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//! Boa's implementation of ECMAScript's global `Symbol` object.
//!
//! The data type symbol is a primitive data type.
//! The `Symbol()` function returns a value of type symbol, has static properties that expose
//! several members of built-in objects, has static methods that expose the global symbol registry,
//! and resembles a built-in object class, but is incomplete as a constructor because it does not
//! support the syntax "`new Symbol()`".
//!
//! Every symbol value returned from `Symbol()` is unique.
//!
//! More information:
//! - [MDN documentation][mdn]
//! - [ECMAScript reference][spec]
//!
//! [spec]: https://tc39.es/ecma262/#sec-symbol-value
//! [mdn]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Symbol
#![deny(
unsafe_op_in_unsafe_fn,
clippy::undocumented_unsafe_blocks,
clippy::missing_safety_doc
)]
use crate::{
js_string,
string::{common::StaticJsStrings, utf16},
tagged::{Tagged, UnwrappedTagged},
JsData, JsString,
};
use boa_gc::{Finalize, Trace};
use num_enum::{IntoPrimitive, TryFromPrimitive};
use std::{
hash::{Hash, Hasher},
sync::{atomic::Ordering, Arc},
};
use portable_atomic::AtomicU64;
/// Reserved number of symbols.
///
/// This is the maximum number of well known and internal engine symbols
/// that can be defined.
const RESERVED_SYMBOL_HASHES: u64 = 127;
fn get_id() -> Option<u64> {
// Symbol hash.
//
// For now this is an incremented u64 number.
static SYMBOL_HASH_COUNT: AtomicU64 = AtomicU64::new(RESERVED_SYMBOL_HASHES + 1);
SYMBOL_HASH_COUNT
.fetch_update(Ordering::Relaxed, Ordering::Relaxed, |value| {
value.checked_add(1)
})
.ok()
}
/// List of well known symbols.
#[derive(Debug, Clone, Copy, TryFromPrimitive, IntoPrimitive)]
#[repr(u8)]
enum WellKnown {
AsyncIterator,
HasInstance,
IsConcatSpreadable,
Iterator,
Match,
MatchAll,
Replace,
Search,
Species,
Split,
ToPrimitive,
ToStringTag,
Unscopables,
}
impl WellKnown {
const fn description(self) -> JsString {
match self {
Self::AsyncIterator => StaticJsStrings::SYMBOL_ASYNC_ITERATOR,
Self::HasInstance => StaticJsStrings::SYMBOL_HAS_INSTANCE,
Self::IsConcatSpreadable => StaticJsStrings::SYMBOL_IS_CONCAT_SPREADABLE,
Self::Iterator => StaticJsStrings::SYMBOL_ITERATOR,
Self::Match => StaticJsStrings::SYMBOL_MATCH,
Self::MatchAll => StaticJsStrings::SYMBOL_MATCH_ALL,
Self::Replace => StaticJsStrings::SYMBOL_REPLACE,
Self::Search => StaticJsStrings::SYMBOL_SEARCH,
Self::Species => StaticJsStrings::SYMBOL_SPECIES,
Self::Split => StaticJsStrings::SYMBOL_SPLIT,
Self::ToPrimitive => StaticJsStrings::SYMBOL_TO_PRIMITIVE,
Self::ToStringTag => StaticJsStrings::SYMBOL_TO_STRING_TAG,
Self::Unscopables => StaticJsStrings::SYMBOL_UNSCOPABLES,
}
}
const fn fn_name(self) -> JsString {
match self {
Self::AsyncIterator => StaticJsStrings::FN_SYMBOL_ASYNC_ITERATOR,
Self::HasInstance => StaticJsStrings::FN_SYMBOL_HAS_INSTANCE,
Self::IsConcatSpreadable => StaticJsStrings::FN_SYMBOL_IS_CONCAT_SPREADABLE,
Self::Iterator => StaticJsStrings::FN_SYMBOL_ITERATOR,
Self::Match => StaticJsStrings::FN_SYMBOL_MATCH,
Self::MatchAll => StaticJsStrings::FN_SYMBOL_MATCH_ALL,
Self::Replace => StaticJsStrings::FN_SYMBOL_REPLACE,
Self::Search => StaticJsStrings::FN_SYMBOL_SEARCH,
Self::Species => StaticJsStrings::FN_SYMBOL_SPECIES,
Self::Split => StaticJsStrings::FN_SYMBOL_SPLIT,
Self::ToPrimitive => StaticJsStrings::FN_SYMBOL_TO_PRIMITIVE,
Self::ToStringTag => StaticJsStrings::FN_SYMBOL_TO_STRING_TAG,
Self::Unscopables => StaticJsStrings::FN_SYMBOL_UNSCOPABLES,
}
}
const fn hash(self) -> u64 {
self as u64
}
fn from_tag(tag: usize) -> Option<Self> {
Self::try_from_primitive(u8::try_from(tag).ok()?).ok()
}
}
/// The inner representation of a JavaScript symbol.
