driver: Remove needsTemplateHaskellOrQQ from ModuleGraph

The idea of the needsTemplateHaskellOrQQ query is to check if any of the
modules in a module graph need Template Haskell then enable -dynamic-too
if necessary. This is quite imprecise though as it will enable
-dynamic-too for all modules in the module graph even if only one module
uses template haskell, with multiple home units, this is obviously even
worse.

With -fno-code we already have similar logic to enable code generation
just for the modules which are dependeded on my TemplateHaskell modules
so we use the same code path to decide whether to enable -dynamic-too
rather than using this big hammer.

This is part of the larger overall goal of moving as much statically
known configuration into the downsweep as possible in order to have
fully decided the build plan and all the options before starting to
build anything.

I also included a fix to #21095, a long standing bug with with the logic
which is supposed to enable the external interpreter if we don't have
the internal interpreter.

Fixes #20696 #21095

1 files changed, 2 insertions, 19 deletions

diff --git a/compiler/GHC/Unit/Module/Graph.hs b/compiler/GHC/Unit/Module/Graph.hs
index 913c51ef10..2a791b42b5 100644
--- a/compiler/GHC/Unit/Module/Graph.hs
+++ b/compiler/GHC/Unit/Module/Graph.hs
@@ -12,14 +12,13 @@ module GHC.Unit.Module.Graph
    , extendMG
    , extendMGInst
    , extendMG'
+   , isTemplateHaskellOrQQNonBoot
    , filterToposortToModules
    , mapMG
    , mgModSummaries
    , mgModSummaries'
    , mgLookupModule
    , mgTransDeps
-   , needsTemplateHaskellOrQQ
-   , isTemplateHaskellOrQQNonBoot
    , showModMsg
    , moduleGraphNodeModule
    , moduleGraphNodeModSum
@@ -135,20 +134,8 @@ data ModuleGraph = ModuleGraph
     -- repeated whenever the transitive dependencies need to be calculated (for example, hptInstances)
   , mg_non_boot :: ModuleEnv ModSummary
     -- a map of all non-boot ModSummaries keyed by Modules
-  , mg_needs_th_or_qq :: !Bool
-    -- does any of the modules in mg_mss require TemplateHaskell or
-    -- QuasiQuotes?
   }
 
--- | Determines whether a set of modules requires Template Haskell or
--- Quasi Quotes
---
--- Note that if the session's 'DynFlags' enabled Template Haskell when
--- 'depanal' was called, then each module in the returned module graph will
--- have Template Haskell enabled whether it is actually needed or not.
-needsTemplateHaskellOrQQ :: ModuleGraph -> Bool
-needsTemplateHaskellOrQQ mg = mg_needs_th_or_qq mg
-
 -- | Map a function 'f' over all the 'ModSummaries'.
 -- To preserve invariants 'f' can't change the isBoot status.
 mapMG :: (ModSummary -> ModSummary) -> ModuleGraph -> ModuleGraph
@@ -169,15 +156,12 @@ mgModSummaries mg = [ m | ModuleNode _ m <- mgModSummaries' mg ]
 mgModSummaries' :: ModuleGraph -> [ModuleGraphNode]
 mgModSummaries' = mg_mss
 
-mgElemModule :: ModuleGraph -> Module -> Bool
-mgElemModule ModuleGraph{..} m = elemModuleEnv m mg_non_boot
-
 -- | Look up a ModSummary in the ModuleGraph
 mgLookupModule :: ModuleGraph -> Module -> Maybe ModSummary
 mgLookupModule ModuleGraph{..} m = lookupModuleEnv mg_non_boot m
 
 emptyMG :: ModuleGraph
-emptyMG = ModuleGraph [] Map.empty emptyModuleEnv False
+emptyMG = ModuleGraph [] Map.empty emptyModuleEnv
 
 isTemplateHaskellOrQQNonBoot :: ModSummary -> Bool
 isTemplateHaskellOrQQNonBoot ms =
@@ -194,7 +178,6 @@ extendMG ModuleGraph{..} deps ms = ModuleGraph
   , mg_non_boot = case isBootSummary ms of
       IsBoot -> mg_non_boot
       NotBoot -> extendModuleEnv mg_non_boot (ms_mod ms) ms
-  , mg_needs_th_or_qq = mg_needs_th_or_qq || isTemplateHaskellOrQQNonBoot ms
   }
   where
     (gg, _lookup_node) = moduleGraphNodes False (ModuleNode deps ms : mg_mss)