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, 1 insertions, 1 deletions

diff --git a/compiler/GHC.hs b/compiler/GHC.hs
index 4c8864014f..bd3f0b6d9f 100644
--- a/compiler/GHC.hs
+++ b/compiler/GHC.hs
@@ -1682,7 +1682,7 @@ interpretPackageEnv dflags = do
         return dflags
       Just envfile -> do
         content <- readFile envfile
-        compilationProgressMsg dflags ("Loaded package environment from " ++ envfile)
+        compilationProgressMsg dflags (text "Loaded package environment from " <> text envfile)
         let (_, dflags') = runCmdLine (runEwM (setFlagsFromEnvFile envfile content)) dflags
 
         return dflags'