Fix some clippy lints, possible edge case API incompatibility around HashMap

src/conversion.rs

@@ -1,5 +1,5 @@
 use std::collections::{BTreeMap, HashMap};
-use std::hash::Hash;
+use std::hash::{BuildHasher, Hash};
 use std::string::String as StdString;
 
 use error::*;
@@ -266,13 +266,15 @@ impl<'lua, T: FromLua<'lua>> FromLua<'lua> for Vec<T> {
     }
 }
 
-impl<'lua, K: Eq + Hash + ToLua<'lua>, V: ToLua<'lua>> ToLua<'lua> for HashMap<K, V> {
+impl<'lua, K: Eq + Hash + ToLua<'lua>, V: ToLua<'lua>, S: BuildHasher> ToLua<'lua>
+    for HashMap<K, V, S> {
     fn to_lua(self, lua: &'lua Lua) -> Result<Value<'lua>> {
         Ok(Value::Table(lua.create_table_from(self)?))
     }
 }
 
-impl<'lua, K: Eq + Hash + FromLua<'lua>, V: FromLua<'lua>> FromLua<'lua> for HashMap<K, V> {
+impl<'lua, K: Eq + Hash + FromLua<'lua>, V: FromLua<'lua>, S: BuildHasher + Default> FromLua<'lua>
+    for HashMap<K, V, S> {
     fn from_lua(value: Value<'lua>, _: &'lua Lua) -> Result<Self> {
         if let Value::Table(table) = value {
             table.pairs().collect()

src/ffi.rs

@@ -36,7 +36,7 @@ pub const LUA_NOREF: c_int = -2;
 pub const LUA_REFNIL: c_int = -1;
 
 pub const LUA_MULTRET: c_int = -1;
-pub const LUAI_MAXSTACK: c_int = 1000000;
+pub const LUAI_MAXSTACK: c_int = 1_000_000;
 pub const LUA_REGISTRYINDEX: c_int = -LUAI_MAXSTACK - 1000;
 pub const LUA_RIDX_MAINTHREAD: lua_Integer = 1;
 pub const LUA_RIDX_GLOBALS: lua_Integer = 2;

src/lua.rs

@@ -64,8 +64,7 @@ impl<'lua> Value<'lua> {
             Value::Table(_) => "table",
             Value::Function(_) => "function",
             Value::Thread(_) => "thread",
-            Value::UserData(_) => "userdata",
+            Value::UserData(_) | Value::Error(_) => "userdata",
-            Value::Error(_) => "userdata",
         }
     }
 }

src/util.rs

@@ -260,8 +260,7 @@ pub unsafe fn pnext(state: *mut ffi::lua_State, index: c_int) -> Result<c_int> {
 pub unsafe fn handle_error(state: *mut ffi::lua_State, err: c_int) -> Result<()> {
     if err == ffi::LUA_OK || err == ffi::LUA_YIELD {
         Ok(())
-    } else {
+    } else if let Some(err) = pop_wrapped_error(state) {
-        if let Some(err) = pop_wrapped_error(state) {
         Err(err)
     } else if is_wrapped_panic(state, -1) {
         let panic = get_userdata::<WrappedPanic>(state, -1);
@@ -272,8 +271,7 @@ pub unsafe fn handle_error(state: *mut ffi::lua_State, err: c_int) -> Result<()>
             lua_panic!(state, "internal error: panic was resumed twice")
         }
     } else {
-            let err_string =
+        let err_string = if let Some(s) = ffi::lua_tolstring(state, -1, ptr::null_mut()).as_ref() {
-                if let Some(s) = ffi::lua_tolstring(state, -1, ptr::null_mut()).as_ref() {
             CStr::from_ptr(s)
                 .to_str()
                 .unwrap_or_else(|_| "<unprintable error>")
@@ -316,7 +314,6 @@ pub unsafe fn handle_error(state: *mut ffi::lua_State, err: c_int) -> Result<()>
             _ => lua_panic!(state, "internal error: unrecognized lua error code"),
         })
     }
-    }
 }
 
 pub unsafe fn push_string(state: *mut ffi::lua_State, s: &str) {
@@ -695,7 +692,7 @@ pub unsafe fn is_wrapped_panic(state: *mut ffi::lua_State, index: c_int) -> bool
     get_panic_metatable(state);
     let res = ffi::lua_rawequal(state, -1, -2) != 0;
     ffi::lua_pop(state, 2);
-    return res;
+    res
 }
 
 pub unsafe fn get_error_metatable(state: *mut ffi::lua_State) -> c_int {