From a05bb1d6a1d963d14cb0bafade1e7c1072ac94a5 Mon Sep 17 00:00:00 2001
From: Matthew Pickering <matthewtpickering@gmail.com>
Date: Mon, 27 Sep 2021 16:24:57 +0100
Subject: Recompilation: Handle -plugin-package correctly

If a plugins was specified using the -plugin-package-(id) flag then the
module it applied to was always recompiled.

The recompilation checker was previously using `findImportedModule`,
which looked for packages in the HPT and then in the package database
but only for modules specified using `-package`.

The correct lookup function for plugins is `findPluginModule`, therefore
we check normal imports with `findImportedModule` and plugins with
`findPluginModule`.

Fixes #20417
---
 compiler/GHC/Iface/Recomp.hs          | 14 +++++++++-----
 testsuite/tests/plugins/Makefile      |  6 ++++++
 testsuite/tests/plugins/T20417.stderr |  3 +++
 testsuite/tests/plugins/all.T         |  7 +++++++
 4 files changed, 25 insertions(+), 5 deletions(-)
 create mode 100644 testsuite/tests/plugins/T20417.stderr

diff --git a/compiler/GHC/Iface/Recomp.hs b/compiler/GHC/Iface/Recomp.hs
index 4cc03d488d..6bbf8f58cb 100644
--- a/compiler/GHC/Iface/Recomp.hs
+++ b/compiler/GHC/Iface/Recomp.hs
@@ -506,11 +506,9 @@ checkMergedSignatures hsc_env mod_summary iface = do
 checkDependencies :: HscEnv -> ModSummary -> ModIface -> IfG RecompileRequired
 checkDependencies hsc_env summary iface
  = do
-    res <- liftIO $ traverse (\(mb_pkg, L _ mod) ->
-              let reason = ModuleChanged mod
-              in classify reason <$> findImportedModule fc fopts units home_unit mod (mb_pkg))
-              (ms_imps summary ++ ms_srcimps summary)
-    case sequence (res ++ [Right (fake_ghc_prim_import)| ms_ghc_prim_import summary]) of
+    res_normal <- classify_import (findImportedModule fc fopts units home_unit) (ms_textual_imps summary ++ ms_srcimps summary)
+    res_plugin <- classify_import (\mod _ -> findPluginModule fc fopts units home_unit mod) (ms_plugin_imps summary)
+    case sequence (res_normal ++ res_plugin ++ [Right (fake_ghc_prim_import)| ms_ghc_prim_import summary]) of
       Left recomp -> return recomp
       Right es -> do
         let (hs, ps) = partitionEithers es
@@ -520,6 +518,12 @@ checkDependencies hsc_env summary iface
         res2 <- liftIO $ check_packages allPkgDeps prev_dep_pkgs
         return (res1 `mappend` res2)
  where
+
+   classify_import find_import imports =
+    liftIO $ traverse (\(mb_pkg, L _ mod) ->
+           let reason = ModuleChanged mod
+           in classify reason <$> find_import mod mb_pkg)
+           imports
    dflags        = hsc_dflags hsc_env
    fopts         = initFinderOpts dflags
    logger        = hsc_logger hsc_env
diff --git a/testsuite/tests/plugins/Makefile b/testsuite/tests/plugins/Makefile
index e242a0a387..710cf827ec 100644
--- a/testsuite/tests/plugins/Makefile
+++ b/testsuite/tests/plugins/Makefile
@@ -146,3 +146,9 @@ plugin-recomp-change-2:
 	"$(TEST_HC)" $(TEST_HC_OPTS) $(ghcPluginWayFlags) -v0 plugin-recomp-test.hs PluginRecompTest.hs -package-db plugin-recomp/pkg.plugins01/local.package.conf -fplugin PurePlugin
 	"$(MAKE)" -s --no-print-directory -C plugin-recomp package.plugins01 TOP=$(TOP) RUN=-DRUN2
 	"$(TEST_HC)" $(TEST_HC_OPTS) $(ghcPluginWayFlags) -v0 plugin-recomp-test.hs PluginRecompTest.hs -package-db plugin-recomp/pkg.plugins01/local.package.conf -fplugin PurePlugin
+
+# Shouldn't recompile the module because the plugin is pure and nothing changed.
+.PHONY: T20417
+T20417:
+	"$(TEST_HC)" $(TEST_HC_OPTS) $(ghcPluginWayFlags) -v0 plugin-recomp-test.hs -package-db plugin-recomp/pkg.plugins01/local.package.conf -hide-all-packages -package base -plugin-package plugin-recompilation-0.1  -fplugin PurePlugin
+	"$(TEST_HC)" $(TEST_HC_OPTS) $(ghcPluginWayFlags) -v0 plugin-recomp-test.hs -package-db plugin-recomp/pkg.plugins01/local.package.conf -hide-all-packages -package base -plugin-package plugin-recompilation-0.1 -fplugin PurePlugin
diff --git a/testsuite/tests/plugins/T20417.stderr b/testsuite/tests/plugins/T20417.stderr
new file mode 100644
index 0000000000..84e15cfa91
--- /dev/null
+++ b/testsuite/tests/plugins/T20417.stderr
@@ -0,0 +1,3 @@
+Simple Plugin Passes Queried
+Got options: 
+Simple Plugin Pass Run
diff --git a/testsuite/tests/plugins/all.T b/testsuite/tests/plugins/all.T
index fc0abca043..0242ab7d93 100644
--- a/testsuite/tests/plugins/all.T
+++ b/testsuite/tests/plugins/all.T
@@ -240,3 +240,10 @@ test('plugin-recomp-change-2',
       pre_cmd('$MAKE -s --no-print-directory -C plugin-recomp package.plugins01 TOP={top}')
       ],
      makefile_test, [])
+
+test('T20417',
+     [extra_files(['plugin-recomp/', 'plugin-recomp-test.hs']),
+      only_ways([config.ghc_plugin_way]),
+      pre_cmd('$MAKE -s --no-print-directory -C plugin-recomp package.plugins01 TOP={top}')
+      ],
+     makefile_test, [])
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