Public libraries using the same library name, in the same context, defined in
different folders.

  $ mkdir -p a b

  $ cat > dune-project << EOF
  > (lang dune 3.13)
  > (package (name bar) (allow_empty))
  > (package (name baz) (allow_empty))
  > EOF

  $ cat > a/dune << EOF
  > (library
  >  (name foo)
  >  (public_name bar.foo))
  > EOF

  $ cat > b/dune << EOF
  > (library
  >  (name foo)
  >  (public_name baz.foo))
  > EOF

Without any consumers of the libraries

  $ dune build

With some consumer

  $ cat > dune << EOF
  > (executable
  >  (name main)
  >  (libraries foo))
  > EOF

  $ cat > main.ml <<EOF
  > let () = Foo.x
  > EOF

  $ dune build
  File "a/dune", lines 1-3, characters 0-44:
  1 | (library
  2 |  (name foo)
  3 |  (public_name bar.foo))
  Error: Library with name "foo" is already defined in b/dune:1. Either change
  one of the names, or enable them conditionally using the 'enabled_if' field.
  [1]