Reproduce ocaml#3636

Signed-off-by: Rudi Grinberg <[email protected]>

test/blackbox-tests/test-cases/virtual-libraries/github3636.t/run.t

@@ -0,0 +1,57 @@
+Reproduce bug in #3636.
+
+The bug occurs when (include_subdirs unqualified) is used.
+
+  $ cat >dune-project <<EOF
+  > (lang dune 2.7)
+  > (package
+  >  (name testpkg))
+  > EOF
+
+  $ mkdir vlib impl
+
+  $ cat >vlib/dune <<EOF
+  > (include_subdirs unqualified)
+  > (library
+  >  (name vlib)
+  >  (public_name testpkg.vlib)
+  >  (virtual_modules greet))
+  > EOF
+  $ cat >vlib/greet.mli <<EOF
+  > val s : string
+  > EOF
+
+  $ cat >impl/dune <<EOF
+  > (library
+  >  (name impl)
+  >  (public_name testpkg.impl)
+  >  (implements vlib))
+  > EOF
+  $ cat >impl/greet.ml <<EOF
+  > let s = "hello world"
+  > EOF
+
+  $ dune build @install
+
+  $ mkdir exe
+  $ cat >exe/dune-project <<EOF
+  > (lang dune 2.7)
+  > EOF
+
+  $ cat >exe/dune <<EOF
+  > (executable
+  >  (name foo)
+  >  (libraries testpkg.vlib testpkg.impl))
+  > EOF
+
+  $ cat >exe/foo.ml <<EOF
+  > print_endline Vlib.Greet.s
+  > EOF
+  $ OCAMLPATH=$PWD/_build/install/default/lib dune exec --root exe -- ./foo.exe
+  Entering directory 'exe'
+  Entering directory 'exe'
+  File "foo.ml", line 1, characters 14-26:
+  1 | print_endline Vlib.Greet.s
+                    ^^^^^^^^^^^^
+  Error: Unbound module Vlib
+  [1]