Partial events and constructors: merge and check symbols

src/Compilers/CSharp/Portable/Binder/BinderFactory.BinderFactoryVisitor.cs

@@ -598,25 +598,16 @@ bool checkSymbol(Symbol sym, TextSpan memberSpan, SymbolKind kind, out Symbol re
                         return false;
                     }
 
-                    if (kind is SymbolKind.Method or SymbolKind.Property)
+                    if (kind is SymbolKind.Method or SymbolKind.Property or SymbolKind.Event)
                     {
                         if (InSpan(sym.GetFirstLocation(), this.syntaxTree, memberSpan))
                         {
                             return true;
                         }
 
-                        // If this is a partial member, the member represents the defining part,
-                        // not the implementation (member.Locations includes both parts). If the
-                        // span is in fact in the implementation, return that member instead.
-                        if (sym switch
-#pragma warning disable format
-                            {
-                                MethodSymbol method => (Symbol)method.PartialImplementationPart,
-                                SourcePropertySymbol property => property.PartialImplementationPart,
-                                _ => throw ExceptionUtilities.UnexpectedValue(sym)
-                            }
-#pragma warning restore format
-                            is { } implementation)
+                        // If this is a partial member, the member represents the defining part, not the implementation.
+                        // If the span is in fact in the implementation, return that member instead.
+                        if (sym.GetPartialImplementationPart() is { } implementation)
                         {
                             if (InSpan(implementation.GetFirstLocation(), this.syntaxTree, memberSpan))
                             {

src/Compilers/CSharp/Portable/CSharpResources.resx

@@ -1171,7 +1171,7 @@
     <value>Cannot implicitly convert type '{0}' to '{1}'. An explicit conversion exists (are you missing a cast?)</value>
   </data>
   <data name="ERR_PartialMisplaced" xml:space="preserve">
-    <value>The 'partial' modifier can only appear immediately before 'class', 'record', 'struct', 'interface', or a method or property return type.</value>
+    <value>The 'partial' modifier can only appear immediately before 'class', 'record', 'struct', 'interface', 'event', an instance constructor name, or a method or property return type.</value>
   </data>
   <data name="ERR_ImportedCircularBase" xml:space="preserve">
     <value>Imported type '{0}' is invalid. It contains a circular base type dependency.</value>
@@ -8047,4 +8047,22 @@ To remove the warning, you can use /reference instead (set the Embed Interop Typ
   <data name="WRN_InterceptsLocationAttributeUnsupportedSignature_Title" xml:space="preserve">
     <value>'InterceptsLocationAttribute(string, int, int)' is not supported. Move to 'InterceptableLocation'-based generation of these attributes instead. (https://github.com/dotnet/roslyn/issues/72133)</value>
   </data>
+  <data name="IDS_FeaturePartialEventsAndConstructors" xml:space="preserve">
+    <value>partial events and constructors</value>
+  </data>
+  <data name="ERR_PartialMemberMissingImplementation" xml:space="preserve">
+    <value>Partial member '{0}' must have an implementation part.</value>
+  </data>
+  <data name="ERR_PartialMemberMissingDefinition" xml:space="preserve">
+    <value>Partial member '{0}' must have a definition part.</value>
+  </data>
+  <data name="ERR_PartialMemberDuplicateDefinition" xml:space="preserve">
+    <value>Partial member '{0}' may not have multiple defining declarations.</value>
+  </data>
+  <data name="ERR_PartialMemberDuplicateImplementation" xml:space="preserve">
+    <value>Partial member '{0}' may not have multiple implementing declarations.</value>
+  </data>
+  <data name="ERR_PartialEventInitializer" xml:space="preserve">
+    <value>'{0}': partial event cannot have initializer</value>
+  </data>
 </root>

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

@@ -2360,6 +2360,13 @@ internal enum ErrorCode
         ERR_ImplicitlyTypedParamsParameter = 9272,
         ERR_VariableDeclarationNamedField = 9273,
 
