Parallel inline_tests: Fix when partition list is empty

Signed-off-by: Hugo Heuzard <[email protected]>

doc/changes/8848.md

@@ -0,0 +1 @@
+- Fix inline_tests when the partition list is empty (#8848, @hhugo)

src/dune_rules/inline_tests.ml

@@ -347,15 +347,18 @@ include Sub_system.Register_end_point (struct
                List.map partitions_flags ~f:(fun p -> action mode (flags p))
                |> Action_builder.all
              and+ () = Action_builder.paths source_files in
-             let run_tests = Action.concurrent actions in
-             let diffs =
-               List.map source_files ~f:(fun fn ->
-                 Path.as_in_build_dir_exn fn
-                 |> Path.Build.extend_basename ~suffix:".corrected"
-                 |> Action.diff ~optional:true fn)
-               |> Action.concurrent
-             in
-             Action.Full.make ~sandbox @@ Action.progn [ run_tests; diffs ]))
+             match actions with
+             | [] -> Action.Full.empty
+             | _ :: _ ->
+               let run_tests = Action.concurrent actions in
+               let diffs =
+                 List.map source_files ~f:(fun fn ->
+                   Path.as_in_build_dir_exn fn
+                   |> Path.Build.extend_basename ~suffix:".corrected"
+                   |> Action.diff ~optional:true fn)
+                 |> Action.concurrent
+               in
+               Action.Full.make ~sandbox @@ Action.progn [ run_tests; diffs ]))
     ;;
 
     let gen_rules c ~(info : Info.t) ~backends =

test/blackbox-tests/test-cases/inline_tests/parallel.t/run.t

@@ -34,12 +34,6 @@ See that we indeed have 3 partitions
       ocamlopt test3/.test_lib3.inline-tests/.test_lib3.inline-tests.eobjs/native/dune__exe__Inline_test_runner_test_lib3.{cmx,o}
       ocamlopt test3/.test_lib3.inline-tests/inline_test_runner_test_lib3.exe
   inline_test_runner_test_lib3 test3/.test_lib3.inline-tests/partitions-best
-  File "test3/dune", line 4, characters 1-40:
-  4 |  (inline_tests (backend fake_backend_2)))
-       ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-  Error: Rule dependencies are configured to require sandboxing, but the rule
-  has no actions that could potentially require sandboxing.
-  [1]
 
 See that we have no partition.