Extensions: Close some tracked follow-ups (using static directives)

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

@@ -133,7 +133,6 @@ internal override void GetCandidateExtensionMembersInSingleBinder(ArrayBuilder<S
         {
             Debug.Assert(members.Count == 0);
 
-            // Tracked by https://github.com/dotnet/roslyn/issues/79440 : using directives, test this flag (see TestUnusedExtensionMarksImportsAsUsed)
             bool callerIsSemanticModel = originalBinder.IsSemanticModelBinder;
 
             // We need to avoid collecting multiple candidates for an extension declaration imported both through a namespace and a static class

src/Compilers/CSharp/Portable/CSharpResources.resx

@@ -8202,4 +8202,7 @@ To remove the warning, you can use /reference instead (set the Embed Interop Typ
   <data name="ERR_ExplicitInterfaceMemberReturnTypeMismatch" xml:space="preserve">
     <value>'{0}': return type must be '{1}' to match implemented member '{2}'</value>
   </data>
+  <data name="ParameterRequiresTypeOrIdentifier" xml:space="preserve">
+    <value>ParameterSyntax requires either a type or an identifier.</value>
+  </data>
 </root>

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

@@ -1181,7 +1181,6 @@ forSemanticModel.Syntax is { } semanticModelSyntax &&
                                                             });
                             }
 
-                            // Tracked by https://github.com/dotnet/roslyn/issues/78957 : public API, Ensure we are not messing up relative order of events for extension members (with relation to events for enclosing types, etc.)
                             _compilation.EventQueue.TryEnqueue(new SymbolDeclaredCompilationEvent(
                                 _compilation, methodSymbol, semanticModelWithCachedBoundNodes));
                         }

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

@@ -310,7 +310,6 @@ Cci.ITypeDefinition Cci.ITypeDefinitionMember.ContainingTypeDefinition
                     return synthesizedGlobalMethod.ContainingPrivateImplementationDetailsType;
                 }
 
-                // Tracked by https://github.com/dotnet/roslyn/issues/78827 : code quality, share logic with Cci.ITypeMemberReference.GetContainingType implementation?
                 if (AdaptedMethodSymbol is SynthesizedExtensionMarker marker)
                 {
                     return ((SourceMemberContainerTypeSymbol)AdaptedMethodSymbol.ContainingType.ContainingType).GetExtensionGroupingInfo().GetCorrespondingMarkerType(marker);

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

@@ -221,7 +221,6 @@ ITypeDefinition ITypeDefinitionMember.ContainingTypeDefinition
             {
                 CheckDefinitionInvariant();
 
-                // Tracked by https://github.com/dotnet/roslyn/issues/78827 : code quality, share logic with Cci.ITypeMemberReference.GetContainingType implementation?
                 if (AdaptedPropertySymbol.GetIsNewExtensionMember())
                 {
                     var containingType = AdaptedPropertySymbol.ContainingType;
@@ -249,7 +248,6 @@ ITypeReference ITypeMemberReference.GetContainingType(EmitContext context)
         {
             CheckDefinitionInvariant();
 
-            // Tracked by https://github.com/dotnet/roslyn/issues/78827 : code quality, share logic with Cci.ITypeMemberReference.GetContainingType implementation in MethodSymbolAdapter?
             if (AdaptedPropertySymbol.GetIsNewExtensionMember())
             {
                 var containingType = AdaptedPropertySymbol.ContainingType;

src/Compilers/CSharp/Portable/Generated/CSharpSyntaxGenerator/CSharpSyntaxGenerator.SourceGenerator/Syntax.xml.Syntax.Generated.cs

@@ -13766,8 +13766,11 @@ public sealed partial class ParameterSyntax : BaseParameterSyntax
     internal ParameterSyntax(InternalSyntax.CSharpSyntaxNode green, SyntaxNode? parent, int position)
       : base(green, parent, position)
     {
+        Validate();
     }
 
+    private partial void Validate();
+
     /// <summary>Gets the attribute declaration list.</summary>
     public override SyntaxList<AttributeListSyntax> AttributeLists => new SyntaxList<AttributeListSyntax>(GetRed(ref this.attributeLists, 0));
 

src/Compilers/CSharp/Portable/Syntax/ParameterSyntax.cs

@@ -13,5 +13,13 @@ internal bool IsArgList
                 return this.Type == null && this.Identifier.ContextualKind() == SyntaxKind.ArgListKeyword;
             }
         }
+
+        private partial void Validate()
+        {
+            if (Type is null && Identifier.IsKind(SyntaxKind.None))
+            {
+                throw new System.ArgumentException(CSharpResources.ParameterRequiresTypeOrIdentifier);
+            }
+        }
     }
 }

src/Compilers/CSharp/Portable/Syntax/Syntax.xml

@@ -4342,7 +4342,7 @@
     </Field>
     <Field Name="Type" Type="TypeSyntax" Optional="true"/>
   </AbstractNode>
-  <Node Name="ParameterSyntax" Base="BaseParameterSyntax" SkipConvenienceFactories="true">
+  <Node Name="ParameterSyntax" Base="BaseParameterSyntax" SkipConvenienceFactories="true" HasValidate="true"> 
     <TypeComment>
       <summary>Parameter syntax.</summary>
     </TypeComment>
@@ -4357,9 +4357,8 @@
         <summary>Gets the modifier list.</summary>
       </PropertyComment>
     </Field>
-    <Field Name="Type" Type="TypeSyntax" Optional="true" Override="true"/>
+    <Field Name="Type" Type="TypeSyntax" Optional="true" RequiredForTest="true" Override="true"/>
     <Field Name="Identifier" Type="SyntaxToken" Optional="true">
-      <!-- Tracked by https://github.com/dotnet/roslyn/issues/78961 : enforce that a ParameterSyntax cannot be created with both Type and Identifier missing -->
       <PropertyComment>
         <summary>Gets the identifier.</summary>
       </PropertyComment>

