Constants.Config distRelativeDir: use ghc instead of Cabal version

This is a followup fix to the discussion in #5866 about
'.stack-work/dist/<platform>/Cabal-*' causing ghc compilation version confusion.

With this change the path now becomes '.stack-work/dist/<platform>/ghc-*':
ie it disambiguates the path for ghc minor versions, which typically share
the same Cabal minor version.

Further using a ghc versioned build directories makes it much easier
to recognize and clean up old stack build artifacts built with an
older ghc (given that ghc minor versions change faster than Cabal).

Author: juhp

ChangeLog.md

@@ -13,6 +13,10 @@ Major changes:
 
 Behavior changes:
 
+* The path dist directory path '.stack-work/dist/<platform>/Cabal-*/'
+  changes to '.stack-work/dist/<platform>/ghc-*/' so that build artifacts are
+  clearly distinguished by ghc version.
+
 Other enhancements:
 
 * Avoid the duplicate resolving of usage files when parsing `*.hi` files into a

src/Stack/Constants/Config.hs

@@ -24,11 +24,11 @@ module Stack.Constants.Config
   ) where
 
 import           Path ( (</>), mkRelDir, mkRelFile, parseRelDir )
-import           Stack.Constants
-                   ( cabalPackageName, relDirDist, relDirGhci, relDirHpc )
+import           Stack.Constants ( relDirDist, relDirGhci, relDirHpc )
 import           Stack.Prelude
 import           Stack.Types.BuildConfig ( HasBuildConfig, projectRootL )
-import           Stack.Types.CompilerPaths ( cabalVersionL )
+import           Stack.Types.Compiler ( compilerVersionString )
+import           Stack.Types.CompilerPaths ( compilerVersionL )
 import           Stack.Types.Config ( Config, HasConfig, stackRootL, workDirL )
 import           Stack.Types.EnvConfig
                    ( HasEnvConfig, platformGhcRelDir, useShaPathOnWindows )
@@ -162,13 +162,11 @@ templatesDir config = view stackRootL config </> $(mkRelDir "templates")
 distRelativeDir :: (MonadThrow m, MonadReader env m, HasEnvConfig env)
                 => m (Path Rel Dir)
 distRelativeDir = do
-    cabalPkgVer <- view cabalVersionL
+    compilerVer <- view compilerVersionL
     platform <- platformGhcRelDir
     -- Cabal version
     envDir <-
-        parseRelDir $
-        packageIdentifierString $
-        PackageIdentifier cabalPackageName cabalPkgVer
+        parseRelDir $ compilerVersionString compilerVer
     platformAndCabal <- useShaPathOnWindows (platform </> envDir)
     allDist <- rootDistRelativeDir
     pure $ allDist </> platformAndCabal