Support SetsRequiredMembersAttribute

The SetsRequiredMembersAttribute prevents the compiler from checking the required member list of a type when calling that constructor, and suppresses any errors from a base type's list being invalid.

Specification: https://github.com/dotnet/csharplang/blob/main/proposals/required-members.md
Test plan: dotnet#57046

src/Compilers/CSharp/Portable/Binder/Binder_Expressions.cs

@@ -5846,25 +5846,7 @@ private BoundExpression BindTypeParameterCreationExpression(ObjectCreationExpres
                 }
             }
 
-            if (suppressUnsupportedRequiredMembersError && useSiteInfo.AccumulatesDiagnostics && useSiteInfo.Diagnostics is { Count: not 0 })
-            {
-                diagnostics.AddDependencies(useSiteInfo);
-                foreach (var diagnostic in useSiteInfo.Diagnostics)
-                {
-                    // We don't want to report this error here because we'll report ERR_RequiredMembersBaseTypeInvalid. That error is suppressable by the
-                    // user using the `SetsRequiredMembers` attribute on the constructor, so reporting this error would prevent that from working.
-                    if ((ErrorCode)diagnostic.Code == ErrorCode.ERR_RequiredMembersInvalid)
-                    {
-                        continue;
-                    }
-
-                    diagnostics.ReportUseSiteDiagnostic(diagnostic, errorLocation);
-                }
-            }
-            else
-            {
-                diagnostics.Add(errorLocation, useSiteInfo);
-            }
+            ReportConstructorUseSiteDiagnostics(errorLocation, diagnostics, suppressUnsupportedRequiredMembersError, useSiteInfo);
 
             if (succeededIgnoringAccessibility)
             {
@@ -5921,6 +5903,31 @@ private BoundExpression BindTypeParameterCreationExpression(ObjectCreationExpres
             return succeededConsideringAccessibility;
         }
 
+        internal static bool ReportConstructorUseSiteDiagnostics(Location errorLocation, BindingDiagnosticBag diagnostics, bool suppressUnsupportedRequiredMembersError, CompoundUseSiteInfo<AssemblySymbol> useSiteInfo)
+        {
+            if (suppressUnsupportedRequiredMembersError && useSiteInfo.AccumulatesDiagnostics && useSiteInfo.Diagnostics is { Count: not 0 })
+            {
+                diagnostics.AddDependencies(useSiteInfo);
+                foreach (var diagnostic in useSiteInfo.Diagnostics)
+                {
+                    // We don't want to report this error here because we'll report ERR_RequiredMembersBaseTypeInvalid. That error is suppressable by the
+                    // user using the `SetsRequiredMembers` attribute on the constructor, so reporting this error would prevent that from working.
+                    if ((ErrorCode)diagnostic.Code == ErrorCode.ERR_RequiredMembersInvalid)
+                    {
+                        continue;
+                    }
+
+                    diagnostics.ReportUseSiteDiagnostic(diagnostic, errorLocation);
+                }
+
+                return true;
+            }
+            else
+            {
+                return diagnostics.Add(errorLocation, useSiteInfo);
+            }
+        }
+
         private ImmutableArray<MethodSymbol> GetAccessibleConstructorsForOverloadResolution(NamedTypeSymbol type, ref CompoundUseSiteInfo<AssemblySymbol> useSiteInfo)
         {
             ImmutableArray<MethodSymbol> allInstanceConstructors;

src/Compilers/CSharp/Portable/Compiler/MethodBodySynthesizer.Lowered.cs

@@ -195,6 +195,8 @@ internal override void GenerateMethodBody(TypeCompilationState compilationState,
                 F.CloseMethod(F.ThrowNull());
             }
         }
+
+        protected sealed override bool HasSetsRequiredMembersImpl => throw ExceptionUtilities.Unreachable;
     }
 
     internal abstract partial class MethodToClassRewriter

src/Compilers/CSharp/Portable/Compiler/MethodCompiler.cs

@@ -2142,7 +2142,9 @@ private static BoundCall GenerateBaseCopyConstructorInitializer(SynthesizedRecor
                 return null;
             }
 
-            if (Binder.ReportUseSite(baseConstructor, diagnostics, diagnosticsLocation))
+            var constructorUseSiteInfo = CompoundUseSiteInfo<AssemblySymbol>.DiscardedDependencies;
+            constructorUseSiteInfo.Add(baseConstructor.GetUseSiteInfo());
+            if (Binder.ReportConstructorUseSiteDiagnostics(diagnosticsLocation, diagnostics, suppressUnsupportedRequiredMembersError: constructor.HasSetsRequiredMembers, constructorUseSiteInfo))
             {
                 return null;
             }

src/Compilers/CSharp/Portable/FlowAnalysis/NullableWalker.cs

@@ -871,6 +871,8 @@ void makeNotNullMembersMaybeNull()
                     }
                 }
 
