Fix a crash when a nullable reference type is used in a pattern. (#45206)

Fixes #45103

src/Compilers/CSharp/Portable/Binder/Binder_Patterns.cs

@@ -399,10 +399,15 @@ private BoundPattern BindDiscardPattern(DiscardPatternSyntax node, TypeSymbol in
                 diagnostics.Add(ErrorCode.ERR_PointerTypeInPatternMatching, typeSyntax.Location);
                 return true;
             }
-            else if (patternType.IsNullableType() || typeSyntax is NullableTypeSyntax)
+            else if (patternType.IsNullableType())
             {
                 // It is an error to use pattern-matching with a nullable type, because you'll never get null. Use the underlying type.
-                Error(diagnostics, ErrorCode.ERR_PatternNullableType, typeSyntax, patternType, patternType.GetNullableUnderlyingType());
+                Error(diagnostics, ErrorCode.ERR_PatternNullableType, typeSyntax, patternType.GetNullableUnderlyingType());
+                return true;
+            }
+            else if (typeSyntax is NullableTypeSyntax)
+            {
+                Error(diagnostics, ErrorCode.ERR_PatternNullableType, typeSyntax, patternType);
                 return true;
             }
             else if (patternType.IsStatic)

src/Compilers/CSharp/Portable/CSharpResources.resx

@@ -5060,7 +5060,7 @@ To remove the warning, you can use /reference instead (set the Embed Interop Typ
     <value>Combined length of user strings used by the program exceeds allowed limit. Try to decrease use of string literals.</value>
   </data>
   <data name="ERR_PatternNullableType" xml:space="preserve">
-    <value>It is not legal to use nullable type '{0}' in a pattern; use the underlying type '{1}' instead.</value>
+    <value>It is not legal to use nullable type '{0}?' in a pattern; use the underlying type '{0}' instead.</value>
   </data>
   <data name="ERR_IsNullableType" xml:space="preserve">
     <value>It is not legal to use nullable reference type '{0}?' in an is-type expression; use the underlying type '{0}' instead.</value>

src/Compilers/CSharp/Portable/xlf/CSharpResources.cs.xlf

@@ -9766,8 +9766,8 @@ Pokud chcete odstranit toto varování, můžete místo toho použít /reference
         <note />
       </trans-unit>
       <trans-unit id="ERR_PatternNullableType">
-        <source>It is not legal to use nullable type '{0}' in a pattern; use the underlying type '{1}' instead.</source>
-        <target state="translated">Ve vzoru se nepovoluje použití typu s možnou hodnotou null {0}; místo toho použijte základní typ {1}.</target>
+        <source>It is not legal to use nullable type '{0}?' in a pattern; use the underlying type '{0}' instead.</source>
+        <target state="new">It is not legal to use nullable type '{0}?' in a pattern; use the underlying type '{0}' instead.</target>
         <note />
       </trans-unit>
       <trans-unit id="ERR_PeWritingFailure">

src/Compilers/CSharp/Portable/xlf/CSharpResources.de.xlf

@@ -9766,8 +9766,8 @@ Um die Warnung zu beheben, können Sie stattdessen /reference verwenden (Einbett
         <note />
       </trans-unit>
       <trans-unit id="ERR_PatternNullableType">
-        <source>It is not legal to use nullable type '{0}' in a pattern; use the underlying type '{1}' instead.</source>
-        <target state="translated">Es ist unzulässig, den Nullable-Typ "{0}" in einem Muster zu verwenden. Verwenden Sie stattdessen den zugrunde liegenden Typ "{1}".</target>
+        <source>It is not legal to use nullable type '{0}?' in a pattern; use the underlying type '{0}' instead.</source>
+        <target state="new">It is not legal to use nullable type '{0}?' in a pattern; use the underlying type '{0}' instead.</target>
         <note />
       </trans-unit>
       <trans-unit id="ERR_PeWritingFailure">

src/Compilers/CSharp/Portable/xlf/CSharpResources.es.xlf

@@ -9766,8 +9766,8 @@ Para eliminar la advertencia puede usar /reference (establezca la propiedad Embe
         <note />
       </trans-unit>
       <trans-unit id="ERR_PatternNullableType">
-        <source>It is not legal to use nullable type '{0}' in a pattern; use the underlying type '{1}' instead.</source>
-        <target state="translated">No se puede usar el tipo '{0}' que acepta valores NULL en un patrón; utilice el tipo '{1}' subyacente.</target>
+        <source>It is not legal to use nullable type '{0}?' in a pattern; use the underlying type '{0}' instead.</source>
+        <target state="new">It is not legal to use nullable type '{0}?' in a pattern; use the underlying type '{0}' instead.</target>
         <note />
       </trans-unit>
       <trans-unit id="ERR_PeWritingFailure">

