Alert the user that on Windows, with configuration executable-dynamic: True executables (including build-tools) cannot be built

[andreasabel]

This issue is singled out from:

• cabal install Agda fails in Setup.hs with executable-dynamic: True in config file (Linux) #9784

Adding executable-dynamic: True to the cabal configuration on Windows will fail executables to build.
This include situations where you just want to build a library, but it has build-tool-depends: alex or similar causing the linking of build-tool alex to fail.

Reproduced on a fresh Haskell installation: https://github.com/agda/agda/actions/runs/8213506540/job/22465003537#step:10:233

Building executable 'alex' for alex-3.5.1.0..
[ 1 of 19] Compiling DFS              ( src\DFS.hs, dist\build\alex\alex-tmp\DFS.dyn_o )

src\DFS.hs:24:8: error: [GHC-88719]
Error:     Could not load module ‘Prelude’.
    Perhaps you haven't installed the "dyn" libraries for package ‘base-4.19.1.0’?

[jasagredo]

Dynamic linking in Windows is simply not supported by GHC. This is not a Cabal bug unless you wanted to imply that executable-dynamic: True should crash before even attempting compilation on Windows.

I'm closing this issue, please re-open of you disagree

[andreasabel]

I do disagree.

This is not a Cabal bug unless you wanted to imply that executable-dynamic: True should crash before even attempting compilation on Windows.

I do think it should exit with an error explaining the problem.

Aren't we Haskell programmers? Aren't we proposing strong typing?
GHC does not compile ill-typed programs. Cabal should not process ill-formed configurations either.

[jasagredo]

Perfectly understandable!

Could you change the title or description so that just with a glance it is clear that is what you would like to see implemented?

I think the idea is very useful and might be worth adding a specific mechanism for it so that other configurations that are known unusable are also included (such as using rpath on Windows which I think also fails)

[jasagredo]

Note this already exists with relocatable builds:

➜ cabal build --enable-relocatable
Resolving dependencies...
Build profile: -w ghc-9.8.2 -O1
In order, the following will be built (use -v for more details):
 - aa-0.1.0.0 (lib) (configuration changed)
Configuring library for aa-0.1.0.0...
Error: [Cabal-3339]
Operating system: windows, does not support relocatable builds

Error: [Cabal-7125]
Failed to build aa-0.1.0.0. The failure occurred during the configure step.

It should just be a matter of doing a very similar check for shared executables if we are on Windows.

[ulysses4ever]

Sounds like a low-hanging fruit then. I'll put the "newcomer" label on it.

[jasagredo]

Ah actually I did it while waiting for some tests, it was barely a 10 lines change in total