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feat(es/compiler): Merge nullish_coalescing into swc_ecma_compiler #11157

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Merged
merged 6 commits into from
Oct 24, 2025
+403 −296
Merged

feat(es/compiler): Merge nullish_coalescing into swc_ecma_compiler #11157

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2315412
feat(es/compiler): Merge nullish_coalescing into swc_ecma_compiler
github-actions[bot] Oct 20, 2025
ff391ee
fix(es/compiler): Fix variable hoisting for nullish coalescing and lo…
github-actions[bot] Oct 20, 2025
cacb2e8
fix(es/compiler): Fix nullish coalescing visitor order to match origi…
github-actions[bot] Oct 23, 2025
7a5c3a0
Merge branch 'main' into autodev/merge-nullish-coalescing
kdy1 Oct 24, 2025
1cc3c46
fix(es/compiler): Use different hoisting strategies for logical assig…
github-actions[bot] Oct 24, 2025
6105399
rename
kdy1 Oct 24, 2025
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3 changes: 1 addition & 2 deletions crates/swc_ecma_compat_es2020/src/lib.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -18,10 +18,9 @@ pub fn es2020(config: Config, unresolved_mark: Mark) -> impl Pass {
assumptions.no_document_all = config.nullish_coalescing.no_document_all;

(
nullish_coalescing(config.nullish_coalescing),
optional_chaining(config.optional_chaining, unresolved_mark),
Compiler::new(swc_ecma_compiler::Config {
includes: Features::EXPORT_NAMESPACE_FROM,
includes: Features::EXPORT_NAMESPACE_FROM | Features::NULLISH_COALESCING,
assumptions,
..Default::default()
}),
Expand Down
268 changes: 15 additions & 253 deletions crates/swc_ecma_compat_es2020/src/nullish_coalescing.rs
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Original file line number Diff line number Diff line change
@@ -1,264 +1,26 @@
use std::mem::take;

use serde::Deserialize;
use swc_common::{util::take::Take, Span, DUMMY_SP};
use swc_ecma_ast::*;
use swc_ecma_utils::{alias_ident_for_simple_assign_tatget, alias_if_required, StmtLike};
use swc_ecma_visit::{noop_visit_mut_type, visit_mut_pass, VisitMut, VisitMutWith};

pub fn nullish_coalescing(c: Config) -> impl Pass + 'static {
visit_mut_pass(NullishCoalescing {
c,
..Default::default()
})
}

#[derive(Debug, Default)]
struct NullishCoalescing {
vars: Vec<VarDeclarator>,
c: Config,
}
use swc_ecma_ast::Pass;
use swc_ecma_compiler::{Compiler, Features};
use swc_ecma_transforms_base::assumptions::Assumptions;

/// Configuration for nullish coalescing transformation
#[derive(Debug, Clone, Copy, Default, Deserialize)]
#[serde(rename_all = "camelCase")]
pub struct Config {
#[serde(default)]
pub no_document_all: bool,
}

impl NullishCoalescing {
fn visit_mut_stmt_like<T>(&mut self, stmts: &mut Vec<T>)
where
T: VisitMutWith<Self> + StmtLike,
{
let mut buf = Vec::with_capacity(stmts.len() + 2);

for mut stmt in stmts.take() {
stmt.visit_mut_with(self);

if !self.vars.is_empty() {
buf.push(T::from(
VarDecl {
span: DUMMY_SP,
kind: VarDeclKind::Var,
decls: take(&mut self.vars),
declare: false,
..Default::default()
}
.into(),
));
}

buf.push(stmt);
}

*stmts = buf
}
}

impl VisitMut for NullishCoalescing {
noop_visit_mut_type!(fail);

/// Prevents #1123
fn visit_mut_block_stmt(&mut self, s: &mut BlockStmt) {
let old_vars = self.vars.take();
s.visit_mut_children_with(self);
self.vars = old_vars;
}

/// Prevents #1123
fn visit_mut_switch_case(&mut self, s: &mut SwitchCase) {
// Prevents #6328
s.test.visit_mut_with(self);
let old_vars = self.vars.take();
s.cons.visit_mut_with(self);
self.vars = old_vars;
}

fn visit_mut_module_items(&mut self, n: &mut Vec<ModuleItem>) {
self.visit_mut_stmt_like(n)
}

fn visit_mut_stmts(&mut self, n: &mut Vec<Stmt>) {
self.visit_mut_stmt_like(n)
}

fn visit_mut_expr(&mut self, e: &mut Expr) {
e.visit_mut_children_with(self);

match e {
Expr::Bin(BinExpr {
span,
left,
op: op!("??"),
right,
}) => {
//
let (l, aliased) = alias_if_required(left, "ref");

if aliased {
self.vars.push(VarDeclarator {
span: DUMMY_SP,
name: l.clone().into(),
init: None,
definite: false,
});
}

let var_expr = if aliased {
AssignExpr {
span: DUMMY_SP,
op: op!("="),
left: l.clone().into(),
right: left.take(),
}
.into()
} else {
l.clone().into()
};

