Unused members analyzer: Do not flag write-only properties that are not read

Fixes #30894

src/EditorFeatures/CSharpTest/RemoveUnusedMembers/RemoveUnusedMembersTests.cs

@@ -477,6 +477,32 @@ class C : I
 }");
         }
 
+        [Fact, Trait(Traits.Feature, Traits.Features.CodeActionsRemoveUnusedMembers)]
+        [WorkItem(30894, "https://github.com/dotnet/roslyn/issues/30894")]
+        public async Task WriteOnlyProperty_NotWritten()
+        {
+            await TestInRegularAndScriptAsync(
+@"class C
+{
+    int [|P|] { set { } }
+}",
+@"class C
+{
+}");
+        }
+
+        [Fact, Trait(Traits.Feature, Traits.Features.CodeActionsRemoveUnusedMembers)]
+        [WorkItem(30894, "https://github.com/dotnet/roslyn/issues/30894")]
+        public async Task WriteOnlyProperty_Written()
+        {
+            await TestDiagnosticMissingAsync(
+@"class C
+{
+    int [|P|] { set { } }
+    void M(int i) => P = i;
+}");
+        }
+
         [Fact, Trait(Traits.Feature, Traits.Features.CodeActionsRemoveUnusedMembers)]
         public async Task FieldIsUnused_Const()
         {

src/Features/Core/Portable/RemoveUnusedMembers/AbstractRemoveUnusedMembersDiagnosticAnalyzer.cs

@@ -303,6 +303,14 @@ private void OnSymbolEnd(SymbolAnalysisContext symbolEndContext, bool hasInvalid
                                 ? s_removeUnusedMembersRule
                                 : s_removeUnreadMembersRule;
 
+                            // Do not flag write-only properties that are not read.
+                            if (rule == s_removeUnreadMembersRule &&
+                                member is IPropertySymbol property &&
+                                property.IsWriteOnly)
+                            {
+                                continue;
+                            }
+
                             // Most of the members should have a single location, except for partial methods.
                             // We report the diagnostic on the first location of the member.
                             var diagnostic = Diagnostic.Create(