+        // PROTOTYPE: compact
+        ERR_PartialMemberMissingImplementation = 9400,
+        ERR_PartialMemberMissingDefinition = 9401,
+        ERR_PartialMemberDuplicateDefinition = 9402,
+        ERR_PartialMemberDuplicateImplementation = 9403,
+        ERR_PartialEventInitializer = 9404,
+
         // Note: you will need to do the following after adding errors:
         //  1) Update ErrorFacts.IsBuildOnlyDiagnostic (src/Compilers/CSharp/Portable/Errors/ErrorFacts.cs)
 

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

@@ -2479,6 +2479,11 @@ or ErrorCode.WRN_UnscopedRefAttributeOldRules
                 or ErrorCode.WRN_InterceptsLocationAttributeUnsupportedSignature
                 or ErrorCode.ERR_ImplicitlyTypedParamsParameter
                 or ErrorCode.ERR_VariableDeclarationNamedField
+                or ErrorCode.ERR_PartialMemberMissingImplementation
+                or ErrorCode.ERR_PartialMemberMissingDefinition
+                or ErrorCode.ERR_PartialMemberDuplicateDefinition
+                or ErrorCode.ERR_PartialMemberDuplicateImplementation
+                or ErrorCode.ERR_PartialEventInitializer
                     => false,
             };
 #pragma warning restore CS8524 // The switch expression does not handle some values of its input type (it is not exhaustive) involving an unnamed enum value.

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

@@ -228,6 +228,9 @@ internal virtual bool IsExplicitInterfaceImplementation
         /// </remarks>
         public abstract ImmutableArray<EventSymbol> ExplicitInterfaceImplementations { get; }
 
+        internal virtual EventSymbol? PartialImplementationPart => null;
+        internal virtual EventSymbol? PartialDefinitionPart => null;
+
         /// <summary>
         /// Gets the kind of this symbol.
         /// </summary>

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

@@ -551,7 +551,9 @@ internal static bool IsPartialMember(this Symbol member)
             return member
                 is SourceOrdinaryMethodSymbol { IsPartial: true }
                 or SourcePropertySymbol { IsPartial: true }
-                or SourcePropertyAccessorSymbol { IsPartial: true };
+                or SourcePropertyAccessorSymbol { IsPartial: true }
+                or SourceConstructorSymbol { IsPartial: true }
+                or SourceEventSymbol { IsPartial: true };
         }
 
         internal static bool IsPartialImplementation(this Symbol member)
@@ -560,7 +562,9 @@ internal static bool IsPartialImplementation(this Symbol member)
             return member
                 is SourceOrdinaryMethodSymbol { IsPartialImplementation: true }
                 or SourcePropertySymbol { IsPartialImplementation: true }
-                or SourcePropertyAccessorSymbol { IsPartialImplementation: true };
+                or SourcePropertyAccessorSymbol { IsPartialImplementation: true }
+                or SourceConstructorSymbol { IsPartialImplementation: true }
+                or SourceEventSymbol { IsPartialImplementation: true };
         }
 
         internal static bool IsPartialDefinition(this Symbol member)
@@ -569,9 +573,24 @@ internal static bool IsPartialDefinition(this Symbol member)
             return member
                 is SourceOrdinaryMethodSymbol { IsPartialDefinition: true }
                 or SourcePropertySymbol { IsPartialDefinition: true }
-                or SourcePropertyAccessorSymbol { IsPartialDefinition: true };
+                or SourcePropertyAccessorSymbol { IsPartialDefinition: true }
+                or SourceConstructorSymbol { IsPartialDefinition: true }
+                or SourceEventSymbol { IsPartialDefinition: true };
         }
 
+#nullable enable
+        internal static Symbol? GetPartialImplementationPart(this Symbol member)
+        {
+            return member switch
+            {
+                MethodSymbol method => method.PartialImplementationPart,
+                SourcePropertySymbol property => property.PartialImplementationPart,
+                SourceEventSymbol ev => ev.PartialImplementationPart,
+                _ => null,
+            };
+        }
+#nullable disable
+
         internal static bool ContainsTupleNames(this Symbol member)
         {
             switch (member.Kind)

