Generate AOT-compatible C# primitive responses

[Copilot]

C# convenience methods deserialize primitive responses with BinaryData.ToObjectFromJson<T>(), which relies on reflection and is not Native AOT-compatible.

• Deserialization: Replace reflection-based conversion with typed JsonElement reads for primitive and enum responses, including sync and async methods.
• Compatibility: Preserve nullable values, UTF-8 BOM support, and TimeSpan formatting. Leave plain-text, raw binary, model, and collection handling unchanged.

Generated int32 response conversion:

using Stream stream = result.GetRawResponse().Content.ToStream();
using JsonDocument document = JsonDocument.Parse(stream);
return ClientResult.FromValue(document.RootElement.GetInt32(), result.GetRawResponse());

• Fixes Generate AOT compatible code when an operation returns a primitive #11930

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npm i https://pkg.pr.new/@typespec/http-client-csharp@11931

commit: 9a84ed9

[Copilot]

🟢 Approval recommended

The implementation covers the intended response types and includes focused generation and runtime tests.

Pull request overview

Updates the C# client generator to deserialize primitive and enum responses without reflection, enabling Native AOT compatibility while preserving BOM and nullable handling.

Changes:

• Uses typed JsonElement reads for primitive and enum responses.
• Preserves plain-text behavior and constant-format TimeSpan conversion.
• Adds generation baselines and runtime BOM coverage for sync/async enum responses.

File summaries

File	Description
TestProjects/Local/Sample-TypeSpec/src/Generated/SampleTypeSpecClient.cs	Updates generated enum deserialization.
TestProjects/Local.Tests/ExtensibleEnumTests.cs	Tests sync/async BOM handling.
test/Providers/TestData/ScmMethodProviderCollectionTests/ScalarReturnTypeMethods(TimeSpanNullable).cs	Adds nullable TimeSpan baseline.
test/Providers/TestData/ScmMethodProviderCollectionTests/ScalarReturnTypeMethods(TimeSpan).cs	Updates TimeSpan baseline.
test/Providers/TestData/ScmMethodProviderCollectionTests/ScalarReturnTypeMethods(String).cs	Updates string baseline.
test/Providers/TestData/ScmMethodProviderCollectionTests/ScalarReturnTypeMethods(Single).cs	Updates float baseline.
test/Providers/TestData/ScmMethodProviderCollectionTests/ScalarReturnTypeMethods(Int64).cs	Updates long baseline.
test/Providers/TestData/ScmMethodProviderCollectionTests/ScalarReturnTypeMethods(Int32NullableAsync).cs	Adds async nullable integer baseline.
test/Providers/TestData/ScmMethodProviderCollectionTests/ScalarReturnTypeMethods(Int32Nullable).cs	Adds nullable integer baseline.
test/Providers/TestData/ScmMethodProviderCollectionTests/ScalarReturnTypeMethods(Int32Async).cs	Adds async integer baseline.
test/Providers/TestData/ScmMethodProviderCollectionTests/ScalarReturnTypeMethods(Int32).cs	Updates integer baseline.
test/Providers/TestData/ScmMethodProviderCollectionTests/ScalarReturnTypeMethods(Double).cs	Updates double baseline.
test/Providers/TestData/ScmMethodProviderCollectionTests/ScalarReturnTypeMethods(Decimal).cs	Adds decimal baseline.
test/Providers/TestData/ScmMethodProviderCollectionTests/ScalarReturnTypeMethods(DateTimeOffset).cs	Updates date-time baseline.
test/Providers/TestData/ScmMethodProviderCollectionTests/ScalarReturnTypeMethods(BooleanNullable).cs	Adds nullable boolean baseline.
test/Providers/TestData/ScmMethodProviderCollectionTests/ScalarReturnTypeMethods(Boolean).cs	Updates boolean baseline.
test/Providers/TestData/ScmMethodProviderCollectionTests/PlainTextReturnTypeMethods.cs	Verifies plain-text handling.
test/Providers/TestData/ScmMethodProviderCollectionTests/EnumReturnTypeMethods(True,True,True).cs	Covers nullable extensible string enum.
test/Providers/TestData/ScmMethodProviderCollectionTests/EnumReturnTypeMethods(True,True,False).cs	Covers extensible string enum.
test/Providers/TestData/ScmMethodProviderCollectionTests/EnumReturnTypeMethods(True,False,False).cs	Covers fixed string enum.
test/Providers/TestData/ScmMethodProviderCollectionTests/EnumReturnTypeMethods(False,True,False).cs	Covers extensible integer enum.
test/Providers/TestData/ScmMethodProviderCollectionTests/EnumReturnTypeMethods(False,False,True).cs	Covers nullable fixed integer enum.
test/Providers/TestData/ScmMethodProviderCollectionTests/EnumReturnTypeMethods(False,False,False).cs	Covers fixed integer enum.
test/Providers/ScmMethodProviderCollectionTests.cs	Expands scalar and enum generation tests.
test/Providers/ClientProviders/TestData/ClientProviderTests/BackCompatibility_NewRequiredParameterDoesNotAddBackCompatOverload.cs	Refreshes generated baseline.
test/Providers/ClientProviders/TestData/ClientProviderTests/BackCompatibility_NewOptionalParameterWithReservedName.cs	Refreshes generated baseline.
test/Providers/ClientProviders/TestData/ClientProviderTests/BackCompatibility_NewOptionalNonBodyParameterAddedWithPathAndHeaderParameters.cs	Refreshes generated baseline.
test/Providers/ClientProviders/TestData/ClientProviderTests/BackCompatibility_NewOptionalNonBodyParameterAddedWithModelBody.cs	Refreshes generated baseline.
test/Providers/ClientProviders/TestData/ClientProviderTests/BackCompatibility_NewOptionalNonBodyParameterAdded.cs	Refreshes generated baseline.
test/Providers/ClientProviders/TestData/ClientProviderTests/BackCompatibility_NewOptionalBodyParameterDoesNotAddBackCompatOverload.cs	Refreshes generated baseline.
test/Providers/ClientProviders/TestData/ClientProviderTests/BackCompatibility_MultipleNewOptionalNonBodyParametersAdded.cs	Refreshes generated baseline.
test/Providers/ClientProviders/TestData/ClientProviderTests/BackCompatibility_ConvenienceMethodParamOrderChanged(Sync).cs	Adds sync body baseline.
test/Providers/ClientProviders/TestData/ClientProviderTests/BackCompatibility_ConvenienceMethodParamOrderChanged(Async).cs	Adds async body baseline.
test/Providers/ClientProviders/TestData/ClientProviderTests/BackCompatibility_BothMethodsParamOrderChanged(Sync).cs	Adds sync compatibility baseline.
test/Providers/ClientProviders/TestData/ClientProviderTests/BackCompatibility_BothMethodsParamOrderChanged(Async).cs	Adds async compatibility baseline.
test/Providers/ClientProviders/ClientProviderTests.cs	Moves body assertions to baseline files.
src/Providers/ScmMethodProviderCollection.cs	Implements typed response deserialization.

