Don't prune if buildIsHost

Author: angerman

cabal-install-solver/src/Distribution/Solver/Modular/Solver.hs

@@ -24,7 +24,7 @@ import Distribution.Solver.Types.PackagePreferences
 import Distribution.Solver.Types.PkgConfigDb (PkgConfigDb)
 import Distribution.Solver.Types.LabeledPackageConstraint
 import Distribution.Solver.Types.Settings
-import Distribution.Solver.Types.Toolchain ( Toolchains(..), Toolchain(..) )
+import Distribution.Solver.Types.Toolchain ( Toolchains(..), Toolchain(..), buildIsHost )
 import Distribution.Solver.Types.Variable
 
 import Distribution.Solver.Modular.Assignment
@@ -114,7 +114,7 @@ solve sc toolchains idx pkgConfigDB userPrefs userConstraints userGoals =
   validationCata    .
   traceTree "pruned.json" id .
   trav prunePhase   .
-  trav P.pruneHostFromSetup .
+  (if buildIsHost toolchains then id else trav P.pruneHostFromSetup) .
   -- stageBuildDeps "build: " .
   traceTree "build.json" id $
   buildPhase

cabal-install-solver/src/Distribution/Solver/Types/Toolchain.hs

@@ -1,10 +1,12 @@
 {-# LANGUAGE DeriveGeneric #-}
+{-# LANGUAGE NamedFieldPuns #-}
 
 module Distribution.Solver.Types.Toolchain
   ( Toolchain (..)
   , Toolchains (..)
   , toolchainFor
   , mkToolchainsWithHost
+  , buildIsHost
   ) where
 
 import Distribution.Compat.Prelude
@@ -55,3 +57,7 @@ mkToolchainsWithHost platform compiler =
     { buildToolchain = Toolchain platform compiler (error "build program db missing")
     , hostToolchain = Toolchain platform compiler (error "host program db missing")
     }
+
+buildIsHost :: Toolchains -> Bool
+buildIsHost Toolchains {buildToolchain, hostToolchain} =
+  buildToolchain == hostToolchain