Drop unloadable analyzer versions

build/BenchmarkDotNet.Build/Runners/BuildRunner.cs

@@ -126,7 +126,7 @@ public void BuildAnalyzers()
         context.Information("BuildSystemProvider: " + context.BuildSystem().Provider);
         // Each band must restore as well as build: the PackageReference is chosen by MccVersion, so reusing the
         // default band's project.assets.json silently compiles every band against the default's Roslyn.
-        string[] mccVersions = ["2.8", "3.0", "3.8", "4.4", "4.8", "4.12"];
+        string[] mccVersions = ["4.0", "4.4", "4.8", "4.12"];
         foreach (string version in mccVersions)
         {
             context.DotNetBuild(context.AnalyzersProjectFile.FullPath, new DotNetBuildSettings

build/roslynBands.props

@@ -10,11 +10,10 @@
     <OutputPath>bin\$(Configuration)\roslyn$(MccVersion)\cs</OutputPath>
     <AppendTargetFrameworkToOutputPath>false</AppendTargetFrameworkToOutputPath>
     <!-- We multi-target for different compiler versions. https://github.com/dotnet/roslyn/discussions/81256#discussioncomment-14975130, https://github.com/dotnet/roslyn/blob/main/docs/wiki/NuGet-packages.md#versioning -->
-    <!-- C# 7.3/Roslyn 2.8 is our baseline (min version we support) -->
-    <!-- ITypeSymbol.IsRefLikeType -->
-    <DefineConstants Condition="$([MSBuild]::VersionGreaterThanOrEquals('$(MccVersion)', '3.0'))">$(DefineConstants);CODE_ANALYSIS_3_0</DefineConstants>
-    <!-- C# 9 -->
-    <DefineConstants Condition="$([MSBuild]::VersionGreaterThanOrEquals('$(MccVersion)', '3.8'))">$(DefineConstants);CODE_ANALYSIS_3_8</DefineConstants>
+    <!-- Roslyn 4.0 (VS 2022 RTM, .NET SDK 6) is the lowest band: picking a version-specific analyzer folder at all
+         requires that tooling, so a lower band could only ever be selected by a compiler that cannot select. The
+         lowest band is the fallback for every supported compiler below the next one up, so it needs no successor
+         below it. Older hosts are handed no analyzer at all - see BenchmarkDotNet.Annotations.targets. -->
     <!-- C# 11 -->
     <DefineConstants Condition="$([MSBuild]::VersionGreaterThanOrEquals('$(MccVersion)', '4.4'))">$(DefineConstants);CODE_ANALYSIS_4_4</DefineConstants>
     <!-- C# 12 -->

src/BenchmarkDotNet.Analyzers/AnalyzerHelper.cs

@@ -148,31 +148,22 @@ public static bool MayBeRefLike(ITypeSymbol type)
             return true;
         }
 #endif
-        return IsRefLikeType(type);
+        return type.IsRefLikeType;
     }
 
-    // ref structs are C# 7.2, but no public symbol carries IsRefLikeType until Roslyn 3.0; the oldest band reads
-    // the internal property behind it instead.
-    private static bool IsRefLikeType(ITypeSymbol type)
-#if CODE_ANALYSIS_3_0
-        => type.IsRefLikeType;
-#else
-        => RefLikeTypePolyfill.IsRefLikeType(type);
-#endif
-
     /// <summary>
     /// Names which of the two <see cref="MayBeRefLike"/> found, so a message reads the same from either source analyzer.
     /// </summary>
     public static string ByRefLikeClause(ITypeSymbol type)
-        => IsRefLikeType(type) ? "is a ref struct" : "admits a ref struct";
+        => type.IsRefLikeType ? "is a ref struct" : "admits a ref struct";
 
     /// <summary>
     /// Which of the two rules applies. A ref struct is one the compiler can see, so the source cannot work; a
     /// constraint that merely admits one is decided by the type argument, and one that is not by-ref-like reads
     /// perfectly well - so the two are separate ids, configurable apart.
     /// </summary>
     public static DiagnosticDescriptor ByRefLikeRule(ITypeSymbol type)
-        => IsRefLikeType(type) ? SourceElementMustNotBeByRefLikeRule : SourceElementMayBeByRefLikeRule;
+        => type.IsRefLikeType ? SourceElementMustNotBeByRefLikeRule : SourceElementMayBeByRefLikeRule;
 
