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, 10 insertions, 3 deletions

diff --git a/compiler/GHC/CoreToIface.hs b/compiler/GHC/CoreToIface.hs
index bf713aae53..ed8a68560b 100644
--- a/compiler/GHC/CoreToIface.hs
+++ b/compiler/GHC/CoreToIface.hs
@@ -604,8 +604,12 @@ toIfaceTopBind b =
                       IfLclTopBndr {} -> IfRhs (toIfaceExpr rhs)
           in (top_bndr, rhs')
 
-        already_has_unfolding b =
-                                -- The identifier has an unfolding, which we are going to serialise anyway
+        -- The sharing behaviour is currently disabled due to #22807, and relies on
+        -- finished #220056 to be re-enabled.
+        disabledDueTo22807 = True
+
+        already_has_unfolding b = not disabledDueTo22807
+                                && -- The identifier has an unfolding, which we are going to serialise anyway
                                 hasCoreUnfolding (realIdUnfolding b)
                                 -- But not a stable unfolding, we want the optimised unfoldings.
                                 && not (isStableUnfolding (realIdUnfolding b))
@@ -771,7 +775,10 @@ is that these NOINLINE'd functions now can't be profitably inlined
 outside of the hs-boot loop.
 
 Note [Interface File with Core: Sharing RHSs]
-~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+IMPORTANT: This optimisation is currently disabled due to #22027, it can be
+           re-enabled once #220056 is implemented.
 
 In order to avoid duplicating definitions for bindings which already have unfoldings
 we do some minor headstands to avoid serialising the RHS of a definition if it has