Fix Tuple index infer

Fix #595

Author: CppCXY

crates/emmylua_code_analysis/src/compilation/test/tuple_test.rs

@@ -47,4 +47,20 @@ mod tests {
         );
         assert_eq!(ty, expected_ty);
     }
+
+    #[test]
+    fn test_issue_595() {
+        let mut ws = VirtualWorkspace::new();
+        ws.check_code_for(
+            DiagnosticCode::AssignTypeMismatch,
+            r#"
+                local ret           --- @type [integer?]
+                local h = ret[#ret] -- type is integer??
+                if h then
+                    --- @type integer
+                    local _ = h
+                end
+            "#,
+        );
+    }
 }

crates/emmylua_code_analysis/src/semantic/infer/infer_index.rs

@@ -451,12 +451,12 @@ fn infer_tuple_member(
                 };
             }
             LuaType::Integer => {
-                let mut result = Vec::new();
+                let mut result = LuaType::Unknown;
                 for typ in tuple_type.get_types() {
-                    result.push(typ.clone());
+                    result = TypeOps::Union.apply(db, &result, typ);
                 }
-                result.push(LuaType::Nil);
-                return Ok(LuaType::Union(LuaUnionType::from_vec(result).into()));
+                result = TypeOps::Union.apply(db, &result, &LuaType::Nil);
+                return Ok(result);
             }
             _ => {}
         },