test: demonstrate a dependency cycle between modules field and rule

test/blackbox-tests/test-cases/lib-available-dynamic-modules.t

@@ -0,0 +1,41 @@
+Demonstrate a dependency cycle between library modules field and a rule that
+generates them dynamically in the same directory
+
+  $ cat > dune-project << EOF
+  > (lang dune 3.13)
+  > EOF
+
+  $ mkdir gen
+  $ cat > gen/dune << EOF
+  > (executable
+  >  (name gen)
+  >  (libraries y))
+  > (rule
+  >  (with-stdout-to dyn_modules (run ./gen.exe)))
+  > EOF
+  $ cat > gen/gen.ml <<EOF
+  > let () =
+  >   Format.eprintf "generating. %s from 'y'" Y.x;
+  >   Format.printf "foo"
+  > EOF
+  $ touch foo.ml
+  $ cat > dune << EOF
+  > (library
+  >  (name x)
+  >  (modules %{read:gen/dyn_modules}))
+  > (library
+  >  (name y)
+  >  (modules y))
+  > EOF
+  $ cat > y.ml <<EOF
+  > let x = "hello"
+  > EOF
+  $ dune build ./gen/dyn_modules
+  Error: Dependency cycle between:
+     _build/default/gen/dyn_modules
+  -> %{read:gen/dyn_modules} at dune:3
+  -> (modules) field at dune:1
+  -> _build/default/gen/.merlin-conf/exe-gen
+  -> _build/default/gen/gen.exe
+  -> _build/default/gen/dyn_modules
+  [1]