Apply some @mpickering comments

Author: yvan-sraka

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

@@ -54,7 +54,7 @@ import Distribution.Simple.Setup
 import Distribution.Simple.Utils
          ( ordNubBy )
 import Distribution.Verbosity
-import Distribution.Solver.Modular.Message (SolverTrace (..))
+import Distribution.Solver.Modular.Message (SolverTrace (..), renderSolverTrace)
 
 -- | Ties the two worlds together: classic cabal-install vs. the modular
 -- solver. Performs the necessary translations before and after.
@@ -181,7 +181,7 @@ solve' sc cinfo idx pkgConfigDB pprefs gcs pns =
           -- original goal order.
           goalOrder' = preferGoalsFromConflictSet cs <> fromMaybe mempty (goalOrder sc)
 
-      in unlines ("Could not resolve dependencies:" : map show (messages (toProgress (runSolver True sc'))))
+      in unlines ("Could not resolve dependencies:" : map renderSolverTrace (messages (toProgress (runSolver True sc'))))
 
     printFullLog = solverVerbosity sc >= verbose
 
@@ -228,7 +228,7 @@ tryToMinimizeConflictSet :: forall a . (SolverConfig -> RetryLog SolverTrace Sol
                          -> ConflictMap
                          -> RetryLog SolverTrace SolverFailure a
 tryToMinimizeConflictSet runSolver sc cs cm =
-    foldl (\r v -> retryMap mkErrorMsg $ retryNoSolution (retryMap show r) $ tryToRemoveOneVar v)
+    foldl (\r v -> retryMap mkErrorMsg $ retryNoSolution (retryMap renderSolverTrace r) $ tryToRemoveOneVar v)
           (fromProgress $ Fail $ ExhaustiveSearch cs cm)
           (CS.toList cs)
   where
@@ -261,7 +261,7 @@ tryToMinimizeConflictSet runSolver sc cs cm =
       | otherwise =
         continueWith ("Trying to remove variable " ++ varStr ++ " from the "
                       ++ "conflict set.") $
-        retry (retryMap show $ runSolver sc') $ \case
+        retry (retryMap renderSolverTrace $ runSolver sc') $ \case
             err@(ExhaustiveSearch cs' _)
               | CS.toSet cs' `isSubsetOf` CS.toSet smallestKnownCS ->
                   let msg = if not $ CS.member v cs'

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

@@ -4,6 +4,7 @@ module Distribution.Solver.Modular.Message (
     Message(..),
     SolverTrace(..),
     groupMessages,
+    renderSolverTrace,
   ) where
 
 import qualified Data.List as L
@@ -62,9 +63,9 @@ type Trace = AtLevel Log
 
 data SolverTrace = SolverTrace Trace | ErrorMsg String
 
-instance Show SolverTrace where
-    show (SolverTrace i) = displayMessageAtLevel i
-    show (ErrorMsg s) = show s
+renderSolverTrace :: SolverTrace -> String
+renderSolverTrace (SolverTrace i) = displayMessageAtLevel i
+renderSolverTrace (ErrorMsg s) = s
 
 instance Show Log where
     show = displayMessage

cabal-install/src/Distribution/Client/Dependency.hs

@@ -160,7 +160,7 @@ import Data.List
   )
 import qualified Data.Map as Map
 import qualified Data.Set as Set
-import Distribution.Solver.Modular.Message (SolverTrace)
+import Distribution.Solver.Modular.Message (SolverTrace, renderSolverTrace)
 
 -- ------------------------------------------------------------
 
@@ -838,7 +838,7 @@ resolveDependencies platform comp pkgConfigDB params =
     formatProgress :: Progress SolverTrace String a -> Progress String String a
     formatProgress p = foldProgress (\x xs -> Step (formatter x) xs) Fail Done p
       where
-        formatter = if outputJson then error "FIXME: To be implemented ..." else show
+        formatter = if outputJson then error "FIXME: To be implemented ..." else renderSolverTrace
 
     preferences :: PackageName -> PackagePreferences
     preferences = interpretPackagesPreference targets defpref prefs