nix: use the matching weeder

weeder needs to be compiled with the same GHC that we build postgrest
with.

Before this change, we were relying on the fact that we happened
to set ${compiler} to the same ghc8107 as used by nixpkgs for
haskellPackages, now we explicitly take it from the correct
haskell package set.

default.nix

@@ -149,6 +149,7 @@ rec {
       inherit postgrest devCabalOptions withTools;
       ghc = pkgs.haskell.compiler."${compiler}";
       inherit (pkgs.haskell.packages."${compiler}") hpc-codecov;
+      inherit (pkgs.haskell.packages."${compiler}") weeder;
     };
 
   withTools =

nix/tools/tests.nix

@@ -5,12 +5,12 @@
 , ghc
 , glibcLocales
 , gnugrep
-, haskellPackages
 , hpc-codecov
 , jq
 , postgrest
 , python3
 , runtimeShell
+, weeder
 , withTools
 , yq
 }:
@@ -137,7 +137,7 @@ let
 
         (
           trap 'echo Found dead code: Check file list above.' ERR ;
-          ${haskellPackages.weeder}/bin/weeder --config=./test/weeder.dhall
+          ${weeder}/bin/weeder --config=./test/weeder.dhall
         )
 
         # collect all tests