src/Compilers/CSharp/Portable/xlf/CSharpResources.fr.xlf

@@ -9766,8 +9766,8 @@ Pour supprimer l'avertissement, vous pouvez utiliser la commande /reference (dé
         <note />
       </trans-unit>
       <trans-unit id="ERR_PatternNullableType">
-        <source>It is not legal to use nullable type '{0}' in a pattern; use the underlying type '{1}' instead.</source>
-        <target state="translated">Il n'est pas correct d'utiliser le type Nullable '{0}' dans un modèle. Utilisez le type sous-jacent '{1}' à la place.</target>
+        <source>It is not legal to use nullable type '{0}?' in a pattern; use the underlying type '{0}' instead.</source>
+        <target state="new">It is not legal to use nullable type '{0}?' in a pattern; use the underlying type '{0}' instead.</target>
         <note />
       </trans-unit>
       <trans-unit id="ERR_PeWritingFailure">

src/Compilers/CSharp/Portable/xlf/CSharpResources.it.xlf

@@ -9766,8 +9766,8 @@ Per rimuovere l'avviso, è invece possibile usare /reference (impostare la propr
         <note />
       </trans-unit>
       <trans-unit id="ERR_PatternNullableType">
-        <source>It is not legal to use nullable type '{0}' in a pattern; use the underlying type '{1}' instead.</source>
-        <target state="translated">Non è consentito usare il tipo nullable '{0}' in un criterio. Usare il tipo sottostante '{1}'.</target>
+        <source>It is not legal to use nullable type '{0}?' in a pattern; use the underlying type '{0}' instead.</source>
+        <target state="new">It is not legal to use nullable type '{0}?' in a pattern; use the underlying type '{0}' instead.</target>
         <note />
       </trans-unit>
       <trans-unit id="ERR_PeWritingFailure">

src/Compilers/CSharp/Portable/xlf/CSharpResources.ja.xlf

@@ -9766,8 +9766,8 @@ To remove the warning, you can use /reference instead (set the Embed Interop Typ
         <note />
       </trans-unit>
       <trans-unit id="ERR_PatternNullableType">
-        <source>It is not legal to use nullable type '{0}' in a pattern; use the underlying type '{1}' instead.</source>
-        <target state="translated">パターンで Null 許容型 '{0}' を使用することはできません。代わりに基になる型 '{1}' をご使用ください。</target>
+        <source>It is not legal to use nullable type '{0}?' in a pattern; use the underlying type '{0}' instead.</source>
+        <target state="new">It is not legal to use nullable type '{0}?' in a pattern; use the underlying type '{0}' instead.</target>
         <note />
       </trans-unit>
       <trans-unit id="ERR_PeWritingFailure">

src/Compilers/CSharp/Portable/xlf/CSharpResources.ko.xlf

@@ -9766,8 +9766,8 @@ To remove the warning, you can use /reference instead (set the Embed Interop Typ
         <note />
       </trans-unit>
       <trans-unit id="ERR_PatternNullableType">
-        <source>It is not legal to use nullable type '{0}' in a pattern; use the underlying type '{1}' instead.</source>
-        <target state="translated">패턴에 nullable 형식 '{0}'을(를) 사용하는 것은 올바르지 않습니다. 대신 기본 형식 '{1}'을(를) 사용하세요.</target>
+        <source>It is not legal to use nullable type '{0}?' in a pattern; use the underlying type '{0}' instead.</source>
+        <target state="new">It is not legal to use nullable type '{0}?' in a pattern; use the underlying type '{0}' instead.</target>
         <note />
       </trans-unit>
       <trans-unit id="ERR_PeWritingFailure">

src/Compilers/CSharp/Portable/xlf/CSharpResources.pl.xlf

@@ -9766,8 +9766,8 @@ Aby usunąć ostrzeżenie, możesz zamiast tego użyć opcji /reference (ustaw w
         <note />
       </trans-unit>
       <trans-unit id="ERR_PatternNullableType">
-        <source>It is not legal to use nullable type '{0}' in a pattern; use the underlying type '{1}' instead.</source>
-        <target state="translated">Użycie typu dopuszczającego wartość null „{0}” jest niedozwolone we wzorcu. Użyj zamiast tego bazowego typu „{1}”.</target>
+        <source>It is not legal to use nullable type '{0}?' in a pattern; use the underlying type '{0}' instead.</source>
+        <target state="new">It is not legal to use nullable type '{0}?' in a pattern; use the underlying type '{0}' instead.</target>
         <note />
       </trans-unit>
       <trans-unit id="ERR_PeWritingFailure">