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

@@ -223,6 +223,26 @@ internal static void CheckFeatureAvailabilityForStaticAbstractMembersInInterface
             }
         }
 
+#nullable enable
+        internal static void CheckFeatureAvailabilityForPartialEventsAndConstructors(Location location, BindingDiagnosticBag diagnostics)
+        {
+            Debug.Assert(location.SourceTree is not null);
+
+            LanguageVersion availableVersion = ((CSharpParseOptions)location.SourceTree.Options).LanguageVersion;
+            LanguageVersion requiredVersion = MessageID.IDS_FeaturePartialEventsAndConstructors.RequiredVersion();
+            if (availableVersion < requiredVersion)
+            {
+                ReportUnsupportedModifiersForLanguageVersion(
+                    DeclarationModifiers.Partial,
+                    DeclarationModifiers.Partial,
+                    location,
+                    diagnostics,
+                    availableVersion,
+                    requiredVersion);
+            }
+        }
+#nullable disable
+
         internal static DeclarationModifiers AdjustModifiersForAnInterfaceMember(DeclarationModifiers mods, bool hasBody, bool isExplicitInterfaceImplementation)
         {
             if (isExplicitInterfaceImplementation)

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

@@ -2,8 +2,6 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 // See the LICENSE file in the project root for more information.
 
-#nullable disable
-
 using System.Diagnostics;
 using Microsoft.CodeAnalysis.CSharp.Syntax;
 using Roslyn.Utilities;
@@ -12,6 +10,9 @@ namespace Microsoft.CodeAnalysis.CSharp.Symbols
 {
     internal sealed class SourceConstructorSymbol : SourceConstructorSymbolBase
     {
+        private SourceConstructorSymbol? _otherPartOfPartial;
+
+#nullable disable
         public static SourceConstructorSymbol CreateConstructorSymbol(
             SourceMemberContainerTypeSymbol containingType,
             ConstructorDeclarationSyntax syntax,
@@ -88,10 +89,11 @@ private static (DeclarationModifiers, Flags) MakeModifiersAndFlags(
             out bool modifierErrors,
             out bool report_ERR_StaticConstructorWithAccessModifiers)
         {
-            DeclarationModifiers declarationModifiers = MakeModifiers(containingType, syntax, methodKind, syntax.HasAnyBody(), location, diagnostics, out modifierErrors, out report_ERR_StaticConstructorWithAccessModifiers);
-            Flags flags = MakeFlags(
-                methodKind, RefKind.None, declarationModifiers, returnsVoid: true, returnsVoidIsSet: true,
-                isExpressionBodied: syntax.IsExpressionBodied(), isExtensionMethod: false, isVarArg: syntax.IsVarArg(),
+            bool hasAnyBody = syntax.HasAnyBody();
+            DeclarationModifiers declarationModifiers = MakeModifiers(containingType, syntax, methodKind, hasAnyBody, location, diagnostics, out modifierErrors, out report_ERR_StaticConstructorWithAccessModifiers);
+            Flags flags = new Flags(
+                methodKind, RefKind.None, declarationModifiers, returnsVoid: true, returnsVoidIsSet: true, hasAnyBody: hasAnyBody,
+                isExpressionBodied: syntax.IsExpressionBodied(), isExtensionMethod: false, isVararg: syntax.IsVarArg(),
                 isNullableAnalysisEnabled: isNullableAnalysisEnabled, isExplicitInterfaceImplementation: false,
                 hasThisInitializer: hasThisInitializer);
 
@@ -126,12 +128,17 @@ private static DeclarationModifiers MakeModifiers(
             var defaultAccess = (methodKind == MethodKind.StaticConstructor) ? DeclarationModifiers.None : DeclarationModifiers.Private;
 
