[browser] Marshalling support float[], Span<float> and ArraySegment<float>

[ArcadeMode]

Fixes #97380.
Fixes #123706

Implementation is functional for CoreCLR and Mono. Added import and export tests to demonstrate.

How do I go about updating the docs? (and which version might see these changes for that matter, net10/11?)

[pavelsavara]

@ArcadeMode feel free to ping me on your PRs, so that I can label it properly.

[ArcadeMode]

@pavelsavara to verify that i am following contribution guidelines: I have already changed and implemented an API change, is it okay to ask for API review in PR like this?

i.e. would a similar approach suffice for #97381 or should this be done through the issue or otherwise?

[Copilot]

Pull request overview

This pull request adds marshaling support for float[], Span<float>, and ArraySegment<float> between C# and JavaScript in the browser WASM interop layer, addressing issue #97380.

Changes:

• Added MemoryViewType.Single enum value and corresponding Float32Array handling
• Implemented C# marshaling methods for float arrays, spans, and array segments
• Updated TypeScript marshaling code to handle Single type in both native and mono implementations
• Added comprehensive test coverage for JSImport and JSExport scenarios with float types
• Updated code generator to recognize Single type patterns

Reviewed changes

Copilot reviewed 16 out of 16 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
src/native/libs/System.Runtime.InteropServices.JavaScript.Native/interop/marshaled-types.ts	Added MemoryViewType.Single enum and Float32Array view creation
src/native/libs/System.Runtime.InteropServices.JavaScript.Native/interop/marshal.ts	Added Single to elementSizeMap with 4-byte size
src/native/libs/System.Runtime.InteropServices.JavaScript.Native/interop/marshal-to-js.ts	Implemented Single type marshaling for arrays, spans, and array segments
src/native/libs/System.Runtime.InteropServices.JavaScript.Native/interop/marshal-to-cs.ts	Implemented Single type unmarshaling and view type checking
src/mono/browser/runtime/marshal.ts	Added Single to array_element_size function and MemoryViewType enum, refactored to if-else chains
src/mono/browser/runtime/marshal-to-js.ts	Implemented Single type marshaling for arrays, spans, and array segments in mono runtime
src/mono/browser/runtime/marshal-to-cs.ts	Implemented Single type unmarshaling and view type checking in mono runtime
src/libraries/System.Runtime.InteropServices.JavaScript/src/System/Runtime/InteropServices/JavaScript/Marshaling/JSMarshalerArgument.Single.cs	Added ToJS/ToManaged methods for float[], Span, and ArraySegment
src/libraries/System.Runtime.InteropServices.JavaScript/src/System/Runtime/InteropServices/JavaScript/Marshaling/JSMarshalerArgument.Object.cs	Added float[] handling in ToJS method for object parameters
src/libraries/System.Runtime.InteropServices.JavaScript/src/System/Runtime/InteropServices/JavaScript/JSMarshalerType.cs	Updated validation methods to accept Single type in arrays, spans, and segments; removed extraneous blank line
src/libraries/System.Runtime.InteropServices.JavaScript/ref/System.Runtime.InteropServices.JavaScript.cs	Added public API surface for float[], Span, and ArraySegment marshaling
src/libraries/System.Runtime.InteropServices.JavaScript/gen/JSImportGenerator/JSGeneratorFactory.cs	Added generator patterns for Single type arrays, spans, and array segments
src/libraries/System.Runtime.InteropServices.JavaScript/tests/.../JavaScriptTestHelper.cs	Added test helper methods for Single type JSImport and JSExport scenarios
src/libraries/System.Runtime.InteropServices.JavaScript/tests/.../JSInteropTestBase.cs	Added MarshalSingleArrayCases test data
src/libraries/System.Runtime.InteropServices.JavaScript/tests/.../JSImportTest.cs	Added comprehensive tests for float arrays, spans, and array segments; improved variable naming in Double/Int32 tests
src/libraries/System.Runtime.InteropServices.JavaScript/tests/.../JSExportTest.cs	Added JSExport tests for Span and ArraySegment

[pavelsavara]

is it okay to ask for API review in PR like this?

The process is described here https://github.com/dotnet/runtime/blob/main/docs/project/api-review-process.md

You need to create dedicated issue according to the issue template for API suggestion.

You can also look at successfully approved APIs

[pavelsavara]

The code looks good. I added NO-MERGE label until we pass the API review.

[Copilot]

Pull request overview

Copilot reviewed 16 out of 16 changed files in this pull request and generated 1 comment.

[pavelsavara]

Please add few float signatures so that the generated code appears in src/libraries/System.Runtime.InteropServices.JavaScript/tests/JSImportGenerator.UnitTest/Compiles.cs

[Copilot]

Pull request overview

Copilot reviewed 16 out of 16 changed files in this pull request and generated no new comments.