src/Compilers/CSharp/Portable/Syntax/SyntaxKindFacts.cs

@@ -853,7 +853,6 @@ public static SyntaxKind GetBaseTypeDeclarationKind(SyntaxKind kind)
             return kind == SyntaxKind.EnumKeyword ? SyntaxKind.EnumDeclaration : GetTypeDeclarationKind(kind);
         }
 
-        // Tracked by https://github.com/dotnet/roslyn/issues/78957 : public API, decide what we want for extension declaration
         public static SyntaxKind GetTypeDeclarationKind(SyntaxKind kind)
         {
             switch (kind)
@@ -866,6 +865,8 @@ public static SyntaxKind GetTypeDeclarationKind(SyntaxKind kind)
                     return SyntaxKind.InterfaceDeclaration;
                 case SyntaxKind.RecordKeyword:
                     return SyntaxKind.RecordDeclaration;
+                case SyntaxKind.ExtensionKeyword:
+                    return SyntaxKind.ExtensionBlockDeclaration;
                 default:
                     return SyntaxKind.None;
             }

src/Compilers/CSharp/Test/Emit3/Semantics/ExtensionOperatorsTests.cs

@@ -7718,7 +7718,7 @@ static void Main()
                 Diagnostic(ErrorCode.ERR_AmbigCall, "--").WithArguments("Extensions1.extension(C1).operator checked --()", "Extensions2.extension(C1).operator --()").WithLocation(36, 17)
                 );
 #else
-            // https://github.com/dotnet/roslyn/issues/78968: Understand what is causing DEBUG/RELEASE behavior difference
+            // Ordering difference is acceptable and doesn't affect determinism. It is caused by ConditionallyDeOrder
             comp.VerifyEmitDiagnostics(
                 // (32,13): error CS0121: The call is ambiguous between the following methods or properties: 'Extensions1.extension(C1).operator --()' and 'Extensions2.extension(C1).operator --()'
                 //         _ = --c1;
@@ -23800,7 +23800,7 @@ static void Main()
                 Diagnostic(ErrorCode.ERR_AmbigCall, "-=").WithArguments("Extensions1.extension(C1).operator checked -=(C1)", "Extensions2.extension(C1).operator -=(C1)").WithLocation(39, 20)
                 );
 #else
-            // https://github.com/dotnet/roslyn/issues/78968: Understand what is causing DEBUG/RELEASE behavior difference
+            // Ordering difference is acceptable and doesn't affect determinism. It is caused by ConditionallyDeOrder
             comp.VerifyEmitDiagnostics(
                 // (35,16): error CS0121: The call is ambiguous between the following methods or properties: 'Extensions1.extension(C1).operator -=(C1)' and 'Extensions2.extension(C1).operator -=(C1)'
                 //         _ = c1 -= c1;

src/Compilers/CSharp/Test/Emit3/Semantics/ExtensionTests.cs

@@ -38148,6 +38148,41 @@ public void M() { }
         Assert.Empty(model.LookupNamespacesAndTypes(position, o, name: "M"));
     }
 
+    [Fact]
+    public void LookupSymbols_UsedImports()
+    {
+        var src = """
+// here
+
+using N;
+
+namespace N
+{
+    public static class E
+    {
+        extension(object)
+        {
+            public static void M() => throw null;
+        }
+    }
+}
+""";
+
+        var comp = CreateCompilation(src);
+
+        var tree = comp.SyntaxTrees.Single();
+        var model = comp.GetSemanticModel(tree);
+
+        var o = ((Compilation)comp).GetSpecialType(SpecialType.System_Object);
+        AssertEqualAndNoDuplicates(["void N.E.<G>$C43E2675C7BBF9284AF22FB8A9BF0280.M()"],
+            model.LookupSymbols(position: 0, o, name: "M", includeReducedExtensionMethods: true).ToTestDisplayStrings());
+
+        model.GetDiagnostics().Verify(
+            // (3,1): hidden CS8019: Unnecessary using directive.
+            // using N;
+            Diagnostic(ErrorCode.HDN_UnusedUsingDirective, "using N;").WithLocation(3, 1));
+    }
+
     [Fact]
     public void GetMemberGroup_01()
     {
@@ -44472,9 +44507,6 @@ static class E
             Diagnostic(ErrorCode.ERR_MainClassNotFound).WithArguments("E.<G>$BA41CFE2B5EDAEB8C1B9062F59ED4D69").WithLocation(1, 1));
 
         AssertEx.Equal("<G>$BA41CFE2B5EDAEB8C1B9062F59ED4D69", comp.GetTypeByMetadataName("E").GetTypeMembers().Single().ExtensionGroupingName);
-
-        // Tracked by https://github.com/dotnet/roslyn/issues/78968 : we should find the unspeakable nested type
-        Assert.Null(comp.GetTypeByMetadataName("E+<G>$BA41CFE2B5EDAEB8C1B9062F59ED4D69"));
     }
 
     [Fact]