Refactor UnitId pretty-printing

When we pretty-print a UnitId for the user, we try to map it back to its
origin package name, version and component to print
"package-version:component" instead of some hash.

The UnitId type doesn't carry these information, so we have to look into
a UnitState to find them. This is why the Outputable instance of
UnitId used `sdocWithDynFlags` in order to access the `unitState` field
of DynFlags.

This is wrong for several reasons:

1. The DynFlags are accessed when the message is printed, not when it is
   generated. So we could imagine that the unitState may have changed
   in-between. Especially if we want to allow unit unloading.

2. We want GHC to support several independent sessions at once, hence
   several UnitState. The current approach supposes there is a unique
   UnitState as a UnitId doesn't indicate which UnitState to use.

See the Note [Pretty-printing UnitId] in GHC.Unit for the new approach
implemented by this patch.

One step closer to remove `sdocDynFlags` field from `SDocContext`
(#10143).

Fix #18124.

Also fix some Backpack code to use SDoc instead of String.

1 files changed, 6 insertions, 11 deletions

diff --git a/compiler/GHC/Unit/State.hs b/compiler/GHC/Unit/State.hs
index f35437be11..ec8cafe170 100644
--- a/compiler/GHC/Unit/State.hs
+++ b/compiler/GHC/Unit/State.hs
@@ -68,10 +68,9 @@ module GHC.Unit.State (
         pprUnitIdForUser,
         pprUnitInfoForUser,
         pprModuleMap,
+        pprWithUnitState,
 
         -- * Utils
-        mkIndefUnitId,
-        updateIndefUnitId,
         unwireUnit
     )
 where
@@ -2128,15 +2127,6 @@ pprUnitInfoForUser info = ppr (mkUnitPprInfo unitIdFS info)
 lookupUnitPprInfo :: UnitState -> UnitId -> Maybe UnitPprInfo
 lookupUnitPprInfo state uid = fmap (mkUnitPprInfo unitIdFS) (lookupUnitId state uid)
 
--- | Create a IndefUnitId.
-mkIndefUnitId :: UnitState -> UnitId -> IndefUnitId
-mkIndefUnitId state uid = Indefinite uid $! lookupUnitPprInfo state uid
-
--- | Update component ID details from the database
-updateIndefUnitId :: UnitState -> IndefUnitId -> IndefUnitId
-updateIndefUnitId pkgstate uid = mkIndefUnitId pkgstate (indefUnit uid)
-
-
 -- -----------------------------------------------------------------------------
 -- Displaying packages
 
@@ -2270,3 +2260,8 @@ instModuleToModule :: UnitState -> InstantiatedModule -> Module
 instModuleToModule pkgstate (Module iuid mod_name) =
     mkModule (instUnitToUnit pkgstate iuid) mod_name
 
+-- | Print unit-ids with UnitInfo found in the given UnitState
+pprWithUnitState :: UnitState -> SDoc -> SDoc
+pprWithUnitState state = updSDocContext (\ctx -> ctx
+   { sdocUnitIdForUser = \fs -> pprUnitIdForUser state (UnitId fs)
+   })