Merge pull request #55042 from dotnet/features/struct-ctors

Merge `features/struct-ctors` into `main` branch

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

@@ -5326,7 +5326,7 @@ protected BoundExpression BindClassCreationExpression(
                 ReportDiagnosticsIfObsolete(diagnostics, method, node, hasBaseReceiver: false);
                 // NOTE: Use-site diagnostics were reported during overload resolution.
 
-                ConstantValue constantValueOpt = (initializerSyntaxOpt == null && method.IsDefaultValueTypeConstructor()) ?
+                ConstantValue constantValueOpt = (initializerSyntaxOpt == null && method.IsDefaultValueTypeConstructor(requireZeroInit: true)) ?
                     FoldParameterlessValueTypeConstructor(type) :
                     null;
 

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

@@ -3306,7 +3306,7 @@ private BindValueKind GetRequiredReturnValueKind(RefKind refKind)
             return requiredValueKind;
         }
 
-        public virtual BoundNode BindMethodBody(CSharpSyntaxNode syntax, BindingDiagnosticBag diagnostics)
+        public virtual BoundNode BindMethodBody(CSharpSyntaxNode syntax, BindingDiagnosticBag diagnostics, bool includesFieldInitializers = false)
         {
             switch (syntax)
             {
@@ -3316,7 +3316,7 @@ public virtual BoundNode BindMethodBody(CSharpSyntaxNode syntax, BindingDiagnost
                 case BaseMethodDeclarationSyntax method:
                     if (method.Kind() == SyntaxKind.ConstructorDeclaration)
                     {
-                        return BindConstructorBody((ConstructorDeclarationSyntax)method, diagnostics);
+                        return BindConstructorBody((ConstructorDeclarationSyntax)method, diagnostics, includesFieldInitializers);
                     }
 
                     return BindMethodBody(method, method.Body, method.ExpressionBody, diagnostics);
@@ -3388,32 +3388,41 @@ internal virtual BoundExpressionStatement BindConstructorInitializer(PrimaryCons
             return constructorInitializer;
         }
 
-        private BoundNode BindConstructorBody(ConstructorDeclarationSyntax constructor, BindingDiagnosticBag diagnostics)
+        private BoundNode BindConstructorBody(ConstructorDeclarationSyntax constructor, BindingDiagnosticBag diagnostics, bool includesFieldInitializers)
         {
-            if (constructor.Initializer == null && constructor.Body == null && constructor.ExpressionBody == null)
+            ConstructorInitializerSyntax initializer = constructor.Initializer;
+            if (initializer == null && constructor.Body == null && constructor.ExpressionBody == null)
             {
                 return null;
             }
 
             Binder bodyBinder = this.GetBinder(constructor);
             Debug.Assert(bodyBinder != null);
 
-            if (constructor.Initializer?.IsKind(SyntaxKind.ThisConstructorInitializer) != true &&
+            bool thisInitializer = initializer?.IsKind(SyntaxKind.ThisConstructorInitializer) == true;
+            if (!thisInitializer &&
                 ContainingType.GetMembersUnordered().OfType<SynthesizedRecordConstructor>().Any())
             {
                 var constructorSymbol = (MethodSymbol)this.ContainingMember();
                 if (!constructorSymbol.IsStatic &&
                     !SynthesizedRecordCopyCtor.IsCopyConstructor(constructorSymbol))
                 {
                     // Note: we check the constructor initializer of copy constructors elsewhere
-                    Error(diagnostics, ErrorCode.ERR_UnexpectedOrMissingConstructorInitializerInRecord, constructor.Initializer?.ThisOrBaseKeyword ?? constructor.Identifier);
+                    Error(diagnostics, ErrorCode.ERR_UnexpectedOrMissingConstructorInitializerInRecord, initializer?.ThisOrBaseKeyword ?? constructor.Identifier);
                 }
             }
 