             // Check that the set of modifiers is allowed
-            const DeclarationModifiers allowedModifiers =
+            DeclarationModifiers allowedModifiers =
                 DeclarationModifiers.AccessibilityMask |
                 DeclarationModifiers.Static |
                 DeclarationModifiers.Extern |
                 DeclarationModifiers.Unsafe;
 
+            if (methodKind == MethodKind.Constructor)
+            {
+                allowedModifiers |= DeclarationModifiers.Partial;
+            }
+
             bool isInterface = containingType.IsInterface;
             var mods = ModifierUtils.MakeAndCheckNonTypeMemberModifiers(isOrdinaryMethod: false, isForInterfaceMember: isInterface, syntax.Modifiers, defaultAccess, allowedModifiers, location, diagnostics, out modifierErrors);
 
@@ -164,7 +171,7 @@ private static DeclarationModifiers MakeModifiers(
 
         private void CheckModifiers(MethodKind methodKind, bool hasBody, Location location, BindingDiagnosticBag diagnostics)
         {
-            if (!hasBody && !IsExtern)
+            if (!hasBody && !IsExtern && !IsPartial)
             {
                 diagnostics.Add(ErrorCode.ERR_ConcreteMissingBody, location, this);
             }
@@ -176,6 +183,15 @@ private void CheckModifiers(MethodKind methodKind, bool hasBody, Location locati
             {
                 diagnostics.Add(ErrorCode.ERR_ConstructorInStaticClass, location);
             }
+            else if (IsPartial && !ContainingType.IsPartial())
+            {
+                diagnostics.Add(ErrorCode.ERR_PartialMemberOnlyInPartialClass, location);
+            }
+
+            if (IsPartial)
+            {
+                ModifierUtils.CheckFeatureAvailabilityForPartialEventsAndConstructors(location, diagnostics);
+            }
         }
 
         internal override OneOrMany<SyntaxList<AttributeListSyntax>> GetAttributeDeclarations()
@@ -213,5 +229,35 @@ protected override bool IsWithinExpressionOrBlockBody(int position, out int offs
             offset = -1;
             return false;
         }
+
+#nullable enable
+        public sealed override bool IsExtern => PartialImplementationPart is { } implementation ? implementation.IsExtern : HasExternModifier;
+
+        private bool HasAnyBody => flags.HasAnyBody;
+
+        internal bool IsPartialDefinition => IsPartial && !HasAnyBody && !HasExternModifier;
+
+        internal bool IsPartialImplementation => IsPartial && (HasAnyBody || HasExternModifier);
+
+        internal SourceConstructorSymbol? OtherPartOfPartial => _otherPartOfPartial;
+
+        public override MethodSymbol? PartialDefinitionPart => IsPartialImplementation ? OtherPartOfPartial : null;
+
+        public override MethodSymbol? PartialImplementationPart => IsPartialDefinition ? OtherPartOfPartial : null;
+
+        internal static void InitializePartialConstructorParts(SourceConstructorSymbol definition, SourceConstructorSymbol implementation)
+        {
+            Debug.Assert(definition.IsPartialDefinition);
+            Debug.Assert(implementation.IsPartialImplementation);
+
+            Debug.Assert(definition._otherPartOfPartial is not { } alreadySetImplPart || alreadySetImplPart == implementation);
+            Debug.Assert(implementation._otherPartOfPartial is not { } alreadySetDefPart || alreadySetDefPart == definition);
+
+            definition._otherPartOfPartial = implementation;
+            implementation._otherPartOfPartial = definition;
+
+            Debug.Assert(definition._otherPartOfPartial == implementation);
+            Debug.Assert(implementation._otherPartOfPartial == definition);
+        }
     }
 }

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

@@ -170,6 +170,8 @@ internal SourceCustomEventSymbol(SourceMemberContainerTypeSymbol containingType,
                     ImmutableArray.Create<EventSymbol>(explicitlyImplementedEvent);
         }
 
+        protected override bool IsFieldLike => false;
+
         public override TypeWithAnnotations TypeWithAnnotations
         {
             get { return _type; }