Rework plugin initialisation points

In general this patch pushes plugin initialisation points to earlier in
the pipeline. As plugins can modify the `HscEnv`, it's imperative that
the plugins are initialised as soon as possible and used thereafter.

For example, there are some new tests which modify hsc_logger and other
hooks which failed to fire before (and now do)

One consequence of this change is that the error for specifying the
usage of a HPT plugin from the command line has changed, because it's
now attempted to be loaded at initialisation rather than causing a
cyclic module import.

Closes #21279

Co-authored-by: Matthew Pickering <matthewtpickering@gmail.com>

16 files changed, 130 insertions, 22 deletions

diff --git a/compiler/GHC/Driver/Make.hs b/compiler/GHC/Driver/Make.hs
index c047056ea6..2cc762b9cd 100644
--- a/compiler/GHC/Driver/Make.hs
+++ b/compiler/GHC/Driver/Make.hs
@@ -694,6 +694,9 @@ data WorkerLimit
 -- produced by calling 'depanal'.
 load' :: GhcMonad m => Maybe ModIfaceCache -> LoadHowMuch -> Maybe Messager -> ModuleGraph -> m SuccessFlag
 load' mhmi_cache how_much mHscMessage mod_graph = do
+    -- In normal usage plugins are initialised already by ghc/Main.hs this is protective
+    -- for any client who might interact with GHC via load'.
+    initializeSessionPlugins
     modifySession $ \hsc_env -> hsc_env { hsc_mod_graph = mod_graph }
     guessOutputFile
     hsc_env <- getSession
@@ -2852,13 +2855,11 @@ label_self thread_name = do
 runPipelines :: WorkerLimit -> HscEnv -> Maybe Messager -> [MakeAction] -> IO ()
 -- Don't even initialise plugins if there are no pipelines
 runPipelines _ _ _ [] = return ()
-runPipelines n_job orig_hsc_env mHscMessager all_pipelines = do
+runPipelines n_job hsc_env mHscMessager all_pipelines = do
   liftIO $ label_self "main --make thread"
-
-  plugins_hsc_env <- initializePlugins orig_hsc_env
   case n_job of
-    NumProcessorsLimit n | n <= 1 -> runSeqPipelines plugins_hsc_env mHscMessager all_pipelines
-    _n -> runParPipelines n_job plugins_hsc_env mHscMessager all_pipelines
+    NumProcessorsLimit n | n <= 1 -> runSeqPipelines hsc_env mHscMessager all_pipelines
+    _n -> runParPipelines n_job hsc_env mHscMessager all_pipelines
 
 runSeqPipelines :: HscEnv -> Maybe Messager -> [MakeAction] -> IO ()
 runSeqPipelines plugin_hsc_env mHscMessager all_pipelines =
diff --git a/compiler/GHC/Driver/Pipeline.hs b/compiler/GHC/Driver/Pipeline.hs
index e539c3fcbf..f709ad801c 100644
--- a/compiler/GHC/Driver/Pipeline.hs
+++ b/compiler/GHC/Driver/Pipeline.hs
@@ -244,6 +244,7 @@ compileOne' mHscMessage
              addFilesToClean tmpfs TFL_GhcSession $
                  [ml_obj_file $ ms_location summary]
 
+   -- Initialise plugins here for any plugins enabled locally for a module.
    plugin_hsc_env <- initializePlugins hsc_env
    let pipe_env = mkPipeEnv NoStop input_fn Nothing pipelineOutput
    status <- hscRecompStatus mHscMessage plugin_hsc_env upd_summary
@@ -526,7 +527,11 @@ findHSLib platform ws dirs lib = do
 -- Compile files in one-shot mode.
 