+            // The `: this()` initializer is ignored when it is a default value type constructor
+            // and we need to include field initializers into the constructor.
+            bool skipInitializer = includesFieldInitializers
+                && thisInitializer
+                && ContainingType.IsDefaultValueTypeConstructor(initializer);
+
             // Using BindStatement to bind block to make sure we are reusing results of partial binding in SemanticModel
             return new BoundConstructorMethodBody(constructor,
                                                   bodyBinder.GetDeclaredLocalsForScope(constructor),
-                                                  constructor.Initializer == null ? null : bodyBinder.BindConstructorInitializer(constructor.Initializer, diagnostics),
+                                                  skipInitializer ? new BoundNoOpStatement(constructor, NoOpStatementFlavor.Default)
+                                                      : initializer == null ? null : bodyBinder.BindConstructorInitializer(initializer, diagnostics),
                                                   constructor.Body == null ? null : (BoundBlock)bodyBinder.BindStatement(constructor.Body, diagnostics),
                                                   constructor.ExpressionBody == null ?
                                                       null :

src/Compilers/CSharp/Portable/BoundTree/BoundNodes.xml

@@ -2185,7 +2185,7 @@
 
   <Node Name="BoundConstructorMethodBody" Base="BoundMethodBodyBase">
     <Field Name="Locals" Type="ImmutableArray&lt;LocalSymbol&gt;"/>
-    <Field Name="Initializer" Type="BoundExpressionStatement?"/>
+    <Field Name="Initializer" Type="BoundStatement?"/>
   </Node>
 
   <!-- Node only used during nullability flow analysis to represent an expression with an updated nullability -->

src/Compilers/CSharp/Portable/CSharpResources.resx

@@ -1691,9 +1691,6 @@ If such a class is used as a base class and if the deriving class defines a dest
   <data name="ERR_InterfacesCantContainConversionOrEqualityOperators" xml:space="preserve">
     <value>Conversion, equality, or inequality operators declared in interfaces must be abstract</value>
   </data>
-  <data name="ERR_StructsCantContainDefaultConstructor" xml:space="preserve">
-    <value>Structs cannot contain explicit parameterless constructors</value>
-  </data>
   <data name="ERR_EnumsCantContainDefaultConstructor" xml:space="preserve">
     <value>Enums cannot contain explicit parameterless constructors</value>
   </data>
@@ -1709,9 +1706,6 @@ If such a class is used as a base class and if the deriving class defines a dest
   <data name="ERR_BadTypeReference" xml:space="preserve">
     <value>'{0}': cannot reference a type through an expression; try '{1}' instead</value>
   </data>
-  <data name="ERR_FieldInitializerInStruct" xml:space="preserve">
-    <value>'{0}': cannot have instance property or field initializers in structs</value>
-  </data>
   <data name="ERR_BadDestructorName" xml:space="preserve">
     <value>Name of destructor must match name of type</value>
   </data>
@@ -6597,6 +6591,12 @@ To remove the warning, you can use /reference instead (set the Embed Interop Typ
   <data name="IDS_FeaturePositionalFieldsInRecords" xml:space="preserve">
     <value>positional fields in records</value>
   </data>
+  <data name="IDS_FeatureParameterlessStructConstructors" xml:space="preserve">
+    <value>parameterless struct constructors</value>
+  </data>
+  <data name="IDS_FeatureStructFieldInitializers" xml:space="preserve">
+    <value>struct field initializers</value>
+  </data>
   <data name="IDS_FeatureVarianceSafetyForStaticInterfaceMembers" xml:space="preserve">
     <value>variance safety for static interface members</value>
   </data>
@@ -6736,6 +6736,9 @@ To remove the warning, you can use /reference instead (set the Embed Interop Typ
   <data name="ERR_InterpolatedStringHandlerCreationCannotUseDynamic" xml:space="preserve">
     <value>An interpolated string handler construction cannot use dynamic. Manually construct an instance of '{0}'.</value>
   </data>
+  <data name="ERR_NonPublicParameterlessStructConstructor" xml:space="preserve">
+    <value>The parameterless struct constructor must be 'public'.</value>
+  </data>
   <data name="IDS_FeatureStaticAbstractMembersInInterfaces" xml:space="preserve">
     <value>static abstract members in interfaces</value>
   </data>

