[import-bytes] add initial tests for import bytes proposal by styfle · Pull Request #4648 · tc39/test262

styfle · 2025-11-09T20:53:23Z

Closes Test plan for import bytes #4647

ljharb · 2025-11-10T00:21:13Z

test/language/import/import-bytes/bytes-from-empty.js

+import value from './bytes-from-empty-FIXTURE.bin' with { type: 'bytes' };
+
+assert(value instanceof Uint8Array);
+assert(value.buffer instanceof ArrayBuffer);


there should be some kind of assertion that it's immutable (not sure what that'd look like tho)

same throughout

The lines below are checking for immutable (asserts that an error is thrown on resize and also on transfer)

assert.throws(TypeError, function() { value.buffer.resize(0); }); assert.throws(TypeError, function() { value.buffer.transfer(); });

Let me know if there is a better way to check for immutability.

Directly call the immutable accessor property https://tc39.es/proposal-immutable-arraybuffer/#sec-get-arraybuffer.prototype.immutable ?

Interesting. I don't see any existing tests for ArrayBuffer.prototype.immutable.

I was basing this new test on the existing tests here:

test262/test/built-ins/ArrayBuffer/prototype/transfer/this-is-immutable-arraybuffer.js

Lines 27 to 30 in 3fd4ec2

var ab = (new ArrayBuffer(4)).transferToImmutable();

assert.throws(TypeError, function() {

ab.transfer();

});

test262/test/built-ins/ArrayBuffer/prototype/resize/this-is-immutable-arraybuffer-object.js

Lines 20 to 23 in 3fd4ec2

var ab = (new ArrayBuffer(4)).transferToImmutable();

assert.throws(TypeError, function() {

ab.resize(0);

});

I went ahead and added the new assertion in cafcddc

Interesting. I don't see any existing tests for ArrayBuffer.prototype.immutable.

Still in PR, alas.

ptomato · 2025-11-10T18:39:07Z

Note, the empty file is failing because fixture files need to contain the string _FIXTURE and these have a dash where they should have an underscore: https://github.com/tc39/test262/blob/main/INTERPRETING.md#modules

styfle · 2025-12-22T15:09:27Z

@ptomato Thanks! I updated the fixtures to use underscores and that solved the Test262File: missing "contents" error.

However, I ran into another error.

  File "/home/runner/work/test262/test262/tools/generation/lib/test.py", line 29, in load
    self.source = handle.read()
                  ~~~~~~~~~~~^^
  File "<frozen codecs>", line 325, in decode
UnicodeDecodeError: 'utf-8' codec can't decode byte 0x89 in position 0: invalid start byte

So I pushed some changes to the python code to ignore binary files.

I see there are still a few engines on circleci that are failing. Please let me know how to proceed, thanks!

ptomato · 2026-01-20T23:20:17Z

@styfle instead of hardcoding binary extensions I think it'd be better to just skip cleaning any files with _FIXTURE in the name? Would that work for you?

The CI jobs are timing out because they are detecting hundreds of tests as different in this PR than from main. Probably if you rebase on the latest state of the main branch, that'll go away.

styfle · 2026-01-22T03:02:45Z

@ptomato Thanks! I rebased on main and force pushed. That seemed to fix CI ✅

I also applied your suggestion to skip files with _FIXTURE in 7d42a35.

Let me know how that looks, thanks!

ptomato

👍 on the modifications to the test generator, everything else generally looks good.

ptomato · 2026-01-22T17:56:31Z

test/language/import/import-bytes/bytes-from-js.js

+assert.sameValue(value.buffer.byteLength, 16);
+assert.sameValue(value.buffer.immutable, true);
+
+assert.compareArray(


This will fail, no? Comments won't be stripped from the JS file?

The comments are only here for the human reader to make it clear that each byte represents a character in the js file that was imported, in this case:

var foo = 'bar'

It should work just fine. Am I misunderstanding you?

By my reading, the imported byte array should contain the UTF-8 encoding of

// Copyright (C) 2025 @styfle. All rights reserved. // This code is governed by the BSD license found in the LICENSE file. var foo = 'bar'

and not

var foo = 'bar'

but this test expects the latter.

I understand now, thanks!

You're right, I pushed commit fdc288c to remove it but then lint fails.

Is there a recommended way to disable lint on the FIXTURE files?

I think I figured it out. I pushed ac5338b to disable license checks on files containing _FIXTURE in the name.

Might be nicer to go the other way and include the bytes of the comment here instead of messing with the lint rules.

I considered that but I figured I would fix it for everyone since fixture files are not source code.

It seems like this was the first fixture file to be js perhaps?

On the contrary, fixture files are source code and this is not the first JS fixture file. JS fixture files are used extensively in other importing tests.

I think the best course of action is to keep the license header and include the bytes of the comment in the test, as annoying as that may be.

(You could say that it's ridiculous to license var foo = 'bar' and you would be right, but we don't want to get into the weeds of "is this JS file big enough to merit a license header". All JS files just need to have either the license header or the public domain declaration.)

