Clear the mi_globals field when generating an iface

GHC populates the mi_global field in interfaces for GHCi if we are using the bytecode
interpreter.
However, this field is expensive in terms of heap usage, and we don't use it in HLS
anywhere. So we zero it out.
The field is not serialized or deserialised from disk, so we don't need to remove it
while reading an iface from disk, only if we just generated an iface in memory

Author: wz1000

ghcide/src/Development/IDE/Core/Compile.hs

@@ -427,14 +427,23 @@ tcRnModule hsc_env tc_helpers pmod = do
       tc_gbl_env = tc_gbl_env' { tcg_ann_env = extendAnnEnvList (tcg_ann_env tc_gbl_env') mod_env_anns }
   pure (TcModuleResult pmod rn_info tc_gbl_env splices False mod_env)
 
+
+-- Note [Clearing mi_globals after generating an iface]
+-- GHC populates the mi_global field in interfaces for GHCi if we are using the bytecode
+-- interpreter.
+-- However, this field is expensive in terms of heap usage, and we don't use it in HLS
+-- anywhere. So we zero it out.
+-- The field is not serialized or deserialised from disk, so we don't need to remove it
+-- while reading an iface from disk, only if we just generated an iface in memory
+
 mkHiFileResultNoCompile :: HscEnv -> TcModuleResult -> IO HiFileResult
 mkHiFileResultNoCompile session tcm = do
   let hsc_env_tmp = hscSetFlags (ms_hspp_opts ms) session
       ms = pm_mod_summary $ tmrParsed tcm
       tcGblEnv = tmrTypechecked tcm
   details <- makeSimpleDetails hsc_env_tmp tcGblEnv
   sf <- finalSafeMode (ms_hspp_opts ms) tcGblEnv
-  iface <- mkIfaceTc hsc_env_tmp sf details ms tcGblEnv
+  iface <- (mkIfaceTc hsc_env_tmp sf details ms tcGblEnv){ mi_globals = Nothing } -- ^ See Note [Clearing mi_globals after generating an iface]
   pure $! mkHiFileResult ms iface details (tmrRuntimeModules tcm) Nothing
 
 mkHiFileResultCompile
@@ -467,15 +476,16 @@ mkHiFileResultCompile se session' tcm simplified_guts = catchErrs $ do
 #endif
                                               simplified_guts
 
-  final_iface <- mkFullIface session partial_iface Nothing
+  final_iface' <- mkFullIface session partial_iface Nothing
 #if MIN_VERSION_ghc(9,4,2)
                     Nothing
 #endif
 
 #else 
   let !partial_iface = force (mkPartialIface session details simplified_guts)
-  final_iface <- mkFullIface session partial_iface
+  final_iface' <- mkFullIface session partial_iface
 #endif
+  let final_iface = final_iface' {mi_globals = Nothing} -- ^ See Note [Clearing mi_globals after generating an iface]
 
   -- Write the core file now
   core_file <- case mguts of