[automated] Merge branch 'main' => 'release/dev18.0'

docs/compilers/CSharp/Compiler Breaking Changes - DotNet 10.md

@@ -314,3 +314,20 @@ CSharpCompilation.Create("test",
 
 Similarly this can be observed when using the command-line argument `/refonly`
 or the `ProduceOnlyReferenceAssembly` MSBuild property.
+
+## `partial` cannot be a return type of methods
+
+***Introduced in Visual Studio 2022 version 17.14***
+
+The [partial events and constructors](https://github.com/dotnet/csharplang/issues/9058) language feature
+allows the `partial` modifier in more places and so it cannot be a return type unless escaped:
+
+```cs
+class C
+{
+    partial F() => new partial(); // previously worked
+    @partial F() => new partial(); // workaround
+}
+
+class partial { }
+```

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>
@@ -7983,14 +7983,14 @@ To remove the warning, you can use /reference instead (set the Embed Interop Typ
   <data name="ERR_PartialPropertyInitMismatch" xml:space="preserve">
     <value>Property accessor '{0}' must be '{1}' to match the definition part</value>
   </data>
-  <data name="ERR_PartialPropertyTypeDifference" xml:space="preserve">
-    <value>Both partial property declarations must have the same type.</value>
+  <data name="ERR_PartialMemberTypeDifference" xml:space="preserve">
+    <value>Both partial member declarations must have the same type.</value>
   </data>
-  <data name="WRN_PartialPropertySignatureDifference" xml:space="preserve">
-    <value>Partial property declarations '{0}' and '{1}' have signature differences.</value>
+  <data name="WRN_PartialMemberSignatureDifference" xml:space="preserve">
+    <value>Partial member declarations '{0}' and '{1}' have signature differences.</value>
   </data>
-  <data name="WRN_PartialPropertySignatureDifference_Title" xml:space="preserve">
-    <value>Partial property declarations have signature differences.</value>
+  <data name="WRN_PartialMemberSignatureDifference_Title" xml:space="preserve">
+    <value>Partial member declarations have signature differences.</value>
   </data>
   <data name="ERR_PartialPropertyRequiredDifference" xml:space="preserve">
     <value>Both partial property declarations must be required or neither may be required</value>
@@ -8050,4 +8050,25 @@ To remove the warning, you can use /reference instead (set the Embed Interop Typ
   <data name="ERR_DataSectionStringLiteralHashCollision" xml:space="preserve">
     <value>Cannot emit this string literal into the data section because it has XXHash128 collision with another string literal: {0}</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>
+  <data name="ERR_PartialConstructorInitializer" xml:space="preserve">
+    <value>'{0}': only the implementing declaration of a partial constructor can have an initializer</value>
+  </data>
 </root>

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

@@ -1800,13 +1800,7 @@ private Symbol GetDeclaredMember(NamespaceOrTypeSymbol container, TextSpan decla
                 }
 
                 // Handle the case of the implementation of a partial member.
-                Symbol partial = symbol switch
-                {
-                    MethodSymbol method => method.PartialImplementationPart,
-                    SourcePropertySymbol property => property.PartialImplementationPart,
-                    _ => null
-                };
-
+                Symbol partial = symbol.GetPartialImplementationPart();
                 if ((object)partial != null)
                 {
                     var loc = partial.GetFirstLocation();

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

@@ -258,13 +258,7 @@ public override void DefaultVisit(Symbol symbol)
             bool shouldSkipPartialDefinitionComments = false;
             if (symbol.IsPartialDefinition())
             {
-                Symbol? implementationPart = symbol switch
-                {
-                    MethodSymbol method => method.PartialImplementationPart,
-                    SourcePropertySymbol property => property.PartialImplementationPart,
-                    _ => null
-                };
-
+                Symbol? implementationPart = symbol.GetPartialImplementationPart();
                 if (implementationPart is not null)
                 {
                     Visit(implementationPart);

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

@@ -2332,8 +2332,8 @@ internal enum ErrorCode
         ERR_PartialPropertyMissingAccessor = 9252,
         ERR_PartialPropertyUnexpectedAccessor = 9253,
         ERR_PartialPropertyInitMismatch = 9254,
-        ERR_PartialPropertyTypeDifference = 9255,
-        WRN_PartialPropertySignatureDifference = 9256,
+        ERR_PartialMemberTypeDifference = 9255,
+        WRN_PartialMemberSignatureDifference = 9256,
         ERR_PartialPropertyRequiredDifference = 9257,
 
