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https://github.com/danbulant/oxc
synced 2026-05-19 04:08:41 +00:00
feat(minifier): fold array concat chaining (#8440)
Compress `[].concat(a).concat(b)` into `[].concat(a, b)`. **References** - [Spec of `Array::concat`](https://tc39.es/ecma262/multipage/indexed-collections.html#sec-array.prototype.concat) --- ### The new assumption I added a new assumption description in `crates/oxc_minifier/README.md`: "Errors thrown when creating a String or an Array that exceeds the maximum length can disappear or moved". This is an assumption held by other minifiers. Without this assumption, we have to treat `+` and array creation/update to have a sideeffect and that limits the minification. For input: ```js [...Array(Number(2n ** 32n - 1n)),""] " ".repeat(Number(2n ** 29n - 24n - 1n)) + ' ' export {} ``` (Note that `2 ** 32 - 1` is the max array length and `2 ** 29 - 24` is the max string length on V8.) This code errors with too long array and too long string on V8 based runtimes. terser outputs: ```js Array(Number(2n**32n-1n))," ".repeat(Number(536870887n));export{}; ``` No error will happen with this code. SWC outputs: ```js [...Array(Number(2n**32n-1n))]," ".repeat(Number(2n**29n-24n-1n));export{}; ``` No error will happen with this code. [playground](https://play.swc.rs/?version=1.10.7&code=H4sIAAAAAAAAA4vW09NzLCpKrNTwK81NSi3SMMpT0NJSMAZSugqGeZqaOkpKsbxcSgpKekWpBamJJajqjCxB6oxMYKoVtBXUFdR5uVIrCvKLShSqa3m5AGRqy%2FBiAAAA&config=H4sIAAAAAAAAA32UO3LjMAyG%2B5zCozrFjostcoDtcgYOTYIyvXxoCNCxJuO7L0RJtjeG3En48AMkAOL7bbfrTmi6j903f%2FLPoAtCuf2zBcdE%2BsKWDkzUaIofqHtf6Qkn5HRAaKbrTDrSpQdqKtz%2F2u8XRRdyRlgViy365N34mNPkOBRAfLCxlUPWCInwf%2F3CSv6aAJX6aD%2FkHECnF0RpVD4R9FCkwCaHoAcEddZFiDKdVBePWUoxwUpg1VDyIPJkPfmcOOcztaCtMtmCgHwBQ%2F4MkoxzsSwhX0%2B4T8MWDrXvW59%2FqOGsQ9Uk5IRLawmfVoh6zB5JuZqkEs5wowYzXIr7U%2BmdKkC1pGfdKfu00ZO%2FAFyBoBGTjiDFbR6O52lL7V4qfXI8sjQKnOdbumWCnouqvHdCZafKQCEvdbOArQamyhrpOAveKB96Cwqc41kRQuOXJ3OUktI4QHYC4P5qJ03VDNTtFW7w6UG8wH%2F4liQP2OIRNR23KY7xkMOLBBHomO0LB24F5W1ceEtchm1ekwUeDbCiS8UGnpcAPwDKKrR9%2BTQb%2FDw4oupDPtzXxOJwve3hqFN%2Ff%2B%2FzKn5bHLqYbW1wWfJTf%2BfV%2FLu7O61beD1B5%2FFzFbac13%2FKOhgeLwYAAA%3D%3D) esbuild outputs: ```js [...Array(Number(2n**32n-1n))]," ".repeat(Number(2n**29n-24n-1n))+"";export{}; ``` No error will happen with this code. [esbuild try](https://esbuild.github.io/try/#dAAwLjI0LjIALS1taW5pZnkAWy4uLkFycmF5KE51bWJlcigybiAqKiAzMm4gLSAxbikpLCIiXQoiICIucmVwZWF0KE51bWJlcigybiAqKiAyOW4gLSAyNG4gLSAxbikpICsgJyAnCmV4cG9ydCB7fQ) OXC outputs: ```js [...Array(Number(2n**32n-1n))]," ".repeat(Number(2n**29n-24n-1n))+" ";export{}; ``` The array error won't happen and the String error will happen with this code. [playground](https://playground.oxc.rs/#eNpVT71OwzAQfhXrlv4QIhpgIBtLR8SOGZxwCUH22To7baMo746dNEVMd5/u+7sRaijhI8/zV2Y1bN96UyFvCxL7vXiM414caLfLJEj4lCRBSMgZHarwn1u8JG7xtCrEndiIjSS8OMtBjJMkyMBCOQL3lIYfKKgLlIF7zEB3FKBslPYR+No6XC9+MJXVKwqsyDeWzZU8ZeAUe+TZ0vZc47HTSMpEAwjoQ/7jY7JjjKQTvitG8n/ilDuL437zXtyC4hZjKUBfPByeITJq+4UtpvoRmI66plu4tTUpIRovNc/fXcx2qr69YRS1+opmJwps9VHbc9KfkCvr43npNU2/v/WIsw==)
This commit is contained in:
sapphi-red
parent
d17021c834
commit
a4ae4505f1
3 changed files with 88 additions and 18 deletions
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@ -29,6 +29,8 @@ The compressor is responsible for rewriting statements and expressions for minim
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- Examples that breaks this assumption: `(() => { console.log(v); let v; })()`
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- `with` statement is not used
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- Examples that breaks this assumption: `with (Math) { console.log(PI); }`
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- Errors thrown when creating a String or an Array that exceeds the maximum length can disappear or moved
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- Examples that breaks this assumption: `try { new Array(Number(2n**53n)) } catch { console.log('log') }`
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## Terser Tests