src/Compilers/CSharp/Portable/CodeGen/EmitExpression.cs

@@ -1481,7 +1481,7 @@ private enum CallKind
 
         private void EmitCallExpression(BoundCall call, UseKind useKind)
         {
-            if (call.Method.IsDefaultValueTypeConstructor())
+            if (call.Method.IsDefaultValueTypeConstructor(requireZeroInit: true))
             {
                 EmitDefaultValueTypeConstructorCallExpression(call);
             }
@@ -1956,7 +1956,7 @@ private void EmitConvertedStackAllocExpression(BoundConvertedStackAllocExpressio
         private void EmitObjectCreationExpression(BoundObjectCreationExpression expression, bool used)
         {
             MethodSymbol constructor = expression.Constructor;
-            if (constructor.IsDefaultValueTypeConstructor())
+            if (constructor.IsDefaultValueTypeConstructor(requireZeroInit: true))
             {
                 EmitInitObj(expression.Type, used, expression.Syntax);
             }

src/Compilers/CSharp/Portable/Compilation/MemberSemanticModel.cs

@@ -2462,7 +2462,7 @@ private BoundNode TryGetBoundNodeFromMap(CSharpSyntaxNode node)
                 return null;
             }
 
-            public override BoundNode BindMethodBody(CSharpSyntaxNode node, BindingDiagnosticBag diagnostics)
+            public override BoundNode BindMethodBody(CSharpSyntaxNode node, BindingDiagnosticBag diagnostics, bool includeInitializersInBody)
             {
                 BoundNode boundNode = TryGetBoundNodeFromMap(node);
 
@@ -2471,7 +2471,7 @@ public override BoundNode BindMethodBody(CSharpSyntaxNode node, BindingDiagnosti
                     return boundNode;
                 }
 
-                boundNode = base.BindMethodBody(node, diagnostics);
+                boundNode = base.BindMethodBody(node, diagnostics, includeInitializersInBody);
 
                 return boundNode;
             }

src/Compilers/CSharp/Portable/Compilation/MethodBodySemanticModel.cs

@@ -23,14 +23,14 @@ internal readonly struct InitialState
         {
             internal readonly CSharpSyntaxNode Syntax;
             internal readonly BoundNode? Body;
-            internal readonly ExecutableCodeBinder? Binder;
+            internal readonly Binder? Binder;
             internal readonly NullableWalker.SnapshotManager? SnapshotManager;
             internal readonly ImmutableDictionary<Symbol, Symbol>? RemappedSymbols;
 
             internal InitialState(
                 CSharpSyntaxNode syntax,
                 BoundNode? bodyOpt = null,
-                ExecutableCodeBinder? binder = null,
+                Binder? binder = null,
                 NullableWalker.SnapshotManager? snapshotManager = null,
                 ImmutableDictionary<Symbol, Symbol>? remappedSymbols = null)
             {

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

@@ -965,7 +965,7 @@ private void CompileMethod(
                 }
 
                 // no need to emit the default ctor, we are not emitting those
-                if (methodSymbol.IsDefaultValueTypeConstructor())
+                if (methodSymbol.IsDefaultValueTypeConstructor(requireZeroInit: true))
                 {
                     return;
                 }
@@ -1036,7 +1036,11 @@ private void CompileMethod(
                             getFinalNullableState: true,
                             out processedInitializers.AfterInitializersState);
                     }
-                    body = BindMethodBody(methodSymbol, compilationState, diagsForCurrentMethod, processedInitializers.AfterInitializersState, out importChain, out originalBodyNested, out forSemanticModel);
+
+                    body = BindMethodBody(methodSymbol, compilationState, diagsForCurrentMethod, processedInitializers.AfterInitializersState,
+                        includeInitializersInBody && !processedInitializers.BoundInitializers.IsEmpty,
+                        out importChain, out originalBodyNested, out forSemanticModel);
+
                     if (diagsForCurrentMethod.HasAnyErrors() && body != null)
                     {
                         body = (BoundBlock)body.WithHasErrors();
@@ -1194,7 +1198,7 @@ forSemanticModel.Syntax is { } semanticModelSyntax &&
                     if (!hasErrors && (hasBody || includeNonEmptyInitializersInBody))
                     {
                         Debug.Assert(!(methodSymbol.IsImplicitInstanceConstructor && methodSymbol.ParameterCount == 0) ||
-                                     !methodSymbol.ContainingType.IsStructType());
+                                     !methodSymbol.IsDefaultValueTypeConstructor(requireZeroInit: true));
 