         WRN_FieldIsAmbiguous = 9258,
@@ -2362,6 +2362,13 @@ internal enum ErrorCode
 
         ERR_DataSectionStringLiteralHashCollision = 9274,
 
+        ERR_PartialMemberMissingImplementation = 9275,
+        ERR_PartialMemberMissingDefinition = 9276,
+        ERR_PartialMemberDuplicateDefinition = 9277,
+        ERR_PartialMemberDuplicateImplementation = 9278,
+        ERR_PartialEventInitializer = 9279,
+        ERR_PartialConstructorInitializer = 9280,
+
         // 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

@@ -566,7 +566,7 @@ internal static int GetWarningLevel(ErrorCode code)
                 case ErrorCode.WRN_CollectionExpressionRefStructMayAllocate:
                 case ErrorCode.WRN_CollectionExpressionRefStructSpreadMayAllocate:
                 case ErrorCode.WRN_ConvertingLock:
-                case ErrorCode.WRN_PartialPropertySignatureDifference:
+                case ErrorCode.WRN_PartialMemberSignatureDifference:
                 case ErrorCode.WRN_FieldIsAmbiguous:
                 case ErrorCode.WRN_UninitializedNonNullableBackingField:
                 case ErrorCode.WRN_AccessorDoesNotUseBackingField:
@@ -2464,8 +2464,8 @@ or ErrorCode.ERR_PartialPropertyDuplicateImplementation
                 or ErrorCode.ERR_PartialPropertyMissingAccessor
                 or ErrorCode.ERR_PartialPropertyUnexpectedAccessor
                 or ErrorCode.ERR_PartialPropertyInitMismatch
-                or ErrorCode.ERR_PartialPropertyTypeDifference
-                or ErrorCode.WRN_PartialPropertySignatureDifference
+                or ErrorCode.ERR_PartialMemberTypeDifference
+                or ErrorCode.WRN_PartialMemberSignatureDifference
                 or ErrorCode.ERR_PartialPropertyRequiredDifference
                 or ErrorCode.WRN_FieldIsAmbiguous
                 or ErrorCode.ERR_InlineArrayAttributeOnRecord
@@ -2481,6 +2481,12 @@ 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
+                or ErrorCode.ERR_PartialConstructorInitializer
                     => 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/Errors/MessageID.cs

@@ -296,6 +296,8 @@ internal enum MessageID
         IDS_FeatureFirstClassSpan = MessageBase + 12849,
         IDS_FeatureUnboundGenericTypesInNameof = MessageBase + 12850,
         IDS_FeatureSimpleLambdaParameterModifiers = MessageBase + 12851,
+
+        IDS_FeaturePartialEventsAndConstructors = MessageBase + 12852,
     }
 
     // Message IDs may refer to strings that need to be localized.
@@ -480,6 +482,7 @@ internal static LanguageVersion RequiredVersion(this MessageID feature)
                 case MessageID.IDS_FeatureFirstClassSpan:
                 case MessageID.IDS_FeatureUnboundGenericTypesInNameof:
                 case MessageID.IDS_FeatureSimpleLambdaParameterModifiers:
+                case MessageID.IDS_FeaturePartialEventsAndConstructors:
                     return LanguageVersion.Preview;
 
                 // C# 13.0 features.

src/Compilers/CSharp/Portable/Parser/LanguageParser.cs

@@ -1634,24 +1634,25 @@ private bool IsPartialType()
 
         private bool IsPartialMember()
         {
-            // note(cyrusn): this could have been written like so:
-            //
-            //  return
-            //    this.CurrentToken.ContextualKind == SyntaxKind.PartialKeyword &&
-            //    this.PeekToken(1).Kind == SyntaxKind.VoidKeyword;
-            //
-            // However, we want to be lenient and allow the user to write 
-            // 'partial' in most modifier lists.  We will then provide them with
-            // a more specific message later in binding that they are doing 
-            // something wrong.
-            //
-            // Some might argue that the simple check would suffice.
-            // However, we'd like to maintain behavior with 
-            // previously shipped versions, and so we're keeping this code.
+            Debug.Assert(this.CurrentToken.ContextualKind == SyntaxKind.PartialKeyword);
+
+            // Check for:
+            //   partial event
+            if (this.PeekToken(1).Kind == SyntaxKind.EventKeyword)
+            {
+                return true;
+            }
+
+            // Check for constructor:
+            //   partial Identifier(
+            if (this.PeekToken(1).Kind == SyntaxKind.IdentifierToken &&
+                this.PeekToken(2).Kind == SyntaxKind.OpenParenToken)
+            {
+                return IsFeatureEnabled(MessageID.IDS_FeaturePartialEventsAndConstructors);
+            }
 