 oneShot :: HscEnv -> StopPhase -> [(String, Maybe Phase)] -> IO ()
-oneShot hsc_env stop_phase srcs = do
+oneShot orig_hsc_env stop_phase srcs = do
+  -- In oneshot mode, initialise plugins specified on command line
+  -- we also initialise in ghc/Main but this might be used as an entry point by API clients who
+  -- should initialise their own plugins but may not.
+  hsc_env <- initializePlugins orig_hsc_env
   o_files <- mapMaybeM (compileFile hsc_env stop_phase) srcs
   case stop_phase of
     StopPreprocess -> return ()
diff --git a/compiler/GHC/Driver/Pipeline/Execute.hs b/compiler/GHC/Driver/Pipeline/Execute.hs
index 75f33834e2..7694975e80 100644
--- a/compiler/GHC/Driver/Pipeline/Execute.hs
+++ b/compiler/GHC/Driver/Pipeline/Execute.hs
@@ -62,7 +62,6 @@ import GHC.Parser.Header
 import GHC.Data.StringBuffer
 import GHC.Types.SourceError
 import GHC.Unit.Finder
-import GHC.Runtime.Loader
 import Data.IORef
 import GHC.Types.Name.Env
 import GHC.Platform.Ways
@@ -82,6 +81,7 @@ import GHC.StgToJS.Linker.Linker (embedJsFile)
 
 import Language.Haskell.Syntax.Module.Name
 import GHC.Unit.Home.ModInfo
+import GHC.Runtime.Loader (initializePlugins)
 
 newtype HookedUse a = HookedUse { runHookedUse :: (Hooks, PhaseHook) -> IO a }
   deriving (Functor, Applicative, Monad, MonadIO, MonadThrow, MonadCatch) via (ReaderT (Hooks, PhaseHook) IO)
@@ -724,9 +724,11 @@ runHscPhase pipe_env hsc_env0 input_fn src_flavour = do
       new_includes = addImplicitQuoteInclude paths [current_dir]
       paths = includePaths dflags0
       dflags = dflags0 { includePaths = new_includes }
-      hsc_env = hscSetFlags dflags hsc_env0
-
+      hsc_env1 = hscSetFlags dflags hsc_env0
 
+  -- Initialise plugins as the flags passed into runHscPhase might have local plugins just
+  -- specific to this module.
+  hsc_env <- initializePlugins hsc_env1
 
   -- gather the imports and module name
   (hspp_buf,mod_name,imps,src_imps, ghc_prim_imp) <- do
@@ -786,18 +788,17 @@ runHscPhase pipe_env hsc_env0 input_fn src_flavour = do
   -- run the compiler!
   let msg :: Messager
       msg hsc_env _ what _ = oneShotMsg (hsc_logger hsc_env) what
-  plugin_hsc_env' <- initializePlugins hsc_env
 
   -- Need to set the knot-tying mutable variable for interface
   -- files. See GHC.Tc.Utils.TcGblEnv.tcg_type_env_var.
   -- See also Note [hsc_type_env_var hack]
   type_env_var <- newIORef emptyNameEnv
-  let plugin_hsc_env = plugin_hsc_env' { hsc_type_env_vars = knotVarsFromModuleEnv (mkModuleEnv [(mod, type_env_var)]) }
+  let hsc_env' = hsc_env { hsc_type_env_vars = knotVarsFromModuleEnv (mkModuleEnv [(mod, type_env_var)]) }
 
-  status <- hscRecompStatus (Just msg) plugin_hsc_env mod_summary
+  status <- hscRecompStatus (Just msg) hsc_env' mod_summary
                         Nothing emptyHomeModInfoLinkable (1, 1)
 
-  return (plugin_hsc_env, mod_summary, status)
+  return (hsc_env', mod_summary, status)
 
 -- | Calculate the ModLocation from the provided DynFlags. This function is only used
 -- in one-shot mode and therefore takes into account the effect of -o/-ohi flags
diff --git a/compiler/GHC/Runtime/Loader.hs b/compiler/GHC/Runtime/Loader.hs
index 29f61fe591..3349ed0020 100644
--- a/compiler/GHC/Runtime/Loader.hs
+++ b/compiler/GHC/Runtime/Loader.hs
@@ -2,7 +2,7 @@
 
