Support UnscopedRefAttribute (#62783)

docs/compilers/CSharp/Compiler Breaking Changes - DotNet 7.md

@@ -128,15 +128,24 @@ static ref T ReturnOutParamByRef<T>(out T t)
 }
 ```
 
-A possible workaround is to change the method signature to pass the parameter by `ref` instead.
+Possible workarounds are:
+1. Use `System.Diagnostics.CodeAnalysis.UnscopedRefAttribute` to mark the reference as unscoped.
+    ```csharp
+    static ref T ReturnOutParamByRef<T>([UnscopedRef] out T t)
+    {
+        t = default;
+        return ref t; // ok
+    }
+    ```
 
-```csharp
-static ref T ReturnRefParamByRef<T>(ref T t)
-{
-    t = default;
-    return ref t; // ok
-}
-```
+1. Change the method signature to pass the parameter by `ref`.
+    ```csharp
+    static ref T ReturnRefParamByRef<T>(ref T t)
+    {
+        t = default;
+        return ref t; // ok
+    }
+    ```
 
 ## Method ref struct return escape analysis depends on ref escape of ref arguments
 

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

@@ -782,7 +782,7 @@ private uint GetParameterValEscape(ParameterSymbol parameter)
         {
             if (UseUpdatedEscapeRules)
             {
-                return parameter.Scope == DeclarationScope.ValueScoped ?
+                return parameter.EffectiveScope == DeclarationScope.ValueScoped ?
                     Binder.TopLevelScope :
                     Binder.ExternalScope;
             }
@@ -796,7 +796,7 @@ private uint GetParameterRefEscape(ParameterSymbol parameter)
         {
             if (UseUpdatedEscapeRules)
             {
-                return parameter.RefKind is RefKind.None || parameter.Scope != DeclarationScope.Unscoped ? Binder.TopLevelScope : Binder.ExternalScope;
+                return parameter.RefKind is RefKind.None || parameter.EffectiveScope != DeclarationScope.Unscoped ? Binder.TopLevelScope : Binder.ExternalScope;
             }
             else
             {
@@ -1822,7 +1822,7 @@ bool considerParameter(ParameterSymbol? parameter)
                     // SPEC: For a given argument `a` that is passed to parameter `p`:
                     // SPEC:  1. ...
                     // SPEC: 2. If `p` is `scoped` then `a` does not contribute *safe-to-escape* when considering arguments.
-                    if (parameter?.Scope == DeclarationScope.ValueScoped)
+                    if (parameter?.EffectiveScope == DeclarationScope.ValueScoped)
                     {
                         return false;
                     }
@@ -1909,7 +1909,7 @@ private static RefKind GetEffectiveRefKind(
                 }
             }
 
-            scope = paramIndex >= 0 ? parameters[paramIndex].Scope : DeclarationScope.Unscoped;
+            scope = paramIndex >= 0 ? parameters[paramIndex].EffectiveScope : DeclarationScope.Unscoped;
             return effectiveRefKind;
         }
 
@@ -2227,6 +2227,8 @@ internal uint GetRefEscape(BoundExpression expr, uint scopeOfTheContainingExpres
                     return ((BoundLocal)expr).LocalSymbol.RefEscapeScope;
 
                 case BoundKind.ThisReference:
+                    Debug.Assert(this.ContainingMember() is MethodSymbol { ThisParameter: not null });
+
                     var thisref = (BoundThisReference)expr;
 
                     // "this" is an RValue, unless in a struct.
@@ -2235,6 +2237,15 @@ internal uint GetRefEscape(BoundExpression expr, uint scopeOfTheContainingExpres
                         break;
                     }
 
+                    if (UseUpdatedEscapeRules)
+                    {
+                        if (this.ContainingMember() is MethodSymbol { ThisParameter: var thisParameter } &&
+                            thisParameter.EffectiveScope == DeclarationScope.Unscoped)
+                        {
+                            return Binder.ExternalScope;
+                        }
+                    }
+
                     //"this" is not returnable by reference in a struct.
                     // can ref escape to any other level
                     return Binder.TopLevelScope;
@@ -2481,6 +2492,8 @@ internal bool CheckRefEscape(SyntaxNode node, BoundExpression expr, uint escapeF
                     return CheckLocalRefEscape(node, local, escapeTo, checkingReceiver, diagnostics);
 
                 case BoundKind.ThisReference:
+                    Debug.Assert(this.ContainingMember() is MethodSymbol { ThisParameter: not null });
+
                     var thisref = (BoundThisReference)expr;
 
                     // "this" is an RValue, unless in a struct.