+                return;
+
                 ImmutableArray<Symbol> getMembersNeedingDefaultInitialState()
                 {
                     if (_hasInitialState)
@@ -880,12 +882,13 @@ ImmutableArray<Symbol> getMembersNeedingDefaultInitialState()
 
                     // We don't use a default initial state for value type instance constructors without `: this()` because
                     // any usages of uninitialized fields will get definite assignment errors anyway.
-                    bool hasConstructorInitializer = method.HasThisConstructorInitializer(out _);
-                    if (!hasConstructorInitializer && (!method.ContainingType.IsValueType || method.IsStatic))
+                    if (!method.HasThisConstructorInitializer(out _) && (!method.ContainingType.IsValueType || method.IsStatic))
                     {
                         return membersToBeInitialized(method.ContainingType, includeAllMembers: true);
                     }
 
+                    // We want to presume all required members of the type are uninitialized, and in addition we want to set all fields to
+                    // default if we can get to this constructor by doing so (ie, : this() in a value type).
                     return membersToBeInitialized(method.ContainingType, includeAllMembers: method.IncludeFieldInitializersInBody());
 
                     static ImmutableArray<Symbol> membersToBeInitialized(NamedTypeSymbol containingType, bool includeAllMembers)

src/Compilers/CSharp/Portable/Lowering/IteratorRewriter/IteratorFinallyMethodSymbol.cs

@@ -255,5 +255,7 @@ internal override int CalculateLocalSyntaxOffset(int localPosition, SyntaxTree l
         {
             return _stateMachineType.KickoffMethod.CalculateLocalSyntaxOffset(localPosition, localTree);
         }
+
+        protected sealed override bool HasSetsRequiredMembersImpl => throw ExceptionUtilities.Unreachable;
     }
 }

src/Compilers/CSharp/Portable/Symbols/AnonymousTypes/SynthesizedSymbols/AnonymousType.SynthesizedMethodBase.cs

@@ -231,6 +231,8 @@ internal sealed override int CalculateLocalSyntaxOffset(int localPosition, Synta
             {
                 throw ExceptionUtilities.Unreachable;
             }
+
+            protected sealed override bool HasSetsRequiredMembersImpl => throw ExceptionUtilities.Unreachable;
         }
     }
 }

src/Compilers/CSharp/Portable/Symbols/ErrorMethodSymbol.cs

@@ -6,6 +6,7 @@
 
 using System.Collections.Generic;
 using System.Collections.Immutable;
+using System.Diagnostics;
 using Roslyn.Utilities;
 
 namespace Microsoft.CodeAnalysis.CSharp.Symbols
@@ -274,5 +275,14 @@ internal override bool GenerateDebugInfo
         }
 
         internal sealed override bool IsNullableAnalysisEnabled() => false;
+
+        protected override bool HasSetsRequiredMembersImpl
+        {
+            get
+            {
+                Debug.Assert(MethodKind == MethodKind.Constructor);
+                return false;
+            }
+        }
     }
 }

src/Compilers/CSharp/Portable/Symbols/FunctionPointers/FunctionPointerMethodSymbol.cs

@@ -830,5 +830,6 @@ public override bool IsVararg
         internal override int CalculateLocalSyntaxOffset(int localPosition, SyntaxTree localTree) => throw ExceptionUtilities.Unreachable;
         internal override IEnumerable<SecurityAttribute> GetSecurityInformation() => throw ExceptionUtilities.Unreachable;
         internal sealed override bool IsNullableAnalysisEnabled() => throw ExceptionUtilities.Unreachable;
+        protected sealed override bool HasSetsRequiredMembersImpl => throw ExceptionUtilities.Unreachable;
     }
 }

src/Compilers/CSharp/Portable/Symbols/Metadata/PE/PEMethodSymbol.cs

@@ -47,7 +47,7 @@ private struct PackedFlags
         {
             // We currently pack everything into a 32-bit int with the following layout:
             //
-            // |u|t|s|r|q|p|ooo|n|m|l|k|j|i|h|g|f|e|d|c|b|aaaaa|
+            // |w|v|u|t|s|r|q|p|ooo|n|m|l|k|j|i|h|g|f|e|d|c|b|aaaaa|
             // 
             // a = method kind. 5 bits.
             // b = method kind populated. 1 bit.
@@ -72,7 +72,9 @@ private struct PackedFlags
             // s = IsInitOnlyBit. 1 bit.
             // t = IsInitOnlyPopulatedBit. 1 bit.
             // u = IsUnmanagedCallersOnlyAttributePopulated. 1 bit.
-            // 6 bits remain for future purposes.
+            // v = IsSetsRequiredMembersBit. 1 bit.
+            // w = IsSetsRequiredMembersPopulated. 1 bit.
+            // 4 bits remain for future purposes.
 