#[derive(Debug, Clone)]
struct Inner {
hash: u64,
// must be a `Box`, since this needs to be shareable between many threads.
description: Option<Box<[u16]>>,
}
/// This represents a JavaScript symbol primitive.
#[derive(Trace, Finalize, JsData)]
// Safety: JsSymbol does not contain any objects which needs to be traced,
// so this is safe.
#[boa_gc(unsafe_empty_trace)]
pub struct JsSymbol {
repr: Tagged<Inner>,
}
// SAFETY: `JsSymbol` uses `Arc` to do the reference counting, making this type thread-safe.
unsafe impl Send for JsSymbol {}
// SAFETY: `JsSymbol` uses `Arc` to do the reference counting, making this type thread-safe.
unsafe impl Sync for JsSymbol {}
macro_rules! well_known_symbols {
( $( $(#[$attr:meta])* ($name:ident, $variant:path) ),+$(,)? ) => {
$(
$(#[$attr])* #[must_use] pub const fn $name() -> JsSymbol {
JsSymbol {
// the cast shouldn't matter since we only have 127 const symbols
repr: Tagged::from_tag($variant.hash() as usize),
}
}
)+
};
}
impl JsSymbol {
/// Creates a new symbol.
///
/// Returns `None` if the maximum number of possible symbols has been reached (`u64::MAX`).
#[inline]
#[must_use]
pub fn new(description: Option<JsString>) -> Option<Self> {
let hash = get_id()?;
let arc = Arc::new(Inner {
hash,
description: description.map(|s| Box::from(&*s)),
});
Some(Self {
// SAFETY: Pointers returned by `Arc::into_raw` must be non-null.
repr: unsafe { Tagged::from_ptr(Arc::into_raw(arc).cast_mut()) },
})
}
/// Returns the `Symbol` description.
#[inline]
#[must_use]
pub fn description(&self) -> Option<JsString> {
match self.repr.unwrap() {
UnwrappedTagged::Ptr(ptr) => {
// SAFETY: `ptr` comes from `Arc`, which ensures the validity of the pointer
// as long as we correctly call `Arc::from_raw` on `Drop`.
unsafe { ptr.as_ref().description.as_ref().map(|v| js_string!(&**v)) }
}
UnwrappedTagged::Tag(tag) => {
// SAFETY: All tagged reprs always come from `WellKnown` itself, making
// this operation always safe.
let wk = unsafe { WellKnown::from_tag(tag).unwrap_unchecked() };
Some(wk.description())
}
}
}
/// Returns the `Symbol` as a function name.
///
/// Equivalent to `[description]`, but returns the empty string if the symbol doesn't have a
/// description.
#[inline]
#[must_use]
pub fn fn_name(&self) -> JsString {
if let UnwrappedTagged::Tag(tag) = self.repr.unwrap() {
// SAFETY: All tagged reprs always come from `WellKnown` itself, making
// this operation always safe.
let wk = unsafe { WellKnown::from_tag(tag).unwrap_unchecked() };
return wk.fn_name();
}
self.description()
.map(|s| js_string!(utf16!("["), &*s, utf16!("]")))
.unwrap_or_default()
}
/// Returns the `Symbol`s hash.
///
/// The hash is guaranteed to be unique.
