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LibJS: Make Value() default-construct the undefined value

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The special empty value (that we use for array holes, Optional<Value>
when empty and a few other other placeholder/sentinel tasks) still
exists, but you now create one via JS::js_special_empty_value() and
check for it with Value::is_special_empty_value().

The main idea here is to make it very unlikely to accidentally create an
unexpected special empty value.
This commit is contained in:
Andreas Kling 2025-04-04 23:16:34 +02:00 • committed by Andreas Kling
commit 3cf50539ec
Notes: github-actions[bot] 2025-04-05 09:21:31 +00:00
43 changed files with 165 additions and 122 deletions
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29
Libraries/LibJS/Runtime/Value.h
View file

@ -95,7 +95,7 @@ public:
[[nodiscard]] u16 tag() const { return m_value.tag; }
bool is_empty() const { return m_value.tag == EMPTY_TAG; }
bool is_special_empty_value() const { return m_value.tag == EMPTY_TAG; }
bool is_undefined() const { return m_value.tag == UNDEFINED_TAG; }
bool is_null() const { return m_value.tag == NULL_TAG; }
bool is_number() const { return is_double() || is_int32(); }
@ -155,7 +155,7 @@ public:
}
Value()
: Value(EMPTY_TAG << GC::TAG_SHIFT, (u64)0)
: Value(UNDEFINED_TAG << GC::TAG_SHIFT, (u64)0)
{
}
@ -379,12 +379,14 @@ public:
[[nodiscard]] String to_string_without_side_effects() const;
#if 0
Value value_or(Value fallback) const
{
if (is_empty())
if (is_special_empty_value())
return fallback;
return *this;
}
#endif
[[nodiscard]] GC::Ref<PrimitiveString> typeof_(VM&) const;
@ -424,6 +426,13 @@ private:
ThrowCompletionOr<Value> to_numeric_slow_case(VM&) const;
ThrowCompletionOr<Value> to_primitive_slow_case(VM&, PreferredType) const;
enum class EmptyTag { Empty };
Value(EmptyTag)
: Value(EMPTY_TAG << GC::TAG_SHIFT, (u64)0)
{
}
Value(u64 tag, u64 val)
{
ASSERT(!(tag & val));
@ -460,6 +469,7 @@ private:
friend Value js_undefined();
friend Value js_null();
friend Value js_special_empty_value();
friend ThrowCompletionOr<Value> greater_than(VM&, Value lhs, Value rhs);
friend ThrowCompletionOr<Value> greater_than_equals(VM&, Value lhs, Value rhs);
friend ThrowCompletionOr<Value> less_than(VM&, Value lhs, Value rhs);
@ -478,6 +488,11 @@ inline Value js_null()
return Value(NULL_TAG << GC::TAG_SHIFT, (u64)0);
}
inline Value js_special_empty_value()
{
return Value(Value::EmptyTag::Empty);
}
inline Value js_nan()
{
return Value(NAN);
@ -600,12 +615,12 @@ public:
void clear()
{
m_value = {};
m_value = JS::js_special_empty_value();
}
[[nodiscard]] bool has_value() const
{
return !m_value.is_empty();
return !m_value.is_special_empty_value();
}
[[nodiscard]] JS::Value& value() &
@ -634,7 +649,7 @@ public:
}
private:
JS::Value m_value;
JS::Value m_value { JS::js_special_empty_value() };
};
}
@ -690,7 +705,7 @@ template<>
struct Formatter<JS::Value> : Formatter<StringView> {
ErrorOr<void> format(FormatBuilder& builder, JS::Value value)
{
if (value.is_empty())
if (value.is_special_empty_value())
return Formatter<StringView>::format(builder, "<empty>"sv);
return Formatter<StringView>::format(builder, value.to_string_without_side_effects());
}