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@ -7,7 +7,7 @@ use oxc_ecmascript::{
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constant_evaluation::ConstantEvaluation, StringCharAt, StringCharCodeAt, StringIndexOf,
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StringLastIndexOf, StringSubstring, ToInt32,
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};
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use oxc_traverse::{traverse_mut_with_ctx, ReusableTraverseCtx, Traverse, TraverseCtx};
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use oxc_traverse::{traverse_mut_with_ctx, Ancestor, ReusableTraverseCtx, Traverse, TraverseCtx};
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use crate::{ctx::Ctx, CompressorPass};
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@ -26,6 +26,7 @@ impl<'a> CompressorPass<'a> for PeepholeReplaceKnownMethods {
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impl<'a> Traverse<'a> for PeepholeReplaceKnownMethods {
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fn exit_expression(&mut self, node: &mut Expression<'a>, ctx: &mut TraverseCtx<'a>) {
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self.try_fold_array_concat(node, ctx);
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self.try_fold_known_string_methods(node, ctx);
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}
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}
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@ -338,6 +339,83 @@ impl<'a> PeepholeReplaceKnownMethods {
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}
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result.into_iter().rev().collect()
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}
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/// `[].concat(a).concat(b)` -> `[].concat(a, b)`
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fn try_fold_array_concat(&mut self, node: &mut Expression<'a>, ctx: &mut TraverseCtx<'a>) {
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if matches!(ctx.parent(), Ancestor::StaticMemberExpressionObject(_)) {
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return;
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}
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let original_span = if let Expression::CallExpression(root_call_expr) = node {
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root_call_expr.span
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} else {
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return;
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};
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let mut current_node: &mut Expression = node;
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let mut collected_arguments = ctx.ast.vec();
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let new_root_callee: &mut Expression<'a>;
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loop {
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let Expression::CallExpression(ce) = current_node else {
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return;
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};
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let Expression::StaticMemberExpression(member) = &ce.callee else {
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return;
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};
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if member.optional || member.property.name != "concat" {
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return;
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}
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// We don't need to check if the arguments has a side effect here.
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//
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// The only side effect Array::concat can cause is throwing an error when the created array is too long.
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// With the compressor assumption, that error can be moved.
