Implement `Int64` as a wrapper for `int` when targeting native and Wasm #905

osa1 · 2025-09-05T11:08:21Z

This PR adds another Int64 implementation that is just a wrapper around int, to be used in targets where int is 64 bits.

Because dart doc generates using the native class, all documentation comments are moved to the native class.

The conditional import is implemented based on availability of the library dart:html, which is only available on dart2js.

Improves #172. It could be further improved by having Int64 as an extension class when targeting native and Wasm, but that would be a breaking change, and we would have to remove the IntX superclass as extensions cannot extend or implement other classes.

This PR adds another `Int64` implementation that is just a wrapper around `int`, to be used in targets where `int` is 64 bits. Becuase `dart doc` generates using the native class, all documentation comments are moved to the native class. The conditional import is implemented based on availability of the library `dart:html`, which is only available on dart2js. Improves dart-lang#172. It could be further improved by having `Int64` as an extension class when targeting native and Wasm, but that would be a breaking change.

github-actions · 2025-09-05T11:10:24Z

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Breaking changes

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Package	Change	Current Version	New Version	Needed Version	Looking good?
fixnum	Breaking	1.1.1	1.2.0-wip	2.0.0 Got "1.2.0-wip" expected >= "2.0.0" (breaking changes)	⚠️

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File	Coverage
pkgs/fixnum/lib/fixnum.dart	💔 Not covered
pkgs/fixnum/lib/src/int32.dart	💚 94 %
pkgs/fixnum/lib/src/int64.dart	💔 0 % ⬇️ 100 %
pkgs/fixnum/lib/src/int64_emulated.dart	💔 Not covered
pkgs/fixnum/lib/src/int64_native.dart	💚 96 %

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// 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.

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lrhn

I assume most code that doesn't do arithmetics is just copied, so LGTM.

(Any comments are nice-to-have, but not something introduced by this CL.)

lrhn · 2025-09-05T12:35:49Z

pkgs/fixnum/lib/src/int64_native.dart

+  factory Int64.fromInts(int high, int low) =>
+      Int64((high << 32) | (low & 0xFFFFFFFF));
+
+  factory Int64.fromBytes(List<int> bytes) => Int64(((bytes[7] & 0xFF) << 56) |


(If the bytes is a Uint8List, could possibly use an internal getterto read the bytes. I don't know if doing the type check costs more than just reading eight bytes.)

I also don't know. This is existing code, we can benchmark and optimize it later if needed. For now doing the same as before won't regress anything so it's safe.

pkgs/fixnum/lib/src/int64_native.dart

lrhn · 2025-09-05T12:44:05Z

pkgs/fixnum/lib/src/int64.dart

+// `dart:html` is only available on dart2js (dart2wasm won't support it), so we
+// can check availability of it to test whether we're compiling to JS. Other
+// targets (AOT, JIT, Wasm) support 64-bit `int`s.
+export 'int64_native.dart' if (dart.library.html) 'int64_emulated.dart';


I think dart:html is deprecated. When it goes away, which we should assume it will, this version of the package will then break. (If the library goes away in Dart 4.0, the SDK versioning will probably handle it, but it could be sooner.)

We could add some kind of ensurance against running int64_native.dart with JS number semantics.

Maybe add something like this to the native library:

class _Assert { const _Assert(bool b) : assert(b); } const _notWebNumbers = _Assert(0x10000000000000 != 0x10000000000000 + 1);

That should run that assert at compile-time.

We could also assert that you do have web numbers in the int64_emulated.dart file, just to catch the detection going wrong in the other direction for some reason.

(We should just define some compilation environment keys that allows asking the question directly, like if (dart.runtime.js_numbers) ....)

I think dart:html is deprecated. When it goes away, which we should assume it will, this version of the package will then break.

Good point. I'm not sure how else to import different things in dart2js and dart2wasm. The only libraries we can use right now are the deprecated ones as dart2wasm won't support those.

(We should just define some compilation environment keys that allows asking the question directly, like if (dart.runtime.js_numbers) ...

That's dart-lang/sdk#53811, which was opened in 2023.

