make initial implementation

credit
- https://github.com/AlphaModder/include-lua

src/searcher.rs

@@ -0,0 +1,61 @@
+use rlua::{Context, MetaMethod, RegistryKey, Table, UserData, UserDataMethods, Value};
+use std::collections::HashMap;
+
+use crate::types::Result;
+
+/// Stores Lua modules indexed by module name, and provides an
+/// `rlua::MetaMethod` to enable `require`ing the stored modules by name
+/// in an `rlua::Context`.
+struct Searcher {
+    /// A `HashMap` of Lua modules in `String` representation, indexed
+    /// by module name.
+    modules: HashMap<String, String>,
+
+    /// An `rlua::RegistryKey` whose value is the Lua environment within
+    /// which the user made the request to instantiate a `Searcher` for
+    /// `modules`.
+    globals: RegistryKey,
+}
+
+impl Searcher {
+    fn new(modules: HashMap<String, String>, globals: RegistryKey) -> Self {
+        Self { modules, globals }
+    }
+}
+
+impl UserData for Searcher {
+    fn add_methods<'lua, M: UserDataMethods<'lua, Self>>(methods: &mut M) {
+        methods.add_meta_method(MetaMethod::Call, |lua_ctx, this, name: String| {
+            match this.modules.get(&name) {
+                Some(content) => Ok(Value::Function(
+                    lua_ctx
+                        .load(content)
+                        .set_name(&name)?
+                        .set_environment(lua_ctx.registry_value::<Table>(&this.globals)?)?
+                        .into_function()?,
+                )),
+                None => Ok(Value::Nil),
+            }
+        });
+    }
+}
+
+/// Extend `rlua::Context` to support `require`ing Lua modules by name.
+pub trait AddSearcher<'a> {
+    /// Add a `HashMap` of Lua modules indexed by module name to Lua’s
+    /// `package.searchers` table in an `rlua::Context`, with lookup
+    /// functionality provided by the `rlua_searcher::Searcher` struct.
+    fn add_searcher(&self, modules: HashMap<String, String>) -> Result<()>;
+}
+
+impl<'a> AddSearcher<'a> for Context<'a> {
+    fn add_searcher(&self, modules: HashMap<String, String>) -> Result<()> {
+        let globals = self.globals();
+        let searchers: Table = globals.get::<_, Table>("package")?.get("searchers")?;
+        let registry_key = self.create_registry_value(globals)?;
+        let searcher = Searcher::new(modules, registry_key);
+        searchers
+            .set(searchers.len()? + 1, searcher)
+            .map_err(|e| e.into())
+    }
+}