roslyn.props

<Project>
  <!--
    The Roslyn API version the OPC UA analyzers and source generators are built
    against, and the runtime assemblies that version implies.

    Lives at the repository root, not under tools/, because Directory.Packages.props
    imports it: a partial-copy context that only takes the root files (the sample
    Dockerfiles do exactly that) must still be able to restore.

    Each analyzer ships under `analyzers/dotnet/<folder>/cs`. The .NET SDK loads the
    highest folder its compiler supports and silently ignores folders above it. Using a
    versioned folder rather than a bare `analyzers/dotnet/cs` is deliberate: a host older
    than the band below skips the analyzer instead of loading it and then failing at
    generator-initialization time.

    See https://learn.microsoft.com/visualstudio/extensibility/roslyn-version-support
    for the Roslyn package version to Visual Studio mapping.

    RoslynRuntimeVersion is the critical part. The compiler supplies
    System.Collections.Immutable and System.Reflection.Metadata itself, and the version it
    supplies is fixed by its Roslyn band (4.8 -> 7.x, 4.14 -> 9.x, 5.0 -> 9.x). An analyzer
    must therefore reference a version at or BELOW its band's - .NET satisfies a reference
    from a higher assembly version but never from a lower one - and must never ship a copy
    of its own, because a second copy binds a separate ImmutableArray<T> identity and the
    generator dies with MissingMethodException on its first Roslyn call. Either failure
    surfaces only as warning CS8784, so the consumer silently gets no generated code.

    Directory.Packages.props pins both packages to $(RoslynRuntimeVersion) and central
    transitive pinning propagates that through the whole analyzer closure - the generator,
    Opc.Ua.SourceGeneration.Core and Opc.Ua.Types. Keeping the pin here rather than as a
    loose version literal is what stops the closure drifting above the band again.

    Adding a band below the current floor is therefore not just another entry in this
    file. It only stays cheap while the new band shares $(RoslynRuntimeVersion): Roslyn
    4.14 and 5.0 both depend on System.Collections.Immutable 9.0.0, so one build of the
    non-Roslyn part of the closure serves both. Going lower - Roslyn 4.8 wants 7.x -
    would require building that whole closure, Opc.Ua.Types included, a second time
    against the older runtime.
  -->
  <PropertyGroup>
    <!-- Visual Studio 2026 18.0+ / .NET 10 SDK. -->
    <RoslynApiVersionVS2026>5.0.0</RoslynApiVersionVS2026>
    <!-- Visual Studio 2022 17.14+ / .NET 9 SDK. -->
    <RoslynApiVersionVS2022>4.14.0</RoslynApiVersionVS2022>
    <!-- System.Collections.Immutable / System.Reflection.Metadata that both
         Microsoft.CodeAnalysis $(RoslynApiVersionVS2022) and $(RoslynApiVersionVS2026)
         depend on. The two bands share it, so a single build of the non-Roslyn part of
         the closure (Opc.Ua.SourceGeneration.Core, Opc.Ua.Types) serves both. Roslyn
         4.14's csc runs on net9.0 and takes these from the shared framework, which is
         9.0.0.0 - matching this pin exactly. -->
    <RoslynRuntimeVersion>9.0.0</RoslynRuntimeVersion>
  </PropertyGroup>
  <PropertyGroup>
    <RoslynAnalyzerFolderVS2026>roslyn$(RoslynApiVersionVS2026.Substring(0, $(RoslynApiVersionVS2026.LastIndexOf('.'))))</RoslynAnalyzerFolderVS2026>
    <RoslynAnalyzerFolderVS2022>roslyn$(RoslynApiVersionVS2022.Substring(0, $(RoslynApiVersionVS2022.LastIndexOf('.'))))</RoslynAnalyzerFolderVS2022>
  </PropertyGroup>
</Project>