[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.

This reverts commit ac5338b.

This reverts commit fdc288c.

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.

juice928 · 2026-02-03T20:09:40Z

👋 Hi, I'm an automated AI code review bot. I ran some checks on this PR and found 2 points that might be worth attention (could be false positives, please use your judgment):

Some referenced fixture files appear to be missing from the commit
- test/language/import/import-bytes/bytes-from-empty.js:L11
- Impact: This might lead to module resolution errors as the tests expect specific .bin, .json, .png, and .txt files that aren't currently in the diff.
- Suggestion: Please double-check if all necessary fixture files have been added to the commit.
The length assertion in bytes-from-js.js might need a quick adjustment
- test/language/import/import-bytes/bytes-from-js.js:L16-L17
- Impact: The current assertion for a length of 16 may cause the test to fail since the fixture content appears to be approximately 139 bytes.
- Suggestion: Consider updating the assertion to match the actual size of the fixture file.

If you find these suggestions disruptive, you can reply "stop" , and I'll automatically skip this repository in the future.

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?

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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21 tasks

ljharb reviewed Nov 10, 2025

View reviewed changes

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 added 9 commits January 21, 2026 21:46

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

5eeb3ca

rename -FIXTURE to _FIXTURE

3c59ad9

add tests for json and js

4c53bb7

fix copyright

a55b2a2

fix typo

895b983

add missing copyright

5441e96

fix: ignore binary files in python generator

df2f48e

chore: revert test.py since its no longer instatiated

17662ce

add assertion for value.buffer.immutable

25407a1

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

skip clean for files containing _FIXTURE

7d42a35

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

ptomato requested changes Jan 22, 2026

View reviewed changes

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

styfle added 2 commits January 25, 2026 14:33

fix: remove unnecessary comment

fdc288c

fix: disable check license for _FIXTURE

ac5338b

styfle added 3 commits January 26, 2026 23:00

Revert "fix: disable check license for _FIXTURE"

66f5f1c

This reverts commit ac5338b.

Revert "fix: remove unnecessary comment"

4028c63

This reverts commit fdc288c.

update bytes to match js code including comments

8eda568

ptomato approved these changes Jan 27, 2026

View reviewed changes

add windows caveat to interpreting.md

c7ec727

	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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