new-freeze freezes the dependencies of unused components.

[grayjay]

I reproduced this issue by adding an executable to a package that is used only as a library dependency in one of the tests in #5135: grayjay@abba0dc. The new executable has a dependency on the package exe-dependency. Since exe-dependency isn't required by any other component, new-build shouldn't need to build it. However, new-freeze adds a constraint on the package. (The commit adds an assertion checking for the constraint, and it passes.) I think that this type of constraint shouldn't be necessary in new-build, especially once we implement component-based dependency solving, and the solver doesn't need to choose dependencies for unused components.

I think this is related to the old-freeze issue #1896.

[phadej]

By playing with cabal-plan I noticed that executables of dependencies end up in the plan. For example:

servant-server-0.13 % cabal new-build --dry-run --disable-tests --disable-benchmarks
servant-server-0.13 % cabal-plan --hide-builtin dot --tred --path-from servant-server --path-to wai-app-static | dot -Tpng -odeps.png

note the exe:warp above the red line. I think it shouldn't be there.

I don't know how this works regarding store. Do we optimistically^† solve for exes too, so they end up in the plan?

EDIT But then it has a side-effect of executable showing in the plan:

servant-server-0.13 % cabal-plan list-bins
servant-server:exe:greet  .../mess/servant-server-0.13/dist-newstyle/build/x86_64-linux/ghc-8.2.2/servant-server-0.13/build/greet/greet
wai-app-static:exe:warp .../.cabal/store/ghc-8.2.2/wai-app-static-3.1.6.1-a95001e75ff661a67f5af490d2687020725f222047cf4c4377e2228e846ec3e9/bin/warp

† so solver is free to turn them off, if their deps get in the way

[grayjay]

The solver always solves for all components of every dependency, because it doesn't yet have a way to determine which components are needed. That is a big part of #4087. I had assumed that new-build immediately pruned the solver's install plan to remove unnecessary components, but it looks like that isn't true. I just checked plan.json for the small example, and it also contains the exe dependency.