Disable unfolding sharing for interface files with core definitionswip/disable-iface-sharing

Ticket #22807 pointed out that the RHS sharing was not compatible with
-fignore-interface-pragmas because the flag would remove unfoldings from
identifiers before the `extra-decls` field was populated.

For the 9.6 timescale the only solution is to disable this sharing,
which will make interface files bigger but this is acceptable for the
first release of `-fwrite-if-simplified-core`.

For 9.8 it would be good to fix this by implementing #20056 due to the
large number of other bugs that would fix.

I also improved the error message in tc_iface_binding to avoid the "no match
in record selector" error but it should never happen now as the entire
sharing logic is disabled.

Also added the currently broken test for #22807 which could be fixed by
!6080

Fixes #22807

1 files changed, 7 insertions, 1 deletions

diff --git a/compiler/GHC/IfaceToCore.hs b/compiler/GHC/IfaceToCore.hs
index fa714448ac..40cc7e34f0 100644
--- a/compiler/GHC/IfaceToCore.hs
+++ b/compiler/GHC/IfaceToCore.hs
@@ -933,7 +933,13 @@ tc_iface_bindings (IfaceRec bs) = do
 
 -- | See Note [Interface File with Core: Sharing RHSs]
 tc_iface_binding :: Id -> IfaceMaybeRhs -> IfL CoreExpr
-tc_iface_binding i IfUseUnfoldingRhs = return (unfoldingTemplate $ realIdUnfolding i)
+tc_iface_binding i IfUseUnfoldingRhs =
+  case maybeUnfoldingTemplate $ realIdUnfolding i of
+    Just e -> return e
+    Nothing -> pprPanic "tc_iface_binding" (vcat [text "Binding" <+> quotes (ppr i) <+> text "had an unfolding when the interface file was created"
+                                                 , text "which has now gone missing, something has badly gone wrong."
+                                                 , text "Unfolding:" <+> ppr (realIdUnfolding i)])
+
 tc_iface_binding _ (IfRhs rhs) = tcIfaceExpr rhs
 
 mk_top_id :: IfaceTopBndrInfo -> IfL Id