Add support for `-g` option

[bitonic]

-g builds libraries with DWARF symbols, but it's quite awkward to use it:

cabal install --disable-library-stripping --ghc-options="-g -rtsopts"

I think we should have a flag that automatically does the above.

Moreover, I'd also like a flag that stores the downloaded source, so that the debug symbols will refer to sources which still exist.

[cartazio]

i think you can add that to your ~/.cabal/config file as a default ghc options flag

[23Skidoo]

This seems to be already implemented (fbf8499). Try cabal install --disable-library-stripping --enable-debug-info.

/cc @tibbe

[bitonic]

OK, I'd still like the second part to happen:

Moreover, I'd also like a flag that stores the downloaded source, so that the debug symbols will refer to sources which still exist.

It's extremely nice to get perf output side-by-side to the Haskell source.

[bitonic]

Also, I'd say that --enable-debug-info should automatically disable library stripping, if that's not the case already.

[23Skidoo]

Yes, makes sense.

[mpickering]

Just to point out that debug-info doesn't imply --disable-library-stripping still, which makes debug-info on its own rather useless. If someone points me to the right file then I will prepare a patch.

[lukel97]

@mpickering see also this TODO left here https://www.haskell.org/cabal/users-guide/nix-local-build.html#cfg-field-executable-stripping

[23Skidoo]

@mpickering Good place to start is running rg stripLib and rg stripExe. We should also add a warning to cabal-install that fires when the user explicitly enables both one of library/executable-stripping: True and debug-info: True in the config file.

I think that normally one will want to either enable debug-info on per-project basis, or enable it system-wide just for libraries and use the default (strip exes) for exes cabal installed system-wide. So perhaps we need a separate library-debug-info option?

[mpickering]

@23Skidoo It seems the natural place to implement this is Cabal.Distribution.Simple.Configure.configure but by that point we have lost the knowledge about how the option came to be set. Where is the right place to implement warnings about things found in cabal.project files?

[mpickering]

defaultConfigFlags also seems to set the default to Flag True rather than NoFlag.

Unless there is a similar warning I can look at to see where to implement this check it seems like a lot of untangling to implement the logic where a warning happens if the user has explicitly set the option.