driver: Fix -fdefer-diagnostics flag

The `withDeferredDiagnostics` wrapper wasn't doing anything because the
session it was modifying wasn't used in hsc_env. Therefore the fix is
simple, just push the `getSession` call into the scope of
`withDeferredDiagnostics`.

Fixes #22391

compiler/GHC/Driver/Make.hs

@@ -741,8 +741,8 @@ load' mhmi_cache how_much mHscMessage mod_graph = do
                     Just n  -> return n
 
     setSession $ hscUpdateHUG (unitEnv_map pruneHomeUnitEnv) hsc_env
-    hsc_env <- getSession
-    (upsweep_ok, hsc_env1) <- withDeferredDiagnostics $
+    (upsweep_ok, hsc_env1) <- withDeferredDiagnostics $ do
+      hsc_env <- getSession
       liftIO $ upsweep n_jobs hsc_env mhmi_cache mHscMessage (toCache pruned_cache) build_plan
     setSession hsc_env1
     case upsweep_ok of

testsuite/tests/driver/t22391/Makefile

+TOP=../../..
+include $(TOP)/mk/boilerplate.mk
+include $(TOP)/mk/test.mk
+
+warnings-ghc-deferred: clean
+	"$GHC" --make -Wall -fdefer-diagnostics src/Lib.hs src/Lib/A.hs src/Lib/B.hs"
+	ghc --version
+
+warnings-ghc-regular: clean
+	bash -c "ghc --make -Wall src/Lib.hs src/Lib/A.hs src/Lib/B.hs"
+	ghc --version
+
+.PHONY: warnings-ghc
+
+clean:
+	rm -rf src/**/*.{hi,o}
+	rm -rf **/*.{hi,o}
+
+.PHONY: clean

testsuite/tests/driver/t22391/all.T

+test('t22391', [extra_files(['src'])],
+     multimod_compile, ['Lib', '-v1 -Wall -fhide-source-paths -isrc -fdefer-diagnostics'])
+
+test('t22391j', [req_smp, extra_files(['src'])],
+     multimod_compile, ['Lib', '-v1 -Wall -fhide-source-paths -isrc -fdefer-diagnostics -j2'])

testsuite/tests/driver/t22391/src/Lib.hs

+module Lib
+    ( someFunc
+    ) where
+
+import Lib.A
+import Lib.B
+
+blah = 3
+
+someFunc :: IO ()
+someFunc = putStrLn "someFunc"

testsuite/tests/driver/t22391/src/Lib/A.hs

+module Lib.A where
+
+blast = 1

testsuite/tests/driver/t22391/src/Lib/B.hs

+module Lib.B where
+
+warnmeup = 4

testsuite/tests/driver/t22391/t22391.stderr

+[1 of 3] Compiling Lib.A
+[2 of 3] Compiling Lib.B
+[3 of 3] Compiling Lib
+
+src/Lib/A.hs:3:1: warning: [GHC-38417] [-Wmissing-signatures (in -Wall)]
+    Top-level binding with no type signature: blast :: Integer
+
+src/Lib/A.hs:3:9: warning: [GHC-18042] [-Wtype-defaults (in -Wall)]
+    • Defaulting the type variable ‘a0’ to type ‘Integer’ in the following constraint
+        Num a0 arising from the literal ‘1’
+    • In the expression: 1
+      In an equation for ‘blast’: blast = 1
+
+src/Lib/B.hs:3:1: warning: [GHC-38417] [-Wmissing-signatures (in -Wall)]
+    Top-level binding with no type signature: warnmeup :: Integer
+
+src/Lib/B.hs:3:12: warning: [GHC-18042] [-Wtype-defaults (in -Wall)]
+    • Defaulting the type variable ‘a0’ to type ‘Integer’ in the following constraint
+        Num a0 arising from the literal ‘4’
+    • In the expression: 4
+      In an equation for ‘warnmeup’: warnmeup = 4
+
+src/Lib.hs:5:1: warning: [-Wunused-imports (in -Wextra)]
+    The import of ‘Lib.A’ is redundant
+      except perhaps to import instances from ‘Lib.A’
+    To import instances alone, use: import Lib.A()
+
+src/Lib.hs:6:1: warning: [-Wunused-imports (in -Wextra)]
+    The import of ‘Lib.B’ is redundant
+      except perhaps to import instances from ‘Lib.B’
+    To import instances alone, use: import Lib.B()
+
+src/Lib.hs:8:1: warning: [GHC-38417] [-Wmissing-signatures (in -Wall)]
+    Top-level binding with no type signature: blah :: Integer
+
+src/Lib.hs:8:1: warning: [-Wunused-top-binds (in -Wextra, -Wunused-binds)]
+    Defined but not used: ‘blah’
+
+src/Lib.hs:8:8: warning: [GHC-18042] [-Wtype-defaults (in -Wall)]
+    • Defaulting the type variable ‘a0’ to type ‘Integer’ in the following constraint
+        Num a0 arising from the literal ‘3’
+    • In the expression: 3
+      In an equation for ‘blah’: blah = 3