-            // Here we check for:
+            // Check for method/property:
             //   partial ReturnType MemberName
-            Debug.Assert(this.CurrentToken.ContextualKind == SyntaxKind.PartialKeyword);
             using var _ = this.GetDisposableResetPoint(resetOnDispose: true);
 
             this.EatToken(); // partial
@@ -5681,7 +5682,7 @@ private bool IsTrueIdentifier()
         {
             if (this.CurrentToken.Kind == SyntaxKind.IdentifierToken)
             {
-                if (!IsCurrentTokenPartialKeywordOfPartialMethodOrType() &&
+                if (!IsCurrentTokenPartialKeywordOfPartialMemberOrType() &&
                     !IsCurrentTokenQueryKeywordInQuery() &&
                     !IsCurrentTokenWhereOfConstraintClause())
                 {
@@ -5728,7 +5729,7 @@ private SyntaxToken ParseIdentifierToken(ErrorCode code = ErrorCode.ERR_Identifi
                 // show the correct parameter help in this case.  So, when we see "partial" we check if it's being used
                 // as an identifier or as a contextual keyword.  If it's the latter then we bail out.  See
                 // Bug: vswhidbey/542125
-                if (IsCurrentTokenPartialKeywordOfPartialMethodOrType() || IsCurrentTokenQueryKeywordInQuery())
+                if (IsCurrentTokenPartialKeywordOfPartialMemberOrType() || IsCurrentTokenQueryKeywordInQuery())
                 {
                     var result = CreateMissingIdentifierToken();
                     result = this.AddError(result, ErrorCode.ERR_InvalidExprTerm, this.CurrentToken.Text);
@@ -5755,7 +5756,7 @@ private bool IsCurrentTokenQueryKeywordInQuery()
             return this.IsInQuery && this.IsCurrentTokenQueryContextualKeyword;
         }
 
-        private bool IsCurrentTokenPartialKeywordOfPartialMethodOrType()
+        private bool IsCurrentTokenPartialKeywordOfPartialMemberOrType()
         {
             if (this.CurrentToken.ContextualKind == SyntaxKind.PartialKeyword)
             {

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

@@ -228,6 +228,10 @@ internal virtual bool IsExplicitInterfaceImplementation
         /// </remarks>
         public abstract ImmutableArray<EventSymbol> ExplicitInterfaceImplementations { get; }
 
+        internal virtual EventSymbol? PartialImplementationPart => null;
+        internal virtual EventSymbol? PartialDefinitionPart => null;
+        internal virtual bool IsPartialDefinition => false;
+
         /// <summary>
         /// Gets the kind of this symbol.
         /// </summary>

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

@@ -551,7 +551,10 @@ 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 }
+                or SourceEventAccessorSymbol { IsPartial: true };
         }
 
         internal static bool IsPartialImplementation(this Symbol member)
@@ -560,7 +563,10 @@ 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 }
+                or SourceEventAccessorSymbol { IsPartialImplementation: true };
         }
 
         internal static bool IsPartialDefinition(this Symbol member)
@@ -569,9 +575,38 @@ 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 }
+                or SourceEventAccessorSymbol { IsPartialDefinition: true };
         }
 
+#nullable enable
+        internal static Symbol? GetPartialImplementationPart(this Symbol member)
+        {
+            Debug.Assert(member.IsDefinition);
+            return member switch
+            {
+                MethodSymbol method => method.PartialImplementationPart,
+                SourcePropertySymbol property => property.PartialImplementationPart,
+                SourceEventSymbol ev => ev.PartialImplementationPart,
+                _ => null,
+            };
+        }
+
+        internal static Symbol? GetPartialDefinitionPart(this Symbol member)
+        {
+            Debug.Assert(member.IsDefinition);
+            return member switch
+            {
+                MethodSymbol method => method.PartialDefinitionPart,
+                SourcePropertySymbol property => property.PartialDefinitionPart,
+                SourceEventSymbol ev => ev.PartialDefinitionPart,
+                _ => null,
+            };
+        }
+#nullable disable
+
         internal static bool ContainsTupleNames(this Symbol member)
         {
             switch (member.Kind)

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

@@ -88,6 +88,12 @@ ImmutableArray<IEventSymbol> IEventSymbol.ExplicitInterfaceImplementations
 
         bool IEventSymbol.IsWindowsRuntimeEvent => _underlying.IsWindowsRuntimeEvent;
 
+        IEventSymbol? IEventSymbol.PartialDefinitionPart => _underlying.PartialDefinitionPart.GetPublicSymbol();
+
+        IEventSymbol? IEventSymbol.PartialImplementationPart => _underlying.PartialImplementationPart.GetPublicSymbol();
+
+        bool IEventSymbol.IsPartialDefinition => _underlying.IsPartialDefinition;
+
         #region ISymbol Members
 
         protected override void Accept(SymbolVisitor visitor)