test(melange): virtual library compilation with private libs (#11246)

Signed-off-by: Antonio Nuno Monteiro <[email protected]>

test/blackbox-tests/test-cases/melange/virtual-lib-private.t

@@ -0,0 +1,46 @@
+Test private virtual libraries and implementations
+
+  $ mkdir -p vlib js_impl test
+  $ cat > dune-project <<EOF
+  > (lang dune 3.13)
+  > (using melange 0.1)
+  > EOF
+  $ cat > vlib/dune <<EOF
+  > (library
+  >  (name the_lib)
+  >  (modes melange native)
+  >  (virtual_modules virt))
+  > EOF
+  $ cat > vlib/the_lib.mli <<EOF
+  > module Time : sig
+  >   val gettimeofday : unit -> float
+  > end
+  > EOF
+  $ cat > vlib/the_lib.ml <<EOF
+  > module Time = struct
+  >   let gettimeofday () = Virt.gettimeofday ()
+  > end
+  > EOF
+  $ cat > vlib/virt.mli <<EOF
+  > val gettimeofday : unit -> float
+  > EOF
+
+  $ cat > js_impl/dune <<EOF
+  > (library
+  >  (name timeJs)
+  >  (implements the_lib)
+  >  (modes melange)
+  >  (preprocess (pps melange.ppx)))
+  > EOF
+  $ cat > js_impl/virt.ml <<EOF
+  > let gettimeofday : unit -> float = fun () -> 42.
+  > EOF
+
+  $ cat > test/dune <<EOF
+  > (melange.emit
+  >  (target output)
+  >  (libraries the_lib timeJs)
+  >  (emit_stdlib false))
+  > EOF
+
+  $ dune build @melange