib) (requires download & build)
 - aeson-1.5.6.0 (lib) (requires download & build)
 - cabal-plan-0.6.2.0 (lib) (requires download & build)
Downloading  base-orphans-0.8.4

See the missing goal

 - cabal-plan-0.6.2.0 (exe:cabal-plan) (requires download & build)

And the logs also report:

...
 Completed    cabal-plan-0.6.2.0 (lib)
Warning:
@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
@ WARNING: Installation might not be completed as desired! @
@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
Without flags, the command "cabal install" doesn't expose libraries in a
usable manner. You might have wanted to run "cabal install --lib cabal-plan". 

This is a work-around to force cabal to always build the exe (At least I hope that is what it does.)

[fendor]

cc @Mikolaj

[Mikolaj]

I think we need this ASAP. If anybody finds the root cause and a better fix, this can be reverted.

[fgaz]

@Mergifyio backport 3.6

[mergify]

Command backport 3.6: pending

Waiting for the pull request to get merged

[mergify]

Command backport 3.6: failure

No backport have been created
GitHub App like Mergify are not allowed to create pull request where .github/workflows is changed.

[fgaz]

@fendor could you backport manually?

[fendor]

@fgaz sure, branch 3.6?