Why does Stack rebuild unrelated source files? What are the recommended project structures?

[SmartHypercube]

Example repo: https://github.com/SmartHypercube/aoc2023-haskell

When I add another executable (by adding an executable in package.yaml and adding a file in src directory), and run stack run <new executable name>, Stack rebuilds all other executables. I would like to know why does this happen. I guess it is because I used a bad project structure, but I have tried some other ways to organized the files and directories, and each structure has its own problems.

I wish Stack could provide some tips about how should people organize project files for different types of projects (e.g. 1 lib + 1 exe, 1 lib + many exe, 0 lib + many exe, etc.). A good project structure should mean that adding / removing / updating source files should always result in the minimum set of files recompiled.

[mpilgrem]

Purportedly due to a bug in some versions of Cabal (the library), the first time Stack builds any component of a local package, it builds all the executable components. So, for an example package foo with executables foo1 and foo2:

❯ stack ide targets
foo:lib
foo:exe:foo1-exe
foo:exe:foo2-exe
foo:test:foo-test

❯ stack build foo:lib # Just build the library components
Building all executables for foo once. After a successful build of all of them, only specified
executables will be rebuilt.
foo> configure (lib + exe)
...
Installing executable foo1-exe in D:\Users\mike\Code\Haskell\foo\.stack-work\install\3f52e67e\bin
Installing executable foo2-exe in D:\Users\mike\Code\Haskell\foo\.stack-work\install\3f52e67e\bin
Registering library for foo-0.1.0.0..

❯ stack build foo:lib # Second time around (nothing will build; already all built)

When you add a new executable component to an existing local package description, Stack knows it has to unregister the previous version of the package and re-build the 'new' package - and the above applies to the building of the 'new' package.

[mpilgrem]

See #3486 for background to the bug in some versions of Cabal (the library). Stack may be able to move forward with this problem after Stack 2.15.1, because I am proposing that Stack cease supporting Cabal < 2.2. See #6377.