From da2677e780c5c0266b382bee69a3de2eb52da867 Mon Sep 17 00:00:00 2001
From: Matthew Pickering <matthewtpickering@gmail.com>
Date: Mon, 11 Oct 2021 17:23:42 +0100
Subject: Make ms_ghc_prim_import field strict

If you don't promptly force this field then it ends up retaining a lot
of data structures related to parsing.

For example, the following retaining chain can be observed when using
GHCi.

```
PState 0x4289365ca0 0x4289385d68 0x4289385db0 0x7f81b37a7838 0x7f81b3832fd8 0x4289365cc8 0x4289365cd8 0x4289365cf0 0x4289365cd8 0x4289365d08 0x4289385e48 0x7f81b4e4c290 0x7f818f63f440 0x7f818f63f440 0x7f81925ccd18 0x7f81b4e41230 0x7f818f63f440 0x7f81925ccd18 0x7f818f63f4a8 0x7f81b3832fd8 0x7f81b3832fd8 0x4289365d20 0x7f81b38233b8 0 19 <PState:GHC.Parser.Lexer:_build-ipe/stage1/compiler/build/GHC/Parser/Lexer.hs:3779:46>
_thunk(  ) 0x4289384230 0x4289384160 <([LEpaComment], [LEpaComment]):GHC.Parser.Lexer:>
_thunk(  ) 0x4289383250 <EpAnnComments:GHC.Parser.Lexer:compiler/GHC/Parser/Lexer.x:2306:19-40>
_thunk(  ) 0x4289399850 0x7f818f63f440 0x4289399868 <SrcSpanAnnA:GHC.Parser:_build-ipe/stage1/compiler/build/GHC/Parser.hs:12527:13-30>
L 0x4289397600 0x42893975a8 <GenLocated:GHC.Parser:_build-ipe/stage1/compiler/build/GHC/Parser.hs:12527:32>
0x4289c4e8c8 : 0x4289c4e8b0 <[]:GHC.Parser.Header:compiler/GHC/Parser/Header.hs:104:36-54>
(0x4289c4da70,0x7f818f63f440) <(,):GHC.Parser.Header:compiler/GHC/Parser/Header.hs:104:36-54>
_thunk(  ) 0x4289c4d030 <Bool:GHC.Parser.Header:compiler/GHC/Parser/Header.hs:(112,22)-(115,27)>
ExtendedModSummary 0x422e9c8998 0x7f81b617be78 0x422e9c89b0 0x4289c4c0c0 0x7f81925ccd18 0x7f81925ccd18 0x7f81925ccd18 0x7f81925ccd18 0x7f818f63f440 0x4289c4c0d8 0x4289c4c0f0 0x7f81925ccd18 0x422e9c8a20 0x4289c4c108 0x4289c4c730 0x7f818f63f440 <ExtendedModSummary:GHC.Driver.Make:compiler/GHC/Driver/Make.hs:2041:30-38>
ModuleNode 0x4289c4b850 <ModuleGraphNode:GHC.Unit.Module.Graph:compiler/GHC/Unit/Module/Graph.hs:139:14-36>
0x4289c4b590 : 0x4289c4b578 <[]:GHC.Unit.Module.Graph:compiler/GHC/Unit/Module/Graph.hs:139:31-36>
ModuleGraph 0x4289c4b2f8 0x4289c4b310 0x4289c4b340 0x7f818f63f4a0 <ModuleGraph:GHC.Driver.Make:compiler/GHC/Driver/Make.hs:(242,19)-(244,40)>
HscEnv 0x4289d9a4a8 0x4289d9aad0 0x4289d9aae8 0x4217062a88 0x4217060b38 0x4217060b58 0x4217060b68 0x7f81b38a7ce0 0x4217060b78 0x7f818f63f440 0x7f818f63f440 0x4217062af8 0x4289d9ab10 0x7f81b3907b60 0x4217060c00 114 <HscEnv:GHC.Runtime.Eval:compiler/GHC/Runtime/Eval.hs:790:31-44>
```
---
 compiler/GHC/Unit/Module/ModSummary.hs | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/compiler/GHC/Unit/Module/ModSummary.hs b/compiler/GHC/Unit/Module/ModSummary.hs
index c584385aef..1a8cddec61 100644
--- a/compiler/GHC/Unit/Module/ModSummary.hs
+++ b/compiler/GHC/Unit/Module/ModSummary.hs
@@ -91,7 +91,7 @@ data ModSummary
           -- ^ Source imports of the module
         ms_textual_imps :: [(Maybe FastString, Located ModuleName)],
           -- ^ Non-source imports of the module from the module *text*
-        ms_ghc_prim_import :: Bool,
+        ms_ghc_prim_import :: !Bool,
           -- ^ Whether the special module GHC.Prim was imported explicitliy
         ms_parsed_mod   :: Maybe HsParsedModule,
           -- ^ The parsed, nonrenamed source, if we have it.  This is also
-- 
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