clean up ClosureSearcher api with hrtb

see
- https://stackoverflow.com/questions/35592750/how-does-for-syntax-differ-from-a-regular-lifetime-bound/35595491#35595491
- https://doc.rust-lang.org/nomicon/hrtb.html

src/searcher.rs

@@ -1,5 +1,5 @@
 use rlua::prelude::LuaError;
-use rlua::{Context, MetaMethod, RegistryKey, Table, UserData, UserDataMethods, Value};
+use rlua::{Context, Function, MetaMethod, RegistryKey, Table, UserData, UserDataMethods, Value};
 use std::collections::HashMap;
 use std::fs::File;
 use std::io::Read;
@@ -132,20 +132,38 @@ where
 /// up an `rlua::Context` with Rust code.
 ///
 /// Enables exposing `UserData` types to an `rlua::Context`.
-///
-/// Closures must return an `rlua::Result`-wrapped `&'static str`. This string is
-/// subsequently passed into `rlua::Context.load()` and evaluated.
 pub struct ClosureSearcher {
-    /// Closures must accept an `rlua::Context` as their only parameter, and can do with
-    /// it what they wish. Closures must return an `rlua::Result`-wrapped `&'static str`.
-    modules: HashMap<&'static str, Box<dyn Fn(Context) -> rlua::Result<&'static str> + Send>>,
+    /// Closures must accept three parameters:
+    ///
+    /// 1. An `rlua::Context`, which the closure can do what it wants with.
+    ///
+    /// 2. An `rlua::Table` containing globals (i.e. Lua’s `_G`), which can be passed
+    ///    to `Chunk.set_environment()`.
+    ///
+    /// 3. The name of the module to be loaded (`&str`).
+    ///
+    /// Closures must return an `rlua::Result`-wrapped `Function`. This `Function`
+    /// acts as the module loader.
+    modules: HashMap<
+        &'static str,
+        Box<
+            dyn for<'ctx> Fn(Context<'ctx>, Table<'ctx>, &str) -> rlua::Result<Function<'ctx>>
+                + Send,
+        >,
+    >,
 
     globals: RegistryKey,
 }
 
 impl ClosureSearcher {
     pub fn new(
-        modules: HashMap<&'static str, Box<dyn Fn(Context) -> rlua::Result<&'static str> + Send>>,
+        modules: HashMap<
+            &'static str,
+            Box<
+                dyn for<'ctx> Fn(Context<'ctx>, Table<'ctx>, &str) -> rlua::Result<Function<'ctx>>
+                    + Send,
+            >,
+        >,
         globals: RegistryKey,
     ) -> Self {
         Self { modules, globals }
@@ -157,22 +175,20 @@ impl UserData for ClosureSearcher {
     where
         M: UserDataMethods<'lua, Self>,
     {
-        methods.add_meta_method(MetaMethod::Call, |lua_ctx, this, name: String| {
-            let name = name.as_str();
-            match this.modules.get(name) {
-                Some(ref loader) => {
-                    let content = loader(lua_ctx)?;
-                    Ok(Value::Function(
-                        lua_ctx
-                            .load(content)
-                            .set_name(name)?
-                            .set_environment(lua_ctx.registry_value::<Table>(&this.globals)?)?
-                            .into_function()?,
-                    ))
+        methods.add_meta_method(
+            MetaMethod::Call,
+            |lua_ctx: Context<'lua>, this, name: String| {
+                let name = name.as_str();
+                match this.modules.get(name) {
+                    Some(ref closure) => Ok(Value::Function(closure(
+                        lua_ctx,
+                        lua_ctx.registry_value::<Table>(&this.globals)?,
+                        name,
+                    )?)),
+                    None => Ok(Value::Nil),
                 }
-                None => Ok(Value::Nil),
-            }
-        });
+            },
+        );
     }
 }
 
@@ -207,7 +223,13 @@ pub trait AddSearcher {
     /// setup.
     fn add_closure_searcher(
         &self,
-        modules: HashMap<&'static str, Box<dyn Fn(Context) -> rlua::Result<&'static str> + Send>>,
+        modules: HashMap<
+            &'static str,
+            Box<
+                dyn for<'ctx> Fn(Context<'ctx>, Table<'ctx>, &str) -> rlua::Result<Function<'ctx>>
+                    + Send,
+            >,
+        >,
     ) -> Result<()>;
 }
 
@@ -266,7 +288,13 @@ impl<'a> AddSearcher for Context<'a> {
 
     fn add_closure_searcher(
         &self,
-        modules: HashMap<&'static str, Box<dyn Fn(Context) -> rlua::Result<&'static str> + Send>>,
+        modules: HashMap<
+            &'static str,
+            Box<
+                dyn for<'ctx> Fn(Context<'ctx>, Table<'ctx>, &str) -> rlua::Result<Function<'ctx>>
+                    + Send,
+            >,
+        >,
     ) -> Result<()> {
         let globals = self.globals();
         let searchers: Table = globals.get::<_, Table>("package")?.get("searchers")?;

tests/tests.rs

@@ -1,4 +1,4 @@
-use rlua::{Context, Lua, Table, UserData, UserDataMethods, Value};
+use rlua::{Context, Function, Lua, Table, UserData, UserDataMethods, Value};
 use rlua_searcher::{AddSearcher, Result};
 use std::collections::HashMap;
 use std::fs::File;
@@ -166,10 +166,15 @@ fn add_closure_searcher_works() {
 
     let mut modules: HashMap<
         &'static str,
-        Box<dyn Fn(Context) -> rlua::Result<&'static str> + Send>,
+        Box<
+            dyn for<'ctx> Fn(Context<'ctx>, Table<'ctx>, &str) -> rlua::Result<Function<'ctx>>
+                + Send,
+        >,
     > = HashMap::new();
 
-    let instrument_loader = Box::new(|lua_ctx: Context| {
+    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))
@@ -177,7 +182,11 @@ fn add_closure_searcher_works() {
         let tbl = lua_ctx.create_table()?;
         tbl.set("new", new)?;
         globals.set("instrument", tbl)?;
-        Ok("return instrument")
+        Ok(lua_ctx
+            .load("return instrument")
+            .set_name(name)?
+            .set_environment(env)?
+            .into_function()?)
     });
 
     modules.insert("instrument", instrument_loader);