             private const int MethodKindOffset = 0;
             private const int MethodKindMask = 0x1F;
@@ -98,6 +100,8 @@ private struct PackedFlags
             private const int IsInitOnlyBit = 0x1 << 24;
             private const int IsInitOnlyPopulatedBit = 0x1 << 25;
             private const int IsUnmanagedCallersOnlyAttributePopulatedBit = 0x1 << 26;
+            private const int HasSetsRequiredMembersBit = 0x1 << 27;
+            private const int HasSetsRequiredMembersPopulatedBit = 0x1 << 28;
 
             private int _bits;
 
@@ -134,6 +138,8 @@ public MethodKind MethodKind
             public bool IsInitOnly => (_bits & IsInitOnlyBit) != 0;
             public bool IsInitOnlyPopulated => (_bits & IsInitOnlyPopulatedBit) != 0;
             public bool IsUnmanagedCallersOnlyAttributePopulated => (_bits & IsUnmanagedCallersOnlyAttributePopulatedBit) != 0;
+            public bool HasSetsRequiredMembers => (_bits & HasSetsRequiredMembersBit) != 0;
+            public bool HasSetsRequiredMembersPopulated => (_bits & HasSetsRequiredMembersPopulatedBit) != 0;
 
 #if DEBUG
             static PackedFlags()
@@ -240,6 +246,14 @@ public void SetIsUnmanagedCallersOnlyAttributePopulated()
             {
                 ThreadSafeFlagOperations.Set(ref _bits, IsUnmanagedCallersOnlyAttributePopulatedBit);
             }
+
+            public bool InitializeSetsRequiredMembersBit(bool value)
+            {
+                int bitsToSet = HasSetsRequiredMembersPopulatedBit;
+                if (value) bitsToSet |= HasSetsRequiredMembersBit;
+
+                return ThreadSafeFlagOperations.Set(ref _bits, bitsToSet);
+            }
         }
 
         /// <summary>
@@ -1407,6 +1421,21 @@ internal override ImmutableArray<string> GetAppliedConditionalSymbols()
             }
         }
 
+        protected override bool HasSetsRequiredMembersImpl
+        {
+            get
+            {
+                Debug.Assert(MethodKind == MethodKind.Constructor);
+                if (!_packedFlags.HasSetsRequiredMembersPopulated)
+                {
+                    var result = _containingType.ContainingPEModule.Module.HasAttribute(_handle, AttributeDescription.SetsRequiredMembersAttribute);
+                    _packedFlags.InitializeSetsRequiredMembersBit(result);
+                }
+
+                return _packedFlags.HasSetsRequiredMembers;
+            }
+        }
+
         internal override int CalculateLocalSyntaxOffset(int localPosition, SyntaxTree localTree)
         {
             throw ExceptionUtilities.Unreachable;

src/Compilers/CSharp/Portable/Symbols/MethodSymbol.cs

@@ -579,6 +579,13 @@ public bool IsConditional
             }
         }
 
+        /// <summary>
+        /// Returns true if this is a constructor attributed with HasSetsRequiredMembers
+        /// </summary>
+        internal bool HasSetsRequiredMembers => MethodKind == MethodKind.Constructor && HasSetsRequiredMembersImpl;
+
+        protected abstract bool HasSetsRequiredMembersImpl { get; }
+
         /// <summary>
         /// Some method kinds do not participate in overriding/hiding (e.g. constructors).
         /// </summary>

src/Compilers/CSharp/Portable/Symbols/ReducedExtensionMethodSymbol.cs

@@ -588,6 +588,8 @@ public override int GetHashCode()
             return _reducedFrom.GetHashCode();
         }
 
+        protected sealed override bool HasSetsRequiredMembersImpl => throw ExceptionUtilities.Unreachable;
+
 #nullable enable
 
         private sealed class ReducedExtensionMethodParameterSymbol : WrappedParameterSymbol

src/Compilers/CSharp/Portable/Symbols/SignatureOnlyMethodSymbol.cs

@@ -172,6 +172,8 @@ internal override bool IsMetadataFinal
 
         internal override int CalculateLocalSyntaxOffset(int localPosition, SyntaxTree localTree) { throw ExceptionUtilities.Unreachable; }
 
