Merge pull request #37373 from mavasani/Issue37213

Handle reduced extension method invocations in remove unused member a…

src/EditorFeatures/CSharpTest/RemoveUnusedMembers/RemoveUnusedMembersTests.cs

@@ -2349,5 +2349,17 @@ public class MyClass
 }", new TestParameters(retainNonFixableDiagnostics: true, parseOptions: new CSharpParseOptions(LanguageVersion.CSharp8)),
     expected: Diagnostic("IDE0052"));
         }
+
+        [Fact, Trait(Traits.Feature, Traits.Features.CodeActionsRemoveUnusedMembers)]
+        [WorkItem(37213, "https://github.com/dotnet/roslyn/issues/37213")]
+        public async Task UsedPrivateExtensionMethod()
+        {
+            await TestDiagnosticMissingAsync(
+@"public static class B
+{
+    public static void PublicExtensionMethod(this string s) => s.PrivateExtensionMethod();
+    private static void [|PrivateExtensionMethod|](this string s) { }
+}");
+        }
     }
 }

src/EditorFeatures/VisualBasicTest/RemoveUnusedMembers/RemoveUnusedMembersTests.vb

@@ -1560,5 +1560,23 @@ End Class")
     End Sub
 End Class")
         End Function
+
+        <Fact, Trait(Traits.Feature, Traits.Features.CodeActionsRemoveUnusedMembers)>
+        <WorkItem(37213, "https://github.com/dotnet/roslyn/issues/37213")>
+        Public Async Function UsedPrivateExtensionMethod() As Task
+            Await TestMissingInRegularAndScriptAsync(
+"Imports System.Runtime.CompilerServices
+
+Public Module B
+    <Extension()>
+    Sub PublicExtensionMethod(s As String)
+        s.PrivateExtensionMethod()
+    End Sub
+
+    <Extension()>
+    Private Sub [|PrivateExtensionMethod|](s As String)
+    End Sub
+End Module")
+        End Function
     End Class
 End Namespace

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

@@ -288,6 +288,13 @@ private void AnalyzeInvocationOperation(OperationAnalysisContext operationContex
                 // A method invocation is considered as a read reference to the symbol
                 // to ensure that we consider the method as "used".
                 OnSymbolUsage(targetMethod, ValueUsageInfo.Read);
+
+                // If the invoked method is a reduced extension method, also mark the original
+                // method from which it was reduced as "used".
+                if (targetMethod.ReducedFrom != null)
+                {
+                    OnSymbolUsage(targetMethod.ReducedFrom, ValueUsageInfo.Read);
+                }
             }
 
             private void AnalyzeNameOfOperation(OperationAnalysisContext operationContext)