                         // Fields must be initialized before constructor initializer (which is the first statement of the analyzed body, if specified),
                         // so that the initialization occurs before any method overridden by the declaring class can be invoked from the base constructor
@@ -1673,12 +1677,13 @@ private static void GetStateMachineSlotDebugInfo(
         // NOTE: can return null if the method has no body.
         internal static BoundBlock BindMethodBody(MethodSymbol method, TypeCompilationState compilationState, BindingDiagnosticBag diagnostics)
         {
-            return BindMethodBody(method, compilationState, diagnostics, nullableInitialState: null, out _, out _, out _);
+            return BindMethodBody(method, compilationState, diagnostics, nullableInitialState: null, includesFieldInitializers: false, out _, out _, out _);
         }
 
         // NOTE: can return null if the method has no body.
         private static BoundBlock BindMethodBody(MethodSymbol method, TypeCompilationState compilationState, BindingDiagnosticBag diagnostics,
                                                  NullableWalker.VariableState nullableInitialState,
+                                                 bool includesFieldInitializers,
                                                  out ImportChain importChain, out bool originalBodyNested,
                                                  out MethodBodySemanticModel.InitialState forSemanticModel)
         {
@@ -1707,18 +1712,17 @@ syntaxNode is ConstructorDeclarationSyntax constructorSyntax &&
                         constructorSyntax.Identifier.ValueText);
                 }
 
-                ExecutableCodeBinder bodyBinder = sourceMethod.TryGetBodyBinder();
-
-                if (sourceMethod.IsExtern || sourceMethod.IsDefaultValueTypeConstructor())
+                Debug.Assert(!sourceMethod.IsDefaultValueTypeConstructor(requireZeroInit: false));
+                if (sourceMethod.IsExtern)
                 {
                     return null;
                 }
 
+                Binder bodyBinder = sourceMethod.TryGetBodyBinder();
                 if (bodyBinder != null)
                 {
                     importChain = bodyBinder.ImportChain;
-
-                    BoundNode methodBody = bodyBinder.BindMethodBody(syntaxNode, diagnostics);
+                    BoundNode methodBody = bodyBinder.BindMethodBody(syntaxNode, diagnostics, includesFieldInitializers);
                     BoundNode methodBodyForSemanticModel = methodBody;
                     NullableWalker.SnapshotManager snapshotManager = null;
                     ImmutableDictionary<Symbol, Symbol> remappedSymbols = null;
@@ -1760,9 +1764,15 @@ syntaxNode is ConstructorDeclarationSyntax constructorSyntax &&
                             var constructor = (BoundConstructorMethodBody)methodBody;
                             body = constructor.BlockBody ?? constructor.ExpressionBody;
 
-                            if (constructor.Initializer != null)
+                            if (constructor.Initializer is BoundNoOpStatement)
+                            {
+                                // We have field initializers and `: this()` is a default value type constructor.
+                                Debug.Assert(body is not null);
+                                return body;
+                            }
+                            else if (constructor.Initializer is BoundExpressionStatement expressionStatement)
                             {
-                                ReportCtorInitializerCycles(method, constructor.Initializer.Expression, compilationState, diagnostics);
+                                ReportCtorInitializerCycles(method, expressionStatement.Expression, compilationState, diagnostics);
 
