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fix(next-swc): Fix interestingness detection for React Compiler (15.3) #79558

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Merged
merged 1 commit into from
May 23, 2025
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fix(next-swc): Fix interestingness detection for React Compiler (15.3) #79558

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224 changes: 197 additions & 27 deletions crates/next-custom-transforms/src/react_compiler.rs
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Original file line number Diff line number Diff line change
@@ -1,5 +1,8 @@
use swc_core::ecma::{
ast::{Callee, Expr, FnDecl, FnExpr, Pat, Program, ReturnStmt, Stmt, VarDeclarator},
ast::{
Callee, ExportDefaultDecl, ExportDefaultExpr, Expr, FnDecl, FnExpr, Pat, Program, Stmt,
VarDeclarator,
},
visit::{Visit, VisitWith},
};

Expand Down Expand Up @@ -34,18 +37,40 @@ impl Visit for Finder {
node.visit_children_with(self);
}

fn visit_export_default_decl(&mut self, node: &ExportDefaultDecl) {
let old = self.is_interested;
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nit: is there some kind of 'drop guard' we could use for this pattern

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Drop guard is possible, but we need drop guard for each pass. Other option is to define a method that takes a closure, but I'm not sure if this pass is complex enough to justify it.


self.is_interested = true;

node.visit_children_with(self);

self.is_interested = old;
}

fn visit_export_default_expr(&mut self, node: &ExportDefaultExpr) {
let old = self.is_interested;

self.is_interested = true;

node.visit_children_with(self);

self.is_interested = old;
}

fn visit_expr(&mut self, node: &Expr) {
if self.found {
return;
}
if matches!(
node,
Expr::JSXMember(..)
| Expr::JSXNamespacedName(..)
| Expr::JSXEmpty(..)
| Expr::JSXElement(..)
| Expr::JSXFragment(..)
) {
if self.is_interested
&& matches!(
node,
Expr::JSXMember(..)
| Expr::JSXNamespacedName(..)
| Expr::JSXEmpty(..)
| Expr::JSXElement(..)
| Expr::JSXFragment(..)
)
{
self.found = true;
return;
}
Expand All @@ -55,6 +80,7 @@ impl Visit for Finder {

fn visit_fn_decl(&mut self, node: &FnDecl) {
let old = self.is_interested;

self.is_interested = node.ident.sym.starts_with("use")
|| node.ident.sym.starts_with(|c: char| c.is_ascii_uppercase());

Expand All @@ -75,19 +101,6 @@ impl Visit for Finder {
self.is_interested = old;
}

fn visit_return_stmt(&mut self, node: &ReturnStmt) {
if self.is_interested {
if let Some(Expr::JSXElement(..) | Expr::JSXEmpty(..) | Expr::JSXFragment(..)) =
node.arg.as_deref()
{
self.found = true;
return;
}
}

node.visit_children_with(self);
}

fn visit_stmt(&mut self, node: &Stmt) {
if self.found {
return;
Expand All @@ -98,15 +111,172 @@ impl Visit for Finder {
fn visit_var_declarator(&mut self, node: &VarDeclarator) {
let old = self.is_interested;

if let Pat::Ident(ident) = &node.name {
self.is_interested = ident.sym.starts_with("use")
|| ident.sym.starts_with(|c: char| c.is_ascii_uppercase());
} else {
self.is_interested = false;
if matches!(node.init.as_deref(), Some(Expr::Fn(..) | Expr::Arrow(..))) {
if let Pat::Ident(ident) = &node.name {
self.is_interested = ident.sym.starts_with("use")
|| ident.sym.starts_with(|c: char| c.is_ascii_uppercase());
} else {
self.is_interested = false;
}
}

node.visit_children_with(self);

self.is_interested = old;
}
}

#[cfg(test)]
mod tests {
use swc_core::{
common::FileName,
ecma::parser::{parse_file_as_program, EsSyntax},
};
use testing::run_test2;

use super::*;

fn assert_required(code: &str, required: bool) {
run_test2(false, |cm, _| {
let fm = cm.new_source_file(FileName::Custom("test.tsx".into()).into(), code.into());

let program = parse_file_as_program(
&fm,
swc_core::ecma::parser::Syntax::Es(EsSyntax {
jsx: true,
..Default::default()
}),
Default::default(),
Default::default(),
&mut vec![],
)
.unwrap();

assert_eq!(is_required(&program), required);

Ok(())
})
.unwrap();
}

#[test]
fn lazy_return() {
assert_required(
"
function Foo() {
const a = <div>Hello</div>;

return a
}
",
true,
);

assert_required(
"
function Foo() {
",
false,
);
}

#[test]
fn return_jsx() {
assert_required(
"
function Foo() {
return <div>Hello</div>;
}
",
true,
);
}

#[test]
fn use_hooks() {
assert_required(
"
function Foo(props) {
const [a, b] = useState(0);

return props.children;
}
",
true,
);
}

#[test]
fn arrow_function() {
assert_required(
"
const Foo = () => <div>Hello</div>;
",
true,
);

assert_required(
"
const Foo = () => {
return <div>Hello</div>;
};
",
true,
);
}

#[test]
fn export_const_arrow_function() {
assert_required(
"
export const Foo = () => <div>Hello</div>;
",
true,
);

assert_required(
"
export const Foo = () => {
return <div>Hello</div>;
};
",
true,
);
}

#[test]
fn normal_arrow_function() {
assert_required(
"
const Foo = () => {
const a = 1;
console.log(a);
};
",
false,
);
}

#[test]
fn export_default_arrow_function() {
assert_required(
"
export default () => <div>Hello</div>;
",
true,
);
}

#[test]
fn not_required_arrow_function() {
assert_required(
"
export default () => {
const a = 1;
console.log(a);
};
",
false,
);
}
}
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