*e = make_cond(self.c, *span, &l, var_expr, right.take());
}

Expr::Assign(ref mut assign @ AssignExpr { op: op!("??="), .. }) => {
match &mut assign.left {
AssignTarget::Simple(SimpleAssignTarget::Ident(i)) => {
*e = AssignExpr {
span: assign.span,
op: op!("="),
left: i.clone().into(),
right: Box::new(make_cond(
self.c,
assign.span,
&Ident::from(&*i),
Expr::Ident(Ident::from(&*i)),
assign.right.take(),
)),
}
.into();
}

AssignTarget::Simple(left) => {
let alias = alias_ident_for_simple_assign_tatget(left, "refs");
self.vars.push(VarDeclarator {
span: DUMMY_SP,
name: alias.clone().into(),
init: None,
definite: false,
});

// TODO: Check for computed.
let right_expr = AssignExpr {
span: assign.span,
left: left.clone().into(),
op: op!("="),
right: assign.right.take(),
}
.into();

let var_expr = AssignExpr {
span: DUMMY_SP,
op: op!("="),
left: alias.clone().into(),
right: left.take().into(),
}
.into();

*e = AssignExpr {
span: assign.span,
op: op!("="),
left: alias.clone().into(),
right: Box::new(make_cond(
self.c,
assign.span,
&alias,
var_expr,
right_expr,
)),
}
.into();
}

_ => {}
}
}

_ => {}
}
}

fn visit_mut_block_stmt_or_expr(&mut self, n: &mut BlockStmtOrExpr) {
let vars = self.vars.take();
n.visit_mut_children_with(self);

if !self.vars.is_empty() {
if let BlockStmtOrExpr::Expr(expr) = n {
// expr
// { var decl = init; return expr; }
let stmts = vec![
VarDecl {
span: DUMMY_SP,
kind: VarDeclKind::Var,
decls: self.vars.take(),
declare: false,
..Default::default()
}
.into(),
Stmt::Return(ReturnStmt {
span: DUMMY_SP,
arg: Some(expr.take()),
}),
];
*n = BlockStmtOrExpr::BlockStmt(BlockStmt {
span: DUMMY_SP,
stmts,
..Default::default()
});
}
}

self.vars = vars;
}
}
/// Creates a nullish coalescing transformation pass
///
/// This is now a thin wrapper around the Compiler implementation.
pub fn nullish_coalescing(c: Config) -> impl Pass + 'static {
let mut assumptions = Assumptions::default();
assumptions.no_document_all = c.no_document_all;

#[tracing::instrument(level = "debug", skip_all)]
fn make_cond(c: Config, span: Span, alias: &Ident, var_expr: Expr, init: Box<Expr>) -> Expr {
if c.no_document_all {
CondExpr {
span,
test: BinExpr {
span: DUMMY_SP,
left: Box::new(var_expr),
op: op!("!="),
right: Box::new(Expr::Lit(Lit::Null(Null { span: DUMMY_SP }))),
}
.into(),
cons: alias.clone().into(),
alt: init,
}
} else {
CondExpr {
span,
test: BinExpr {
span: DUMMY_SP,
left: Box::new(Expr::Bin(BinExpr {
span: DUMMY_SP,
left: Box::new(var_expr),
op: op!("!=="),
right: Box::new(Expr::Lit(Lit::Null(Null { span: DUMMY_SP }))),
})),
op: op!("&&"),
right: Box::new(Expr::Bin(BinExpr {
span: DUMMY_SP,
left: Box::new(Expr::Ident(alias.clone())),
op: op!("!=="),
right: Expr::undefined(DUMMY_SP),
})),
}
.into(),
cons: alias.clone().into(),
alt: init,
}
}
.into()
Compiler::new(swc_ecma_compiler::Config {
includes: Features::NULLISH_COALESCING,
assumptions,
..Default::default()
})
}
1 change: 1 addition & 0 deletions crates/swc_ecma_compiler/src/es2020/mod.rs
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Original file line number Diff line number Diff line change
@@ -1 +1,2 @@
pub(crate) mod export_namespace_from;
pub(crate) mod nullish_coalescing;
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