src/Compilers/CSharp/Portable/xlf/CSharpResources.pt-BR.xlf

@@ -9764,8 +9764,8 @@ Para incorporar informações de tipo de interoperabilidade para os dois assembl
         <note />
       </trans-unit>
       <trans-unit id="ERR_PatternNullableType">
-        <source>It is not legal to use nullable type '{0}' in a pattern; use the underlying type '{1}' instead.</source>
-        <target state="translated">É ilegal usar o tipo que permite valor nulo '{0}' em um padrão; em vez disso, use o tipo subjacente '{1}'.</target>
+        <source>It is not legal to use nullable type '{0}?' in a pattern; use the underlying type '{0}' instead.</source>
+        <target state="new">It is not legal to use nullable type '{0}?' in a pattern; use the underlying type '{0}' instead.</target>
         <note />
       </trans-unit>
       <trans-unit id="ERR_PeWritingFailure">

src/Compilers/CSharp/Portable/xlf/CSharpResources.ru.xlf

@@ -9766,8 +9766,8 @@ To remove the warning, you can use /reference instead (set the Embed Interop Typ
         <note />
       </trans-unit>
       <trans-unit id="ERR_PatternNullableType">
-        <source>It is not legal to use nullable type '{0}' in a pattern; use the underlying type '{1}' instead.</source>
-        <target state="translated">Запрещено использовать тип "{0}", допускающий значение NULL, в шаблоне. Используйте вместо него базовый тип "{1}".</target>
+        <source>It is not legal to use nullable type '{0}?' in a pattern; use the underlying type '{0}' instead.</source>
+        <target state="new">It is not legal to use nullable type '{0}?' in a pattern; use the underlying type '{0}' instead.</target>
         <note />
       </trans-unit>
       <trans-unit id="ERR_PeWritingFailure">

src/Compilers/CSharp/Portable/xlf/CSharpResources.tr.xlf

@@ -9766,8 +9766,8 @@ Uyarıyı kaldırmak için, /reference kullanabilirsiniz (Birlikte Çalışma T
         <note />
       </trans-unit>
       <trans-unit id="ERR_PatternNullableType">
-        <source>It is not legal to use nullable type '{0}' in a pattern; use the underlying type '{1}' instead.</source>
-        <target state="translated">Boş değer atanabilir '{0}' türünün bir desende kullanılması yasaktır; bunun yerine temel alınan '{1}' türünü kullanın.</target>
+        <source>It is not legal to use nullable type '{0}?' in a pattern; use the underlying type '{0}' instead.</source>
+        <target state="new">It is not legal to use nullable type '{0}?' in a pattern; use the underlying type '{0}' instead.</target>
         <note />
       </trans-unit>
       <trans-unit id="ERR_PeWritingFailure">

src/Compilers/CSharp/Portable/xlf/CSharpResources.zh-Hans.xlf

@@ -9766,8 +9766,8 @@ To remove the warning, you can use /reference instead (set the Embed Interop Typ
         <note />
       </trans-unit>
       <trans-unit id="ERR_PatternNullableType">
-        <source>It is not legal to use nullable type '{0}' in a pattern; use the underlying type '{1}' instead.</source>
-        <target state="translated">在模式中使用可以为 null 的类型“{0}”是非法的；请改用基础类型“{1}”。</target>
+        <source>It is not legal to use nullable type '{0}?' in a pattern; use the underlying type '{0}' instead.</source>
+        <target state="new">It is not legal to use nullable type '{0}?' in a pattern; use the underlying type '{0}' instead.</target>
         <note />
       </trans-unit>
       <trans-unit id="ERR_PeWritingFailure">

src/Compilers/CSharp/Portable/xlf/CSharpResources.zh-Hant.xlf

@@ -9766,8 +9766,8 @@ To remove the warning, you can use /reference instead (set the Embed Interop Typ
         <note />
       </trans-unit>
       <trans-unit id="ERR_PatternNullableType">
-        <source>It is not legal to use nullable type '{0}' in a pattern; use the underlying type '{1}' instead.</source>
-        <target state="translated">在模式中使用可為 Null 的型別 '{0}' 不合法; 請改用基礎類型 '{1}'。</target>
+        <source>It is not legal to use nullable type '{0}?' in a pattern; use the underlying type '{0}' instead.</source>
+        <target state="new">It is not legal to use nullable type '{0}?' in a pattern; use the underlying type '{0}' instead.</target>
         <note />
       </trans-unit>
       <trans-unit id="ERR_PeWritingFailure">

