From da25ac0d48e728cb424f1fce7f266563ec6f96b0 Mon Sep 17 00:00:00 2001
From: Luke Wilde <lukew@serenityos.org>
Date: Sun, 10 Jul 2022 21:37:28 +0100
Subject: [PATCH] AK: Treat empty string as invalid JSON

Previously we would treat the empty string as `null`. This caused
JavaScript like this to fail:
```js
var object = {};
try {
    object = JSON.parse("");
} catch {}
var array = object.array || [];
```
Since `JSON.parse("")` returned null instead of throwing, it would set
`object` to null and then try and use it instead of using the default
backup value.
---
 AK/JsonValue.cpp                                           | 2 --
 Tests/AK/TestJSON.cpp                                      | 2 +-
 Userland/Libraries/LibJS/Tests/builtins/JSON/JSON.parse.js | 1 +
 3 files changed, 2 insertions(+), 3 deletions(-)

diff --git a/AK/JsonValue.cpp b/AK/JsonValue.cpp
index 9a6536b6196..f11fd4bc11d 100644
--- a/AK/JsonValue.cpp
+++ b/AK/JsonValue.cpp
@@ -236,8 +236,6 @@ void JsonValue::clear()
 #ifndef KERNEL
 ErrorOr<JsonValue> JsonValue::from_string(StringView input)
 {
-    if (input.is_empty())
-        return JsonValue();
     return JsonParser(input).parse();
 }
 #endif
diff --git a/Tests/AK/TestJSON.cpp b/Tests/AK/TestJSON.cpp
index 36f0b8cebc0..c55d21ed662 100644
--- a/Tests/AK/TestJSON.cpp
+++ b/Tests/AK/TestJSON.cpp
@@ -126,7 +126,7 @@ TEST_CASE(json_u64_roundtrip)
 TEST_CASE(json_parse_empty_string)
 {
     auto value = JsonValue::from_string("");
-    EXPECT_EQ(value.value().is_null(), true);
+    EXPECT_EQ(value.is_error(), true);
 }
 
 TEST_CASE(json_parse_long_decimals)
diff --git a/Userland/Libraries/LibJS/Tests/builtins/JSON/JSON.parse.js b/Userland/Libraries/LibJS/Tests/builtins/JSON/JSON.parse.js
index a05e579e2a4..ff4d4bd30e2 100644
--- a/Userland/Libraries/LibJS/Tests/builtins/JSON/JSON.parse.js
+++ b/Userland/Libraries/LibJS/Tests/builtins/JSON/JSON.parse.js
@@ -29,6 +29,7 @@ test("syntax errors", () => {
         "[1,2,3, ]",
         '{ "foo": "bar",}',
         '{ "foo": "bar", }',
+        "",
     ].forEach(test => {
         expect(() => {
             JSON.parse(test);