Emit CompilerFeaturesRequiredAttribute

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

@@ -952,14 +952,26 @@ public override ImmutableArray<CSharpAttributeData> GetAttributes()
                      ? _packedFlags.IsReadOnly
                      : IsValidReadOnlyTarget;
 
+                bool checkForRequiredMembers = this.ShouldCheckRequiredMembers() && this.ContainingType.HasAnyRequiredMembers;
+
                 bool isExtensionMethod = false;
                 bool isReadOnly = false;
-                if (checkForExtension || checkForIsReadOnly)
+                if (checkForExtension || checkForIsReadOnly || checkForRequiredMembers)
                 {
-                    containingPEModuleSymbol.LoadCustomAttributesFilterCompilerAttributes(_handle,
-                        ref attributeData,
-                        out isExtensionMethod,
-                        out isReadOnly);
+                    attributeData = containingPEModuleSymbol.GetCustomAttributesForToken(_handle,
+                        filteredOutAttribute1: out CustomAttributeHandle extensionAttribute,
+                        filterOut1: AttributeDescription.CaseSensitiveExtensionAttribute,
+                        filteredOutAttribute2: out CustomAttributeHandle isReadOnlyAttribute,
+                        filterOut2: AttributeDescription.IsReadOnlyAttribute,
+                        filteredOutAttribute3: out _,
+                        filterOut3: (checkForRequiredMembers && DeriveCompilerFeatureRequiredDiagnostic() is null) ? AttributeDescription.CompilerFeatureRequiredAttribute : default,
+                        filteredOutAttribute4: out _,
+                        filterOut4: (checkForRequiredMembers && ObsoleteAttributeData is null) ? AttributeDescription.ObsoleteAttribute : default,
+                        filteredOutAttribute5: out _,
+                        filterOut5: default);
+
+                    isExtensionMethod = !extensionAttribute.IsNil;
+                    isReadOnly = !isReadOnlyAttribute.IsNil;
                 }
                 else
                 {

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

@@ -283,15 +283,6 @@ internal void LoadCustomAttributes(EntityHandle token, ref ImmutableArray<CSharp
             ImmutableInterlocked.InterlockedInitialize(ref customAttributes, loaded);
         }
 
-        internal void LoadCustomAttributesFilterCompilerAttributes(EntityHandle token,
-            ref ImmutableArray<CSharpAttributeData> customAttributes,
-            out bool foundExtension,
-            out bool foundReadOnly)
-        {
-            var loadedCustomAttributes = GetCustomAttributesFilterCompilerAttributes(token, out foundExtension, out foundReadOnly);
-            ImmutableInterlocked.InterlockedInitialize(ref customAttributes, loadedCustomAttributes);
-        }
-
         internal void LoadCustomAttributesFilterExtensions(EntityHandle token,
             ref ImmutableArray<CSharpAttributeData> customAttributes)
         {
@@ -303,7 +294,7 @@ internal ImmutableArray<CSharpAttributeData> GetCustomAttributesForToken(EntityH
             out CustomAttributeHandle filteredOutAttribute1,
             AttributeDescription filterOut1)
         {
-            return GetCustomAttributesForToken(token, out filteredOutAttribute1, filterOut1, out _, default, out _, default, out _, default);
+            return GetCustomAttributesForToken(token, out filteredOutAttribute1, filterOut1, out _, default, out _, default, out _, default, out _, default);
         }
 
         /// <summary>
@@ -318,12 +309,15 @@ internal ImmutableArray<CSharpAttributeData> GetCustomAttributesForToken(EntityH
             out CustomAttributeHandle filteredOutAttribute3,
             AttributeDescription filterOut3,
             out CustomAttributeHandle filteredOutAttribute4,
-            AttributeDescription filterOut4)
+            AttributeDescription filterOut4,
+            out CustomAttributeHandle filteredOutAttribute5,
+            AttributeDescription filterOut5)
         {
             filteredOutAttribute1 = default;
             filteredOutAttribute2 = default;
             filteredOutAttribute3 = default;
             filteredOutAttribute4 = default;
+            filteredOutAttribute5 = default;
             ArrayBuilder<CSharpAttributeData> customAttributesBuilder = null;
 
             try
@@ -357,6 +351,12 @@ internal ImmutableArray<CSharpAttributeData> GetCustomAttributesForToken(EntityH
                         continue;
                     }
 
