fix(crypto): update conditional import for js interop library

[tyllark]

For web builds only sha512_slowsinks.dart is supported and sha512_fastsinks.dart is not supported. The conditional importing of sha512_slowsinks.dart uses dart:js instead of the new js interop library dart:js_interop, which does not work for WebAssembly builds. This change aligns us with the recommended conditional import to differentiate between native and web.

#913

• I’ve reviewed the contributor guide and applied the relevant portions to this PR.

Contribution guidelines:

• See our contributor guide for general expectations for PRs.
• Larger or significant changes should be discussed in an issue before creating a PR.
• Contributions to our repos should follow the Dart style guide and use dart format.
• Most changes should add an entry to the changelog and may need to rev the pubspec package version.
• Changes to packages require corresponding tests.

Many Dart repos have a weekly cadence for reviewing PRs - please allow for some latency before initial review feedback.

Note: The Dart team is trialing Gemini Code Assist. Don't take its comments as final Dart team feedback. Use the suggestions if they're helpful; otherwise, wait for a human reviewer.

[tyllark]

Previous changes to this conditional import 686d021 and 61dca74 did not add unit tests so I didn't either.

I could potentially add WASM to the Crypto test matrix via dart test --platform chrome --compiler dart2wasm and use @TestOn and visibleForTesting to check if _Sha64BitSink._digest has a type of Uint32List (web builds) or Uint64List (native builds). Let me know if you think this is necessary.

[mosuem]

Thanks!

[mosuem]

Nit: Is this ignore really necessary?

[mosuem]

Suggested change

	- Updated web conditional import to use `js_interop` to support WebAssembly
	- Updated web conditional import to use `js_interop` to support WebAssembly.

;)

[github-actions]

PR Health

Breaking changes ✔️

Package	Change	Current Version	New Version	Needed Version	Looking good?
crypto	None	3.0.6	3.0.7-wip	3.0.6	✔️

This check can be disabled by tagging the PR with skip-breaking-check.

Changelog Entry ✔️

Package	Changed Files

Changes to files need to be accounted for in their respective changelogs.

This check can be disabled by tagging the PR with skip-changelog-check.

Coverage ✔️

File	Coverage
pkgs/crypto/lib/src/sha512.dart	💚 100 %

This check for test coverage is informational (issues shown here will not fail the PR).

This check can be disabled by tagging the PR with skip-coverage-check.

API leaks ✔️

The following packages contain symbols visible in the public API, but not exported by the library. Export these symbols or remove them from your publicly visible API.

Package	Leaked API symbol	Leaking sources

This check can be disabled by tagging the PR with skip-leaking-check.

License Headers ✔️

// Copyright (c) 2025, the Dart project authors. Please see the AUTHORS file
// for details. All rights reserved. Use of this source code is governed by a
// BSD-style license that can be found in the LICENSE file.

Files
no missing headers

All source files should start with a license header.

This check can be disabled by tagging the PR with skip-license-check.