Handle newly added property sub-pattern operation in OperationExtensions.GetValueUsageInfo

Fix #40499

src/EditorFeatures/CSharpTest/RemoveUnusedParametersAndValues/RemoveUnusedValueAssignmentTests.cs

@@ -7415,6 +7415,60 @@ string M(object obj)
 }", new TestParameters(options: PreferUnusedLocal, parseOptions: new CSharpParseOptions(LanguageVersion.CSharp8)));
         }
 
+        [WorkItem(40499, "https://github.com/dotnet/roslyn/issues/40499")]
+        [Fact, Trait(Traits.Feature, Traits.Features.CodeActionsRemoveUnusedValues)]
+        public async Task LocalUsedWithPropertySubPattern()
+        {
+            await TestDiagnosticMissingAsync(
+@"class C
+{
+    public object P { get; }
+    void M()
+    {
+        C [|c|] = new C();
+        var x = c is { P : int i };
+    }
+}", new TestParameters(options: PreferDiscard, parseOptions: new CSharpParseOptions(LanguageVersion.CSharp8)));
+        }
+
+        [WorkItem(40499, "https://github.com/dotnet/roslyn/issues/40499")]
+        [Fact, Trait(Traits.Feature, Traits.Features.CodeActionsRemoveUnusedValues)]
+        public async Task UnusedLocalDefinedInPropertySubPattern_PreferDiscard()
+        {
+            await TestInRegularAndScriptAsync(
+@"class C
+{
+    public object P { get; }
+    void M(C c)
+    {
+        var x = c is { P : int [|i|] };
+    }
+}",
+@"class C
+{
+    public object P { get; }
+    void M(C c)
+    {
+        var x = c is { P : int _ };
+    }
+}", options: PreferDiscard, parseOptions: new CSharpParseOptions(LanguageVersion.CSharp8));
+        }
+
+        [WorkItem(40499, "https://github.com/dotnet/roslyn/issues/40499")]
+        [Fact, Trait(Traits.Feature, Traits.Features.CodeActionsRemoveUnusedValues)]
+        public async Task UnusedLocalDefinedInPropertySubPattern_PreferUnusedLocal()
+        {
+            await TestDiagnosticMissingAsync(
+@"class C
+{
+    public object P { get; }
+    void M(C c)
+    {
+        var x = c is { P : int [|i|] };
+    }
+}", new TestParameters(options: PreferUnusedLocal, parseOptions: new CSharpParseOptions(LanguageVersion.CSharp8)));
+        }
+
         [WorkItem(38640, "https://github.com/dotnet/roslyn/issues/38640")]
         [Fact, Trait(Traits.Feature, Traits.Features.CodeActionsRemoveUnusedValues)]
         public async Task DeclarationPatternInSwitchExpressionArm_UnusedLocal_PreferDiscard()

src/Workspaces/Core/Portable/Extensions/OperationExtensions.cs

@@ -91,6 +91,14 @@ public static ValueUsageInfo GetValueUsageInfo(this IOperation operation)
                         //
                         return ValueUsageInfo.Write;
 
+                    case IPropertySubpatternOperation _:
+                        // A declaration pattern within a property sub-pattern is a
+                        // write for the declared local.
+                        // For example, 'x' is defined and assigned the value from 'obj.Property' below:
+                        //      if (obj is { Property : int x })
+                        //
+                        return ValueUsageInfo.Write;
+
                     default:
                         Debug.Fail("Unhandled declaration pattern context");