+                    if (matchesFilter(customAttributeHandle, filterOut5))
+                    {
+                        filteredOutAttribute5 = customAttributeHandle;
+                        continue;
+                    }
+
                     if (customAttributesBuilder == null)
                     {
                         customAttributesBuilder = ArrayBuilder<CSharpAttributeData>.GetInstance();
@@ -438,7 +438,8 @@ internal ImmutableArray<CSharpAttributeData> GetCustomAttributesFilterCompilerAt
                 filteredOutAttribute2: out CustomAttributeHandle isReadOnlyAttribute,
                 filterOut2: AttributeDescription.IsReadOnlyAttribute,
                 filteredOutAttribute3: out _, filterOut3: default,
-                filteredOutAttribute4: out _, filterOut4: default);
+                filteredOutAttribute4: out _, filterOut4: default,
+                filteredOutAttribute5: out _, filterOut5: default);
 
             foundExtension = !extensionAttribute.IsNil;
             foundReadOnly = !isReadOnlyAttribute.IsNil;

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

@@ -679,7 +679,10 @@ public override ImmutableArray<CSharpAttributeData> GetAttributes()
                     IsReadOnly ? AttributeDescription.IsReadOnlyAttribute : default,
                     out _,
                     // Filter out [IsByRefLike]
-                    IsRefLikeType ? AttributeDescription.IsByRefLikeAttribute : default);
+                    IsRefLikeType ? AttributeDescription.IsByRefLikeAttribute : default,
+                    out _,
+                    // Filter out [CompilerFeatureRequired]
+                    (IsRefLikeType && DeriveCompilerFeatureRequiredDiagnostic() is null) ? AttributeDescription.CompilerFeatureRequiredAttribute : default);
 
                 ImmutableInterlocked.InterlockedInitialize(ref uncommon.lazyCustomAttributes, loadedCustomAttributes);
             }

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

@@ -997,6 +997,8 @@ public override ImmutableArray<CSharpAttributeData> GetAttributes()
                             out isReadOnlyAttribute,
                             filterIsReadOnlyAttribute ? AttributeDescription.IsReadOnlyAttribute : default,
                             out _,
+                            default,
+                            out _,
                             default);
 
                     if (!paramArrayAttribute.IsNil || !constantAttribute.IsNil)

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

@@ -1219,15 +1219,19 @@ protected static void AddRequiredMembersMarkerAttributes(ref ArrayBuilder<Synthe
                 var obsoleteData = methodToAttribute.ObsoleteAttributeData;
                 Debug.Assert(obsoleteData != ObsoleteAttributeData.Uninitialized, "getting synthesized attributes before attributes are decoded");
 
+                CSharpCompilation declaringCompilation = methodToAttribute.DeclaringCompilation;
                 if (obsoleteData == null)
                 {
-                    CSharpCompilation declaringCompilation = methodToAttribute.DeclaringCompilation;
                     AddSynthesizedAttribute(ref attributes, declaringCompilation.TrySynthesizeAttribute(WellKnownMember.System_ObsoleteAttribute__ctor,
                         ImmutableArray.Create(
                             new TypedConstant(declaringCompilation.GetSpecialType(SpecialType.System_String), TypedConstantKind.Primitive, PEModule.RequiredMembersMarker), // message
                             new TypedConstant(declaringCompilation.GetSpecialType(SpecialType.System_Boolean), TypedConstantKind.Primitive, true)) // error
                         ));
                 }
+
+                AddSynthesizedAttribute(ref attributes, declaringCompilation.TrySynthesizeAttribute(WellKnownMember.System_Runtime_CompilerServices_CompilerFeatureRequiredAttribute__ctor,
+                    ImmutableArray.Create(new TypedConstant(declaringCompilation.GetSpecialType(SpecialType.System_String), TypedConstantKind.Primitive, nameof(CompilerFeatureRequiredFeatures.RequiredMembers)))
+                    ));
             }
         }
     }

