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minify: do not fold new Array(x, ...spread) into an array literal #41828

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Merged
Jarred-Sumner merged 3 commits into from
Sep 7, 2026
Merged

minify: do not fold new Array(x, ...spread) into an array literal #41828

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170fe39
minify: do not fold new Array(x, ...spread) into an array literal
robobun Sep 6, 2026
7c18c2c
Bump the runtime transpiler cache version
robobun Sep 6, 2026
fb5b797
[autofix.ci] apply automated fixes
autofix-ci[bot] Sep 7, 2026
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10 changes: 9 additions & 1 deletion src/ast/known_global.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -243,7 +243,15 @@ impl KnownGlobal {
// > 1
_ => {
// new Array(1, 2, 3) -> [1, 2, 3]
// But NOT new Array(3) which creates an array with 3 empty slots
// But NOT new Array(3) which creates an array with 3 empty slots,
// and `new Array(5, ...rest)` is `new Array(5)` when `rest` is empty.
Comment on lines +246 to +247

@github-actions github-actions Bot Sep 7, 2026

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If you need a paragraph-long comment to justify why the workaround is OK, the code is wrong — fix the code

if e.args
.slice()
.iter()
.any(|arg| matches!(arg.data, js_ast::ExprData::ESpread(_)))
{
return Some(Self::call_from_new(e, loc));
}
Some(js_ast::Expr::init(
E::Array {
items: bun_alloc::AstAlloc::take(&mut e.args),
Expand Down
3 changes: 2 additions & 1 deletion src/jsc/RuntimeTranspilerCache.rs
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Expand Up @@ -56,7 +56,8 @@ bun_core::declare_scope!(cache, visible);
/// u8/u16/u32 ids and implied slots dropped, instead of fixed u32 arrays.
/// Version 27: ModuleInfo string table holds Latin-1 / UTF-16 bodies, not WTF-8.
/// Version 28: the define table and `--drop` entries participate in the features hash.
const EXPECTED_VERSION: u32 = 28;
/// Version 29: `new Array(x, ...spread)` is no longer folded into an array literal.
const EXPECTED_VERSION: u32 = 29;

/// Source files smaller than this are not written to / read from the on-disk
/// transpiler cache. Originally 50 KiB, which excluded almost every file in a
Expand Down
14 changes: 13 additions & 1 deletion test/bundler/bundler_minify.test.ts
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Expand Up @@ -1197,6 +1197,8 @@ describe("bundler", () => {
capture(new Array());
capture(new Array(3));
capture(new Array(1, 2, 3));
capture(new Array(...unknownValue));
capture(new Array(5, ...unknownValue));

// Test Array with non-numeric single arguments (should convert to literal)
capture(new Array("string"));
Expand Down Expand Up @@ -1237,6 +1239,8 @@ describe("bundler", () => {
2,
3
]`, // new Array(1, 2, 3) -> [1, 2, 3]
"Array(...unknownValue)", // a spread may leave a single number behind, which is a length
"Array(5, ...unknownValue)",
`[
"string"
]`, // new Array("string") -> ["string"]
Expand Down Expand Up @@ -1329,6 +1333,12 @@ describe("bundler", () => {
const a3 = new Array(n);
const a4 = Array(n);
capture(a3.length === a4.length && a3.length === 3 && a3[0] === undefined);

// A spread can leave a single number behind at runtime, and then it is a length
const none = [];
const a5 = new Array(5, ...none);
capture(a5.length === 5);
capture(0 in a5 === false);

// Test Object semantics
const o1 = new Object();
Expand Down Expand Up @@ -1357,6 +1367,8 @@ describe("bundler", () => {
"0 in sparse === !1",
'JSON.stringify(sparse) === "[null,null,null,null,null]"',
"a3.length === a4.length && a3.length === 3 && a3[0] === void 0",
"a5.length === 5",
"0 in a5 === !1",
"typeof o1 === typeof o2",
"o1.constructor === o2.constructor",
"typeof f1 === typeof f2",
Expand All @@ -1367,7 +1379,7 @@ describe("bundler", () => {
minifySyntax: true,
target: "bun",
run: {
stdout: "true\ntrue\ntrue\ntrue\ntrue\ntrue\ntrue\ntrue\ntrue\ntrue\ntrue\ntrue",
stdout: "true\ntrue\ntrue\ntrue\ntrue\ntrue\ntrue\ntrue\ntrue\ntrue\ntrue\ntrue\ntrue\ntrue",
},
});

Expand Down
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