@@ -2492,6 +2505,15 @@ internal bool CheckRefEscape(SyntaxNode node, BoundExpression expr, uint escapeF
                     //"this" is not returnable by reference in a struct.
                     if (escapeTo == Binder.ExternalScope)
                     {
+                        if (UseUpdatedEscapeRules)
+                        {
+                            if (this.ContainingMember() is MethodSymbol { ThisParameter: var thisParameter } &&
+                                thisParameter.EffectiveScope == DeclarationScope.Unscoped)
+                            {
+                                // can ref escape to any other level
+                                return true;
+                            }
+                        }
                         Error(diagnostics, ErrorCode.ERR_RefReturnStructThis, node);
                         return false;
                     }

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

@@ -8846,8 +8846,8 @@ private MethodGroupResolution ResolveDefaultMethodGroup(
             }
 
             var parameters = method.Parameters;
-            var parameterScopes = parameters.Any(p => p.Scope != DeclarationScope.Unscoped) ?
-                parameters.SelectAsArray(p => p.Scope) :
+            var parameterScopes = parameters.Any(p => p.EffectiveScope != DeclarationScope.Unscoped) ?
+                parameters.SelectAsArray(p => p.EffectiveScope) :
                 default;
             return GetMethodGroupOrLambdaDelegateType(node.Syntax, method.RefKind, method.ReturnTypeWithAnnotations, method.ParameterRefKinds, parameterScopes, method.ParameterTypesWithAnnotations);
         }

src/Compilers/CSharp/Portable/CSharpResources.resx

@@ -7205,4 +7205,7 @@ To remove the warning, you can use /reference instead (set the Embed Interop Typ
   <data name="ERR_ScopedTypeNameDisallowed" xml:space="preserve">
     <value>Types and aliases cannot be named 'scoped'.</value>
   </data>
+  <data name="ERR_UnscopedRefAttributeUnsupportedTarget" xml:space="preserve">
+    <value>UnscopedRefAttribute can only be applied to 'out' parameters, 'ref' parameters that refer to 'ref struct' types, and instance methods and properties on 'struct' types other than constructors and 'init' accessors.</value>
+  </data>
 </root>

src/Compilers/CSharp/Portable/Errors/ErrorCode.cs

@@ -2111,6 +2111,7 @@ internal enum ErrorCode
         ERR_CannotMatchOnINumberBase = 9060,
         ERR_MisplacedScoped = 9061,
         ERR_ScopedTypeNameDisallowed = 9062,
+        ERR_UnscopedRefAttributeUnsupportedTarget = 9063,
 
         #endregion
 

src/Compilers/CSharp/Portable/Errors/ErrorFacts.cs

@@ -2212,6 +2212,7 @@ internal static bool IsBuildOnlyDiagnostic(ErrorCode code)
                 case ErrorCode.ERR_CannotMatchOnINumberBase:
                 case ErrorCode.ERR_MisplacedScoped:
                 case ErrorCode.ERR_ScopedTypeNameDisallowed:
+                case ErrorCode.ERR_UnscopedRefAttributeUnsupportedTarget:
                     return false;
                 default:
                     // NOTE: All error codes must be explicitly handled in this switch statement

src/Compilers/CSharp/Portable/Lowering/StateMachineRewriter/SynthesizedStateMachineProperty.cs

@@ -153,6 +153,8 @@ public override bool IsExtern
 
         internal override bool IsRequired => false;
 
+        internal sealed override bool HasUnscopedRefAttribute => false;
+
         internal override ObsoleteAttributeData ObsoleteAttributeData
         {
             get { return null; }

src/Compilers/CSharp/Portable/Lowering/SynthesizedMethodBaseSymbol.cs

@@ -136,7 +136,7 @@ private ImmutableArray<ParameterSymbol> MakeParameters()
                     ordinal++,
                     p.RefKind,
                     p.Name,
-                    p.Scope,
+                    p.DeclaredScope,
                     // the synthesized parameter doesn't need to have the same ref custom modifiers as the base
                     refCustomModifiers: default,
                     inheritAttributes ? p as SourceComplexParameterSymbolBase : null));

src/Compilers/CSharp/Portable/SymbolDisplay/SymbolDisplayVisitor.Members.cs

@@ -612,7 +612,7 @@ void visitFunctionPointerSignature(IMethodSymbol symbol)
                 foreach (var param in symbol.Parameters)
                 {
                     // https://github.com/dotnet/roslyn/issues/61647: Use public API.
-                    Debug.Assert((param as Symbols.PublicModel.ParameterSymbol)?.GetSymbol<ParameterSymbol>().Scope switch
+                    Debug.Assert((param as Symbols.PublicModel.ParameterSymbol)?.GetSymbol<ParameterSymbol>().EffectiveScope switch
                     {
                         null => true,
                         DeclarationScope.Unscoped => param.RefKind != RefKind.Out,
@@ -780,7 +780,7 @@ public override void VisitParameter(IParameterSymbol symbol)
                 AddCustomModifiersIfNeeded(symbol.RefCustomModifiers, leadingSpace: false, trailingSpace: true);
 
                 // https://github.com/dotnet/roslyn/issues/61647: Use public API.
