Force module recompilation if '*' prefix was used to load modules in ghci (#8042)

Usually pre-compiled code is preferred to be loaded in ghci if available, which means
that if we try to load module with '*' prefix and compilation artifacts are available
on disc (.o and .hi files) or the source code was untouched, the driver would think
no recompilation is required. Therefore, we need to force recompilation so that desired
byte-code is generated and loaded. Forcing in this case should be ok, since this is what
happens for interpreted code anyways when reloading modules.

4 files changed, 24 insertions, 3 deletions

diff --git a/compiler/GHC/Driver/Pipeline.hs b/compiler/GHC/Driver/Pipeline.hs
index 1a3e256710..717cd71369 100644
--- a/compiler/GHC/Driver/Pipeline.hs
+++ b/compiler/GHC/Driver/Pipeline.hs
@@ -339,14 +339,18 @@ compileOne' m_tc_result mHscMessage
        current_dir = takeDirectory basename
        old_paths   = includePaths dflags2
        !prevailing_dflags = hsc_dflags hsc_env0
+       loadAsByteCode
+         | Just (Target _ obj _) <- findTarget summary (hsc_targets hsc_env0)
+         , not obj
+         = True
+         | otherwise = False
        -- Figure out which backend we're using
        (bcknd, dflags3)
          -- #8042: When module was loaded with `*` prefix in ghci, but DynFlags
          -- suggest to generate object code (which may happen in case -fobject-code
          -- was set), force it to generate byte-code. This is NOT transitive and
          -- only applies to direct targets.
-         | Just (Target _ obj _) <- findTarget summary (hsc_targets hsc_env0)
-         , not obj
+         | loadAsByteCode
          = (Interpreter, dflags2 { backend = Interpreter })
          | otherwise
          = (backend dflags, dflags2)
@@ -362,7 +366,10 @@ compileOne' m_tc_result mHscMessage
        -- -fforce-recomp should also work with --make
        force_recomp = gopt Opt_ForceRecomp dflags
        source_modified
-         | force_recomp = SourceModified
+         -- #8042: Usually pre-compiled code is preferred to be loaded in ghci
+         -- if available. So, if the "*" prefix was used, force recompilation
+         -- to make sure byte-code is loaded.
+         | force_recomp || loadAsByteCode = SourceModified
          | otherwise = source_modified0
 
        always_do_basic_recompilation_check = case bcknd of
diff --git a/testsuite/tests/ghci/scripts/T8042recomp.script b/testsuite/tests/ghci/scripts/T8042recomp.script
new file mode 100644
index 0000000000..d8fa2b54cc
--- /dev/null
+++ b/testsuite/tests/ghci/scripts/T8042recomp.script
@@ -0,0 +1,7 @@
+:set -v1
+System.IO.writeFile "T8042B.hs" "module T8042B where { fooB = \"T8042B\"; }"
+System.IO.writeFile "T8042A.hs" "module T8042A where { import T8042B; run = putStrLn fooB }"
+:set -fobject-code
+:load T8042A
+:load *T8042A
+:break run
diff --git a/testsuite/tests/ghci/scripts/T8042recomp.stdout b/testsuite/tests/ghci/scripts/T8042recomp.stdout
new file mode 100644
index 0000000000..49250577dc
--- /dev/null
+++ b/testsuite/tests/ghci/scripts/T8042recomp.stdout
@@ -0,0 +1,6 @@
+[1 of 2] Compiling T8042B           ( T8042B.hs, T8042B.o )
+[2 of 2] Compiling T8042A           ( T8042A.hs, T8042A.o )
+Ok, two modules loaded.
+[2 of 2] Compiling T8042A           ( T8042A.hs, interpreted )
+Ok, two modules loaded.
+Breakpoint 0 activated at T8042A.hs:1:44-56
diff --git a/testsuite/tests/ghci/scripts/all.T b/testsuite/tests/ghci/scripts/all.T
index 29b01a0b0c..6fec18bd92 100755
--- a/testsuite/tests/ghci/scripts/all.T
+++ b/testsuite/tests/ghci/scripts/all.T
@@ -175,6 +175,7 @@ test('T7873', normal, ghci_script, ['T7873.script'])
 test('T7939', normal, ghci_script, ['T7939.script'])
 test('T7894', normal, ghci_script, ['T7894.script'])
 test('T8042', normal, ghci_script, ['T8042.script'])
+test('T8042recomp', normal, ghci_script, ['T8042recomp.script'])
 test('T8116', normal, ghci_script, ['T8116.script'])
 test('T8113', normal, ghci_script, ['T8113.script'])
 test('T8172', when(opsys('mingw32'), normalise_drive_letter),