Directory.Build.targets

<Project>
  <!--
    Per-project opt-in for the CI per-TFM build matrix: when a `.csproj`
    sets `<RestrictForLegacyTfm>true</RestrictForLegacyTfm>` in its main
    `PropertyGroup`, this Directory.Build.targets makes the project a
    no-op build (empty Library, no compile items, no references) for
    `dotnet build … /p:CustomTestTarget=<legacy>` invocations where
    `<legacy>` is one of `net472` / `net48` / `netstandard2.0` /
    `netstandard2.1`.  Use this for projects that are `.NET 8+` only
    (e.g. `PublishAot=true`, `ModelContextProtocol` server, TUnit AOT
    tests) and therefore can't participate in a `UA.slnx` build pinned
    to a legacy TFM via `CustomTestTarget`.

    The project still loads in the `.slnx` graph so the matrix prep
    script discovers it, but `Compile` / `ProjectReference` /
    `PackageReference` / `AdditionalFiles` / `None` / `Content` are all
    cleared and `OutputType` flips to `Library`, producing an empty
    assembly without dragging the project's `.NET 8+` source through
    the C# compiler against the restricted dependency set.

    Targets are deliberately NOT overridden here - same-named targets
    in `Directory.Build.targets` ALWAYS replace the SDK definitions
    (the `Condition` only gates execution, not registration), which
    would silently break the SDK's restore in unrestricted builds
    (e.g. the GitHub Actions `dotnet publish` / `dotnet test` flows
    that don't pass `CustomTestTarget`).

    Projects that don't set `RestrictForLegacyTfm` are completely
    unaffected by this file - every condition below evaluates to
    false and no items / properties / targets are touched.
  -->
  <PropertyGroup>
    <_RestrictedToLegacyTfm
        Condition="'$(RestrictForLegacyTfm)' == 'true' and ('$(CustomTestTarget)' == 'net48' or '$(CustomTestTarget)' == 'net472' or '$(CustomTestTarget)' == 'netstandard2.0' or '$(CustomTestTarget)' == 'netstandard2.1')">true</_RestrictedToLegacyTfm>
  </PropertyGroup>
  <PropertyGroup Condition="'$(_RestrictedToLegacyTfm)' == 'true'">
    <OutputType>Library</OutputType>
    <EnableDefaultCompileItems>false</EnableDefaultCompileItems>
    <EnableDefaultEmbeddedResourceItems>false</EnableDefaultEmbeddedResourceItems>
    <EnableDefaultNoneItems>false</EnableDefaultNoneItems>
    <EnableDefaultContentItems>false</EnableDefaultContentItems>
    <IsPackable>false</IsPackable>
    <PackAsTool>false</PackAsTool>
    <PublishAot>false</PublishAot>
    <GenerateAssemblyInfo>false</GenerateAssemblyInfo>
    <GenerateTargetFrameworkAttribute>false</GenerateTargetFrameworkAttribute>
  </PropertyGroup>
  <ItemGroup Condition="'$(_RestrictedToLegacyTfm)' == 'true'">
    <Compile Remove="@(Compile)" />
    <ProjectReference Remove="@(ProjectReference)" />
    <PackageReference Remove="@(PackageReference)" />
    <AdditionalFiles Remove="@(AdditionalFiles)" />
    <None Remove="@(None)" />
    <Content Remove="@(Content)" />
  </ItemGroup>
  <Target Name="_LogSkippedForLegacyTfm" BeforeTargets="Build" Condition="'$(_RestrictedToLegacyTfm)' == 'true'">
    <Message Importance="high" Text="Skipping $(MSBuildProjectName) for CustomTestTarget=$(CustomTestTarget) (.NET 8+ only)." />
  </Target>
</Project>