Silence GHC 8.4's "ignoring (possibly broken) abi-depends field for packages" warning

[hvr]

GHC 8.4 started emitting the following noisy warning whenever a package registration (IPI) includes a abi-depends: field (see https://ghc.haskell.org/trac/ghc/ticket/14381 for more details) cluttering the output:

Building cabal-doctest-1.0.6 (lib)...
ignoring (possibly broken) abi-depends field for packages
Configuring reflection-2.1.3 (lib)...
ignoring (possibly broken) abi-depends field for packages
Configuring semigroups-0.18.4 (lib)...
Building reflection-2.1.3 (lib)...
ignoring (possibly broken) abi-depends field for packages

This affects GHC 8.4.3 (but it probably won't affect GHC 8.4.4); since abi-depends is ignored loudly we ought to simply omit populating this field for GHCs which noisy warn about it being ignored anyway.

More generally, as it's effectively redundant (it would mostly provide an additional check in case cabal screws up the nix-style hash computation) and some distributions started to patch GHC 8.2.2; so we might as well never populate abi-depends.

[vrom911]

Unfortunately, I couldn't make it done yet. I was trying to make abiDepends = [] as I've noticed the following check in ghc that eventually prints this warning:

• https://github.com/ghc/ghc/blob/ghc-8.4/utils/ghc-pkg/Main.hs#L1222-L1223

But that doesn't help. I even tried to comment abiDepends and abiHash fields in InstalledPackageInfo but the warning is still there.

Could you please give me some advice where to go further?

[hvr]

@vrom911 I did a very crude empiric test,

diff --git a/Cabal/Distribution/Simple/Register.hs b/Cabal/Distribution/Simple/Register.hs
index 1756833..e2c704f 100644
--- a/Cabal/Distribution/Simple/Register.hs
+++ b/Cabal/Distribution/Simple/Register.hs
@@ -437,7 +437,7 @@ generalInstalledPackageInfo adjustRelIncDirs pkg abi_hash lib lbi clbi installDi
     IPI.includeDirs        = absinc ++ adjustRelIncDirs relinc,
     IPI.includes           = includes bi,
     IPI.depends            = depends,
-    IPI.abiDepends         = abi_depends,
+    IPI.abiDepends         = [], -- abi_depends,
     IPI.ccOptions          = [], -- Note. NOT ccOptions bi!
                                  -- We don't want cc-options to be propagated
                                  -- to C compilations in other packages.

which did have the effect to silence GHC 8.4.3's ghc-pkg register; are you sure you tested the correct cabal executable?

[hvr]

@vrom911 oh, there's one thing I forgot to mention: setting abiDepends to [] won't silence the warnings for packages using custom Setup.hs (i.e. build-type: Custom)! So unfortunately this won't be a perfect fix.

[hvr]

reopening to keep track for a potential backport to 2.2