Handle NotPattern (RR0133)

Author: josefpihrt

src/Refactorings/CSharp/Refactorings/ConvertIfToSwitchRefactoring.cs

@@ -100,9 +100,9 @@ private static (bool success, ExpressionSyntax switchExpression) Analyze(
 
                         PatternSyntax pattern = isPatternExpression.Pattern;
 
-                        SyntaxDebug.Assert(pattern.IsKind(SyntaxKind.DeclarationPattern, SyntaxKind.ConstantPattern), pattern);
+                        SyntaxDebug.Assert(pattern.IsKind(SyntaxKind.DeclarationPattern, SyntaxKind.ConstantPattern, SyntaxKind.NotPattern), pattern);
 
-                        if (!pattern.IsKind(SyntaxKind.DeclarationPattern, SyntaxKind.ConstantPattern))
+                        if (!pattern.IsKind(SyntaxKind.DeclarationPattern, SyntaxKind.ConstantPattern, SyntaxKind.NotPattern))
                             return default;
 
                         ExpressionSyntax expression = isPatternExpression.Expression.WalkDownParentheses();
@@ -270,6 +270,12 @@ private static SyntaxList<SwitchLabelSyntax> CreateSwitchLabels(IfStatementSynta
                         {
                             return SingletonList<SwitchLabelSyntax>(CasePatternSwitchLabel(pattern, Token(SyntaxKind.ColonToken)));
                         }
+                        else if (pattern.IsKind(SyntaxKind.NotPattern))
+                        {
+                            var notPattern = (UnaryPatternSyntax)pattern;
+
+                            return SingletonList<SwitchLabelSyntax>(CasePatternSwitchLabel(notPattern, Token(SyntaxKind.ColonToken)));
+                        }
                         else
                         {
                             throw new InvalidOperationException();

src/Tests/Refactorings.Tests/RR0133ConvertIfToSwitchTests.cs

@@ -126,6 +126,53 @@ int M()
 ", equivalenceKey: RefactoringId);
         }
 
+        [Fact, Trait(Traits.Refactoring, RefactoringIdentifiers.ConvertIfToSwitch)]
+        public async Task Test_NotPattern()
+        {
+            await VerifyRefactoringAsync(@"
+class C
+{
+    int M()
+    {
+        object x = null;
+
+        [||]if (x is string s)
+        {
+            return 1;
+        }
+        else if (x is not null)
+        {
+        }
+
+        return 0;
+    }
+}
+", @"
+class C
+{
+    int M()
+    {
+        object x = null;
+
+        switch (x)
+        {
+            case string s:
+                {
+                    return 1;
+                }
+
+            case not null:
+                {
+                    break;
+                }
+        }
+
+        return 0;
+    }
+}
+", equivalenceKey: RefactoringId);
+        }
+
         [Fact, Trait(Traits.Refactoring, RefactoringIdentifiers.ConvertIfToSwitch)]
         public async Task Test_ConstantAndPattern()
         {