[ArcadeMode]

@pavelsavara just a heads up that I've adressed your review comment

[stephentoub]

🤖 Copilot Code Review — PR #123642

Holistic Assessment

Motivation: This PR addresses a legitimate gap in the JS interop marshalling layer. Issue #97380 and #123706 clearly document the need for float[], Span<float>, and ArraySegment<float> support for WebGPU and neural network scenarios where float is preferred over double for memory bandwidth and GPU RAM constraints.

Approach: The implementation correctly mirrors the existing double marshalling patterns. The C# marshalling code in JSMarshalerArgument.Single.cs follows the same structure as JSMarshalerArgument.Double.cs, and the TypeScript changes consistently add Single support across both Mono browser runtime and CoreCLR interop layers.

Summary: ⚠️ Needs Human Review. The core implementation appears correct and follows established patterns. However, there are a few items requiring attention before merge, and one outstanding reviewer request that should be addressed.

---

Detailed Findings

✅ C# Marshalling Implementation — Correct

The JSMarshalerArgument.Single.cs additions are correct:

• ToManaged(out float[]? value) / ToJS(float[] value) correctly use Marshal.Copy with proper allocation size (value.Length * sizeof(float)) and set ElementType = MarshalerType.Single.
• ToManaged(out ArraySegment<float> value) / ToJS(ArraySegment<float> value) correctly compute byte offsets using sizeof(float).
• ToManaged(out Span<float> value) / ToJS(Span<float> value) follow the exact same pattern as double.

✅ TypeScript MemoryViewType Enum Alignment — Correct

Both src/mono/browser/runtime/marshal.ts and src/native/libs/System.Runtime.InteropServices.JavaScript.Native/interop/marshaled-types.ts define:

export const enum MemoryViewType {
    Byte = 0,
    Int32 = 1,
    Double = 2,
    Single = 3,  // New
}

The values are consistent between Mono and CoreCLR implementations.

✅ fixupPointer Alignment — Correct

The TypeScript uses fixupPointer(bufferPtr, 2) for Single (4-byte alignment, 2^2 = 4) vs fixupPointer(bufferPtr, 3) for Double (8-byte alignment, 2^3 = 8). This is correct.

✅ JSMarshalerType Validation — Correct

CheckArray and CheckArraySegment in JSMarshalerType.cs now include MarshalerType.Single.

✅ Object Marshalling — Correct

JSMarshalerArgument.Object.cs properly handles float[] in both ToManaged (when slot.ElementType == MarshalerType.Single) and ToJS (when typeof(float[]) == type).

⚠️ Ref Assembly API Placement — Minor Inconsistency

The new APIs in System.Runtime.InteropServices.JavaScript.cs are split:

• float[] APIs (lines 246-247) are correctly placed after float? and before double.
• Span<float> and ArraySegment<float> APIs (lines 314-317) are appended at the end, after ArraySegment<double>.

This is technically fine for binary compatibility but slightly inconsistent with the grouping pattern where Span/ArraySegment of the same element type should ideally be adjacent. The existing file doesn't follow strict type ordering anyway, so this is acceptable but could be cleaned up for consistency.

⚠️ Missing Generator Unit Test Signatures — Outstanding Reviewer Request

Per @pavelsavara's review comment, float[] signatures should be added to src/libraries/System.Runtime.InteropServices.JavaScript/tests/JSImportGenerator.UnitTest/CodeSnippets.cs so that the generated marshalling code appears in Compiles.cs output. Currently line 31 has:

string[] aa1, byte[] aab, double[] aad, int[] aai

This should also include float[] aaf to validate the generator produces correct code for the new float[] marshalling support.

💡 ToManaged(out float[]?) — Consider Checking ElementType

In ToManaged(out float[]? value), the code only checks slot.Type == MarshalerType.None but doesn't verify that slot.ElementType == MarshalerType.Single. This matches the double[] implementation pattern exactly, but if JS passes a different array type, the behavior would be undefined. This is consistent with existing code, so no change needed, but worth noting for the area owner.

💡 Test Coverage — Good but Could Be Expanded

The tests cover:

• Basic round-tripping with echo1_SingleArray, echo1_SpanOfSingle, echo1_ArraySegmentOfSingle
• Special float values: float.Pi, float.MaxValue, float.MinValue, float.NaN, float.PositiveInfinity, float.NegativeInfinity
• Export tests for ArraySegment<float> and Span<float>

Per @pavelsavara's review comment about testing "JS Array values of wrong type or JS number (double) above float.max", issue #123731 was filed to address type assertion issues separately.

✅ API Review Status

The PR correctly has NO-MERGE label pending API review approval for issue #123706. The proposed API surface matches the API proposal in the issue.

---

Summary

The implementation is well-structured and follows established patterns correctly. Before merge:

1. Required: API review approval for issue [API Proposal]: JavaScript marshalling support float[], Span<float> and ArraySegment<float> #123706
2. Should address: Add float[] signature to CodeSnippets.cs generator unit tests per reviewer request

The code itself is sound and ready for merge once these items are resolved.

[Copilot]

Pull request overview

Copilot reviewed 19 out of 19 changed files in this pull request and generated no new comments.

[pavelsavara]

/ba-g CI failures are OOM on helix (exit code 137)