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feat(minifier): fold string concat chaining #8441

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Jan 17, 2025
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feat(minifier): fold string concat chaining #8441

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27 changes: 22 additions & 5 deletions crates/oxc_minifier/src/ast_passes/peephole_replace_known_methods.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -26,7 +26,7 @@ impl<'a> CompressorPass<'a> for PeepholeReplaceKnownMethods {

impl<'a> Traverse<'a> for PeepholeReplaceKnownMethods {
fn exit_expression(&mut self, node: &mut Expression<'a>, ctx: &mut TraverseCtx<'a>) {
self.try_fold_array_concat(node, ctx);
self.try_fold_concat_chain(node, ctx);
self.try_fold_known_string_methods(node, ctx);
}
}
Expand Down Expand Up @@ -341,7 +341,8 @@ impl<'a> PeepholeReplaceKnownMethods {
}

/// `[].concat(a).concat(b)` -> `[].concat(a, b)`
fn try_fold_array_concat(&mut self, node: &mut Expression<'a>, ctx: &mut TraverseCtx<'a>) {
/// `"".concat(a).concat(b)` -> `"".concat(a, b)`
fn try_fold_concat_chain(&mut self, node: &mut Expression<'a>, ctx: &mut TraverseCtx<'a>) {
if matches!(ctx.parent(), Ancestor::StaticMemberExpressionObject(_)) {
return;
}
Expand All @@ -368,7 +369,7 @@ impl<'a> PeepholeReplaceKnownMethods {

// We don't need to check if the arguments has a side effect here.
//
// The only side effect Array::concat can cause is throwing an error when the created array is too long.
// The only side effect Array::concat / String::concat can cause is throwing an error when the created array is too long.
// With the compressor assumption, that error can be moved.
//
// For example, if we have `[].concat(a).concat(b)`, the steps before the compression is:
Expand All @@ -387,10 +388,13 @@ impl<'a> PeepholeReplaceKnownMethods {
let CallExpression { callee, arguments, .. } = ce.as_mut();
collected_arguments.push(arguments);

// [].concat()
// [].concat() or "".concat()
let is_root_expr_concat = {
let Expression::StaticMemberExpression(member) = callee else { unreachable!() };
matches!(&member.object, Expression::ArrayExpression(_))
matches!(
&member.object,
Expression::ArrayExpression(_) | Expression::StringLiteral(_)
)
};
if is_root_expr_concat {
new_root_callee = callee;
Expand Down Expand Up @@ -1162,6 +1166,7 @@ mod test {

#[test]
fn test_fold_concat_chaining() {
// array
fold("[1,2].concat(1).concat(2,['abc']).concat('abc')", "[1,2].concat(1,2,['abc'],'abc')");
fold("[].concat(['abc']).concat(1).concat([2,3])", "[].concat(['abc'],1,[2,3])");

Expand All @@ -1170,6 +1175,18 @@ mod test {
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

fold_same("[].concat(1)");

// string
fold("'1'.concat(1).concat(2,['abc']).concat('abc')", "'1'.concat(1,2,['abc'],'abc')");
fold("''.concat(['abc']).concat(1).concat([2,3])", "''.concat(['abc'],1,[2,3])");

fold("var x, y; ''.concat(x).concat(y)", "var x, y; ''.concat(x, y)");
fold("var y; ''.concat(x).concat(y)", "var y; ''.concat(x, y)"); // x might have a getter that updates y, but that side effect is preserved correctly
fold("var x; ''.concat(x.a).concat(x)", "var x; ''.concat(x.a, x)"); // x.a might have a getter that updates x, but that side effect is preserved correctly

fold_same("''.concat(1)");

// other
fold_same("obj.concat([1,2]).concat(1)");
}

Expand Down
6 changes: 3 additions & 3 deletions tasks/minsize/minsize.snap
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Original file line number Diff line number Diff line change
Expand Up @@ -17,11 +17,11 @@ Original | minified | minified | gzip | gzip | Fixture

1.25 MB | 652.88 kB | 646.76 kB | 163.54 kB | 163.73 kB | three.js

2.14 MB | 725.56 kB | 724.14 kB | 180.06 kB | 181.07 kB | victory.js
2.14 MB | 724.06 kB | 724.14 kB | 179.94 kB | 181.07 kB | victory.js

3.20 MB | 1.01 MB | 1.01 MB | 332.01 kB | 331.56 kB | echarts.js

6.69 MB | 2.32 MB | 2.31 MB | 492.65 kB | 488.28 kB | antd.js
6.69 MB | 2.32 MB | 2.31 MB | 492.44 kB | 488.28 kB | antd.js

10.95 MB | 3.49 MB | 3.49 MB | 907.34 kB | 915.50 kB | typescript.js
10.95 MB | 3.49 MB | 3.49 MB | 907.09 kB | 915.50 kB | typescript.js

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