Don't offer to remove as cast from using statements or declarations (#48110)

src/Analyzers/CSharp/Analyzers/UsePatternMatching/CSharpAsAndNullCheckDiagnosticAnalyzer.cs

@@ -114,6 +114,20 @@ private void SyntaxNodeAction(SyntaxNodeAnalysisContext syntaxContext)
                 return;
             }
 
+            // Don't convert if the as is part of a using statement
+            // eg using (var x = y as MyObject) { }
+            if (localStatement is UsingStatementSyntax)
+            {
+                return;
+            }
+
+            // Don't convert if the as is part of a local declaration with a using keyword
+            // eg using var x = y as MyObject;
+            if (localStatement is LocalDeclarationStatementSyntax localDecl && localDecl.UsingKeyword != default)
+            {
+                return;
+            }
+
             var typeNode = asExpression.Right;
             var asType = semanticModel.GetTypeInfo(typeNode, cancellationToken).Type;
             if (asType.IsNullable())

src/Analyzers/CSharp/Tests/UsePatternMatching/CSharpAsAndNullCheckTests.cs

@@ -1599,6 +1599,42 @@ class Program
         }
         return dictionary;
     }
+}");
+        }
+
+        [WorkItem(45596, "https://github.com/dotnet/roslyn/issues/45596")]
+        [Fact, Trait(Traits.Feature, Traits.Features.CodeActionsInlineTypeCheck)]
+        public async Task TestMissingInUsingDeclaration()
+        {
+            await TestMissingInRegularAndScriptAsync(
+@"class C
+{
+    void M()
+    {
+        using [|var|] x = o as IDisposable;
+        if (x != null)
+        {
+        }
+    }
+}");
+        }
+
+        [WorkItem(45596, "https://github.com/dotnet/roslyn/issues/45596")]
+        [Fact, Trait(Traits.Feature, Traits.Features.CodeActionsInlineTypeCheck)]
+        public async Task TestMissingInUsingStatement()
+        {
+            await TestMissingInRegularAndScriptAsync(
+@"class C
+{
+    void M()
+    {
+        using ([|var|] x = o as IDisposable)
+        {
+            if (x != null)
+            {
+            }
+        }
+    }
 }");
         }
     }