+        protected sealed override bool HasSetsRequiredMembersImpl => throw ExceptionUtilities.Unreachable;
+
         #endregion
     }
 }

src/Compilers/CSharp/Portable/Symbols/Source/SourceConstructorSymbolBase.cs

@@ -246,5 +246,40 @@ internal sealed override int CalculateLocalSyntaxOffset(int position, SyntaxTree
         protected abstract CSharpSyntaxNode GetInitializer();
 
         protected abstract bool IsWithinExpressionOrBlockBody(int position, out int offset);
+
+#nullable enable
+        protected sealed override bool HasSetsRequiredMembersImpl
+            => GetEarlyDecodedWellKnownAttributeData()?.HasSetsRequiredMembersAttribute == true;
+
+        internal sealed override (CSharpAttributeData?, BoundAttribute?) EarlyDecodeWellKnownAttribute(ref EarlyDecodeWellKnownAttributeArguments<EarlyWellKnownAttributeBinder, NamedTypeSymbol, AttributeSyntax, AttributeLocation> arguments)
+        {
+            if (arguments.SymbolPart == AttributeLocation.None)
+            {
+                if (CSharpAttributeData.IsTargetEarlyAttribute(arguments.AttributeType, arguments.AttributeSyntax, AttributeDescription.SetsRequiredMembersAttribute))
+                {
+                    var earlyData = arguments.GetOrCreateData<MethodEarlyWellKnownAttributeData>();
+                    earlyData.HasSetsRequiredMembersAttribute = true;
+
+                    if (ContainingType.IsWellKnownSetsRequiredMembersAttribute())
+                    {
+                        // Avoid a binding cycle for this scenario.
+                        return (null, null);
+                    }
+
+                    var (attributeData, boundAttribute) = arguments.Binder.GetAttribute(arguments.AttributeSyntax, arguments.AttributeType, beforeAttributePartBound: null, afterAttributePartBound: null, out bool hasAnyDiagnostics);
+
+                    if (!hasAnyDiagnostics)
+                    {
+                        return (attributeData, boundAttribute);
+                    }
+                    else
+                    {
+                        return (null, null);
+                    }
+                }
+            }
+
+            return base.EarlyDecodeWellKnownAttribute(ref arguments);
+        }
     }
 }

src/Compilers/CSharp/Portable/Symbols/Source/SourceMethodSymbol.cs

@@ -5,6 +5,7 @@
 using System.Collections.Immutable;
 using System.Linq;
 using Microsoft.CodeAnalysis.CSharp.Syntax;
+using Roslyn.Utilities;
 
 namespace Microsoft.CodeAnalysis.CSharp.Symbols
 {
@@ -78,5 +79,7 @@ internal void ReportAsyncParameterErrors(BindingDiagnosticBag diagnostics, Locat
             static Location getLocation(ParameterSymbol parameter, Location location)
                 => parameter.Locations.FirstOrDefault() ?? location;
         }
+
+        protected override bool HasSetsRequiredMembersImpl => throw ExceptionUtilities.Unreachable;
     }
 }

src/Compilers/CSharp/Portable/Symbols/Source/SourceMethodSymbolWithAttributes.cs

@@ -318,7 +318,7 @@ public override ImmutableArray<CSharpAttributeData> GetReturnTypeAttributes()
         }
 
 #nullable enable
-        internal sealed override (CSharpAttributeData?, BoundAttribute?) EarlyDecodeWellKnownAttribute(ref EarlyDecodeWellKnownAttributeArguments<EarlyWellKnownAttributeBinder, NamedTypeSymbol, AttributeSyntax, AttributeLocation> arguments)
+        internal override (CSharpAttributeData?, BoundAttribute?) EarlyDecodeWellKnownAttribute(ref EarlyDecodeWellKnownAttributeArguments<EarlyWellKnownAttributeBinder, NamedTypeSymbol, AttributeSyntax, AttributeLocation> arguments)
         {
             Debug.Assert(arguments.SymbolPart == AttributeLocation.None || arguments.SymbolPart == AttributeLocation.Return);
 

src/Compilers/CSharp/Portable/Symbols/SymbolExtensions.cs

@@ -843,7 +843,6 @@ internal static bool HasAsyncMethodBuilderAttribute(this Symbol symbol, [NotNull
         internal static bool IsRequired(this Symbol symbol) => symbol is FieldSymbol { IsRequired: true } or PropertySymbol { IsRequired: true };
 
         internal static bool ShouldCheckRequiredMembers(this MethodSymbol method)
-            // PROTOTYPE(req): Check for the SetsRequiredMembersAttribute and return false for that case
-            => method.MethodKind == MethodKind.Constructor;
+            => method.MethodKind == MethodKind.Constructor && !method.HasSetsRequiredMembers;
     }
 }

src/Compilers/CSharp/Portable/Symbols/Synthesized/Records/SynthesizedRecordCopyCtor.cs

