Update SA1024 for extended property patterns

Author: sharwell

StyleCop.Analyzers/StyleCop.Analyzers.Test.CSharp10/SpacingRules/SA1024CSharp10UnitTests.cs

@@ -3,9 +3,59 @@
 
 namespace StyleCop.Analyzers.Test.CSharp10.SpacingRules
 {
+    using System.Threading;
+    using System.Threading.Tasks;
+    using Microsoft.CodeAnalysis.Testing;
     using StyleCop.Analyzers.Test.CSharp9.SpacingRules;
+    using Xunit;
+    using static StyleCop.Analyzers.SpacingRules.SA1024ColonsMustBeSpacedCorrectly;
+    using static StyleCop.Analyzers.Test.Verifiers.StyleCopCodeFixVerifier<
+        StyleCop.Analyzers.SpacingRules.SA1024ColonsMustBeSpacedCorrectly,
+        StyleCop.Analyzers.SpacingRules.TokenSpacingCodeFixProvider>;
 
     public partial class SA1024CSharp10UnitTests : SA1024CSharp9UnitTests
     {
+        [Fact]
+        [WorkItem(3984, "https://github.com/DotNetAnalyzers/StyleCopAnalyzers/issues/3984")]
+        public async Task TestExtendedPropertyPatternSpacingAsync()
+        {
+            var testCode = @"
+public class TestClass
+{
+    public bool Test(SomeType value) => value is { Nested.Value: 1, Other.Value {|#0::|} 2, Third.Value{|#1::|}3 };
+}
+
+public class SomeType
+{
+    public SomeType Nested { get; set; }
+    public SomeType Other { get; set; }
+    public SomeType Third { get; set; }
+    public SomeType Child { get; set; }
+    public int Value { get; set; }
+}";
+
+            var fixedCode = @"
+public class TestClass
+{
+    public bool Test(SomeType value) => value is { Nested.Value: 1, Other.Value: 2, Third.Value: 3 };
+}
+
+public class SomeType
+{
+    public SomeType Nested { get; set; }
+    public SomeType Other { get; set; }
+    public SomeType Third { get; set; }
+    public SomeType Child { get; set; }
+    public int Value { get; set; }
+}";
+
+            DiagnosticResult[] expected =
+            {
+                Diagnostic(DescriptorNotPreceded).WithLocation(0),
+                Diagnostic(DescriptorFollowed).WithLocation(1),
+            };
+
+            await VerifyCSharpFixAsync(testCode, expected, fixedCode, CancellationToken.None).ConfigureAwait(false);
+        }
     }
 }

StyleCop.Analyzers/StyleCop.Analyzers/Lightup/SyntaxKindEx.cs

@@ -79,6 +79,7 @@ internal static class SyntaxKindEx
         public const SyntaxKind PrimaryConstructorBaseType = (SyntaxKind)9065;
         public const SyntaxKind FunctionPointerUnmanagedCallingConventionList = (SyntaxKind)9066;
         public const SyntaxKind RecordStructDeclaration = (SyntaxKind)9068;
+        public const SyntaxKind ExpressionColon = (SyntaxKind)9069;
         public const SyntaxKind CollectionExpression = (SyntaxKind)9076;
     }
 }

StyleCop.Analyzers/StyleCop.Analyzers/SpacingRules/SA1024ColonsMustBeSpacedCorrectly.cs

@@ -137,6 +137,7 @@ private static void HandleColonToken(SyntaxTreeAnalysisContext context, SyntaxTo
             case SyntaxKindEx.CasePatternSwitchLabel:
             // NameColon is not explicitly listed in the description of this warning, but the behavior is inferred
             case SyntaxKind.NameColon:
+            case SyntaxKindEx.ExpressionColon:
                 requireBefore = false;
                 break;
 

documentation/SA1024.md

@@ -51,6 +51,14 @@ A colon that appears as part of a string interpolation formatting component shou
 var s = $"{x:N}";
 ```
 
+When a colon appears within a property pattern, including nested members referenced through extended property pattern syntax, it is treated like a named element separator. The colon should not be preceded by whitespace, and it should normally be followed by a single space.
+
+```csharp
+if (item is { Outer.Inner: value })
+{
+}
+```
+
 Finally, when a colon is used within a conditional statement, it should always contain a single space on either side, unless the colon is the first or last character on the line. For example:
 
 ```csharp