 -- | Dynamically lookup up values from modules and loading them.
 module GHC.Runtime.Loader (
-        initializePlugins,
+        initializePlugins, initializeSessionPlugins,
         -- * Loading plugins
         loadFrontendPlugin,
 
@@ -74,7 +74,11 @@ import Unsafe.Coerce     ( unsafeCoerce )
 import GHC.Linker.Types
 import Data.List (unzip4)
 import GHC.Iface.Errors.Ppr
+import GHC.Driver.Monad
 
+-- | Initialise plugins specified by the current DynFlags and update the session.
+initializeSessionPlugins :: GhcMonad m => m ()
+initializeSessionPlugins = getSession >>= liftIO . initializePlugins >>= setSession
 
 -- | Loads the plugins specified in the pluginModNames field of the dynamic
 -- flags. Should be called after command line arguments are parsed, but before
diff --git a/ghc/Main.hs b/ghc/Main.hs
index ef3de102c0..5b1f33bb4e 100644
--- a/ghc/Main.hs
+++ b/ghc/Main.hs
@@ -41,7 +41,7 @@ import GHC.Platform.Host
 import GHCi.UI              ( interactiveUI, ghciWelcomeMsg, defaultGhciSettings )
 #endif
 
-import GHC.Runtime.Loader   ( loadFrontendPlugin )
+import GHC.Runtime.Loader   ( loadFrontendPlugin, initializeSessionPlugins )
 
 import GHC.Unit.Env
 import GHC.Unit (UnitId, homeUnitDepends)
@@ -257,16 +257,23 @@ main' postLoadMode units dflags0 args flagWarnings = do
   -- we've finished manipulating the DynFlags, update the session
   _ <- GHC.setSessionDynFlags dflags5
   dflags6 <- GHC.getSessionDynFlags
-  hsc_env <- GHC.getSession
+
+  -- Must do this before loading plugins
+  liftIO $ initUniqSupply (initialUnique dflags6) (uniqueIncrement dflags6)
+
+  -- Initialise plugins here because the plugin author might already expect this
+  -- subsequent call to `getLogger` to be affected by a plugin.
+  initializeSessionPlugins
+  hsc_env <- getSession
   logger <- getLogger
 
+
         ---------------- Display configuration -----------
   case verbosity dflags6 of
     v | v == 4 -> liftIO $ dumpUnitsSimple hsc_env
       | v >= 5 -> liftIO $ dumpUnits       hsc_env
       | otherwise -> return ()
 
-  liftIO $ initUniqSupply (initialUnique dflags6) (uniqueIncrement dflags6)
         ---------------- Final sanity checking -----------
   liftIO $ checkOptions postLoadMode dflags6 srcs objs units
 
