Support 'scoped' modifier for parameters and locals

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

@@ -48,6 +48,7 @@ public override bool HasExplicitReturnType(out RefKind refKind, out TypeWithAnno
             public override bool IsAsync { get { return false; } }
             public override bool IsStatic => false;
             public override RefKind RefKind(int index) { return Microsoft.CodeAnalysis.RefKind.None; }
+            public override DeclarationScope Scope(int index) => DeclarationScope.Unscoped;
             public override MessageID MessageID { get { return MessageID.IDS_FeatureQueryExpression; } } // TODO: what is the correct ID here?
             public override Location ParameterLocation(int index) { return _parameters[index].Locations[0]; }
             public override TypeWithAnnotations ParameterTypeWithAnnotations(int index) { throw new ArgumentException(); } // implicitly typed

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

@@ -2814,6 +2814,7 @@ private BoundExpression BindOutVariableDeclarationArgument(
                     CheckFeatureAvailability(declarationExpression, MessageID.IDS_FeatureExpressionVariablesInQueriesAndInitializers, diagnostics);
                 }
 
+                // PROTOTYPE: Test with 'out scoped R' and 'out scoped var', with -langversion:10 and -langversion:11.
                 bool isConst = false;
                 AliasSymbol alias;
                 var declType = BindVariableTypeWithAnnotations(declarationExpression, diagnostics, typeSyntax, ref isConst, out isVar, out alias);
@@ -7105,7 +7106,7 @@ protected BoundExpression BindFieldAccess(
             // If this is a ref field from another compilation, check for support for ref fields.
             // No need to check for a reference to a field declared in this compilation since
             // we check at the declaration site. (Check RefKind after checking compilation to
-            // avoid cycles for source symbols.
+            // avoid cycles for source symbols.)
             if ((object)Compilation.SourceModule != fieldSymbol.OriginalDefinition.ContainingModule &&
                 fieldSymbol.RefKind != RefKind.None)
             {

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

@@ -40,6 +40,7 @@ private UnboundLambda AnalyzeAnonymousFunction(
 
             ImmutableArray<string> names = default;
             ImmutableArray<RefKind> refKinds = default;
+            ImmutableArray<DeclarationScope> scopes = default;
             ImmutableArray<bool> nullCheckedOpt = default;
             ImmutableArray<TypeWithAnnotations> types = default;
             RefKind returnRefKind = RefKind.None;
@@ -99,10 +100,10 @@ private UnboundLambda AnalyzeAnonymousFunction(
             if (parameterSyntaxList != null)
             {
                 var hasExplicitlyTypedParameterList = true;
-                var allValue = true;
 
                 var typesBuilder = ArrayBuilder<TypeWithAnnotations>.GetInstance();
                 var refKindsBuilder = ArrayBuilder<RefKind>.GetInstance();
+                var scopesBuilder = ArrayBuilder<DeclarationScope>.GetInstance();
                 var nullCheckedBuilder = ArrayBuilder<bool>.GetInstance();
                 var attributesBuilder = ArrayBuilder<SyntaxList<AttributeListSyntax>>.GetInstance();
 
@@ -138,31 +139,31 @@ private UnboundLambda AnalyzeAnonymousFunction(
                     var typeSyntax = p.Type;
                     TypeWithAnnotations type = default;
                     var refKind = RefKind.None;
+                    var scope = DeclarationScope.Unscoped;
 
                     if (typeSyntax == null)
                     {
                         hasExplicitlyTypedParameterList = false;
                     }
                     else
                     {
+                        bool scopedBeforeRef = false;
+                        bool scopedAfterRef = false;
                         type = BindType(typeSyntax, diagnostics);
                         foreach (var modifier in p.Modifiers)
                         {
                             switch (modifier.Kind())
                             {
                                 case SyntaxKind.RefKeyword:
                                     refKind = RefKind.Ref;
-                                    allValue = false;
                                     break;
 
                                 case SyntaxKind.OutKeyword:
                                     refKind = RefKind.Out;
-                                    allValue = false;
                                     break;
 
                                 case SyntaxKind.InKeyword:
                                     refKind = RefKind.In;
-                                    allValue = false;
                                     break;
 
                                 case SyntaxKind.ParamsKeyword:
@@ -175,13 +176,34 @@ private UnboundLambda AnalyzeAnonymousFunction(
                                 case SyntaxKind.ThisKeyword:
                                     Error(diagnostics, ErrorCode.ERR_ThisInBadContext, modifier);
                                     break;
+
+                                case SyntaxKind.ScopedKeyword:
+                                    ModifierUtils.CheckScopedModifierAvailability(p, modifier, diagnostics);
+                                    if (refKind == RefKind.None)
+                                    {
+                                        scopedBeforeRef = true;
+                                    }
+                                    else
+                                    {
+                                        scopedAfterRef = true;
+                                    }
+                                    break;
                             }
                         }
+                        if (scopedAfterRef)
+                        {
+                            scope = DeclarationScope.ValueScoped;
+                        }
+                        else if (scopedBeforeRef)
+                        {
+                            scope = (refKind == RefKind.None) ? DeclarationScope.ValueScoped : DeclarationScope.RefScoped;
+                        }
                     }
 
                     namesBuilder.Add(p.Identifier.ValueText);
                     typesBuilder.Add(type);
                     refKindsBuilder.Add(refKind);
+                    scopesBuilder.Add(scope);
                     nullCheckedBuilder.Add(isNullChecked(p));
                     attributesBuilder.Add(syntax.Kind() == SyntaxKind.ParenthesizedLambdaExpression ? p.AttributeLists : default);
                 }
@@ -193,11 +215,16 @@ private UnboundLambda AnalyzeAnonymousFunction(
                     types = typesBuilder.ToImmutable();
                 }
 