-                if ((symbol as Symbols.PublicModel.ParameterSymbol)?.GetSymbol<ParameterSymbol>().Scope == DeclarationScope.ValueScoped &&
+                if ((symbol as Symbols.PublicModel.ParameterSymbol)?.GetSymbol<ParameterSymbol>().EffectiveScope == DeclarationScope.ValueScoped &&
                     format.CompilerInternalOptions.IncludesOption(SymbolDisplayCompilerInternalOptions.IncludeScoped))
                 {
                     AddKeyword(SyntaxKind.ScopedKeyword);
@@ -1079,7 +1079,7 @@ private void AddParameterRefKindIfNeeded(IParameterSymbol symbol)
             if (format.ParameterOptions.IncludesOption(SymbolDisplayParameterOptions.IncludeParamsRefOut))
             {
                 // https://github.com/dotnet/roslyn/issues/61647: Use public API.
-                if ((symbol as Symbols.PublicModel.ParameterSymbol)?.GetSymbol<ParameterSymbol>().Scope == DeclarationScope.RefScoped &&
+                if ((symbol as Symbols.PublicModel.ParameterSymbol)?.GetSymbol<ParameterSymbol>().EffectiveScope == DeclarationScope.RefScoped &&
                     symbol.RefKind != RefKind.Out &&
                     format.CompilerInternalOptions.IncludesOption(SymbolDisplayCompilerInternalOptions.IncludeScoped))
                 {

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

@@ -131,6 +131,8 @@ public override bool IsAbstract
 
             internal override bool IsRequired => false;
 
+            internal sealed override bool HasUnscopedRefAttribute => false;
+
             internal sealed override ObsoleteAttributeData ObsoleteAttributeData
             {
                 get { return null; }

src/Compilers/CSharp/Portable/Symbols/Attributes/WellKnownAttributeData/MethodWellKnownAttributeData.cs

@@ -44,6 +44,22 @@ public bool HasSkipLocalsInitAttribute
             }
         }
 
+        private bool _hasUnscopedRefAttribute;
+        public bool HasUnscopedRefAttribute
+        {
+            get
+            {
+                VerifySealed(expected: true);
+                return _hasUnscopedRefAttribute;
+            }
+            set
+            {
+                VerifySealed(expected: false);
+                _hasUnscopedRefAttribute = value;
+                SetDataStored();
+            }
+        }
+
         private ImmutableArray<string> _memberNotNullAttributeData = ImmutableArray<string>.Empty;
 
         public void AddNotNullMember(string memberName)

src/Compilers/CSharp/Portable/Symbols/Attributes/WellKnownAttributeData/ParameterEarlyWellKnownAttributeData.cs

@@ -11,5 +11,20 @@ namespace Microsoft.CodeAnalysis.CSharp.Symbols
     /// </summary>
     internal sealed class ParameterEarlyWellKnownAttributeData : CommonParameterEarlyWellKnownAttributeData
     {
+        private bool _hasUnscopedRefAttribute;
+        public bool HasUnscopedRefAttribute
+        {
+            get
+            {
+                VerifySealed(expected: true);
+                return _hasUnscopedRefAttribute;
+            }
+            set
+            {
+                VerifySealed(expected: false);
+                _hasUnscopedRefAttribute = value;
+                SetDataStored();
+            }
+        }
     }
 }

src/Compilers/CSharp/Portable/Symbols/Attributes/WellKnownAttributeData/PropertyWellKnownAttributeData.cs

@@ -94,6 +94,22 @@ public bool HasSkipLocalsInitAttribute
             }
         }
 
+        private bool _hasUnscopedRefAttribute;
+        public bool HasUnscopedRefAttribute
+        {
+            get
+            {
+                VerifySealed(expected: true);
+                return _hasUnscopedRefAttribute;
+            }
+            set
+            {
+                VerifySealed(expected: false);
+                _hasUnscopedRefAttribute = value;
+                SetDataStored();
+            }
+        }
+
         private ImmutableArray<string> _memberNotNullAttributeData = ImmutableArray<string>.Empty;
 
         public void AddNotNullMember(string memberName)

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

@@ -284,5 +284,7 @@ protected override bool HasSetsRequiredMembersImpl
                 return false;
             }
         }
+
+        internal sealed override bool HasUnscopedRefAttribute => false;
     }
 }

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

@@ -79,6 +79,8 @@ public ErrorPropertySymbol(Symbol containingSymbol, TypeSymbol type, string name
 
         internal override bool IsRequired => false;
 
+        internal sealed override bool HasUnscopedRefAttribute => false;
+