diff --git a/testsuite/tests/plugins/all.T b/testsuite/tests/plugins/all.T
index ef0096f064..c782ad13cd 100644
--- a/testsuite/tests/plugins/all.T
+++ b/testsuite/tests/plugins/all.T
@@ -317,3 +317,17 @@ test('plugins-external',
       pre_cmd('$MAKE -s --no-print-directory -C shared-plugin package.plugins01 TOP={top}'),
       when(opsys('linux') and not ghc_dynamic(), expect_broken(20706))],
      makefile_test, [])
+
+test('test-phase-hooks-plugin',
+     [extra_files(['hooks-plugin/']),
+      pre_cmd('$MAKE -s --no-print-directory -C hooks-plugin package.test-phase-hooks-plugin TOP={top}'),
+
+      when(opsys('linux') and not ghc_dynamic(), expect_broken(20706))],
+     compile,
+     ['-package-db hooks-plugin/pkg.test-phase-hooks-plugin/local.package.conf -fplugin Hooks.PhasePlugin -package hooks-plugin ' + config.plugin_way_flags])
+
+test('test-log-hooks-plugin',
+     [extra_files(['hooks-plugin/']),
+      pre_cmd('$MAKE -s --no-print-directory -C hooks-plugin package.test-log-hooks-plugin TOP={top}')],
+     compile_fail,
+     ['-package-db hooks-plugin/pkg.test-log-hooks-plugin/local.package.conf -fplugin Hooks.LogPlugin -package hooks-plugin ' + config.plugin_way_flags])
diff --git a/testsuite/tests/plugins/hooks-plugin/Hooks/LogPlugin.hs b/testsuite/tests/plugins/hooks-plugin/Hooks/LogPlugin.hs
new file mode 100644
index 0000000000..10591240f9
--- /dev/null
+++ b/testsuite/tests/plugins/hooks-plugin/Hooks/LogPlugin.hs
@@ -0,0 +1,24 @@
+module Hooks.LogPlugin (plugin) where
+
+import GHC.Plugins
+import GHC.Driver.Hooks
+import GHC.Tc.Utils.Monad
+import GHC.Utils.Logger
+import GHC.Driver.Pipeline.Execute
+import System.IO
+
+plugin :: Plugin
+plugin = defaultPlugin { driverPlugin = hooksP }
+
+hooksP :: [CommandLineOption] -> HscEnv -> IO HscEnv
+hooksP opts hsc_env = do
+  hSetBuffering stdout NoBuffering
+  let logger  = hsc_logger hsc_env
+      logger' = pushLogHook logHook logger
+      hsc_env' = hsc_env { hsc_logger = logger' }
+  return hsc_env'
+
+logHook :: LogAction -> LogAction
+logHook action logFlags messageClass srcSpan msgDoc = do
+  putStrLn "Log hook called"
+  action logFlags messageClass srcSpan msgDoc
diff --git a/testsuite/tests/plugins/hooks-plugin/Hooks/Plugin.hs b/testsuite/tests/plugins/hooks-plugin/Hooks/MetaPlugin.hs
index bf717b26c0..29c1dab2b7 100644
--- a/testsuite/tests/plugins/hooks-plugin/Hooks/Plugin.hs
+++ b/testsuite/tests/plugins/hooks-plugin/Hooks/MetaPlugin.hs
@@ -1,5 +1,5 @@
 {-# OPTIONS_GHC -Wall #-}
-module Hooks.Plugin (plugin) where
+module Hooks.MetaPlugin (plugin) where
 
 import GHC.Types.SourceText
 import GHC.Plugins
diff --git a/testsuite/tests/plugins/hooks-plugin/Hooks/PhasePlugin.hs b/testsuite/tests/plugins/hooks-plugin/Hooks/PhasePlugin.hs
new file mode 100644
index 0000000000..51cff77404
--- /dev/null
+++ b/testsuite/tests/plugins/hooks-plugin/Hooks/PhasePlugin.hs
@@ -0,0 +1,30 @@
+{-# LANGUAGE GADTs #-}
+{-# OPTIONS_GHC -Wall #-}
+module Hooks.PhasePlugin (plugin) where
+
+import GHC.Plugins
+import GHC.Driver.Hooks
+import GHC.Tc.Utils.Monad
+import GHC.Driver.Pipeline.Execute
+import GHC.Driver.Pipeline.Phases
+import System.IO
+
+plugin :: Plugin
+plugin = defaultPlugin { driverPlugin = hooksP }
+
+hooksP :: [CommandLineOption] -> HscEnv -> IO HscEnv
+hooksP opts hsc_env = do
+  hSetBuffering stdout NoBuffering
+  let hooks  = hsc_hooks hsc_env
+      hooks' = hooks { runPhaseHook = Just fakeRunPhaseHook }
+      hsc_env' = hsc_env { hsc_hooks = hooks' }
+  return hsc_env'
+
+fakeRunPhaseHook :: PhaseHook
+fakeRunPhaseHook = PhaseHook $ \tPhase -> do
+  liftIO $ case tPhase of
+    T_Cpp{} -> putStrLn "Cpp hook fired"
+    T_Hsc{} -> putStrLn "Hsc hook fired"
+    T_FileArgs{} -> putStrLn "FileArgs hook fired"
+    _ -> pure ()
+  runPhase tPhase
diff --git a/testsuite/tests/plugins/hooks-plugin/hooks-plugin.cabal b/testsuite/tests/plugins/hooks-plugin/hooks-plugin.cabal
index 3c1cf61184..b19ad6f18e 100644
--- a/testsuite/tests/plugins/hooks-plugin/hooks-plugin.cabal
+++ b/testsuite/tests/plugins/hooks-plugin/hooks-plugin.cabal
@@ -4,6 +4,6 @@ version:             0.1
 build-type:          Simple
 