testsuite/tests/driver/t22391/t22391j.stderr

+[1 of 3] Compiling Lib.A
+[2 of 3] Compiling Lib.B
+[3 of 3] Compiling Lib
+
+src/Lib/A.hs:3:1: warning: [GHC-38417] [-Wmissing-signatures (in -Wall)]
+    Top-level binding with no type signature: blast :: Integer
+
+src/Lib/A.hs:3:9: warning: [GHC-18042] [-Wtype-defaults (in -Wall)]
+    • Defaulting the type variable ‘a0’ to type ‘Integer’ in the following constraint
+        Num a0 arising from the literal ‘1’
+    • In the expression: 1
+      In an equation for ‘blast’: blast = 1
+
+src/Lib/B.hs:3:1: warning: [GHC-38417] [-Wmissing-signatures (in -Wall)]
+    Top-level binding with no type signature: warnmeup :: Integer
+
+src/Lib/B.hs:3:12: warning: [GHC-18042] [-Wtype-defaults (in -Wall)]
+    • Defaulting the type variable ‘a0’ to type ‘Integer’ in the following constraint
+        Num a0 arising from the literal ‘4’
+    • In the expression: 4
+      In an equation for ‘warnmeup’: warnmeup = 4
+
+src/Lib.hs:5:1: warning: [-Wunused-imports (in -Wextra)]
+    The import of ‘Lib.A’ is redundant
+      except perhaps to import instances from ‘Lib.A’
+    To import instances alone, use: import Lib.A()
+
+src/Lib.hs:6:1: warning: [-Wunused-imports (in -Wextra)]
+    The import of ‘Lib.B’ is redundant
+      except perhaps to import instances from ‘Lib.B’
+    To import instances alone, use: import Lib.B()
+
+src/Lib.hs:8:1: warning: [GHC-38417] [-Wmissing-signatures (in -Wall)]
+    Top-level binding with no type signature: blah :: Integer
+
+src/Lib.hs:8:1: warning: [-Wunused-top-binds (in -Wextra, -Wunused-binds)]
+    Defined but not used: ‘blah’
+
+src/Lib.hs:8:8: warning: [GHC-18042] [-Wtype-defaults (in -Wall)]
+    • Defaulting the type variable ‘a0’ to type ‘Integer’ in the following constraint
+        Num a0 arising from the literal ‘3’
+    • In the expression: 3
+      In an equation for ‘blah’: blah = 3

testsuite/tests/ghci/prog018/prog018.stdout

 [1 of 3] Compiling A                ( A.hs, interpreted )
+[2 of 3] Compiling B                ( B.hs, interpreted )
+[3 of 3] Compiling C                ( C.hs, interpreted )
 
 A.hs:5:1: warning: [GHC-62161] [-Wincomplete-patterns (in -Wextra)]
     Pattern match(es) are non-exhaustive
@@ -7,19 +9,14 @@ A.hs:5:1: warning: [GHC-62161] [-Wincomplete-patterns (in -Wextra)]
 
 A.hs:8:15: warning: [-Wunused-matches (in -Wextra)]
     Defined but not used: ‘x’
-[2 of 3] Compiling B                ( B.hs, interpreted )
 
 B.hs:7:1: warning: [-Wunused-imports (in -Wextra)]
     The import of ‘Data.Tuple’ is redundant
       except perhaps to import instances from ‘Data.Tuple’
     To import instances alone, use: import Data.Tuple()
-[3 of 3] Compiling C                ( C.hs, interpreted )
 
 C.hs:6:7: error: [GHC-88464]
     Variable not in scope: variableNotInScope :: ()
 Failed, two modules loaded.
 [3 of 3] Compiling C                ( C.hs, interpreted )
-
-C.hs:6:7: error: [GHC-88464]
-    Variable not in scope: variableNotInScope :: ()
 Failed, two modules loaded.