Change `Backend` type and remove direct dependencieswip/backend-as-record

With this change, `Backend` becomes an abstract type
(there are no more exposed value constructors).
Decisions that were formerly made by asking "is the
current back end equal to (or different from) this named value
constructor?" are now made by interrogating the back end about
its properties, which are functions exported by `GHC.Driver.Backend`.

There is a description of how to migrate code using `Backend` in the
user guide.

Clients using the GHC API can find a backdoor to access the Backend
datatype in GHC.Driver.Backend.Internal.

Bumps haddock submodule.

Fixes #20927

1 files changed, 1 insertions, 8 deletions

diff --git a/compiler/GHC/Cmm/Switch.hs b/compiler/GHC/Cmm/Switch.hs
index f8c6c674ef..b0f22ce1b3 100644
--- a/compiler/GHC/Cmm/Switch.hs
+++ b/compiler/GHC/Cmm/Switch.hs
@@ -8,7 +8,7 @@ module GHC.Cmm.Switch (
      switchTargetsToList, eqSwitchTargetWith,
 
      SwitchPlan(..),
-     backendSupportsSwitch,
+     backendHasNativeSwitch,
      createSwitchPlan,
   ) where
 
@@ -312,13 +312,6 @@ and slowed down all other cases making it not worthwhile.
 -}
 
 
--- | Does the backend support switch out of the box? Then leave this to the
--- backend!
-backendSupportsSwitch :: Backend -> Bool
-backendSupportsSwitch ViaC = True
-backendSupportsSwitch LLVM = True
-backendSupportsSwitch _    = False
-
 -- | This function creates a SwitchPlan from a SwitchTargets value, breaking it
 -- down into smaller pieces suitable for code generation.
 createSwitchPlan :: SwitchTargets -> SwitchPlan