fix infer_union_binary_expr EmmyLuaLs#406

Author: xuhuanzy

crates/emmylua_code_analysis/src/diagnostic/test/undefined_field_test.rs

@@ -538,4 +538,33 @@ mod test {
         "#
         ));
     }
+
+    #[test]
+    fn test_string_add_enum_key() {
+        let mut ws = VirtualWorkspace::new();
+        assert!(ws.check_code_for(
+            DiagnosticCode::UndefinedField,
+            r#"
+                ---@class py.GameAPI
+                GameAPI = {}
+
+                function GameAPI.get_kv_pair_value_unit_entity(handle, key) end
+
+                function GameAPI.get_kv_pair_value_unit_name() end
+
+                ---@enum(key) KV.SupportTypeEnum
+                local apiAlias = {
+                    Unit         = 'unit_entity',
+                    UnitKey      = 'unit_name',
+                }
+
+                ---@param lua_type 'boolean' | 'number' | 'integer' | 'string' | 'table' | KV.SupportTypeEnum
+                ---@return any
+                local function kv_load_from_handle(lua_type)
+                    local alias = apiAlias[lua_type]
+                    local api = GameAPI['get_kv_pair_value_' .. alias]
+                end
+        "#
+        ));
+    }
 }

crates/emmylua_code_analysis/src/semantic/infer/infer_binary/mod.rs

@@ -41,22 +41,26 @@ fn infer_union_binary_expr(
     left_type: &LuaType,
     right_type: &LuaType,
 ) -> Option<LuaType> {
-    let (u, other) = if let LuaType::Union(u) = left_type {
-        (u, right_type)
+    let (u, other, is_left_union) = if let LuaType::Union(u) = left_type {
+        (u, right_type, true)
     } else if let LuaType::Union(u) = right_type {
-        (u, left_type)
+        (u, left_type, false)
     } else {
         return None;
     };
 
     let mut result = LuaType::Unknown;
     let types = u.get_types();
     for ty in types.iter() {
-        if let Ok(ty) = infer_binary_expr_type(db, ty.clone(), other.clone(), op) {
+        if let Ok(ty) = if is_left_union {
+            infer_binary_expr_type(db, ty.clone(), other.clone(), op)
+        } else {
+            infer_binary_expr_type(db, other.clone(), ty.clone(), op)
+        } {
             result = TypeOps::Union.apply(&result, &ty);
         }
     }
-    return Some(result);
+    Some(result)
 }
 
 fn infer_binary_expr_type(