-                if (!allValue)
+                if (refKindsBuilder.Any(r => r != RefKind.None))
                 {
                     refKinds = refKindsBuilder.ToImmutable();
                 }
 
+                if (scopesBuilder.Any(s => s != DeclarationScope.Unscoped))
+                {
+                    scopes = scopesBuilder.ToImmutable();
+                }
+
                 if (nullCheckedBuilder.Contains(true))
                 {
                     nullCheckedOpt = nullCheckedBuilder.ToImmutable();
@@ -209,6 +236,7 @@ private UnboundLambda AnalyzeAnonymousFunction(
                 }
 
                 typesBuilder.Free();
+                scopesBuilder.Free();
                 refKindsBuilder.Free();
                 nullCheckedBuilder.Free();
                 attributesBuilder.Free();
@@ -221,7 +249,7 @@ private UnboundLambda AnalyzeAnonymousFunction(
 
             namesBuilder.Free();
 
-            return UnboundLambda.Create(syntax, this, diagnostics.AccumulatesDependencies, returnRefKind, returnType, parameterAttributes, refKinds, types, names, discardsOpt, nullCheckedOpt, isAsync, isStatic);
+            return UnboundLambda.Create(syntax, this, diagnostics.AccumulatesDependencies, returnRefKind, returnType, parameterAttributes, refKinds, scopes, types, names, discardsOpt, nullCheckedOpt, isAsync, isStatic);
 
             static bool isNullChecked(ParameterSyntax parameter)
                 => parameter.ExclamationExclamationToken.IsKind(SyntaxKind.ExclamationExclamationToken);
@@ -322,10 +350,17 @@ private UnboundLambda BindAnonymousFunction(AnonymousFunctionExpressionSyntax sy
                 for (int i = 0; i < lambda.ParameterCount; i++)
                 {
                     // UNDONE: Where do we report improper use of pointer types?
-                    var type = lambda.Data.ParameterTypeWithAnnotations(i);
-                    if (type.HasType && type.IsStatic)
+                    var type = data.ParameterTypeWithAnnotations(i).Type;
+                    if (type is { })
                     {
-                        Error(diagnostics, ErrorFacts.GetStaticClassParameterCode(useWarning: false), syntax, type.Type);
+                        if (type.IsStatic)
+                        {
+                            Error(diagnostics, ErrorFacts.GetStaticClassParameterCode(useWarning: false), syntax, type);
+                        }
+                        if (data.Scope(i) == DeclarationScope.ValueScoped && !type.IsErrorTypeOrRefLikeType())
+                        {
+                            diagnostics.Add(ErrorCode.ERR_ScopedRefAndRefStructOnly, data.ParameterLocation(i));
+                        }
                     }
                 }
             }

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

@@ -694,6 +694,22 @@ private BoundStatement BindDeclarationStatementParts(LocalDeclarationStatementSy
             var typeSyntax = node.Declaration.Type.SkipRef(out _);
             bool isConst = node.IsConst;
 
+            foreach (var modifier in node.Modifiers)
+            {
+                // Check for support for 'scoped'. Duplicate modifiers are reported
+                // as errors in parsing rather than here.
+                if (modifier.Kind() == SyntaxKind.ScopedKeyword)
+                {
+                    ModifierUtils.CheckScopedModifierAvailability(node, modifier, diagnostics);
+                }
+            }
+
+            if (node.Declaration.Type is RefTypeSyntax { ScopedKeyword: var scopedKeyword } &&
+                scopedKeyword.Kind() == SyntaxKind.ScopedKeyword)
+            {
+                ModifierUtils.CheckScopedModifierAvailability(typeSyntax, scopedKeyword, diagnostics);
+            }
+
             bool isVar;
             AliasSymbol alias;
             TypeWithAnnotations declType = BindVariableTypeWithAnnotations(node.Declaration, diagnostics, typeSyntax, ref isConst, isVar: out isVar, alias: out alias);
@@ -1078,6 +1094,11 @@ protected BoundLocalDeclaration BindVariableDeclaration(
                 hasErrors = true;
             }
 
