Remove custom PartialEq for LuaString and use derived one

Lua can compare strings using `lua_rawequal` and it's more efficient
than always compare bytes.
Under the hood Lua compare pointers for interned strings and content for long ones.
Close #694

Author: khvzak

src/string.rs

@@ -23,7 +23,7 @@ use {
 /// Handle to an internal Lua string.
 ///
 /// Unlike Rust strings, Lua strings may not be valid UTF-8.
-#[derive(Clone)]
+#[derive(Clone, PartialEq)]
 pub struct LuaString(pub(crate) ValueRef);
 
 impl LuaString {
@@ -186,12 +186,6 @@ where
     }
 }
 
-impl PartialEq for LuaString {
-    fn eq(&self, other: &LuaString) -> bool {
-        self.as_bytes() == other.as_bytes()
-    }
-}
-
 impl Eq for LuaString {}
 
 impl<T> PartialOrd<T> for LuaString

tests/string.rs

@@ -5,27 +5,37 @@ use mlua::{Lua, LuaString, Result};
 
 #[test]
 fn test_string_compare() {
-    fn with_str<F: FnOnce(LuaString)>(s: &str, f: F) {
-        f(Lua::new().create_string(s).unwrap());
+    let lua = Lua::new();
+
+    fn with_str<F: FnOnce(LuaString)>(lua: &Lua, s: &str, f: F) {
+        f(lua.create_string(s).unwrap());
     }
 
     // Tests that all comparisons we want to have are usable
-    with_str("teststring", |t| assert_eq!(t, "teststring")); // &str
-    with_str("teststring", |t| assert_eq!(t, b"teststring")); // &[u8]
-    with_str("teststring", |t| assert_eq!(t, b"teststring".to_vec())); // Vec<u8>
-    with_str("teststring", |t| assert_eq!(t, "teststring".to_string())); // String
-    with_str("teststring", |t| assert_eq!(t, t)); // mlua::String
-    with_str("teststring", |t| assert_eq!(t, Cow::from(b"teststring".as_ref()))); // Cow (borrowed)
-    with_str("bla", |t| assert_eq!(t, Cow::from(b"bla".to_vec()))); // Cow (owned)
+    with_str(&lua, "teststring", |t| assert_eq!(t, "teststring")); // &str
+    with_str(&lua, "teststring", |t| assert_eq!(t, b"teststring")); // &[u8]
+    with_str(&lua, "teststring", |t| assert_eq!(t, b"teststring".to_vec())); // Vec<u8>
+    with_str(&lua, "teststring", |t| assert_eq!(t, "teststring".to_string())); // String
+    with_str(&lua, "teststring", |t| assert_eq!(t, t)); // mlua::String
+    with_str(&lua, "teststring", |t| {
+        assert_eq!(t, Cow::from(b"teststring".as_ref())) // Cow (borrowed)
+    });
+    with_str(&lua, "bla", |t| assert_eq!(t, Cow::from(b"bla".to_vec()))); // Cow (owned)
 
     // Test ordering
-    with_str("a", |a| {
+    with_str(&lua, "a", |a| {
         assert!(!(a < a));
         assert!(!(a > a));
     });
-    with_str("a", |a| assert!(a < "b"));
-    with_str("a", |a| assert!(a < b"b"));
-    with_str("a", |a| with_str("b", |b| assert!(a < b)));
+    with_str(&lua, "a", |a| assert!(a < "b"));
+    with_str(&lua, "a", |a| assert!(a < b"b"));
+    with_str(&lua, "a", |a| with_str(&lua, "b", |b| assert!(a < b)));
+
+    // Long strings (not interned by Lua)
+    let long_str = "abc".repeat(100);
+    with_str(&lua, &long_str, |s1| {
+        with_str(&lua, &long_str, |s2| assert_eq!(s1, s2))
+    });
 }
 
 #[test]