feat(libcorn): lua support via library export

Introduces the structure for a Lua process to load libcorn.so

README.md

@@ -86,9 +86,36 @@ which can parse Corn into valid JavaScript objects.
 import * as corn from 'libcorn';
 
 const parsed = corn.parse('{foo = "bar"}');
-console.log(parsed) // { foo: "bar" }
+console.log(parsed) // Map(foo -> "bar")
 ```
 
+### Lua
+
+Lua support can be built into the library using __one of__ the feature flags,
+allowing you to bind directly to `libcorn.so`:
+
+- `lua51`
+- `lua52`
+- `lua53`
+- `lua54`
+- `luajit`
+- `luajit52`
+
+So long as `libcorn.so` is in Lua's module path, it can be then be used as below:
+
+```lua
+local libcorn = require("libcorn")
+local success, res = pcall(libcorn.parse, '{foo = "bar"}')
+
+if success then
+    print(res.foo) -- lua table
+else
+    print(res) -- pretty printed error
+end
+```
+
+Thanks to [A-Cloud-Ninja](https://github.com/A-Cloud-Ninja) for adding Lua support!
+
 ## Writing Corn
 
 > This section gives all the outputs in JSON format. Remember you can output in any supported format!

libcorn/Cargo.toml

@@ -11,6 +11,12 @@ keywords = ["configuration", "language", "wasm", "pest", "peg"]
 [features]
 wasm = ["wasm-bindgen", "serde-wasm-bindgen", "console_error_panic_hook", "wee_alloc"]
 bench = ["criterion"]
+lua51 = ["mlua/lua51"]
+lua52 = ["mlua/lua52"]
+lua53 = ["mlua/lua53"]
+lua54 = ["mlua/lua54"]
+luajit = ["mlua/luajit"]
+luajit52 = ["mlua/luajit52"]
 
 [lib]
 name = "corn"
@@ -26,6 +32,7 @@ wasm-bindgen = { version = "0.2.83", optional = true }
 serde-wasm-bindgen = { version = "0.5.0", optional = true }
 console_error_panic_hook = { version = "0.1.7", optional = true }
 wee_alloc = { version = "0.4.5", optional = true }
+mlua = { version = "0.8.9", features = ["vendored", "module", "macros", "serialize"], optional = true }
 
 # bench
 criterion = { version = "0.5.1", features = ["html_reports"], optional = true }

libcorn/src/lib.rs

@@ -10,6 +10,16 @@ pub mod error;
 mod parser;
 
 mod de;
+#[cfg(any(
+    feature = "lua",
+    feature = "lua51",
+    feature = "lua52",
+    feature = "lua53",
+    feature = "lua54",
+    feature = "luajit",
+    feature = "luajit52"
+))]
+mod lua;
 #[cfg(feature = "wasm")]
 mod wasm;
 

libcorn/src/lua.rs

@@ -0,0 +1,24 @@
+use crate::Value;
+use mlua::prelude::*;
+
+impl<'lua> ToLua<'lua> for Value<'lua> {
+    fn to_lua(self, lua: &'lua Lua) -> LuaResult<LuaValue<'lua>> {
+        lua.to_value(&self)
+    }
+}
+
+fn lua_parse(lua: &Lua, config: String) -> LuaResult<LuaValue> {
+    let res = crate::parse(&config);
+    match res {
+        Ok(v) => Ok(lua.to_value(&v)?),
+        Err(e) => Err(LuaError::RuntimeError(e.to_string())),
+    }
+}
+
+#[mlua::lua_module]
+fn libcorn(lua: &Lua) -> LuaResult<LuaTable> {
+    let exports = lua.create_table()?;
+    let parse = lua.create_function(lua_parse)?;
+    exports.set("parse", parse)?;
+    Ok(exports)
+}