Review details

• Files reviewed: 36/37 changed files
• Comments generated: 0
• Review effort level: Balanced

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[Jorge Rangel (jorgerangel-msft)]

Copilot there's spelling errors we should address by simply changing the test to avoid the warning / error :

 cspell --no-progress .
packages/http-client-csharp/generator/TestProjects/Local.Tests/ExtensibleEnumTests.cs:25:62 - Unknown word (FEFF)

[Copilot]

🟢 Approval recommended

The implementation is scoped, preserves documented compatibility behavior, and has representative generation and runtime coverage.

Review details

• Files reviewed: 38/39 changed files
• Comments generated: 0 new
• Review effort level: Balanced

[Copilot]

Copilot there's spelling errors we should address by simply changing the test to avoid the warning / error :

Fixed in 5c0d5d6 by adding a // cspell:ignore FEFF comment at the top of the file. Verified npx cspell --no-progress now reports 0 issues for this file.

[Copilot]

🟡 Changes recommended

BOM-prefixed JSON still fails parsing, and custom duration encodings can now crash generation.

Get a fresh assessment by requesting another Copilot review.

Review details

• Files reviewed: 85/87 changed files
• Comments generated: 2
• Review effort level: Balanced

[Copilot]

🟡 Changes recommended

BOM handling misses some primitive types, and several generated and baseline outputs remain stale.

Get a fresh assessment by requesting another Copilot review.

Review details

Suppressed comments (1)

packages/http-client-csharp/generator/TestProjects/Local.Tests/ExtensibleEnumTests.cs:48

• This BOM test currently calls the checked-in SampleTypeSpecClient, whose changed GetInt32Value methods still use JsonDocument.Parse(stream) (SampleTypeSpecClient.cs:1147-1160) and therefore reject this BOM-prefixed payload. Regenerate the Local sample after the new TrimStart('\uFEFF') generator path so the test exercises—and passes with—the implementation under review.

• Files reviewed: 86/89 changed files
• Comments generated: 2
• Review effort level: Balanced

[Copilot]

🔵 Needs a closer look

Valid custom duration encodings still cause a generation-time exception instead of a diagnostic and fallback.

