no-accumulating-spread

Disallow repeated accumulator spreads within iterations

Spreading an accumulator into its replacement copies every value accumulated so far.
Repeating the replacement in a loop or reduction callback can make total copying grow quadratically.
Instead, you SHOULD use an operation that extends storage without rebuilding the preceding values.

Aliasing can make in-place mutation observably different, so the diagnostic requires a manual rewrite.

- Category: performance
- Level: warning
- Fix: none
- Scope: module

Reported

function copy(source: int32[]): int32[] {
    let output: int32[] = [];
    for (const value of source) {
        output = [...output, value];
    }

    return output;
}
Accepted

function copy(source: int32[]): int32[] {
    let output: int32[] = [];
    for (const value of source) {
        output.push(value);
    }

    return output;
}
Prior art

- Biome · noAccumulatingSpread
- Oxc · no-accumulating-spread

language/linter/src/rules/performance/noaccumulatingspread.rs:7