Chasm.Compatibility.Attributes 2.1.1

Chasm.Compatibility.Attributes

Compiler-interpreted attributes

These attributes are interpreted by the compiler, and are generally not used directly in the compiled assembly.

• [In] (Core 1.0+ / Standard 1.1+ / Framework 1.1+) - ref readonly method return type;
• [CallerFilePath] (Core 1.0+ / Standard 1.0+ / Framework 4.5+);
• [CallerLineNumber] (Core 1.0+ / Standard 1.0+ / Framework 4.5+);
• [CallerMemberName] (Core 1.0+ / Standard 1.0+ / Framework 4.5+);
• [AsyncMethodBuilder] (Core 1.1+ / Standard 2.0+);
• [CallerArgumentExpression] (Core 3.0+);
• [ModuleInitializer] (.NET 5+) - module initializers are a CLI spec feature and work on older targets as well;
• [SkipLocalsInit] (.NET 5+) - simply removes the .locals init flag from metadata;
• IsExternalInit metadata class (.NET 5+) - used for { init; } properties and record types;
• [InterpolatedStringHandler] (.NET 6+) - allows using your own string interpolation handlers;
• [InterpolatedStringHandlerArgument] (.NET 6+);
• [CompilerFeatureRequired] (.NET 7+) - allows declaring required members and ref struct types;
• [RequiredMember] (.NET 7+) - allows declaring required members;
• [RequiresLocation] (.NET 8+) - ref readonly parameters in function pointers.
• [CollectionBuilder] (.NET 8+) - used for creating custom collections from spans.

Nullable analysis attributes

Attributes to assist with C# 8.0's #nullable context and nullable reference type analysis.

• [AllowNull] (Core 3.0+ / Standard 2.1+);
• [DisallowNull];
• [DoesNotReturn];
• [DoesNotReturnIf];
• [MaybeNull];
• [MaybeNullWhen];
• [NotNull];
• [NotNullIfNotNull];
• [NotNullWhen];
• [MemberNotNull] (.NET 5+);
• [MemberNotNullWhen] (.NET 5+).

Code analysis attributes

Attributes for code analyzers, IDE suggestions, syntax highlighting, and other tools.

• [ExcludeFromCodeCoverage] (Core 2.0+ / Standard 2.0+ / Framework 4.0+);
• [UnconditionalSuppressMessage] (.NET 5+);
• [RequiresPreviewFeatures] (.NET 6+);
• [StringSyntax] (.NET 7+);
• [ConstantExpected] (.NET 7+);
• [SetsRequiredMembers] (.NET 7+);
• [UnscopedRef] (.NET 7+);
• [Experimental] (.NET 8+).

Note: ExcludeFromCodeCoverageAttribute.Justification property is not shimmed, since it was added only in .NET 5.

Attributes used at runtime

• [StackTraceHidden] (.NET 6+) - omits the method/type from StackTrace.ToString().

To-do List

Future .NET versions:

• [FeatureGuard] (.NET 9+);
• [FeatureSwitchDefinition] (.NET 9+);
• [OverloadResolutionPriority] (.NET 9+);
• [ParamCollection] (.NET 9+);

I'm not sure how the attributes below work, so I'll put it off for now:

• [DisableRuntimeMarshalling];
• [SuppressGCTransition];
• [UnmanagedCallersOnly];
• [UnsafeAccessor];
• [InlineArray];
• [DynamicallyAccessedMembers];
• enum DynamicallyAccessedMemberTypes;
• [DynamicDependency];
• [RequiresAssemblyFiles];
• [RequiresDynamicCode];
• [RequiresUnreferencedCode];

Not needed

The following attributes are not provided by this package:

• Attributes for C++ and Visual Basic compilers;
• [RefSafetyRules] - generated automatically;
• [ScopedRef] - generated automatically, for scoped ref parameters;
• [NullableContext] - generated automatically, on types and methods in #nullable context;
• [Nullable] - generated automatically, on types, members and parameters in #nullable context;
• [TupleElementNames] - provided in the ValueTuple package;
• [EnumeratorCancellation] - that would require adding TaskAsyncEnumerableExtensions as well;

Can't be added

• [PreserveBaseOverrides] - requires runtime support of covariant return types;