perf(tooling): preserve sparse arrays and avoid redundant copy in assert.deepStrictEqual shim

[danieljbruce]

Summary

Stacked on top of #9460 (bun-runtime/1-test-runner-handwritten-libraries-4-1).

In bin/proxyquire-bun-shim.cjs, assert.deepStrictEqual clones actual and expected arrays when retrying comparisons for Array subclasses with constructor === Array in Bun <= 1.4.

Previously, Array.from(actual) and Array.from(expected) were used before iterating over Reflect.ownKeys and copying every own property descriptor via Object.defineProperty. This had two drawbacks:

1. Sparse array semantics: Array.from() converts holes in sparse arrays into explicit undefined elements (creating own properties for indices that were originally empty slots), altering sparse array semantics because the subsequent Reflect.ownKeys loop only defines properties that exist on the source array and does not delete the filled holes.
2. Redundant work: Array.from() iterates and populates all array indices upfront, only for the subsequent loop to immediately redefine every own property via Object.defineProperty.

Initializing copyA and copyB with new Array(actual.length) and new Array(expected.length) allocates an empty array of the matching length, preserving sparse array holes and avoiding redundant element copying before Object.defineProperty transfers all own property descriptors.

[danieljbruce]

/gemini review

[gemini-code-assist]

Code Review

This pull request updates bin/proxyquire-bun-shim.cjs to replace Array.from() with new Array(length) when creating copies of the actual and expected arrays. This changes how the array copies are initialized before their properties are defined. There are no review comments to evaluate, and I have no feedback to provide.

[gemini-code-assist]

Code Review

This pull request replaces the use of 'Array.from()' with 'new Array(length)' when copying arrays in 'bin/proxyquire-bun-shim.cjs'. The feedback recommends coercing the array lengths to unsigned 32-bit integers using '>>> 0' to avoid potential 'RangeError' exceptions or unexpected behavior if the length property is not a primitive number.

[gemini-code-assist]

Using new Array(actual.length) can lead to unexpected behavior or a RangeError if actual.length is not a primitive number (for example, if it is a string like "5", undefined, or a negative number). In JavaScript, new Array("5") creates an array containing the single element "5" (length 1) instead of an empty array of length 5, and new Array(undefined) creates [undefined] (length 1). To ensure robustness and guarantee that the argument is always treated as a numeric length, coerce the length to an unsigned 32-bit integer using the unsigned right shift operator (>>> 0). This is the standard ECMAScript behavior for array-like length coercion.

              const copyA = new Array(actual.length >>> 0);

[gemini-code-assist]

Similarly, coerce expected.length to an unsigned 32-bit integer using >>> 0 to prevent unexpected behavior or RangeError if expected.length is not a primitive number.

              const copyB = new Array(expected.length >>> 0);