AK+Format: Keep type information for integers in TypeErasedParameter.

It's now save to pass a signed integer as parameter and then use it as
replacement field (previously, this would just cast it to size_t which
would be bad.)

AK/Format.cpp

@@ -168,6 +168,43 @@ void vformat_impl(StringBuilder& builder, FormatStringParser& parser, Span<const
     vformat_impl(builder, parser, parameters, argument_index);
 }
 
+size_t decode_value(size_t value, Span<const AK::TypeErasedParameter> parameters)
+{
+    if (value == AK::StandardFormatter::value_from_next_arg)
+        TODO();
+
+    if (value >= AK::StandardFormatter::value_from_arg) {
+        const auto parameter = parameters.at(value - AK::StandardFormatter::value_from_arg);
+
+        Optional<i64> svalue;
+        if (parameter.type == AK::TypeErasedParameter::Type::UInt8)
+            value = *reinterpret_cast<const u8*>(parameter.value);
+        else if (parameter.type == AK::TypeErasedParameter::Type::UInt16)
+            value = *reinterpret_cast<const u16*>(parameter.value);
+        else if (parameter.type == AK::TypeErasedParameter::Type::UInt32)
+            value = *reinterpret_cast<const u32*>(parameter.value);
+        else if (parameter.type == AK::TypeErasedParameter::Type::UInt64)
+            value = *reinterpret_cast<const u64*>(parameter.value);
+        else if (parameter.type == AK::TypeErasedParameter::Type::Int8)
+            svalue = *reinterpret_cast<const i8*>(parameter.value);
+        else if (parameter.type == AK::TypeErasedParameter::Type::Int16)
+            svalue = *reinterpret_cast<const i16*>(parameter.value);
+        else if (parameter.type == AK::TypeErasedParameter::Type::Int32)
+            svalue = *reinterpret_cast<const i32*>(parameter.value);
+        else if (parameter.type == AK::TypeErasedParameter::Type::Int64)
+            svalue = *reinterpret_cast<const i64*>(parameter.value);
+        else
+            ASSERT_NOT_REACHED();
+
+        if (svalue.has_value()) {
+            ASSERT(svalue.value() >= 0);
+            value = static_cast<size_t>(svalue.value());
+        }
+    }
+
+    return value;
+}
+
 } // namespace
 
 namespace AK {
@@ -307,14 +344,7 @@ void Formatter<T, typename EnableIf<IsIntegral<T>::value>::Type>::format(StringB
         ASSERT_NOT_REACHED();
     }
 
-    size_t width = m_width;
+    auto width = decode_value(m_width, parameters);
-    if (m_width >= value_from_arg) {
-        const auto parameter = parameters.at(m_width - value_from_arg);
-
-        // FIXME: Totally unsave cast. We should store the type in TypeErasedParameter. For compactness it could be smart to
-        //        find a few addresses that can not be valid function pointers and encode the type information there?
-        width = *reinterpret_cast<const size_t*>(parameter.value);
-    }
 
     PrintfImplementation::Align align;
     if (m_align == Align::Left)

AK/Format.h

@@ -39,7 +39,43 @@ template<typename T, typename = void>
 struct Formatter;
 
 struct TypeErasedParameter {
+    enum class Type {
+        UInt8,
+        UInt16,
+        UInt32,
+        UInt64,
+        Int8,
+        Int16,
+        Int32,
+        Int64,
+        Custom
+    };
+
+    template<typename T>
+    static Type get_type()
+    {
+        if (IsSame<T, u8>::value)
+            return Type::UInt8;
+        if (IsSame<T, u16>::value)
+            return Type::UInt16;
+        if (IsSame<T, u32>::value)
+            return Type::UInt32;
+        if (IsSame<T, u64>::value)
+            return Type::UInt64;
+        if (IsSame<T, i8>::value)
+            return Type::Int8;
+        if (IsSame<T, i16>::value)
+            return Type::Int16;
+        if (IsSame<T, i32>::value)
+            return Type::Int32;
+        if (IsSame<T, i64>::value)
+            return Type::Int64;
+
+        return Type::Custom;
+    }
+
     const void* value;
+    Type type;
     void (*formatter)(StringBuilder& builder, const void* value, StringView flags, Span<const TypeErasedParameter> parameters);
 };
 
@@ -92,7 +128,8 @@ struct StandardFormatter {
     };
 
     static constexpr size_t value_not_set = 0;
-    static constexpr size_t value_from_arg = NumericLimits<size_t>::max() - max_format_arguments;
+    static constexpr size_t value_from_next_arg = NumericLimits<size_t>::max();
+    static constexpr size_t value_from_arg = NumericLimits<size_t>::max() - max_format_arguments - 1;
 
     Align m_align = Align::Default;
     Sign m_sign = Sign::NegativeOnly;
@@ -132,7 +169,8 @@ template<typename... Parameters>
 Array<TypeErasedParameter, sizeof...(Parameters)> make_type_erased_parameters(const Parameters&... parameters)
 {
     static_assert(sizeof...(Parameters) <= max_format_arguments);
-    return { TypeErasedParameter { &parameters, Detail::Format::format_value<Parameters> }... };
+
+    return { TypeErasedParameter { &parameters, TypeErasedParameter::get_type<Parameters>(), Detail::Format::format_value<Parameters> }... };
 }
 
 void vformat(StringBuilder& builder, StringView fmtstr, Span<const TypeErasedParameter>);

AK/Tests/TestFormat.cpp

@@ -116,6 +116,9 @@ TEST_CASE(zero_pad)
 TEST_CASE(replacement_field)
 {
     EXPECT_EQ(String::formatted("{:*>{1}}", 13, static_cast<size_t>(10)), "********13");
+    EXPECT_EQ(String::formatted("{:*<{1}}", 7, 4), "7***");
+    EXPECT_EQ(String::formatted("{:{2}}", -5, 8, 16), "              -5");
+    EXPECT_EQ(String::formatted("{{{:*^{1}}}}", 1, 3), "{*1*}");
 }
 
 TEST_MAIN(Format)