         internal sealed override ObsoleteAttributeData ObsoleteAttributeData { get { return null; } }
 
         public override ImmutableArray<ParameterSymbol> Parameters { get { return ImmutableArray<ParameterSymbol>.Empty; } }

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

@@ -831,5 +831,6 @@ public override bool IsVararg
         internal override IEnumerable<SecurityAttribute> GetSecurityInformation() => throw ExceptionUtilities.Unreachable;
         internal sealed override bool IsNullableAnalysisEnabled() => throw ExceptionUtilities.Unreachable;
         protected sealed override bool HasSetsRequiredMembersImpl => throw ExceptionUtilities.Unreachable;
+        internal sealed override bool HasUnscopedRefAttribute => false;
     }
 }

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

@@ -29,7 +29,8 @@ public FunctionPointerParameterSymbol(TypeWithAnnotations typeWithAnnotations, R
         public override int Ordinal { get; }
         public override Symbol ContainingSymbol => _containingSymbol;
         public override ImmutableArray<CustomModifier> RefCustomModifiers { get; }
-        internal override DeclarationScope Scope => RefKind == RefKind.Out ? DeclarationScope.RefScoped : DeclarationScope.Unscoped;
+        internal override DeclarationScope DeclaredScope => RefKind == RefKind.Out ? DeclarationScope.RefScoped : DeclarationScope.Unscoped;
+        internal override DeclarationScope EffectiveScope => DeclaredScope;
 
         public override bool Equals(Symbol other, TypeCompareKind compareKind)
         {

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:
             //
-            // |w|v|u|t|s|r|q|p|ooo|n|m|l|k|j|i|h|g|f|e|d|c|b|aaaaa|
+            // |y|x|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.
@@ -74,7 +74,9 @@ private struct PackedFlags
             // u = IsUnmanagedCallersOnlyAttributePopulated. 1 bit.
             // v = IsSetsRequiredMembersBit. 1 bit.
             // w = IsSetsRequiredMembersPopulated. 1 bit.
-            // 4 bits remain for future purposes.
+            // x = IsUnscopedRef. 1 bit.
+            // y = IsUnscopedRefPopulated. 1 bit.
+            // 2 bits remain for future purposes.
 
             private const int MethodKindOffset = 0;
             private const int MethodKindMask = 0x1F;
@@ -102,6 +104,8 @@ private struct PackedFlags
             private const int IsUnmanagedCallersOnlyAttributePopulatedBit = 0x1 << 26;
             private const int HasSetsRequiredMembersBit = 0x1 << 27;
             private const int HasSetsRequiredMembersPopulatedBit = 0x1 << 28;
+            private const int IsUnscopedRefBit = 0x1 << 29;
+            private const int IsUnscopedRefPopulatedBit = 0x1 << 30;
 
             private int _bits;
 
@@ -140,6 +144,8 @@ public MethodKind MethodKind
             public bool IsUnmanagedCallersOnlyAttributePopulated => (_bits & IsUnmanagedCallersOnlyAttributePopulatedBit) != 0;
             public bool HasSetsRequiredMembers => (_bits & HasSetsRequiredMembersBit) != 0;
             public bool HasSetsRequiredMembersPopulated => (_bits & HasSetsRequiredMembersPopulatedBit) != 0;
+            public bool IsUnscopedRef => (_bits & IsUnscopedRefBit) != 0;
+            public bool IsUnscopedRefPopulated => (_bits & IsUnscopedRefPopulatedBit) != 0;
 
 #if DEBUG
             static PackedFlags()
@@ -254,6 +260,14 @@ public bool InitializeSetsRequiredMembersBit(bool value)
 
                 return ThreadSafeFlagOperations.Set(ref _bits, bitsToSet);
             }
+
+            public bool InitializeIsUnscopedRef(bool value)
+            {
+                int bitsToSet = IsUnscopedRefPopulatedBit;
+                if (value) bitsToSet |= IsUnscopedRefBit;
+
+                return ThreadSafeFlagOperations.Set(ref _bits, bitsToSet);
+            }
         }
 
         /// <summary>
@@ -1610,5 +1624,20 @@ public override bool AreLocalsZeroed
         internal bool TestIsExtensionBitTrue => _packedFlags.IsExtensionMethod;
 
         internal sealed override bool IsNullableAnalysisEnabled() => throw ExceptionUtilities.Unreachable;
+
+        internal sealed override bool HasUnscopedRefAttribute
+        {
+            get
+            {
+                if (!_packedFlags.IsUnscopedRefPopulated)
+                {
+                    var moduleSymbol = _containingType.ContainingPEModule;
+                    bool unscopedRef = moduleSymbol.Module.HasUnscopedRefAttribute(_handle);
+                    _packedFlags.InitializeIsUnscopedRef(unscopedRef);
+                }
+
+                return _packedFlags.IsUnscopedRef;
+            }
+        }
     }
 }