@@ -64,6 +64,11 @@ internal override void AddSynthesizedAttributes(PEModuleBuilder moduleBuilder, r
             var compilation = this.DeclaringCompilation;
             AddSynthesizedAttribute(ref attributes, compilation.TrySynthesizeAttribute(WellKnownMember.System_Runtime_CompilerServices_CompilerGeneratedAttribute__ctor));
             Debug.Assert(WellKnownMembers.IsSynthesizedAttributeOptional(WellKnownMember.System_Runtime_CompilerServices_CompilerGeneratedAttribute__ctor));
+
+            if (HasSetsRequiredMembersImpl)
+            {
+                AddSynthesizedAttribute(ref attributes, compilation.TrySynthesizeAttribute(WellKnownMember.System_Diagnostics_CodeAnalysis_SetsRequiredMembersAttribute__ctor));
+            }
         }
 
         internal static MethodSymbol? FindCopyConstructor(NamedTypeSymbol containingType, NamedTypeSymbol within, ref CompoundUseSiteInfo<AssemblySymbol> useSiteInfo)
@@ -127,5 +132,9 @@ internal static bool HasCopyConstructorSignature(MethodSymbol member)
                 method.Parameters[0].Type.Equals(containingType, TypeCompareKind.AllIgnoreOptions) &&
                 method.Parameters[0].RefKind == RefKind.None;
         }
+
+        protected sealed override bool HasSetsRequiredMembersImpl
+            // If the record type has a required members error, then it does have required members of some kind, we emit the SetsRequiredMembers attribute.
+            => !ContainingType.AllRequiredMembers.IsEmpty || ContainingType.HasRequiredMembersError;
     }
 }

src/Compilers/CSharp/Portable/Symbols/Synthesized/SynthesizedDelegateSymbol.cs

@@ -238,5 +238,7 @@ public override bool IsExtern
         {
             get { return false; }
         }
+
+        protected sealed override bool HasSetsRequiredMembersImpl => throw ExceptionUtilities.Unreachable;
     }
 }

src/Compilers/CSharp/Portable/Symbols/Synthesized/SynthesizedEntryPointSymbol.cs

@@ -307,6 +307,8 @@ private static BoundCall CreateParameterlessCall(CSharpSyntaxNode syntax, BoundE
             { WasCompilerGenerated = true };
         }
 
+        protected sealed override bool HasSetsRequiredMembersImpl => throw ExceptionUtilities.Unreachable;
+
         /// <summary> A synthesized entrypoint that forwards all calls to an async Main Method </summary>
         internal sealed class AsyncForwardEntryPoint : SynthesizedEntryPointSymbol
         {

src/Compilers/CSharp/Portable/Symbols/Synthesized/SynthesizedGlobalMethodSymbol.cs

@@ -335,5 +335,7 @@ internal override int CalculateLocalSyntaxOffset(int localPosition, SyntaxTree l
         }
 
         internal sealed override bool IsNullableAnalysisEnabled() => false;
+
+        protected sealed override bool HasSetsRequiredMembersImpl => throw ExceptionUtilities.Unreachable;
     }
 }

src/Compilers/CSharp/Portable/Symbols/Synthesized/SynthesizedImplementationMethod.cs

@@ -265,5 +265,7 @@ internal override ImmutableArray<string> GetAppliedConditionalSymbols()
         {
             return ImmutableArray<string>.Empty;
         }
+
+        protected sealed override bool HasSetsRequiredMembersImpl => throw ExceptionUtilities.Unreachable;
     }
 }

src/Compilers/CSharp/Portable/Symbols/Synthesized/SynthesizedInstanceConstructor.cs

@@ -316,5 +316,6 @@ internal virtual void GenerateMethodBodyStatements(SyntheticBoundNodeFactory fac
             // overridden in a derived class to add extra statements to the body of the generated constructor
         }
 
+        protected override bool HasSetsRequiredMembersImpl => false;
     }
 }