AK: Add JSON object/array for-each methods for fallible callbacks

This allows the provided callback to return an ErrorOr-like type to
propagate errors back to the caller.

AK/JsonArray.h

@@ -7,6 +7,7 @@
 #pragma once
 
 #include <AK/Concepts.h>
+#include <AK/Error.h>
 #include <AK/JsonArraySerializer.h>
 #include <AK/JsonValue.h>
 #include <AK/Vector.h>
@@ -14,6 +15,9 @@
 namespace AK {
 
 class JsonArray {
+    template<typename Callback>
+    using CallbackErrorType = decltype(declval<Callback>()(declval<JsonValue const&>()).release_error());
+
 public:
     JsonArray() = default;
     ~JsonArray() = default;
@@ -76,6 +80,14 @@ public:
             callback(value);
     }
 
+    template<FallibleFunction<JsonValue const&> Callback>
+    ErrorOr<void, CallbackErrorType<Callback>> try_for_each(Callback&& callback) const
+    {
+        for (auto const& value : m_values)
+            TRY(callback(value));
+        return {};
+    }
+
     [[nodiscard]] Vector<JsonValue> const& values() const { return m_values; }
 
     void ensure_capacity(size_t capacity) { m_values.ensure_capacity(capacity); }

AK/JsonObject.h

@@ -7,6 +7,8 @@
 
 #pragma once
 
+#include <AK/Concepts.h>
+#include <AK/Error.h>
 #include <AK/HashMap.h>
 #include <AK/JsonArray.h>
 #include <AK/JsonObjectSerializer.h>
@@ -16,6 +18,9 @@
 namespace AK {
 
 class JsonObject {
+    template<typename Callback>
+    using CallbackErrorType = decltype(declval<Callback>()(declval<String const&>(), declval<JsonValue const&>()).release_error());
+
 public:
     JsonObject() = default;
     ~JsonObject() = default;
@@ -142,6 +147,14 @@ public:
             callback(member.key, member.value);
     }
 
+    template<FallibleFunction<String const&, JsonValue const&> Callback>
+    ErrorOr<void, CallbackErrorType<Callback>> try_for_each_member(Callback&& callback) const
+    {
+        for (auto const& member : m_members)
+            TRY(callback(member.key, member.value));
+        return {};
+    }
+
     bool remove(StringView key)
     {
         return m_members.remove(key);

Tests/AK/TestJSON.cpp

@@ -267,3 +267,107 @@ TEST_CASE(json_parse_fails_on_invalid_number)
 
 #undef EXPECT_JSON_PARSE_TO_FAIL
 }
+
+struct CustomError {
+};
+
+template<typename T>
+class CustomErrorOr {
+public:
+    CustomErrorOr(T)
+        : m_is_error(false)
+    {
+    }
+
+    CustomErrorOr(CustomError)
+        : m_is_error(true)
+    {
+    }
+
+    bool is_error() const { return m_is_error; }
+    CustomError release_error() { return CustomError {}; }
+    T release_value() { return T {}; }
+
+private:
+    bool m_is_error { false };
+};
+
+TEST_CASE(fallible_json_object_for_each)
+{
+    String raw_json = R"(
+    {
+        "name": "anon",
+        "home": "/home/anon",
+        "default_browser": "Ladybird"
+    })";
+
+    auto json = JsonValue::from_string(raw_json).value();
+    auto const& object = json.as_object();
+
+    MUST(object.try_for_each_member([](auto const&, auto const&) -> ErrorOr<void> {
+        return {};
+    }));
+
+    auto result1 = object.try_for_each_member([](auto const&, auto const&) -> ErrorOr<void> {
+        return Error::from_string_view("nanananana"sv);
+    });
+    EXPECT(result1.is_error());
+    EXPECT_EQ(result1.error().string_literal(), "nanananana"sv);
+
+    auto result2 = object.try_for_each_member([](auto const&, auto const&) -> ErrorOr<void, CustomError> {
+        return CustomError {};
+    });
+    EXPECT(result2.is_error());
+    EXPECT((IsSame<decltype(result2.release_error()), CustomError>));
+
+    auto result3 = object.try_for_each_member([](auto const&, auto const&) -> CustomErrorOr<int> {
+        return 42;
+    });
+    EXPECT(!result3.is_error());
+
+    auto result4 = object.try_for_each_member([](auto const&, auto const&) -> CustomErrorOr<int> {
+        return CustomError {};
+    });
+    EXPECT(result4.is_error());
+    EXPECT((IsSame<decltype(result4.release_error()), CustomError>));
+}
+
+TEST_CASE(fallible_json_array_for_each)
+{
+    String raw_json = R"(
+    [
+        "anon",
+        "/home/anon",
+        "Ladybird"
+    ])";
+
+    auto json = JsonValue::from_string(raw_json).value();
+    auto const& array = json.as_array();
+
+    MUST(array.try_for_each([](auto const&) -> ErrorOr<void> {
+        return {};
+    }));
+
+    auto result1 = array.try_for_each([](auto const&) -> ErrorOr<void> {
+        return Error::from_string_view("nanananana"sv);
+    });
+    EXPECT(result1.is_error());
+    EXPECT_EQ(result1.error().string_literal(), "nanananana"sv);
+
+    auto result2 = array.try_for_each([](auto const&) -> ErrorOr<void, CustomError> {
+        return CustomError {};
+    });
+    EXPECT(result2.is_error());
+    EXPECT((IsSame<decltype(result2.release_error()), CustomError>));
+
+    auto result3 = array.try_for_each([](auto const&) -> CustomErrorOr<int> {
+        return 42;
+    });
+    EXPECT(!result3.is_error());
+
+    auto result4 = array.try_for_each([](auto const&) -> CustomErrorOr<int> {
+        return CustomError {};
+    });
+    EXPECT(result4.is_error());
+    EXPECT((IsSame<decltype(result4.release_error()), CustomError>));
+}