driver: In oneshot mode, look for interface files in hidir

How things should work:

*  -i is the search path for source files
*  -hidir explicitly sets the search path for interface files and the output location for interface files.
*  -odir sets the search path and output location for object files.

Before in one shot mode we would look for the interface file in the
search locations given by `-i`, but then set the path to be in the
`hidir`, so in unusual situations the finder could find an interface
file in the `-i` dir but later fail because it tried to read the
interface file from the `-hidir`.

A bug identified by #20569

5 files changed, 20 insertions, 3 deletions

diff --git a/compiler/GHC/Unit/Finder.hs b/compiler/GHC/Unit/Finder.hs
index c3c517cb18..45057d13e2 100644
--- a/compiler/GHC/Unit/Finder.hs
+++ b/compiler/GHC/Unit/Finder.hs
@@ -412,6 +412,12 @@ findInstalledHomeModule fc fopts home_unit mod_name = do
      home_path = case maybe_working_dir of
                   Nothing -> finder_importPaths fopts
                   Just fp -> augmentImports fp (finder_importPaths fopts)
+     hi_dir_path =
+      case finder_hiDir fopts of
+        Just hiDir -> case maybe_working_dir of
+                        Nothing -> [hiDir]
+                        Just fp -> [fp </> hiDir]
+        Nothing -> home_path
      hisuf = finder_hiSuf fopts
      mod = mkModule home_unit mod_name
 
@@ -431,8 +437,9 @@ findInstalledHomeModule fc fopts home_unit mod_name = do
         -- In compilation manager modes, we look for source files in the home
         -- package because we can compile these automatically.  In one-shot
         -- compilation mode we look for .hi and .hi-boot files only.
-     exts | finder_lookupHomeInterfaces fopts = hi_exts
-          | otherwise                         = source_exts
+     (search_dirs, exts)
+          | finder_lookupHomeInterfaces fopts = (hi_dir_path, hi_exts)
+          | otherwise                         = (home_path, source_exts)
    in
 
    -- special case for GHC.Prim; we won't find it in the filesystem.
@@ -440,7 +447,7 @@ findInstalledHomeModule fc fopts home_unit mod_name = do
    -- is a home module).
    if mod `installedModuleEq` gHC_PRIM
          then return (InstalledFound (error "GHC.Prim ModLocation") mod)
-         else searchPathExts home_path mod exts
+         else searchPathExts search_dirs mod exts
 
 -- | Prepend the working directory to the search path.
 augmentImports :: FilePath -> [FilePath] -> [FilePath]
diff --git a/testsuite/tests/driver/Makefile b/testsuite/tests/driver/Makefile
index 9242c2d512..8d47dba2d5 100644
--- a/testsuite/tests/driver/Makefile
+++ b/testsuite/tests/driver/Makefile
@@ -739,3 +739,8 @@ T20316:
 	"$(TEST_HC)" $(TEST_HC_OPTS) -fno-code T20316.hs -ddump-to-file -ddump-timings;
 	echo "*** non-module.dump-timings ***"
 	cat non-module.dump-timings | grep alloc | sed 's/alloc.*//'
+
+.PHONY: T20569
+T20569:
+	"$(TEST_HC)" $(TEST_HC_OPTS) -c T20569/A.hs -i -iT20569 -hidir=interface
+	"$(TEST_HC)" $(TEST_HC_OPTS) -c T20569/B.hs -i -iT20569 -hidir=interface
diff --git a/testsuite/tests/driver/T20569/A.hs b/testsuite/tests/driver/T20569/A.hs
new file mode 100644
index 0000000000..d843c00b78
--- /dev/null
+++ b/testsuite/tests/driver/T20569/A.hs
@@ -0,0 +1 @@
+module A where
diff --git a/testsuite/tests/driver/T20569/B.hs b/testsuite/tests/driver/T20569/B.hs
new file mode 100644
index 0000000000..ce9e7e4932
--- /dev/null
+++ b/testsuite/tests/driver/T20569/B.hs
@@ -0,0 +1,3 @@
+module B where
+
+import A
diff --git a/testsuite/tests/driver/all.T b/testsuite/tests/driver/all.T
index 07a6ec8c74..92fa6edceb 100644
--- a/testsuite/tests/driver/all.T
+++ b/testsuite/tests/driver/all.T
@@ -304,3 +304,4 @@ test('T20200loop', extra_files(['T20200loop']), multimod_compile,
 test('T20316', normal, makefile_test, [])
 test('MultiRootsErr', normal, multimod_compile_fail, ['MultiRootsErr', 'MultiRootsErr'])
 test('patch-level2', normal, compile, ['-Wcpp-undef'])
+test('T20569', extra_files(["T20569/"]), makefile_test, [])