It's probably not going to happen, we should find another way for now.

I think it's fine to use dart.library.html for now, because (1) AFAIK there's no other way (other than the deprecated interop libs, dart:html or others) to import different things in dart2wasm and dart2js (2) we already have a few other uses (e.g. in protobuf) (3) we need to release another way to distinguish dart2wasm from dart2js before removing dart:html because we can't just start to use the same code with dart2wasm and dart2js, that will cause performance regression and other breakage (due to number semantics differences, and maybe other differences too).

When we release this other way to distinguish dart2wasm from dart2js, we will have to revisit all these use sites and update them, but that's just life.

@lrhn do you see any other way?

Do wasm complies support dart:js_interop?

We discussed this with the dart2js team and it looks like we have some work to do before we can consider removing dart:html. Merging...

lrhn · 2025-09-05T12:50:15Z

pkgs/fixnum/lib/src/int64_emulated.dart

+    } else if (value is int) {
+      return Int64(value);
+    } else if (value is Int32) {
+      return value.toInt64() as Int64;


(This as Int64 looks unnecessary.)

That's because analyzer cannot properly analyze this package with conditional imports, it thinks I have two Int64s:

error - lib/src/int64_emulated.dart:172:14 - A value of type 'Int64 (where Int64 is defined in /usr/local/google/home/omersa/dart/core/pkgs/fixnum/lib/src/int64_native.dart)' can't be returned from the method '_promote' because it has a return type of 'Int64 (where Int64 is defined in /usr/local/google/home/omersa/dart/core/pkgs/fixnum/lib/src/int64_emulated.dart)'. - return_of_invalid_type - Int64 is defined in /usr/local/google/home/omersa/dart/core/pkgs/fixnum/lib/src/int64_native.dart at lib/src/int64_emulated.dart:15:28. - Int64 is defined in /usr/local/google/home/omersa/dart/core/pkgs/fixnum/lib/src/int64_emulated.dart at lib/src/int64_emulated.dart:14:7.

eernstg · 2025-09-05T13:14:39Z

Just a drive-by comment: I guess Int64 couldn't be an extension type on otherwise suitable platforms, because it must be a subtype of IntX?

osa1 · 2025-09-05T13:16:30Z

Just a drive-by comment: I guess Int64 couldn't be an extension type on otherwise suitable platforms, because it must be a subtype of IntX?

Good point. I don't know why Int64 and Int32 need a common superclass. Does anyone know?

eernstg · 2025-09-05T13:19:44Z

Perhaps because IntX <: Comparable<IntX>, which allows various sorting related APIs to be used. So it may not be important that Int32 and Int64 have a shared supertype, but people may want to sort lists of either.

osa1 · 2025-09-05T13:31:28Z

Couldn't we just implement Comparable directly in Int64 and Int32?

eernstg · 2025-09-05T16:48:48Z

I don't know if this will suffice:

extension type Int64(int value) implements num {
  // ...
}

int foo<X extends Comparable<X>>(X x1, X x2) => x1.compareTo(x2); // OK.

void main() => print(foo(Int64(42), Int64(24)));

It makes APIs callable even though they require X extends Comparable<X> for a type parameter X, so it might be possible to use an extension type like this in places where the code has previously used class Int64 extends IntX {...}. Feels like something that would be nice to see before believing it, though. ;-D

One difficulty would be that a return type could be IntX using the old approach (because IntX <: Comparable<IntX>, but it is not true that Int64 <: Comparable<Int64>, so the inferred type argument to foo would be IntX), and this will now have type num (which is inferred because num <: Comparable<num>).

However, I suspect that IntX is hardly ever used as the type of anything, and all those sort related APIs might very well return void.

lrhn · 2025-09-07T08:43:08Z

I don't think Int32 is actually needed for anything.

The original design apparently tried to make number-equivalent behavior for the two classes, including being comparable to each other and generally being compatible with int.

That's not what users needed. The vast majority of uses are just for ID numbers, and would work without any operations other than parse, toString and hashCode/==.

osa1 · 2025-09-08T09:04:29Z

I don't think Int32 is actually needed for anything.

