Revert compilerVersion being project-scope

Turns out the Setup header has the compiler version used to build Setup, not the
version the project is configured to use.

2 files changed, 5 insertions, 8 deletions

diff --git a/lib/Distribution/Helper.hs b/lib/Distribution/Helper.hs
index 167db45..1505063 100644
--- a/lib/Distribution/Helper.hs
+++ b/lib/Distribution/Helper.hs
@@ -279,14 +279,9 @@ compilerVersion = Query $ \qe ->
     --  ^ ASSUMPTION: Here we assume the compiler version is uniform across all
     --  units so we just pick any one.
     case piImpl proj_info of
-      ProjInfoV1 { piV1SetupHeader=UnitHeader{..} } ->
-          return $ first BS8.unpack $ uhCompilerId
-      --  ^ The package name here is restricted to Latin-1 because of the way
-      --  Cabal writes the header. Shouldn't matter too much V1 is legacy
-      --  anyways and GHC and it's glorious ASCII name rule the Haskell world.
+      ProjInfoV1 {} -> uiCompilerId <$> getUnitInfo qe someUnit
       ProjInfoV2 { piV2CompilerId } -> return piV2CompilerId
       ProjInfoStack {} -> uiCompilerId <$> getUnitInfo qe someUnit
-      --  ^ TODO: Any way to get this faster for stack?
 
 -- | All local units currently active in a project\'s build plan.
 projectUnits          :: Query pt (NonEmpty (Unit pt))
diff --git a/src/CabalHelper/Compiletime/Types.hs b/src/CabalHelper/Compiletime/Types.hs
index 653497d..ec24f2d 100644
--- a/src/CabalHelper/Compiletime/Types.hs
+++ b/src/CabalHelper/Compiletime/Types.hs
@@ -246,12 +246,14 @@ data UnitHeader = UnitHeader
     { uhBrokenPackageId  :: !(ByteString, Version)
       -- ^ Name and version of the source package. Don't use this, it's broken
       -- when the package name contains Unicode characters. See 'uiPackageId'
-      -- instead.
+      -- instead. Note: This was fixed by hvr in Cabal HEAD actually.
     , uhSetupId    :: !(ByteString, Version)
       -- ^ Name and version of the @Setup.hs@ implementation. We expect
       -- @"Cabal"@ here, naturally.
     , uhCompilerId :: !(ByteString, Version)
-      -- ^ Name and version of the compiler this Unit is configured to use.
+      -- ^ Name and version of the compiler that was used to build
+      -- Setup.hs. WARNING: This does not identify the GHC version the project
+      -- is configured to use!
     } deriving (Eq, Ord, Read, Show)
 
 newtype UnitId = UnitId String