From 6469fea7c78408db679898168a8e9c50c8c7c5ce Mon Sep 17 00:00:00 2001
From: Matthew Pickering <matthewtpickering@gmail.com>
Date: Mon, 26 Dec 2022 09:56:39 +0000
Subject: Don't write o-boot files in Interactive mode

We should not be producing object files when in interactive mode but we
still produced the dummy o-boot files. These never made it into a
`Linkable` but then confused the recompilation checker.

Fixes #22669
---
 compiler/GHC/Driver/Pipeline/Execute.hs | 42 +++++++++++++++++++++------------
 testsuite/tests/driver/Makefile         |  6 +++++
 testsuite/tests/driver/T22669.hs        |  1 +
 testsuite/tests/driver/T22669.hs-boot   |  1 +
 testsuite/tests/driver/all.T            |  1 +
 5 files changed, 36 insertions(+), 15 deletions(-)
 create mode 100644 testsuite/tests/driver/T22669.hs
 create mode 100644 testsuite/tests/driver/T22669.hs-boot

diff --git a/compiler/GHC/Driver/Pipeline/Execute.hs b/compiler/GHC/Driver/Pipeline/Execute.hs
index 04b641c5d9..75f33834e2 100644
--- a/compiler/GHC/Driver/Pipeline/Execute.hs
+++ b/compiler/GHC/Driver/Pipeline/Execute.hs
@@ -578,21 +578,33 @@ runHscBackendPhase pipe_env hsc_env mod_name src_flavour location result = do
       next_phase = hscPostBackendPhase src_flavour (backend dflags)
   case result of
       HscUpdate iface ->
-          do
-             case src_flavour of
-               HsigFile -> do
-                 -- We need to create a REAL but empty .o file
-                 -- because we are going to attempt to put it in a library
-                 let input_fn = expectJust "runPhase" (ml_hs_file location)
-                     basename = dropExtension input_fn
-                 compileEmptyStub dflags hsc_env basename location mod_name
-
-               -- In the case of hs-boot files, generate a dummy .o-boot
-               -- stamp file for the benefit of Make
-               HsBootFile -> touchObjectFile logger dflags o_file
-               HsSrcFile -> panic "HscUpdate not relevant for HscSrcFile"
-
-             return ([], iface, emptyHomeModInfoLinkable, o_file)
+          if | not (backendGeneratesCode (backend dflags))  ->
+                panic "HscUpdate not relevant for NoBackend"
+             | not (backendGeneratesCodeForHsBoot (backend dflags)) -> do
+                -- In Interpreter way, there is just no linkable for hs-boot files
+                -- and we don't want to write an empty `o-boot` file when we're not
+                -- supposed to be writing any .o files (#22669)
+                return ([], iface, emptyHomeModInfoLinkable, o_file)
+             | otherwise -> do
+                 case src_flavour of
+                   HsigFile -> do
+                     -- We need to create a REAL but empty .o file
+                     -- because we are going to attempt to put it in a library
+                     let input_fn = expectJust "runPhase" (ml_hs_file location)
+                         basename = dropExtension input_fn
+                     compileEmptyStub dflags hsc_env basename location mod_name
+
+                   -- In the case of hs-boot files, generate a dummy .o-boot
+                   -- stamp file for the benefit of Make
+                   HsBootFile -> touchObjectFile logger dflags o_file
+                   HsSrcFile -> panic "HscUpdate not relevant for HscSrcFile"
+
+                 -- MP: I wonder if there are any lurking bugs here because we
+                 -- return Linkable == emptyHomeModInfoLinkable, despite the fact that there is a
+                 -- linkable (.o-boot) which we check for in `Iface/Recomp.hs` and
+                 -- then will carry around the linkable if we're doing
+                 -- recompilation.
+                 return ([], iface, emptyHomeModInfoLinkable, o_file)
       HscRecomp { hscs_guts = cgguts,
                   hscs_mod_location = mod_location,
                   hscs_partial_iface = partial_iface,
diff --git a/testsuite/tests/driver/Makefile b/testsuite/tests/driver/Makefile
index 7c9625570a..77e87c9e6f 100644
--- a/testsuite/tests/driver/Makefile
+++ b/testsuite/tests/driver/Makefile
@@ -786,4 +786,10 @@ T22044:
 	# Test the file exists and is preprocessed
 	"$(TEST_HC)" $(TEST_HC_OPTS) -v0 T22044.hs
 
+.PHONY: T22669
+T22669:
+	echo ":q" | "$(TEST_HC)" $(TEST_HC_OPTS) -v0 --interactive T22669
+	! test -f T22669.o-boot
+
+
 
diff --git a/testsuite/tests/driver/T22669.hs b/testsuite/tests/driver/T22669.hs
new file mode 100644
index 0000000000..33ee925790
--- /dev/null
+++ b/testsuite/tests/driver/T22669.hs
@@ -0,0 +1 @@
+module T22669 where
diff --git a/testsuite/tests/driver/T22669.hs-boot b/testsuite/tests/driver/T22669.hs-boot
new file mode 100644
index 0000000000..33ee925790
--- /dev/null
+++ b/testsuite/tests/driver/T22669.hs-boot
@@ -0,0 +1 @@
+module T22669 where
diff --git a/testsuite/tests/driver/all.T b/testsuite/tests/driver/all.T
index 5592e51e44..ddc0039b55 100644
--- a/testsuite/tests/driver/all.T
+++ b/testsuite/tests/driver/all.T
@@ -319,3 +319,4 @@ test('T21869', [js_broken(22261), when(unregisterised(), skip)], makefile_test,
 test('T22044', normal, makefile_test, [])
 test('T22048', [only_ways(['normal']), grep_errmsg("_rule")], compile, ["-O -fomit-interface-pragmas -ddump-simpl"])
 test('T21722', normal, compile_fail, ['-fno-show-error-context'])
+test('T22669', normal, makefile_test, [])
-- 
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