test: plugin loading + dune exec

test/blackbox-tests/test-cases/dune-site/dune

@@ -0,0 +1,3 @@
+(cram
+ (applies_to plugin-dev-mode-loading)
+ (alias runtest-windows))

test/blackbox-tests/test-cases/dune-site/plugin-dev-mode-loading.t

@@ -0,0 +1,81 @@
+Test that dune-site plugins load correctly in development mode (without
+installing or using --release). This tests the path substitution mechanism
+that embeds plugin locations into the executable.
+
+Setup a minimal project with a main app and a plugin:
+
+  $ cat > dune-project <<EOF
+  > (lang dune 3.8)
+  > (using dune_site 0.1)
+  > (name app)
+  > (package
+  >  (name app)
+  >  (sites (lib plugins)))
+  > EOF
+
+  $ cat > dune <<EOF
+  > (executable
+  >  (public_name app)
+  >  (modules sites app)
+  >  (libraries app.register dune-site dune-site.plugins))
+  > 
+  > (library
+  >  (public_name app.register)
+  >  (name registration)
+  >  (modules registration))
+  > 
+  > (generate_sites_module
+  >  (module sites)
+  >  (plugins (app plugins)))
+  > EOF
+
+  $ cat > registration.ml <<EOF
+  > let plugins_loaded : string list ref = ref []
+  > EOF
+
+  $ cat > app.ml <<EOF
+  > let () = Sites.Plugins.Plugins.load_all ()
+  > let () =
+  >   match !Registration.plugins_loaded with
+  >   | [] -> print_endline "ERROR: No plugins loaded!"
+  >   | plugins ->
+  >     print_endline "Plugins loaded:";
+  >     List.iter (fun p -> print_endline ("  - " ^ p)) plugins
+  > EOF
+
+Create a plugin:
+
+  $ mkdir plugin
+  $ cat > plugin/dune-project <<EOF
+  > (lang dune 3.8)
+  > (using dune_site 0.1)
+  > (generate_opam_files true)
+  > (package (name plugin1))
+  > EOF
+
+  $ cat > plugin/dune <<EOF
+  > (library
+  >  (public_name plugin1.impl)
+  >  (name plugin1_impl)
+  >  (modules plugin1_impl)
+  >  (libraries app.register))
+  > 
+  > (plugin
+  >  (name plugin1)
+  >  (libraries plugin1.impl)
+  >  (site (app plugins)))
+  > EOF
+
+  $ cat > plugin/plugin1_impl.ml <<EOF
+  > let () =
+  >   print_endline "Plugin1 registering...";
+  >   Registration.plugins_loaded := "plugin1" :: !Registration.plugins_loaded
+  > EOF
+
+Build and run via dune exec - plugins should load in dev mode:
+
+  $ dune build @all 2>&1 | dune_cmd sanitize
+  $ dune exec -- ./app.exe
+  Plugin1 registering...
+  Plugins loaded:
+    - plugin1