Ok I reverted those commits and pushed a change to read all the bytes 👍

Please take another look.

ptomato

Thanks!

It occurs to me that these tests will fail if checked out on Windows with git configured for core.autocrlf = true. (The 0x0a bytes will get replaced with 0x0d 0x0a on disk)

Do we need to specify in INTERPRETING.md that test262 consumers must not have core.autocrlf = true in their gitconfig?

styfle · 2026-01-28T21:39:30Z

@ptomato Sounds good. I added a note in c7ec727.

Is there anyone else that needs to approve before this gets merged?

ptomato · 2026-01-28T23:39:16Z

Not really. The rule of thumb I've been trying to stick to is: if it's small, or has 2 reviews already, or is urgent for plenary, I merge it; otherwise, I leave a couple of days to see if anyone else comments.

ptomato · 2026-02-03T20:22:51Z

Some referenced fixture files appear to be missing from the commit

lies

The length assertion in bytes-from-js.js might need a quick adjustment

Seems to be legit, @styfle PTAL?

ptomato · 2026-02-06T16:20:51Z

Some referenced fixture files appear to be missing from the commit

lies

The length assertion in bytes-from-js.js might need a quick adjustment

Seems to be legit, @styfle PTAL?

What is it with these LLM review bots that randomly pop up, leave review comments, and then after you reply to them the comment gets deleted?? It looks like I'm talking to myself.

In any case, the above was my reply to a review bot that made 2 suggestions, one of them nonsense, the other one was a legit comment about the length assertion in bytes-from-js.js not being updated to match the new length of the fixture file.

styfle · 2026-02-14T15:15:24Z

@ptomato Good call! Updated in 73d12de

styfle · 2026-02-14T16:10:30Z

@ljharb @bakkot Any other feedback?

ptomato · 2026-02-16T17:11:55Z

I think it's fine to merge it now, it's been up for several weeks since I approved it.

This reverts commit ac5338b.

This reverts commit fdc288c.

styfle requested review from a team as code owners November 9, 2025 20:53

styfle mentioned this pull request Nov 9, 2025

Road to Stage 3 tc39/proposal-import-bytes#28

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25 tasks

ljharb reviewed Nov 10, 2025

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styfle mentioned this pull request Dec 22, 2025

Test plan for import bytes #4647

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8 tasks

styfle mentioned this pull request Dec 29, 2025

[import-bytes] add initial tests for import bytes proposal web-platform-tests/wpt#56938

Open

ptomato added needs review needs follow-up labels Jan 5, 2026

ptomato removed the needs follow-up label Jan 20, 2026

styfle force-pushed the styfle/proposal-import-bytes branch from cafcddc to 25407a1 Compare January 22, 2026 02:46

styfle requested review from bakkot and ljharb January 22, 2026 03:03

ptomato requested changes Jan 22, 2026

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styfle requested a review from ptomato January 23, 2026 21:12

ptomato approved these changes Jan 27, 2026

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styfle added 4 commits February 16, 2026 09:12

[import-bytes] add initial tests for import bytes proposal

bdf8357

rename -FIXTURE to _FIXTURE

845d2c5

add tests for json and js

c73efc7

fix copyright

035f2a8

styfle added 13 commits February 16, 2026 09:12

fix typo

339abee

add missing copyright

35d9bd4

fix: ignore binary files in python generator

67ef9e5

chore: revert test.py since its no longer instatiated

648c675

add assertion for value.buffer.immutable

8d5e13c

skip clean for files containing _FIXTURE

cecb53e

fix: remove unnecessary comment

e49c3e9

fix: disable check license for _FIXTURE

78ca6eb

Revert "fix: disable check license for _FIXTURE"

bc2cf98

This reverts commit ac5338b.

Revert "fix: remove unnecessary comment"

0f7ab15

This reverts commit fdc288c.

update bytes to match js code including comments

965e219

add windows caveat to interpreting.md

746ebbc

fix: assert proper length

d98d096

ptomato force-pushed the styfle/proposal-import-bytes branch from 73d12de to d98d096 Compare February 16, 2026 17:12

ptomato enabled auto-merge (squash) February 16, 2026 17:12

ptomato merged commit 3af36be into tc39:main Feb 16, 2026
14 checks passed

h8920981945 approved these changes Feb 16, 2026

View reviewed changes

styfle deleted the styfle/proposal-import-bytes branch February 18, 2026 14:28

This was referenced Mar 5, 2026

[import-bytes] add bytes sec-fetch-dest and accept whatwg/fetch#1912

Open

[import-bytes] add import bytes whatwg/html#11657

Draft

	var ab = (new ArrayBuffer(4)).transferToImmutable();
	assert.throws(TypeError, function() {
	ab.transfer();
	});

	var ab = (new ArrayBuffer(4)).transferToImmutable();
	assert.throws(TypeError, function() {
	ab.resize(0);
	});

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