How to track executable dependencies

[phadej]

• When executable components (built-tool-depends) are put into the store, they are just put there.
• However, when InstallPlan checks for dependencies, it checks that the dependencies of an executable are also in the store
  • This is right thing to do, as there might be library with data-files for example
• Yet, there is no way to know, by just looking at the store, whether the executable component has all dependencies (and they are unbroken)
  • For libraries, there are .conf files in package.db

This is important for garbage collection of the store:

• If we look only at ~/.cabal/bin as the roots
• they will retain the executable component
• but the executable component won't retain any of its dependencies

Then, if we clean up the dependencies:

• Executable might stop working if dependencies data files are gone, ... or
• cabal will error out, when checking the integrity of InstallPlan

[phadej]

And I'm answering my own question: we do track dependencies, in cabal-plan.txt of the component:

pkgid: markdown-unlit-0.5.0
component: ComponentExe (UnqualComponentName "markdown-unlit")
src: e72d0d7b82525e2a2c664012ce9dc35835b3fff91040d9f20897ed82f24ec7bf
pkg-config-deps: 
deps: base-4.12.0.0, base-compat-0.10.5-3b5d3efb11225e77473051317734ad1e9266f98a1ce6336434585878bd100296, markdown-unlit-0.5.0-31c3eb468b531f32d377152c509e7b48d3309f30aef14c6e32c9e61edd97873e
compilerid: ghc-8.6.5
platform: x86_64-linux
shared-lib: True
stripped-exe: False
debug-info: 0