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//
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// For example, if we have `[].concat(a).concat(b)`, the steps before the compression is:
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// 1. evaluate `a`
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// 2. `[].concat(a)` creates `[a]`
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// 3. evaluate `b`
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// 4. `.concat(b)` creates `[a, b]`
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//
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// The steps after the compression (`[].concat(a, b)`) is:
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// 1. evaluate `a`
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// 2. evaluate `b`
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// 3. `[].concat(a, b)` creates `[a, b]`
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//
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// The error that has to be thrown in the second step before the compression will be thrown in the third step.
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let CallExpression { callee, arguments, .. } = ce.as_mut();
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collected_arguments.push(arguments);
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// [].concat()
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let is_root_expr_concat = {
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let Expression::StaticMemberExpression(member) = callee else { unreachable!() };
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matches!(&member.object, Expression::ArrayExpression(_))
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};
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if is_root_expr_concat {
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new_root_callee = callee;
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break;
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}
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let Expression::StaticMemberExpression(member) = callee else { unreachable!() };
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current_node = &mut member.object;
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}
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if collected_arguments.len() <= 1 {
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return;
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}
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*node = ctx.ast.expression_call(
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original_span,
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ctx.ast.move_expression(new_root_callee),
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Option::<TSTypeParameterInstantiation>::None,
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ctx.ast.vec_from_iter(
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collected_arguments.into_iter().rev().flat_map(|arg| ctx.ast.move_vec(arg)),
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),
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false,
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);
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self.changed = true;
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}
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}
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/// Port from: <https://github.com/google/closure-compiler/blob/v20240609/test/com/google/javascript/jscomp/PeepholeReplaceKnownMethodsTest.java>
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@ -1083,25 +1161,15 @@ mod test {
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}
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#[test]
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#[ignore]
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fn test_fold_concat_chaining() {
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// enableTypeCheck();
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fold("[1,2].concat(1).concat(2,['abc']).concat('abc')", "[1,2].concat(1,2,['abc'],'abc')");
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fold("[].concat(['abc']).concat(1).concat([2,3])", "['abc'].concat(1,[2,3])");
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fold("[].concat(['abc']).concat(1).concat([2,3])", "[].concat(['abc'],1,[2,3])");
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// cannot fold concat based on type information
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fold_same("returnArrayType().concat(returnArrayType()).concat(1).concat(2)");
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fold_same("returnArrayType().concat(returnUnionType()).concat(1).concat(2)");
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fold(
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"[1,2,1].concat(1).concat(returnArrayType()).concat(2)",
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"[1,2,1].concat(1).concat(returnArrayType(),2)",
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);
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fold(
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"[1].concat(1).concat(2).concat(returnArrayType())",
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"[1].concat(1,2).concat(returnArrayType())",
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);
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fold_same("[].concat(1).concat(returnArrayType())");
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fold("var x, y; [1].concat(x).concat(y)", "var x, y; [1].concat(x, y)");
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fold("var y; [1].concat(x).concat(y)", "var y; [1].concat(x, y)"); // x might have a getter that updates y, but that side effect is preserved correctly
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fold("var x; [1].concat(x.a).concat(x)", "var x; [1].concat(x.a, x)"); // x.a might have a getter that updates x, but that side effect is preserved correctly
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fold_same("[].concat(1)");
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fold_same("obj.concat([1,2]).concat(1)");
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}
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@ -19,7 +19,7 @@ Original | minified | minified | gzip | gzip | Fixture
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2.14 MB | 725.56 kB | 724.14 kB | 180.06 kB | 181.07 kB | victory.js
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3.20 MB | 1.01 MB | 1.01 MB | 332.02 kB | 331.56 kB | echarts.js
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3.20 MB | 1.01 MB | 1.01 MB | 332.01 kB | 331.56 kB | echarts.js
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6.69 MB | 2.32 MB | 2.31 MB | 492.65 kB | 488.28 kB | antd.js
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