#[inline]
#[must_use]
pub fn hash(&self) -> u64 {
match self.repr.unwrap() {
UnwrappedTagged::Ptr(ptr) => {
// SAFETY: `ptr` comes from `Arc`, which ensures the validity of the pointer
// as long as we correctly call `Arc::from_raw` on `Drop`.
unsafe { ptr.as_ref().hash }
}
UnwrappedTagged::Tag(tag) => {
// SAFETY: All tagged reprs always come from `WellKnown` itself, making
// this operation always safe.
unsafe { WellKnown::from_tag(tag).unwrap_unchecked().hash() }
}
}
}
/// Abstract operation `SymbolDescriptiveString ( sym )`
///
/// More info:
/// - [ECMAScript reference][spec]
///
/// [spec]: https://tc39.es/ecma262/#sec-symboldescriptivestring
#[must_use]
pub fn descriptive_string(&self) -> JsString {
self.description().as_ref().map_or_else(
|| js_string!("Symbol()"),
|desc| js_string!(utf16!("Symbol("), desc, utf16!(")")),
)
}
well_known_symbols! {
/// Gets the static `JsSymbol` for `"Symbol.asyncIterator"`.
(async_iterator, WellKnown::AsyncIterator),
/// Gets the static `JsSymbol` for `"Symbol.hasInstance"`.
(has_instance, WellKnown::HasInstance),
/// Gets the static `JsSymbol` for `"Symbol.isConcatSpreadable"`.
(is_concat_spreadable, WellKnown::IsConcatSpreadable),
/// Gets the static `JsSymbol` for `"Symbol.iterator"`.
(iterator, WellKnown::Iterator),
/// Gets the static `JsSymbol` for `"Symbol.match"`.
(r#match, WellKnown::Match),
/// Gets the static `JsSymbol` for `"Symbol.matchAll"`.
(match_all, WellKnown::MatchAll),
/// Gets the static `JsSymbol` for `"Symbol.replace"`.
(replace, WellKnown::Replace),
/// Gets the static `JsSymbol` for `"Symbol.search"`.
(search, WellKnown::Search),
/// Gets the static `JsSymbol` for `"Symbol.species"`.
(species, WellKnown::Species),
/// Gets the static `JsSymbol` for `"Symbol.split"`.
(split, WellKnown::Split),
/// Gets the static `JsSymbol` for `"Symbol.toPrimitive"`.
(to_primitive, WellKnown::ToPrimitive),
/// Gets the static `JsSymbol` for `"Symbol.toStringTag"`.
(to_string_tag, WellKnown::ToStringTag),
/// Gets the static `JsSymbol` for `"Symbol.unscopables"`.
(unscopables, WellKnown::Unscopables),
}
}
impl Clone for JsSymbol {
fn clone(&self) -> Self {
if let UnwrappedTagged::Ptr(ptr) = self.repr.unwrap() {
// SAFETY: the pointer returned by `self.repr` must be a valid pointer
// that came from an `Arc::into_raw` call.
unsafe {
let arc = Arc::from_raw(ptr.as_ptr().cast_const());
// Don't need the Arc since `self` is already a copyable pointer, just need to
// trigger the `clone` impl.
std::mem::forget(arc.clone());
std::mem::forget(arc);
}
}
Self { repr: self.repr }
}
}
impl Drop for JsSymbol {
fn drop(&mut self) {
if let UnwrappedTagged::Ptr(ptr) = self.repr.unwrap() {
// SAFETY: the pointer returned by `self.repr` must be a valid pointer
// that came from an `Arc::into_raw` call.
unsafe { drop(Arc::from_raw(ptr.as_ptr().cast_const())) }
}
}
}
impl std::fmt::Debug for JsSymbol {
fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
f.debug_struct("JsSymbol")
.field("hash", &self.hash())
.field("description", &self.description())
.finish()
}
}
impl std::fmt::Display for JsSymbol {
#[inline]
fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
match &self.description() {
Some(desc) => write!(f, "Symbol({})", desc.to_std_string_escaped()),
None => write!(f, "Symbol()"),
}
}
}
impl Eq for JsSymbol {}
impl PartialEq for JsSymbol {
#[inline]
fn eq(&self, other: &Self) -> bool {
self.hash() == other.hash()
}
}
impl PartialOrd for JsSymbol {
#[inline]
fn partial_cmp(&self, other: &Self) -> Option<std::cmp::Ordering> {
Some(self.cmp(other))
}
}
impl Ord for JsSymbol {
#[inline]
fn cmp(&self, other: &Self) -> std::cmp::Ordering {
self.hash().cmp(&other.hash())
}
}
impl Hash for JsSymbol {
fn hash<H: Hasher>(&self, state: &mut H) {
self.hash().hash(state);
}
}