Use never type for remove

Fix #584

Author: CppCXY

crates/emmylua_code_analysis/src/db_index/type/type_ops/mod.rs

@@ -18,9 +18,8 @@ impl TypeOps {
     pub fn apply(&self, db: &DbIndex, source: &LuaType, target: &LuaType) -> LuaType {
         match self {
             TypeOps::Union => union_type::union_type(source.clone(), target.clone()),
-            TypeOps::Remove => {
-                remove_type::remove_type(db, source.clone(), target.clone()).unwrap_or(LuaType::Any)
-            }
+            TypeOps::Remove => remove_type::remove_type(db, source.clone(), target.clone())
+                .unwrap_or(LuaType::Never),
         }
     }
 }

crates/emmylua_code_analysis/src/db_index/type/type_ops/union_type.rs

@@ -7,6 +7,8 @@ pub fn union_type(source: LuaType, target: LuaType) -> LuaType {
         // ANY | T = ANY
         (LuaType::Any, _) => LuaType::Any,
         (_, LuaType::Any) => LuaType::Any,
+        (LuaType::Never, _) => target,
+        (_, LuaType::Never) => source,
         (LuaType::Unknown, _) => target,
         (_, LuaType::Unknown) => source,
         // int | int const