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use swc_common::{util::take::Take, EqIgnoreSpan, Span, Spanned, DUMMY_SP};
use swc_ecma_ast::*;
use swc_ecma_utils::{ExprExt, Type, Value};
use super::Optimizer;
use crate::program_data::VarUsageInfoFlags;
/// Methods related to the options `bools` and `bool_as_ints`.
impl Optimizer<'_> {
/// Optimizes `typeof` comparisons with `"undefined"`:
///
/// - `typeof x == "undefined"` => `void 0 === x` (when x is declared)
/// - `typeof x == "undefined"` => `typeof x > "u"` (when x is undeclared)
/// - `typeof x != "undefined"` => `typeof x < "u"` (when x is undeclared)
///
/// The `> "u"` optimization works because `"undefined"` is the only typeof
/// result that is greater than `"u"` in lexicographic order.
pub(super) fn compress_typeof_undefined(&mut self, e: &mut BinExpr) {
let is_eq = match e.op {
op!("==") | op!("===") => true,
op!("!=") | op!("!==") => false,
_ => return,
};
let (arg, undefined_expr, reverse) = match (&mut *e.left, &mut *e.right) {
(
Expr::Unary(UnaryExpr {
op: op!("typeof"),
arg,
..
}),
Expr::Lit(Lit::Str(lit_str)),
) if lit_str.value == "undefined" => (arg, &mut e.right, false),
(
Expr::Lit(Lit::Str(lit_str)),
Expr::Unary(UnaryExpr {
op: op!("typeof"),
arg,
..
}),
) if lit_str.value == "undefined" => (arg, &mut e.left, true),
_ => {
return;
}
};
self.changed = true;
if self.is_undeclared_ident(arg) {
// typeof x == "undefined" => typeof x > "u"
// typeof x != "undefined" => typeof x < "u"
// "undefined" == typeof x => "u" < typeof x
// "undefined" != typeof x => "u" > typeof x
e.op = if is_eq ^ reverse { op!(">") } else { op!("<") };
let span = undefined_expr.span();
*undefined_expr = "u".into();
undefined_expr.set_span(span);
report_change!("bools: Optimizing `typeof x == \"undefined\"` into `typeof x > \"u\"`");
return;
}
// "undefined" -> void 0
*undefined_expr = Expr::undefined(undefined_expr.span());
let arg = arg.take();
let typeof_expr = if reverse { &mut e.right } else { &mut e.left };
// typeof x -> x
*typeof_expr = arg;
e.op = if is_eq { op!("===") } else { op!("!==") };
report_change!("bools: Optimizing `typeof x == \"undefined\"` into `x === void 0`");
}
fn is_undeclared_ident(&self, arg: &Expr) -> bool {
arg.as_ident().is_some_and(|ident| {
self.data
.vars
.get(&ident.to_id())
.map(|u| !u.flags.contains(VarUsageInfoFlags::DECLARED))
.unwrap_or(false)
})
}
///
/// - `a === undefined || a === null` => `a == null`
pub(super) fn optimize_optional_chain_generated(&mut self, e: &mut BinExpr) {
if e.op == op!("||") || e.op == op!("&&") {
{
let res = self.optimize_optional_chain_generated_inner(
e.span,
e.op,
&mut e.left,
&mut e.right,
);
if let Some(res) = res {
self.changed = true;
report_change!("bools: Optimizing `=== null || === undefined` to `== null`");
*e = res;
return;
}
}
if let (Expr::Bin(left), right) = (&mut *e.left, &mut *e.right) {
if e.op == left.op {
let res = self.optimize_optional_chain_generated_inner(
right.span(),
e.op,
&mut left.right,
&mut *right,
);
if let Some(res) = res {
self.changed = true;
report_change!(
"bools: Optimizing `=== null || === undefined` to `== null`"
);
*e = BinExpr {
span: e.span,
op: e.op,
left: left.left.take(),
right: res.into(),
};
}
}
}
}
}
fn optimize_optional_chain_generated_inner(
&mut self,
span: Span,
top_op: BinaryOp,
e_left: &mut Expr,
e_right: &mut Expr,
) -> Option<BinExpr> {
let (cmp, op, left, right) = match &mut *e_left {
Expr::Bin(left_bin) => {
if left_bin.op != op!("===") && left_bin.op != op!("!==") {
return None;
}
if top_op == op!("&&") && left_bin.op == op!("===") {
return None;
}
if top_op == op!("||") && left_bin.op == op!("!==") {
return None;
}
match &*left_bin.right {
Expr::Ident(..) | Expr::Lit(..) => {}
Expr::Assign(AssignExpr {
left: AssignTarget::Simple(SimpleAssignTarget::Ident(_)),
..
}) => (),
Expr::Member(MemberExpr {
obj,
prop: MemberProp::Ident(..),
..
}) => {
if self.should_preserve_property_access(
obj,
super::unused::PropertyAccessOpts {
allow_getter: false,
only_ident: false,
},
) {
return None;
}
}
_ => {
return None;
}
}
let right = match &mut *e_right {
Expr::Bin(right_bin) => {
if right_bin.op != left_bin.op {
return None;
}
let same_assign = if let (
Expr::Assign(AssignExpr {
left: AssignTarget::Simple(SimpleAssignTarget::Ident(l_id)),
..
}),
Expr::Ident(r_id),
) = (&*left_bin.right, &*right_bin.right)
{
l_id.id.eq_ignore_span(r_id)
} else {
false
};
if !(same_assign || right_bin.right.eq_ignore_span(&left_bin.right)) {
return None;
}
&mut *right_bin.left
}
_ => return None,
};
(
&mut left_bin.right,
left_bin.op,
&mut *left_bin.left,
&mut *right,
)
}
_ => return None,
};
let lt = left.get_type(self.ctx.expr_ctx);
let rt = right.get_type(self.ctx.expr_ctx);
if let (Value::Known(Type::Undefined), Value::Known(Type::Null))
| (Value::Known(Type::Null), Value::Known(Type::Undefined)) = (lt, rt)
{
if op == op!("===") {
report_change!("Reducing `!== null || !== undefined` check to `!= null`");
return Some(BinExpr {
span,
op: op!("=="),
left: cmp.take(),
right: Lit::Null(Null { span: DUMMY_SP }).into(),
});
} else {
report_change!("Reducing `=== null || === undefined` check to `== null`");
return Some(BinExpr {
span,
op: op!("!="),
left: cmp.take(),
right: Lit::Null(Null { span: DUMMY_SP }).into(),
});
}
}
None
}
}