 library
-  exposed-modules:     Hooks.Plugin
+  exposed-modules:     Hooks.MetaPlugin, Hooks.PhasePlugin, Hooks.LogPlugin
   build-depends:       base, ghc
   default-language:    Haskell2010
diff --git a/testsuite/tests/plugins/plugins04.stderr b/testsuite/tests/plugins/plugins04.stderr
index 67922911fb..a56ed56856 100644
--- a/testsuite/tests/plugins/plugins04.stderr
+++ b/testsuite/tests/plugins/plugins04.stderr
@@ -1,2 +1 @@
-Module graph contains a cycle:
-  module ‘HomePackagePlugin’ (./HomePackagePlugin.hs) imports itself
+attempting to use module ‘main:HomePackagePlugin’ (./HomePackagePlugin.hs) which is not loaded
diff --git a/testsuite/tests/plugins/test-hooks-plugin.hs b/testsuite/tests/plugins/test-hooks-plugin.hs
index bf324f9966..c7bfa9dbce 100644
--- a/testsuite/tests/plugins/test-hooks-plugin.hs
+++ b/testsuite/tests/plugins/test-hooks-plugin.hs
@@ -1,4 +1,4 @@
-{-# OPTIONS -fplugin=Hooks.Plugin #-}
+{-# OPTIONS -fplugin=Hooks.MetaPlugin #-}
 {-# LANGUAGE TemplateHaskell #-}
 module Main where
 
diff --git a/testsuite/tests/plugins/test-log-hooks-plugin.hs b/testsuite/tests/plugins/test-log-hooks-plugin.hs
new file mode 100644
index 0000000000..f0308a3fe6
--- /dev/null
+++ b/testsuite/tests/plugins/test-log-hooks-plugin.hs
@@ -0,0 +1,4 @@
+module Main where
+
+main :: IO ()
+main = pure "type error"
diff --git a/testsuite/tests/plugins/test-log-hooks-plugin.stderr b/testsuite/tests/plugins/test-log-hooks-plugin.stderr
new file mode 100644
index 0000000000..dba4679f52
--- /dev/null
+++ b/testsuite/tests/plugins/test-log-hooks-plugin.stderr
@@ -0,0 +1,9 @@
+Log hook called
+
+test-log-hooks-plugin.hs:4:13: error: [GHC-83865]
+    • Couldn't match type ‘[Char]’ with ‘()’
+      Expected: ()
+        Actual: String
+    • In the first argument of ‘pure’, namely ‘"type error"’
+      In the expression: pure "type error"
+      In an equation for ‘main’: main = pure "type error"
diff --git a/testsuite/tests/plugins/test-phase-hooks-plugin.hs b/testsuite/tests/plugins/test-phase-hooks-plugin.hs
new file mode 100644
index 0000000000..9271fad67b
--- /dev/null
+++ b/testsuite/tests/plugins/test-phase-hooks-plugin.hs
@@ -0,0 +1,5 @@
+{-# LANGUAGE CPP #-}
+module Main where
+
+main :: IO ()
+main = pure ()
diff --git a/testsuite/tests/plugins/test-phase-hooks-plugin.stderr b/testsuite/tests/plugins/test-phase-hooks-plugin.stderr
new file mode 100644
index 0000000000..ae1b36330d
--- /dev/null
+++ b/testsuite/tests/plugins/test-phase-hooks-plugin.stderr
@@ -0,0 +1,5 @@
+FileArgs hook fired
+Cpp hook fired
+FileArgs hook fired
+FileArgs hook fired
+Hsc hook fired