test(x-compilation): demonstrate overlap check failure with ppx_runti…

…me_libraries

Signed-off-by: Antonio Nuno Monteiro <anmonteiro@gmail.com>

test/blackbox-tests/test-cases/custom-cross-compilation/ppx-cross.t

@@ -0,0 +1,68 @@
+Demonstrate a bad interaction between cross-compilation and
+ppx_runtime_libraries
+
+  $ mkdir -p etc/findlib.conf.d
+  $ export OCAMLFIND_CONF=$PWD/etc/findlib.conf
+  $ touch etc/findlib.conf etc/findlib.conf.d/foo.conf
+
+Create lib1, ppx and lib2:
+- lib1 is a regular library
+- ppx has a runtime dep on lib1 (via `ppx_runtime_libraries`)
+- lib2 is a regular library pre-processed by `ppx`
+
+  $ mkdir lib1 ppx lib2
+  $ cat > dune-project <<EOF
+  > (lang dune 3.7)
+  > (package (name ppx-cross))
+  > EOF
+
+  $ cat > lib1/dune <<EOF
+  > (library
+  >  (name lib1)
+  >  (public_name ppx-cross.lib1))
+  > EOF
+
+In the ppx, removing `ppx_runtime_libraries` makes the test pass
+
+  $ cat > ppx/dune <<EOF
+  > (library
+  >  (name ppx)
+  >  (public_name ppx-cross.ppx)
+  >  (kind ppx_rewriter)
+  >  (ppx.driver (main Ppx.main))
+  >  (ppx_runtime_libraries lib1))
+  > EOF
+  $ cat > ppx/ppx.ml <<EOF
+  > let main () =
+  >   let out = ref "" in
+  >   let args =
+  >     [ ("-o", Arg.Set_string out, "")
+  >     ; ("--impl", Arg.Set_string (ref ""), "")
+  >     ; ("--as-ppx", Arg.Set (ref false), "")
+  >     ; ("--cookie", Arg.Set (ref false), "")
+  >     ]
+  >   in
+  >   let anon _ = () in
+  >   Arg.parse (Arg.align args) anon "";
+  >   let out = open_out !out in
+  >   close_out out;
+  > EOF
+
+  $ cat > lib2/dune <<EOF
+  > (library
+  >  (name lib2)
+  >  (public_name ppx-cross.lib2)
+  >  (preprocess (pps ppx)))
+  > EOF
+  $ touch lib2/lib2.ml
+
+  $ dune build @install -x foo
+  Error: Conflict between the following libraries:
+  - "ppx-cross.lib1" in _build/default.foo/lib1
+  - "ppx-cross.lib1" in _build/default/lib1
+  -> required by _build/default.foo/lib2/.lib2.objs/byte/lib2.cmt
+  -> required by _build/install/default.foo/lib/ppx-cross/lib2/lib2.cmt
+  -> required by _build/default.foo/ppx-cross-foo.install
+  -> required by alias install (context default.foo)
+  [1]
+