Analysis: CopyArray mutation usage in endojs/endo

[Copilot]

Identified all arrays declared as CopyArray that are subsequently mutated in the repository, confirming that CopyArray must remain mutable to avoid breaking changes.

Findings

Production code mutations (packages/patterns/src/patterns/patternMatchers.js):

• confirmElementsHasSplit(): Optional inResults and outResults parameters typed as CopyArray are mutated via .push()
• pairsHasSplit(): Optional inResults and outResults parameters typed as CopyArray<[Key, bigint]> are mutated via .push()

Test code mutations (packages/pass-style/src/types.test-d.ts):

• Explicit tests verify CopyArray supports mutation methods (.push(), .shift())

Example Usage

const confirmElementsHasSplit = (
  elements,
  elementPatt,
  bound,
  reject,
  inResults = undefined,     // CopyArray - mutated
  outResults = undefined,    // CopyArray - mutated
) => {
  for (let i = elements.length - 1; i >= 0; i -= 1) {
    const element = elements[i];
    if (count < bound && matches(element, elementPatt)) {
      if (inResults) inResults.push(element);  // mutation
    } else if (outResults) {
      outResults.push(element);  // mutation
    }
  }
};

Analysis confirms that changing CopyArray from Array<T> to ReadonlyArray<T> would break existing code. The separate CopyReadonlyArray type introduced in #3061 maintains backward compatibility.

Complete analysis available in /tmp/copyarray-analysis/FINAL-REPORT.md.

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