Declare the Sdk element in Microsoft.Build.Core.xsd

[Copilot]

Context

Microsoft.Build.Core.xsd declares an Sdk attribute on Project and Import, but never declares the Sdk element. Visual Studio therefore offers no IntelliSense for <Sdk /> or its Name/Version/MinimumVersion attributes, even though MSBuild fully supports the element and translates it into implicit imports.

<Project xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
    <Sdk Name="Microsoft.NET.Sdk" />   <!-- no completion, no attribute hints -->
</Project>

Changes Made

• New SdkType complex type — Name (required, non_empty_string), Version and MinimumVersion (optional), mirroring ProjectSdkElement and ProjectRootElement.GetImplicitImportNodes.
• Referenced Sdk from TargetOrImportType and ProjectLevelTagType — the Project content model requires at least one Target/Import, so membership in TargetOrImportType is what makes a project whose only child is <Sdk /> valid. Consistent with <Sdk> lowering to implicit imports.
• Deliberately not added to ProjectLevelTagExceptTargetOrImportType — the Project model is A* B C*; putting Sdk in both A and B makes it non-deterministic and the schema fails to compile (UPA violation).

Testing

Two tests in ProjectSchemaValidationHandler_Tests.cs: a project using Sdk elements (with all attributes, multiple elements, interleaved with Target) validates; an Sdk element missing Name is rejected.

Those tests are gated on FEATURE_XML_SCHEMA_VALIDATION (net472/Windows), so the schema was additionally exercised on Linux via a standalone XmlSchemaSet harness: the schema set compiles without UPA errors, the cases above behave as expected, and existing shapes (Target-only, Sdk attribute on Project) still validate.

Notes

Schema changes here need to be mirrored into the internal VS repo — see src/MSBuild/Update-MSBuildXsds.ps1 and documentation/wiki/Interactions-with-the-internal-repository.md.

_locID_text comments follow the existing localization convention in the file.

• Fixes Microsoft.Build.Core.xsd omits Sdk element #14603

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[Copilot]

Pull request overview

Adds explicit <Sdk /> element support to the MSBuild core XSD so editors (notably Visual Studio) can provide IntelliSense for SDK-style projects, aligning the schema with MSBuild’s existing behavior of lowering <Sdk /> to implicit imports.

Changes:

• Extends Microsoft.Build.Core.xsd to declare an Sdk element and a corresponding SdkType (with Name, Version, MinimumVersion attributes).
• Updates the schema’s project-level content model groups so <Sdk /> is allowed (including as the required “at least one …” member via TargetOrImportType).
• Adds unit tests validating that projects with <Sdk /> elements validate, and that missing required Name is rejected.

Show a summary per file

File	Description
src/MSBuild/MSBuild/Microsoft.Build.Core.xsd	Declares SdkType and allows <Sdk /> in the relevant project-level schema groups.
src/MSBuild.UnitTests/ProjectSchemaValidationHandler_Tests.cs	Adds schema-validation tests for valid/invalid <Sdk /> element usage.

Copilot's findings

• Files reviewed: 2/2 changed files
• Comments generated: 1