Review details

Suppressed comments (1)

packages/http-client-csharp/generator/Microsoft.TypeSpec.Generator.ClientModel/src/Providers/ScmMethodProviderCollection.cs:988

• Custom DurationKnownEncoding values are valid inputs (Microsoft.TypeSpec.Generator.Input/test/DurationKnownEncodingTests.cs:34-39), so this still crashes generation for a supported code model. Follow the existing unsupported-serialization warning-and-fallback pattern in MrwSerializationTypeDefinition.cs:2064-2071 and update the test that currently expects InvalidOperationException.

                _ => content.As<string>().ParseTimeSpan(Literal(format.ToFormatSpecifier() ?? throw new InvalidOperationException($"Unsupported duration serialization format: {format}")))

• Files reviewed: 86/89 changed files
• Comments generated: 0 new
• Review effort level: Balanced

[Copilot]

Jorge Rangel (@jorgerangel-msft) Unfortunately I hit an unexpected error while processing your comment. I've automatically reported this to GitHub.

You can ask me to try again later by mentioning me in a new comment.

If you want to contact GitHub about this error, please mention the following identifier so they can better serve you: 047a492b-da0e-4683-9a49-834efaf99444

Sorry for the inconvenience!

[Copilot]

🟡 Changes recommended

Some JSON primitive types still bypass BOM-safe parsing, and the new diagnostic is not fully asserted.

Get a fresh assessment by requesting another Copilot review.

Review details

Suppressed comments (1)

packages/http-client-csharp/generator/Microsoft.TypeSpec.Generator.ClientModel/src/Providers/ScmMethodProviderCollection.cs:305

• JSON Uri, byte, and sbyte responses still take this fallback because TypeFactory.cs:157-167 produces those CLR types but IsConvertibleFromBinaryData excludes them. The fallback at lines 310-311 parses BinaryData without the BOM stripping used at lines 650-657, so a BOM-prefixed response still throws; route these primitive types through the same BOM-safe document setup and cover one in the runtime matrix.

                    IsConvertibleFromBinaryData(responseBodyType)
                        || (IsPlainTextParsableType(responseBodyType) && HasOnlyPlainTextContentType())

• Files reviewed: 86/89 changed files
• Comments generated: 1
• Review effort level: Balanced

[Copilot]

🔵 Needs a closer look

The unsupported-duration fallback test does not assert the newly required diagnostic code or severity.

Review details

Suppressed comments (1)

packages/http-client-csharp/generator/Microsoft.TypeSpec.Generator.ClientModel/test/Providers/ScmMethodProviderCollectionTests.cs:1793

• This fallback test only compares generated code, so it still passes if the newly required unsupported-serialization diagnostic is removed or its code/severity regresses. Capture the emitter diagnostic and assert it alongside the fallback baseline so the new diagnostic path is actually covered.

            // An unsupported/custom duration encoding has no known format specifier, so generation reports a
            // diagnostic and falls back to the constant ("c") format instead of throwing.
            Assert.AreEqual(Helpers.GetExpectedFromFile("Constant", method: "PlainTextDurationReturnTypeMethods"), writer.ToString(false));

• Files reviewed: 86/89 changed files
• Comments generated: 0 new
• Review effort level: Balanced

[Copilot]

🟢 Approval recommended

The implementation covers the affected conversion paths with broad baselines and targeted runtime BOM tests.

Review details

• Files reviewed: 89/92 changed files
• Comments generated: 0 new
• Review effort level: Balanced

[Copilot]

🟡 Changes recommended

Supported numeric duration encodings currently emit a spurious unsupported-serialization diagnostic.

Get a fresh assessment by requesting another Copilot review.

Review details

• Files reviewed: 89/92 changed files
• Comments generated: 1
• Review effort level: Balanced

[Copilot]

🟡 Changes recommended

Plain-text media types are matched too strictly, and the primary JSON primitive path lacks runtime coverage.

Get a fresh assessment by requesting another Copilot review.

Review details

• Files reviewed: 87/88 changed files
• Comments generated: 2
• Review effort level: Balanced

[Copilot]

🔵 Needs a closer look

Mixed JSON/plain-text responses can select JSON parsing even when the server legally returns raw text.

Review details

Suppressed comments (1)

packages/http-client-csharp/generator/Microsoft.TypeSpec.Generator.ClientModel/src/Providers/ScmMethodProviderCollection.cs:1061

• Mixed application/json/text/plain responses are always sent down the JSON path, but RestClientProvider.cs:1794-1808 advertises every declared media type, so a server may legally return raw text; a string or enum body such as Monday will then reach JsonDocument.Parse and throw. Choose the conversion from the actual response Content-Type (or request only one representation), and cover the mixed case with a non-JSON-compatible string/enum value.

        private bool HasOnlyPlainTextContentType()
        {
            var contentTypes = ServiceMethod.Operation.Responses
                .Where(r => r.IsErrorResponse is false)
                .SelectMany(r => r.ContentTypes);
            return contentTypes.Any() && contentTypes.All(contentType => contentType.Contains("text/plain", StringComparison.OrdinalIgnoreCase));

• Files reviewed: 87/88 changed files
• Comments generated: 0 new
• Review effort level: Balanced

[JoshLove-msft]

Re-reviewed the updates through 9b2f4e2. The earlier duration wire-encoding finding is addressed, and nullable plain-text null handling now accepts surrounding whitespace. No new actionable findings; existing review threads and explicitly deferred items were not duplicated.

