Compile the MSTest generator against the Roslyn version it is packed for

src/Directory.Build.props

@@ -20,6 +20,15 @@
     <ImportVerifyMsbuildFiles Condition="'$(MSBuildProjectName)' != '' And $(MSBuildProjectName.EndsWith('Tests'))">true</ImportVerifyMsbuildFiles>
     <!-- Work around https://github.com/dotnet/sdk/issues/51265#issuecomment-3407578810 -->
     <RestoreEnablePackagePruning>false</RestoreEnablePackagePruning>
+    <!-- The Roslyn version the MSTest source generator compiles against, and the analyzers
+         folder Verify.MSTest packs it into. The two have to agree: a generator compiled
+         against a higher version than its folder claims is loaded by every compiler in
+         between and then skipped with CS9057, which silently disables [UsesVerify] and
+         surfaces only as "TestContext is null" at run time. Kept here so neither can move
+         without the other. Lower means more compilers are supported, so raise it only for
+         an API the generator actually needs.
+         https://learn.microsoft.com/en-us/visualstudio/extensibility/roslyn-version-support -->
+    <VerifyRoslynVersion>4.4</VerifyRoslynVersion>
   </PropertyGroup>
   <!-- This directory contains two solutions (Verify.slnx and VerifyDangling.slnx), so Verify cannot
        auto-discover the solution when a project is built outside of a solution context. Default to the

src/Verify.MSTest.SourceGenerator/Verify.MSTest.SourceGenerator.csproj

@@ -9,13 +9,15 @@
 
   <ItemGroup>
     <PackageReference Include="Microsoft.CodeAnalysis.Analyzers" PrivateAssets="all" />
-    <PackageReference Include="Microsoft.CodeAnalysis.CSharp" PrivateAssets="all" />
+    <!-- Overrides the central version, which the rest of the solution uses to consume
+         Roslyn. This assembly is loaded by the consumer's compiler instead, so it is
+         compiled against the oldest Roslyn it supports: the one named by the analyzers
+         folder it is packed into. See VerifyRoslynVersion in Directory.Build.props. -->
+    <PackageReference Include="Microsoft.CodeAnalysis.CSharp" PrivateAssets="all" VersionOverride="$(VerifyRoslynVersion).0" />
     <PackageReference Include="ProjectDefaults" PrivateAssets="all" />
   </ItemGroup>
 
   <Target Name="CheckPackageVersion" BeforeTargets="Build">
-    <!-- https://learn.microsoft.com/en-us/visualstudio/extensibility/roslyn-version-support?view=vs-2022 -->
     <Error Condition="'%(PackageVersion.Identity)' == 'Microsoft.CodeAnalysis.Analyzers' AND '%(PackageVersion.Version)' != '3.11.0'" Text="Invalid package version for Microsoft.CodeAnalysis.Analyzers. Expected: 3.11.0." />
-    <Error Condition="'%(PackageVersion.Identity)' == 'Microsoft.CodeAnalysis.CSharp' AND '%(PackageVersion.Version)' != '4.14.0'" Text="Invalid package version for Microsoft.CodeAnalysis.CSharp. Expected: 4.14.0." />
   </Target>
 </Project>

src/Verify.MSTest/Verify.MSTest.csproj

@@ -2,7 +2,6 @@
   <PropertyGroup>
     <TargetFrameworks Condition="'$(OS)' == 'Windows_NT'">net462;net472;net48</TargetFrameworks>
     <TargetFrameworks>$(TargetFrameworks);net8.0;net9.0;net10.0;net11.0</TargetFrameworks>
-    <RoslynVersion>4.4</RoslynVersion>
   </PropertyGroup>
   <ItemGroup>
     <PackageReference Include="Microsoft.Sbom.Targets" PrivateAssets="all" Condition="'$(CI)' == 'true'" />
@@ -16,7 +15,7 @@
     <None Include="buildTransitive\Verify.MSTest.props" Pack="true" PackagePath="build\" />
     <None Include="..\Verify.MSTest.SourceGenerator\bin\Release\netstandard2.0\Verify.MSTest.SourceGenerator.dll"
           Pack="true"
-          PackagePath="analyzers\dotnet\roslyn$(RoslynVersion)\cs\" />
+          PackagePath="analyzers\dotnet\roslyn$(VerifyRoslynVersion)\cs\" />
   </ItemGroup>
   <ItemGroup Condition="'$(TargetFrameworkIdentifier)' == '.NETFramework'">
     <Reference Include="System.IO.Compression" />