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

@@ -10,9 +10,6 @@
 
 namespace Microsoft.CodeAnalysis.CSharp.Symbols
 {
-    // PROTOTYPE(req): Add obsolete marker to constructors if required members and Obsolete hasn't already been emitted
-    // PROTOTYPE(req): Add poison type marker to constructors if required members and Obsolete hasn't already been emitted,
-    //                 pending framework design review
     internal sealed class SourceConstructorSymbol : SourceConstructorSymbolBase
     {
         private readonly bool _isExpressionBodied;

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

@@ -2428,6 +2428,12 @@ private void CheckForRequiredMemberAttribute(BindingDiagnosticBag diagnostics)
             {
                 // Ensure that an error is reported if the required constructor isn't present.
                 _ = Binder.GetWellKnownTypeMember(DeclaringCompilation, WellKnownMember.System_Runtime_CompilerServices_RequiredMemberAttribute__ctor, diagnostics, Locations[0]);
+            }
+
+            if (HasAnyRequiredMembers)
+            {
+                _ = Binder.GetWellKnownTypeMember(DeclaringCompilation, WellKnownMember.System_Runtime_CompilerServices_CompilerFeatureRequiredAttribute__ctor, diagnostics, Locations[0]);
+
                 if (this.IsRecord)
                 {
                     // Copy constructors need to emit SetsRequiredMembers on the ctor

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

@@ -1557,17 +1557,24 @@ internal override void AddSynthesizedAttributes(PEModuleBuilder moduleBuilder, r
                 var obsoleteData = ObsoleteAttributeData;
                 Debug.Assert(obsoleteData != ObsoleteAttributeData.Uninitialized, "getting synthesized attributes before attributes are decoded");
 
-                // If user specified an Obsolete attribute, we cannot emit ours.
-                // NB: we do not check the kind of deprecation. 
-                //     we will not emit Obsolete even if Deprecated or Experimental was used.
-                //     we do not want to get into a scenario where different kinds of deprecation are combined together.
-                //
-                if (obsoleteData == null && !this.IsRestrictedType(ignoreSpanLikeTypes: true))
+                if (!this.IsRestrictedType(ignoreSpanLikeTypes: true))
                 {
-                    AddSynthesizedAttribute(ref attributes, compilation.TrySynthesizeAttribute(WellKnownMember.System_ObsoleteAttribute__ctor,
-                        ImmutableArray.Create(
-                            new TypedConstant(compilation.GetSpecialType(SpecialType.System_String), TypedConstantKind.Primitive, PEModule.ByRefLikeMarker), // message
-                            new TypedConstant(compilation.GetSpecialType(SpecialType.System_Boolean), TypedConstantKind.Primitive, true)), // error=true
+                    // If user specified an Obsolete attribute, we cannot emit ours.
+                    // NB: we do not check the kind of deprecation. 
+                    //     we will not emit Obsolete even if Deprecated or Experimental was used.
+                    //     we do not want to get into a scenario where different kinds of deprecation are combined together.
+                    //
+                    if (obsoleteData == null)
+                    {
+                        AddSynthesizedAttribute(ref attributes, compilation.TrySynthesizeAttribute(WellKnownMember.System_ObsoleteAttribute__ctor,
+                            ImmutableArray.Create(
+                                new TypedConstant(compilation.GetSpecialType(SpecialType.System_String), TypedConstantKind.Primitive, PEModule.ByRefLikeMarker), // message
+                                new TypedConstant(compilation.GetSpecialType(SpecialType.System_Boolean), TypedConstantKind.Primitive, true)), // error=true
+                            isOptionalUse: true));
+                    }
+
+                    AddSynthesizedAttribute(ref attributes, compilation.TrySynthesizeAttribute(WellKnownMember.System_Runtime_CompilerServices_CompilerFeatureRequiredAttribute__ctor,
+                        ImmutableArray.Create(new TypedConstant(compilation.GetSpecialType(SpecialType.System_String), TypedConstantKind.Primitive, nameof(CompilerFeatureRequiredFeatures.RefStructs))),
                         isOptionalUse: true));
                 }
             }