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XmlSerializer: route formatted primitive output through span-based raw writer fast path#128505

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XmlSerializer: route formatted primitive output through span-based raw writer fast path#128505
Copilot wants to merge 3 commits into
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copilot/optimize-xml-serialization-primitives

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Copilot AI commented May 22, 2026 •
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This change targets the primitive-write hot path in XmlSerializationWriter, where formatted values (notably decimal) were still funneled through WriteRaw(char[], ...) and could incur avoidable conversions in the underlying writer stack. It adds an internal span-based raw-write path so default raw text writers can consume formatted primitive data directly.

  • Serializer hot-path update

    • WriteTypedPrimitive now uses a span path when the writer is XmlWellFormedWriter, passing _primitivesBuffer.AsSpan(0, charsWritten) into an internal raw-write overload.
    • Existing char[] fallback remains for non-XmlWellFormedWriter cases.

  • Raw writer pipeline extension

    • Added internal virtual WriteRaw(ReadOnlySpan<char>) to XmlRawWriter (default fallback to existing string-based behavior).
    • Added internal WriteRaw(ReadOnlySpan<char>) in XmlWellFormedWriter to preserve state machine behavior and forward to underlying raw writers.

  • Fast-path implementations

    • XmlUtf8RawTextWriter and XmlEncodedRawTextWriter now override span-based raw writing and feed spans directly into existing raw char-checking/output routines.
    • Matching updates were made in XmlRawTextWriterGenerator.ttinclude and the generated writer sources.
    • Indent writer variants were also updated so span raw writes still set mixed-content state correctly.

  • Coverage update

    • Added Xml_DecimalArrayAsRoot to XmlSerializerTests.RuntimeOnly.cs to exercise primitive-array serialization/round-trip on this path.
// XmlSerializationWriter.WriteTypedPrimitive
if (_w is XmlWellFormedWriter wellFormedWriter)
{
    wellFormedWriter.WriteRaw(_primitivesBuffer.AsSpan(0, charsWritten));
}
else
{
    _w.WriteRaw(_primitivesBuffer, 0, charsWritten);
}