+            if (localSymbol.Scope == DeclarationScope.ValueScoped && !declTypeOpt.Type.IsErrorTypeOrRefLikeType())
+            {
+                localDiagnostics.Add(ErrorCode.ERR_ScopedRefAndRefStructOnly, typeSyntax.Location);
+            }
+
             localSymbol.SetTypeWithAnnotations(declTypeOpt);
 
             if (initializerOpt != null)
@@ -1203,11 +1224,12 @@ private SourceLocalSymbol LocateDeclaredVariableSymbol(SyntaxToken identifier, T
                 localSymbol = SourceLocalSymbol.MakeLocal(
                     ContainingMemberOrLambda,
                     this,
-                    false, // do not allow ref
+                    allowRefKind: false, // do not allow ref
                     typeSyntax,
                     identifier,
                     kind,
-                    equalsValue);
+                    equalsValue,
+                    hasScopedModifier: false);
             }
 
             return localSymbol;

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

@@ -31,7 +31,7 @@ protected override ImmutableArray<LocalSymbol> BuildLocals()
             var declarationOpt = _syntax.Declaration;
             if ((declarationOpt != null) && (declarationOpt.Identifier.Kind() != SyntaxKind.None))
             {
-                locals.Add(SourceLocalSymbol.MakeLocal(this.ContainingMemberOrLambda, this, false, declarationOpt.Type, declarationOpt.Identifier, LocalDeclarationKind.CatchVariable));
+                locals.Add(SourceLocalSymbol.MakeLocal(this.ContainingMemberOrLambda, this, allowRefKind: false, declarationOpt.Type, declarationOpt.Identifier, LocalDeclarationKind.CatchVariable, initializer: null, hasScopedModifier: false));
             }
 
             if (_syntax.Filter != null)

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

@@ -45,7 +45,7 @@ protected override ImmutableArray<LocalSymbol> BuildLocals()
 
                 foreach (VariableDeclaratorSyntax declarator in _syntax.Declaration.Variables)
                 {
-                    locals.Add(MakeLocal(_syntax.Declaration, declarator, LocalDeclarationKind.FixedVariable));
+                    locals.Add(MakeLocal(_syntax.Declaration, declarator, LocalDeclarationKind.FixedVariable, hasScopedModifier: false)); // PROTOTYPE: Handle 'scoped' modifier.
 
                     // also gather expression-declared variables from the bracketed argument lists and the initializers
                     ExpressionVariableFinder.FindExpressionVariables(this, locals, declarator);

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

@@ -45,7 +45,7 @@ protected override ImmutableArray<LocalSymbol> BuildLocals()
 
                 foreach (var vdecl in _syntax.Declaration.Variables)
                 {
-                    var localSymbol = MakeLocal(_syntax.Declaration, vdecl, LocalDeclarationKind.RegularVariable);
+                    var localSymbol = MakeLocal(_syntax.Declaration, vdecl, LocalDeclarationKind.RegularVariable, hasScopedModifier: false); // PROTOTYPE: Handle 'scoped' modifier.
                     locals.Add(localSymbol);
 
                     // also gather expression-declared variables from the bracketed argument lists and the initializers

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

@@ -241,9 +241,10 @@ internal void BuildLocals(Binder enclosingBinder, StatementSyntax statement, Arr
                         {
                             kind = LocalDeclarationKind.RegularVariable;
                         }
+                        bool hasScopedModifier = decl.Modifiers.Any(SyntaxKind.ScopedKeyword);
                         foreach (var vdecl in decl.Declaration.Variables)
                         {
-                            var localSymbol = MakeLocal(decl.Declaration, vdecl, kind, localDeclarationBinder);
+                            var localSymbol = MakeLocal(decl.Declaration, vdecl, kind, hasScopedModifier, localDeclarationBinder);
                             locals.Add(localSymbol);
 
                             // also gather expression-declared variables from the bracketed argument lists and the initializers
@@ -313,7 +314,7 @@ internal void BuildLocalFunctions(StatementSyntax statement, ref ArrayBuilder<Lo
             }
         }
 
-        protected SourceLocalSymbol MakeLocal(VariableDeclarationSyntax declaration, VariableDeclaratorSyntax declarator, LocalDeclarationKind kind, Binder initializerBinderOpt = null)
+        protected SourceLocalSymbol MakeLocal(VariableDeclarationSyntax declaration, VariableDeclaratorSyntax declarator, LocalDeclarationKind kind, bool hasScopedModifier, Binder initializerBinderOpt = null)
         {
             return SourceLocalSymbol.MakeLocal(
                 this.ContainingMemberOrLambda,
@@ -323,6 +324,7 @@ protected SourceLocalSymbol MakeLocal(VariableDeclarationSyntax declaration, Var
                 declarator.Identifier,
                 kind,
                 declarator.Initializer,
+                hasScopedModifier,
                 initializerBinderOpt);
         }
 

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

@@ -55,7 +55,7 @@ protected override ImmutableArray<LocalSymbol> BuildLocals()
 
                 foreach (VariableDeclaratorSyntax declarator in declarationSyntax.Variables)
                 {
-                    locals.Add(MakeLocal(declarationSyntax, declarator, LocalDeclarationKind.UsingVariable));
+                    locals.Add(MakeLocal(declarationSyntax, declarator, LocalDeclarationKind.UsingVariable, hasScopedModifier: false)); // PROTOTYPE: Handle 'scoped' modifier.
 
                     // also gather expression-declared variables from the bracketed argument lists and the initializers
                     ExpressionVariableFinder.FindExpressionVariables(this, locals, declarator);