add StaticClosureSearcher

because evidently one does not merely accept `&'static str` OR `String`

tests/tests.rs

@@ -212,6 +212,58 @@ fn add_closure_searcher_works() {
     assert_eq!(sound, "The ukulele goes twang");
 }
 
+#[test]
+fn add_static_closure_searcher_works() {
+    let lua = Lua::new();
+
+    let mut modules: HashMap<
+        &'static str,
+        Box<
+            dyn for<'ctx> Fn(Context<'ctx>, Table<'ctx>, &str) -> rlua::Result<Function<'ctx>>
+                + Send,
+        >,
+    > = HashMap::new();
+
+    let instrument_loader: Box<
+        dyn for<'ctx> Fn(Context<'ctx>, Table<'ctx>, &str) -> rlua::Result<Function<'ctx>> + Send,
+    > = Box::new(|lua_ctx, env, name| {
+        let globals = lua_ctx.globals();
+        let new = lua_ctx.create_function(|_, (name, sound): (String, String)| {
+            Ok(Instrument::new(name, sound))
+        })?;
+        let tbl = lua_ctx.create_table()?;
+        tbl.set("new", new)?;
+        globals.set("instrument", tbl)?;
+        Ok(lua_ctx
+            .load("return instrument")
+            .set_name(name)?
+            .set_environment(env)?
+            .into_function()?)
+    });
+
+    modules.insert("instrument", instrument_loader);
+
+    let sound = lua
+        .context::<_, Result<String>>(|lua_ctx| {
+            lua_ctx.add_static_closure_searcher(modules)?;
+
+            // Ensure global variable `instrument` is unset.
+            let nil: String = lua_ctx.load("return type(instrument)").eval()?;
+            assert_eq!(nil, "nil");
+
+            Ok(lua_ctx
+                .load(
+                    r#"local instrument = require("instrument")
+                       local ukulele = instrument.new("ukulele", "twang")
+                       return ukulele:play()"#,
+                )
+                .eval()?)
+        })
+        .unwrap();
+
+    assert_eq!(sound, "The ukulele goes twang");
+}
+
 struct Instrument {
     name: String,
     sound: String,