                                 if (body == null)
                                 {
@@ -1778,6 +1788,7 @@ syntaxNode is ConstructorDeclarationSyntax constructorSyntax &&
                             }
                             else
                             {
+                                Debug.Assert(constructor.Initializer is null);
                                 Debug.Assert(constructor.Locals.IsEmpty);
                             }
                             break;

src/Compilers/CSharp/Portable/Emitter/Model/AttributeDataAdapter.cs

@@ -35,10 +35,10 @@ internal abstract partial class CSharpAttributeData : Cci.ICustomAttribute
 
         Cci.IMethodReference Cci.ICustomAttribute.Constructor(EmitContext context, bool reportDiagnostics)
         {
-            if (this.AttributeConstructor.IsDefaultValueTypeConstructor())
+            if (this.AttributeConstructor.IsDefaultValueTypeConstructor(requireZeroInit: true))
             {
-                // Parameter constructors for structs exist in symbol table, but are not emitted.
-                // Produce an error since we cannot use it (instead of crashing):
+                // Default parameterless constructors for structs exist in symbol table, but are not emitted.
+                // Produce an error since we cannot use it (instead of crashing).
                 // Details: https://github.com/dotnet/roslyn/issues/19394
 
                 if (reportDiagnostics)

src/Compilers/CSharp/Portable/Emitter/Model/PEModuleBuilder.cs

@@ -1143,7 +1143,7 @@ internal Cci.IMethodReference Translate(
             BoundArgListOperator optArgList = null,
             bool needDeclaration = false)
         {
-            Debug.Assert(!methodSymbol.IsDefaultValueTypeConstructor());
+            Debug.Assert(!methodSymbol.IsDefaultValueTypeConstructor(requireZeroInit: true));
             Debug.Assert(optArgList == null || (methodSymbol.IsVararg && !needDeclaration));
 
             Cci.IMethodReference unexpandedMethodRef = Translate(methodSymbol, syntaxNodeOpt, diagnostics, needDeclaration);

src/Compilers/CSharp/Portable/Emitter/NoPia/EmbeddedTypesManager.cs

@@ -454,7 +454,7 @@ internal override EmbeddedMethod EmbedMethod(
             DiagnosticBag diagnostics)
         {
             Debug.Assert(method.AdaptedSymbol.IsDefinition);
-            Debug.Assert(!method.AdaptedMethodSymbol.IsDefaultValueTypeConstructor());
+            Debug.Assert(!method.AdaptedMethodSymbol.IsDefaultValueTypeConstructor(requireZeroInit: false));
 
             EmbeddedMethod embedded = new EmbeddedMethod(type, method);
             EmbeddedMethod cached = EmbeddedMethodsMap.GetOrAdd(method, embedded);

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

@@ -384,12 +384,12 @@ internal enum ErrorCode
         ERR_BadBinaryOperatorSignature = 563,
         ERR_BadShiftOperatorSignature = 564,
         ERR_InterfacesCantContainConversionOrEqualityOperators = 567,
-        ERR_StructsCantContainDefaultConstructor = 568,
+        //ERR_StructsCantContainDefaultConstructor = 568,
         ERR_CantOverrideBogusMethod = 569,
         ERR_BindToBogus = 570,
         ERR_CantCallSpecialMethod = 571,
         ERR_BadTypeReference = 572,
-        ERR_FieldInitializerInStruct = 573,
+        //ERR_FieldInitializerInStruct = 573,
         ERR_BadDestructorName = 574,
         ERR_OnlyClassesCanContainDestructors = 575,
         ERR_ConflictAliasAndMember = 576,
@@ -1981,6 +1981,7 @@ internal enum ErrorCode
         ERR_FileScopedAndNormalNamespace = 8955,
         ERR_FileScopedNamespaceNotBeforeAllMembers = 8956,
         ERR_NoImplicitConvTargetTypedConditional = 8957,
+        ERR_NonPublicParameterlessStructConstructor = 8958,
 
         #endregion