--generated by Copilot

[Copilot]

🟡 Changes recommended

Media-type detection can incorrectly route JSON responses through raw-text parsing.

Get a fresh assessment by requesting another Copilot review.

Review details

Suppressed comments (1)

Previously missed (1) — in code that hasn't changed since the last review.

packages/http-client-csharp/generator/Microsoft.TypeSpec.Generator.ClientModel/src/Providers/ScmMethodProviderCollection.cs:654

• The PR’s documented generated shape parses Content.ToStream(), but this instead transcodes every JSON response to a UTF-16 string before parsing. JsonDocument.Parse(Stream) accepts a leading UTF-8 BOM directly, so generate and dispose a content stream here (and in the fallback path) to avoid the extra full-body allocation.

• Files reviewed: 87/88 changed files
• Comments generated: 1
• Review effort level: Balanced

[JoshLove-msft]

Copilot Please remove the BOM-specific handling (TrimStart('\uFEFF')) throughout this PR. We do not expect BOM-prefixed HTTP response bodies and do not want to preserve that compatibility behavior. Parse JSON directly from BinaryData without the intermediate string conversion, and leave plain-text response content unchanged.

Remove the BOM-specific test cases and comments while retaining the normal primitive, enum, nullable, and sync/async coverage. Update the affected baselines and regenerate the test libraries. Please do not reintroduce BOM handling in response to earlier review comments; this is an intentional decision.

--generated by Copilot

[Copilot]

🔵 Needs a closer look

String transcoding weakens malformed UTF-8 validation in both new JSON parsing paths.

Review details

Suppressed comments (2)

Previously missed (1) — in code that hasn't changed since the last review.

packages/http-client-csharp/generator/Microsoft.TypeSpec.Generator.ClientModel/src/Providers/ScmMethodProviderCollection.cs:310

• This fallback also transcodes the raw bytes through a replacement-fallback UTF-8 string before JSON parsing, which can silently accept malformed response bytes. Use the stream overload so BOM handling does not weaken JSON's UTF-8 validation.

This issue also appears on line 650 of the same file.

packages/http-client-csharp/generator/Microsoft.TypeSpec.Generator.ClientModel/src/Providers/ScmMethodProviderCollection.cs:654

• Decoding the response through BinaryData.ToString() replaces malformed UTF-8 with U+FFFD, so an invalid JSON string can now deserialize successfully instead of raising a JSON error. Parse Content.ToStream() directly instead; JsonDocument.Parse(Stream) accepts a leading UTF-8 BOM while preserving strict UTF-8 validation.

                var contentExpression = data.InvokeToString().Invoke(nameof(string.TrimStart), Literal('\uFEFF')).As<string>();
                var statements = new MethodBodyStatement[]
                {
                    Declare("responseContent", typeof(string), contentExpression, out var responseContent),
                    UsingDeclare("document", JsonDocumentSnippets.Parse(responseContent), out var document)

• Files reviewed: 87/88 changed files
• Comments generated: 0 new
• Review effort level: Balanced

[Copilot]

Copilot Please remove the BOM-specific handling (TrimStart('\uFEFF')) throughout this PR. We do not expect BOM-prefixed HTTP response bodies and do not want to preserve that compatibility behavior....

Addressed in 9a84ed9. JSON response conversion now parses BinaryData directly, plain-text content is unchanged, BOM-specific handling and cases are removed, and generated libraries/baselines were regenerated.

[Copilot]

🟡 Changes recommended

Both JSON and plain-text conversion paths currently break the stated UTF-8 BOM compatibility requirement.

Get a fresh assessment by requesting another Copilot review.

Review details

Suppressed comments (1)

packages/http-client-csharp/generator/Microsoft.TypeSpec.Generator.ClientModel/src/Providers/ScmMethodProviderCollection.cs:647

• Parsing BinaryData directly selects the ReadOnlyMemory<byte> JSON overload, which explicitly rejects a UTF-8 BOM, so BOM-prefixed primitive responses fail despite the PR's compatibility requirement. Generate a stream and parse that overload instead, and cover this with a BOM regression test.

                    UsingDeclare("document", data.Parse(), out var document)

• Files reviewed: 87/88 changed files
• Comments generated: 1
• Review effort level: Balanced