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  • bla
    • Triggering command: /home/REDACTED/work/runtime/runtime/artifacts/bin/testhost/net11.0-linux-Debug-x64/dotnet /home/REDACTED/work/runtime/runtime/artifacts/bin/testhost/net11.0-linux-Debug-x64/dotnet exec --runtimeconfig System.Private.Xml.Tests.runtimeconfig.json --depsfile System.Private.Xml.Tests.deps.json /home/REDACTED/.nuget/packages/microsoft.dotnet.xunitconsoleREDACTED/2.9.3-beta.26257.113/build/../tools/net/xunit.console.dll System.Private.Xml.Tests.dll -xml testResults.xml -nologo -notrait category=OuterLoop -notrait category=failing e/.dotnet/bash urity.Cryptograp/home/REDACTED/work/runtime/runtime/.dotnet/dotnet /lib/x86_64-linu/home/REDACTED/work/runtime/runtime/artifacts/bin/ILLink.Tasks/Debug/net/illink.dll /usr/bin/../lib/@/tmp/MSBuildTempZLMhIi/tmp0ef4b4df5791499bb66cd3620b8aacff.rsp PORTS (dns block)
    • Triggering command: /home/REDACTED/work/runtime/runtime/artifacts/bin/testhost/net11.0-linux-Debug-x64/dotnet /home/REDACTED/work/runtime/runtime/artifacts/bin/testhost/net11.0-linux-Debug-x64/dotnet exec --runtimeconfig System.Private.Xml.Tests.runtimeconfig.json --depsfile System.Private.Xml.Tests.deps.json /home/REDACTED/.nuget/packages/microsoft.dotnet.xunitconsoleREDACTED/2.9.3-beta.26257.113/build/../tools/net/xunit.console.dll System.Private.Xml.Tests.dll -xml testResults.xml -nologo -notrait category=OuterLoop -notrait category=failing e/.dotnet/sdk/11.0.100-preview.5.26227.104/MSBuild ORT_SHARED_API -git OS -DHOST_AMD64 e/.dotnet/sdk/11HEAD (dns block)
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    • Triggering command: /home/REDACTED/work/runtime/runtime/artifacts/bin/testhost/net11.0-linux-Debug-x64/dotnet /home/REDACTED/work/runtime/runtime/artifacts/bin/testhost/net11.0-linux-Debug-x64/dotnet exec --runtimeconfig System.Private.Xml.Tests.runtimeconfig.json --depsfile System.Private.Xml.Tests.deps.json /home/REDACTED/.nuget/packages/microsoft.dotnet.xunitconsoleREDACTED/2.9.3-beta.26257.113/build/../tools/net/xunit.console.dll System.Private.Xml.Tests.dll -xml testResults.xml -nologo -notrait category=OuterLoop -notrait category=failing e/.dotnet/sdk/11.0.100-preview.5.26227.104/MSBuild ORT_SHARED_API -git OS -DHOST_AMD64 e/.dotnet/sdk/11HEAD (dns block)
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    • Triggering command: /home/REDACTED/work/runtime/runtime/artifacts/bin/testhost/net11.0-linux-Debug-x64/dotnet /home/REDACTED/work/runtime/runtime/artifacts/bin/testhost/net11.0-linux-Debug-x64/dotnet exec --runtimeconfig System.Private.Xml.Tests.runtimeconfig.json --depsfile System.Private.Xml.Tests.deps.json /home/REDACTED/.nuget/packages/microsoft.dotnet.xunitconsoleREDACTED/2.9.3-beta.26257.113/build/../tools/net/xunit.console.dll System.Private.Xml.Tests.dll -xml testResults.xml -nologo -notrait category=OuterLoop -notrait category=failing e/.dotnet/bash urity.Cryptograp/home/REDACTED/work/runtime/runtime/.dotnet/dotnet /lib/x86_64-linu/home/REDACTED/work/runtime/runtime/artifacts/bin/ILLink.Tasks/Debug/net/illink.dll /usr/bin/../lib/@/tmp/MSBuildTempZLMhIi/tmp0ef4b4df5791499bb66cd3620b8aacff.rsp PORTS (dns block)
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    • Triggering command: /home/REDACTED/work/runtime/runtime/artifacts/bin/testhost/net11.0-linux-Debug-x64/dotnet /home/REDACTED/work/runtime/runtime/artifacts/bin/testhost/net11.0-linux-Debug-x64/dotnet exec --runtimeconfig System.Private.Xml.Tests.runtimeconfig.json --depsfile System.Private.Xml.Tests.deps.json /home/REDACTED/.nuget/packages/microsoft.dotnet.xunitconsoleREDACTED/2.9.3-beta.26257.113/build/../tools/net/xunit.console.dll System.Private.Xml.Tests.dll -xml testResults.xml -nologo -notrait category=OuterLoop -notrait category=failing e/.dotnet/sdk/11.0.100-preview.5.26227.104/MSBuild ORT_SHARED_API -git OS -DHOST_AMD64 e/.dotnet/sdk/11HEAD (dns block)

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Copilot AI requested review from Copilot and removed request for Copilot May 22, 2026 22:40
Copilot AI linked an issue May 22, 2026 that may be closed by this pull request
[Xml Serialization] Possible optimization when writing primitive objects #67222
Open
@StephenMolloy
Optimize XmlSerializer primitive raw writes with span-based raw write…
5d218d2 
…r path

Agent-Logs-Url: https://github.com/dotnet/runtime/sessions/29c71057-04f8-4c4e-9c5f-5442fe10a352

Co-authored-by: StephenMolloy <19562826+StephenMolloy@users.noreply.github.com>
Copilot AI requested review from Copilot and removed request for Copilot May 22, 2026 23:09
@StephenMolloy
XmlSerializer: route formatted primitive output through span-based ra…
c0512d2 
…w writer fast path

Agent-Logs-Url: https://github.com/dotnet/runtime/sessions/29c71057-04f8-4c4e-9c5f-5442fe10a352

Co-authored-by: StephenMolloy <19562826+StephenMolloy@users.noreply.github.com>
Copilot AI requested review from Copilot and removed request for Copilot May 22, 2026 23:30
Copilot AI changed the title [WIP] Optimize Xml serialization for primitive objects XmlSerializer: route formatted primitive output through span-based raw writer fast path May 22, 2026
Copilot AI requested a review from StephenMolloy May 22, 2026 23:31
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[Xml Serialization] Possible optimization when writing primitive objects

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