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, 15 insertions, 0 deletions

diff --git a/compiler/GHC/Utils/Error.hs b/compiler/GHC/Utils/Error.hs
index ef6dd4f07d..8c044c5af9 100644
--- a/compiler/GHC/Utils/Error.hs
+++ b/compiler/GHC/Utils/Error.hs
@@ -58,6 +58,7 @@ module GHC.Utils.Error (
         ghcExit,
         prettyPrintGhcErrors,
         traceCmd,
+        traceSystoolCommand,
 
         sortMsgBag
     ) where
@@ -460,6 +461,20 @@ traceCmd logger phase_name cmd_line action = do
    -- And run it!
   action `catchIO` handle_exn
 
+
+-- * Tracing utility
+
+-- | Record in the eventlog when the given tool command starts
+--   and finishes, prepending the given 'String' with
+--   \"systool:\", to easily be able to collect and process
+--   all the systool events.
+--
+--   For those events to show up in the eventlog, you need
+--   to run GHC with @-v2@ or @-ddump-timings@.
+traceSystoolCommand :: Logger -> String -> IO a -> IO a
+traceSystoolCommand logger tool = withTiming logger (text "systool:" <> text tool) (const ())
+
+
 {- Note [withTiming]
 ~~~~~~~~~~~~~~~~~~~~