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[immutable-arraybuffer] ArrayBuffer.prototype.sliceToImmutable #4553

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[immutable-arraybuffer] ArrayBuffer.prototype.sliceToImmutable #4553

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Ref #4509

New ArrayBuffer.prototype properties

  • ArrayBuffer.prototype.sliceToImmutable
    • verifyPrimordialCallableProperty(ArrayBuffer.prototype, "sliceToImmutable", "sliceToImmutable", 2);
    • brand-checking (throws TypeError unless receiver is an ArrayBuffer and not a SharedArrayBuffer), before resolving bounds
    • throws TypeError if receiver is detached, before resolving bounds
    • resolves bounds after passing the preceding checks—first start, clamping negative values to [0, len - 1] and positive values to [0, len], then end, defaulting to len and clamping negative values to [0, len - 1] and positive values to [0, len] (and capturing len before coercing either start or end)
    • throws TypeError if receiver was detached by bounds resolution, after bounds resolution
    • throws RangeError if length < specified upper bound, after passing the second detachment check and even if length was ≥ specified upper bound until bounds resolution
    • returns an immutable ArrayBuffer with the correct length and contents (both unaffected by subsequent changes to the original receiver, including detachment)

@gibson042 gibson042 requested a review from a team as a code owner August 1, 2025 01:26
@gibson042 gibson042 mentioned this pull request Jul 29, 2025
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@gibson042 gibson042 force-pushed the 2025-07-immutable-arraybuffer-slicetoimmutable branch from 51629c7 to f9ed2c1 Compare August 1, 2025 01:30
ptomato
ptomato approved these changes Aug 25, 2025
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Minor comments, feel free to merge when resolved

test/built-ins/ArrayBuffer/prototype/sliceToImmutable/this-is-sharedarraybuffer.js
---*/

var fn = ArrayBuffer.prototype.sliceToImmutable;
assert.sameValue(typeof fn, "function", "Method must exist.");
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Suggested change
assert.sameValue(typeof fn, "function", "Method must exist.");

I think this is sufficiently implied by the immutable-arraybuffer feature flag.

test/built-ins/ArrayBuffer/prototype/sliceToImmutable/this-is-not-object.js
---*/

var fn = ArrayBuffer.prototype.sliceToImmutable;
assert.sameValue(typeof fn, "function", "Method must exist.");
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Ditto

test/built-ins/ArrayBuffer/prototype/sliceToImmutable/this-is-not-object.js
Comment on lines +45 to +46
var label = badReceivers[i][0];
var value = badReceivers[i][1];
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This will break on implementations without Symbol or BigInt, I think you probably want if (!badReceivers[i]) continue;

test/built-ins/ArrayBuffer/prototype/sliceToImmutable/this-has-no-arraybufferdata-internal.js
---*/

var fn = ArrayBuffer.prototype.sliceToImmutable;
assert.sameValue(typeof fn, "function", "Method must exist.");
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Already implied by feature flag.

test/built-ins/ArrayBuffer/prototype/sliceToImmutable/argument-coercion.js
Comment on lines +124 to +128
"sliceToImmutable(" + repr(rawStart) + ", " + repr(rawEnd) + ")");
assert.compareArray(new Uint8Array(dest), expectContents,
"sliceToImmutable(" + repr(rawStart) + ", " + repr(rawEnd) + ")");
assert.sameValue(dest.immutable, true,
"sliceToImmutable(" + repr(rawStart) + ", " + repr(rawEnd) + ")");
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Minor suggestion, add something to these assertion messages to distinguish which assertion is failing (byte length, contents, or immutability) (Same for below)

iamstolis
iamstolis reviewed Oct 6, 2025
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test/built-ins/ArrayBuffer/prototype/sliceToImmutable/modify-source-after-return.js
var view = new Uint8Array(source);
for (var i = 0; i < 8; i++) view[i] = i + 1;

var dest = new ArrayBuffer.sliceToImmutable();
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new ArrayBuffer.sliceToImmutable() makes no sense. I guess it should be something like source.sliceToImmutable().

iamstolis
iamstolis reviewed Oct 6, 2025
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test/built-ins/ArrayBuffer/prototype/sliceToImmutable/argument-coercion.js
return String(value);
}

var make32ByteArrayBuffer() {
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Typo? var make32ByteArrayBuffer() -> function make32ByteArrayBuffer()

iamstolis
iamstolis reviewed Oct 6, 2025
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test/built-ins/ArrayBuffer/prototype/sliceToImmutable/argument-coercion.js
for (var j = 0; j < goodInputs.length; j++) {
var rawEnd = goodInputs[j][0];
var intEnd = goodInputs[j][1];
var intLength = intEnd - intStart;
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This is not a correct calculation of the length of the slice. It does not work when intStart or intEnd is negative or when intStart > intEnd. Note that there is the same problem on lines 151 and 170.

iamstolis
iamstolis reviewed Oct 6, 2025
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test/built-ins/ArrayBuffer/prototype/sliceToImmutable/argument-coercion.js
calls,
["start[Symbol.toPrimitive](number)", "end[Symbol.toPrimitive](number)"],
"sliceToImmutable" + reprArgs("[Symbol.toPrimitive]", "[Symbol.toPrimitive]"));
);
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@iamstolis iamstolis Oct 6, 2025 •
edited
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SyntaxError, duplicate ); (here and on the previous line). There is the same problem on lines 316 and 324.

iamstolis
iamstolis reviewed Oct 6, 2025
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test/built-ins/ArrayBuffer/prototype/sliceToImmutable/argument-coercion.js
[-1, RangeError],
[9007199254740992, RangeError], // Math.pow(2, 53) = 9007199254740992
[Infinity, RangeError],
[-Infinity, RangeError],
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@iamstolis iamstolis Oct 6, 2025 •
edited
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I don't see why would these out of range numbers caused RangeErrors.

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@ptomato ptomato ptomato approved these changes

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@gibson042 @ptomato @iamstolis