FWIW we have internal users of this type and even IntX.

…hecks

Revisions updated by `dart tools/rev_sdk_deps.dart`. ai (https://github.com/dart-lang/ai/compare/1547a83..bc90433): bc90433 2025-09-04 Greg Spencer Add pub add format guidance (dart-lang/ai#278) 845c126 2025-09-04 dependabot[bot] Bump the github-actions group with 2 updates (dart-lang/ai#277) 5568958 2025-09-04 Jacob MacDonald add a GEMINI.md file (dart-lang/ai#279) core (https://github.com/dart-lang/core/compare/5c3e2c3..a4dc873): a4dc8738 2025-09-09 Ömer Sinan Ağacan Implement `Int64` as a wrapper for `int` when targeting native and Wasm (dart-lang/core#905) 1aa58ef5 2025-09-08 Devon Carew [fixnum] update the min. required dart sdk (dart-lang/core#907) 60f2b5d3 2025-09-08 Ömer Sinan Ağacan Run fixnum tests with dart2wasm (dart-lang/core#906) dartdoc (https://github.com/dart-lang/dartdoc/compare/53222e2..efff7c1): efff7c1f 2025-09-08 Sarah Zakarias Remove runtime_renderers.dart (dart-lang/dartdoc#4101) 4e2daf57 2025-09-05 Sarah Zakarias Rename LanguageFeature and remove FeatureSet mixin (dart-lang/dartdoc#4099) ecc48d00 2025-09-02 dependabot[bot] Bump the github-actions group across 1 directory with 3 updates (dart-lang/dartdoc#4098) protobuf (https://github.com/dart-lang/protobuf/compare/0a13935..971bcae): 971bcae 2025-09-08 Ömer Sinan Ağacan Use a map to cache the `valueOf` functions for enums (google/protobuf.dart#1047) 8750ed7 2025-09-05 Ömer Sinan Ağacan Sync internal Kythe support improvements (google/protobuf.dart#1048) web (https://github.com/dart-lang/web/compare/a152054..e2daa3a): e2daa3a 2025-09-04 Nikechukwu [interop] Add support for Intersection types (dart-lang/web#451) webdev (https://github.com/dart-lang/webdev/compare/52ad019..23aefeb): 23aefebe 2025-09-05 jensjoha Fix CI flake in dwds/test/hot_restart_breakpoints_test.dart (dart-lang/webdev#2685) Change-Id: I36cfbcdd884e8e0e38e24a9c7f3bcfcc15fdd9ff Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/449000 Reviewed-by: Konstantin Shcheglov <[email protected]> Commit-Queue: Konstantin Shcheglov <[email protected]> Auto-Submit: Devon Carew <[email protected]>

github-actions bot added the package:fixnum label Sep 5, 2025

osa1 added 6 commits September 5, 2025 12:13

Revert some of the changes

0d25584

Comment formatting

8bfaa9d

Revert more changes

d92edbd

Suppress test analysis errors

c481b83

Fix warns

6019508

Update changelog

01d91c1

osa1 marked this pull request as ready for review September 5, 2025 11:26

osa1 requested a review from a team as a code owner September 5, 2025 11:26

lrhn approved these changes Sep 5, 2025

View reviewed changes

Add docs to fromBytesBigEndian and fromBytes

1f32d44

osa1 added 2 commits September 9, 2025 09:30

Merge remote-tracking branch 'origin/main' into optimize_int64

440e67b

Access arrays from larger index to smaller to allow omitting bounds c…

cbd4ffd

…hecks

osa1 merged commit a4dc873 into dart-lang:main Sep 9, 2025
15 checks passed

osa1 deleted the optimize_int64 branch September 9, 2025 08:45

Implement Int64 as a wrapper for int when targeting native and Wasm #905

Implement Int64 as a wrapper for int when targeting native and Wasm #905

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Implement `Int64` as a wrapper for `int` when targeting native and Wasm #905

Implement `Int64` as a wrapper for `int` when targeting native and Wasm #905

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