     /// <summary>
     /// Whether <paramref name="type"/> is <paramref name="baseType"/> or derives from it. BenchmarkDotNet resolves

src/BenchmarkDotNet.Analyzers/Attributes/GeneralParameterAttributesAnalyzer.cs

@@ -197,10 +197,7 @@ private static void Analyze(SyntaxNodeAnalysisContext context)
             // `init` counts: the runnable assigns parameters through an object initializer.
             var propertyAccessors = propertyDeclarationSyntax.AccessorList?.Accessors;
             propertyIsMissingAssignableSetter = !HasAssignableAccessor(propertyAccessors, SyntaxKind.SetAccessorDeclaration)
-#if CODE_ANALYSIS_3_8
-                && !HasAssignableAccessor(propertyAccessors, SyntaxKind.InitAccessorDeclaration)
-#endif
-                ;
+                && !HasAssignableAccessor(propertyAccessors, SyntaxKind.InitAccessorDeclaration);
 
             fieldOrPropertyIdentifierLocation = propertyDeclarationSyntax.Identifier.GetLocation();
             declaredNames = ImmutableArray.Create((fieldOrPropertyIdentifier, fieldOrPropertyIdentifierLocation));

src/BenchmarkDotNet.Analyzers/BenchmarkDotNet.Analyzers.csproj

@@ -8,11 +8,12 @@
   <PropertyGroup>
     <!-- Formatting in AnalyzerReleases.Unshipped.md -->
     <NoWarn>$(NoWarn);RS2007</NoWarn>
-    <!-- Suppress false positives due to a bug in v3.8.0. -->
-    <NoWarn Condition="'$(MccVersion)' == '3.8'">$(NoWarn);RS2002</NoWarn>
-  </PropertyGroup>
-  <ItemGroup>
-      <PackageReference Include="Microsoft.CodeAnalysis.CSharp" Version="$(MccPackageVersion)" />
+    <!-- A HashSet built with SymbolEqualityComparer.Default is what RS1024 asks for, but the rule as shipped in
+         Microsoft.CodeAnalysis.Analyzers 3.3.2 (bundled with 4.0.0) reports it anyway. -->
+    <NoWarn Condition="'$(MccVersion)' == '4.0'">$(NoWarn);RS1024</NoWarn>
+  </PropertyGroup>
+  <ItemGroup>
+      <PackageReference Include="Microsoft.CodeAnalysis.CSharp" Version="$(MccPackageVersion)" />
   </ItemGroup>
   <ItemGroup>
     <AdditionalFiles Include="AnalyzerReleases.Shipped.md" />

src/BenchmarkDotNet.Annotations/buildTransitive/netstandard2.0/BenchmarkDotNet.Annotations.targets

@@ -8,4 +8,24 @@
 
   <!-- The weaving logic is shared with BenchmarkDotNet.Weaver.targets. See the common file for details. -->
   <Import Project="$(MSBuildThisFileDirectory)BenchmarkDotNet.Weaver.Common.targets" />
+
+  <Target Name="_BenchmarkDotNetGatherAnalyzers">
+    <ItemGroup>
+      <_BenchmarkDotNetAnalyzer Include="@(Analyzer)" Condition="'%(Analyzer.NuGetPackageId)' == 'BenchmarkDotNet.Annotations'" />
+    </ItemGroup>
+  </Target>
+
+  <!-- The analyzers ship one assembly per compiler version under analyzers/dotnet/roslyn<version>, the lowest being
+       Roslyn 4.0. Choosing among those folders needs SDK 6 or later; every older host is handed all of them at once
+       and, because they share an assembly name, resolves the whole set to one arbitrary path - so nothing loads and
+       every analyzer in it is reported as CS8032, which a consumer building with TreatWarningsAsErrors sees as a
+       build failure. Take them back out again rather than hand over a set that cannot work. -->
+  <Target Name="_BenchmarkDotNetRemoveAnalyzers"
+          Condition="'$(SupportsRoslynComponentVersioning)' != 'true'"
+          AfterTargets="ResolvePackageDependenciesForBuild;ResolveNuGetPackageAssets"
+          DependsOnTargets="_BenchmarkDotNetGatherAnalyzers">
+    <ItemGroup>
+      <Analyzer Remove="@(_BenchmarkDotNetAnalyzer)" />
+    </ItemGroup>
+  </Target>
 </Project>