src/Compilers/CSharp/Test/Semantic/Semantics/PatternMatchingTests.cs

@@ -145,7 +145,7 @@ public static void T(object x)
             compilation.VerifyDiagnostics(
                 // (11,18): error CS8116: It is not legal to use nullable type 'int?' in a pattern; use the underlying type 'int' instead.
                 //         if (x is Nullable<int> y) Console.WriteLine($"expression {x} is Nullable<int> y");
-                Diagnostic(ErrorCode.ERR_PatternNullableType, "Nullable<int>").WithArguments("int?", "int").WithLocation(11, 18)
+                Diagnostic(ErrorCode.ERR_PatternNullableType, "Nullable<int>").WithArguments("int").WithLocation(11, 18)
                 );
         }
 
@@ -219,7 +219,7 @@ public static void Main()
                 Diagnostic(ErrorCode.ERR_BadPatternExpression, "null").WithArguments("<null>").WithLocation(10, 13),
                 // (11,18): error CS8116: It is not legal to use nullable type 'int?' in a pattern; use the underlying type 'int' instead.
                 //         if (s is NullableInt x) { } // error: cannot use nullable type
-                Diagnostic(ErrorCode.ERR_PatternNullableType, "NullableInt").WithArguments("int?", "int").WithLocation(11, 18),
+                Diagnostic(ErrorCode.ERR_PatternNullableType, "NullableInt").WithArguments("int").WithLocation(11, 18),
                 // (12,18): error CS8121: An expression of type 'string' cannot be handled by a pattern of type 'long'.
                 //         if (s is long l) { } // error: cannot convert string to long
                 Diagnostic(ErrorCode.ERR_PatternWrongType, "long").WithArguments("string", "long").WithLocation(12, 18),

src/Compilers/CSharp/Test/Semantic/Semantics/PatternMatchingTests2.cs

@@ -2573,6 +2573,65 @@ public void M(string s)
                 );
         }
 
+        [Fact]
+        public void IsNullableReferenceType_01()
+        {
+            var source =
+@"#nullable enable
+public class C {
+    public void M1(object o) {
+        var t = o is string? { };
+    }
+    public void M2(object o) {
+        var t = o is (string? { });
+    }
+    public void M3(object o) {
+        var t = o is string?;
+    }
+    public void M4(object o) {
+        var t = o is string? _;
+    }
+    public void M5(object o) {
+        var t = o is (string? _);
+    }
+}";
+            CreateCompilation(source, parseOptions: TestOptions.RegularWithPatternCombinators).VerifyDiagnostics(
+                // (4,22): error CS8116: It is not legal to use nullable type 'string?' in a pattern; use the underlying type 'string' instead.
+                //         var t = o is string? { };
+                Diagnostic(ErrorCode.ERR_PatternNullableType, "string?").WithArguments("string").WithLocation(4, 22),
+                // (7,22): error CS8129: No suitable 'Deconstruct' instance or extension method was found for type 'object', with 2 out parameters and a void return type.
+                //         var t = o is (string? { });
+                Diagnostic(ErrorCode.ERR_MissingDeconstruct, "(string? { })").WithArguments("object", "2").WithLocation(7, 22),
+                // (7,29): error CS1003: Syntax error, ',' expected
+                //         var t = o is (string? { });
+                Diagnostic(ErrorCode.ERR_SyntaxError, "?").WithArguments(",", "?").WithLocation(7, 29),
+                // (7,31): error CS1003: Syntax error, ',' expected
+                //         var t = o is (string? { });
+                Diagnostic(ErrorCode.ERR_SyntaxError, "{").WithArguments(",", "{").WithLocation(7, 31),
+                // (10,22): error CS8650: It is not legal to use nullable reference type 'string?' in an is-type expression; use the underlying type 'string' instead.
+                //         var t = o is string?;
+                Diagnostic(ErrorCode.ERR_IsNullableType, "string?").WithArguments("string").WithLocation(10, 22),
+                // (13,30): error CS0103: The name '_' does not exist in the current context
+                //         var t = o is string? _;
+                Diagnostic(ErrorCode.ERR_NameNotInContext, "_").WithArguments("_").WithLocation(13, 30),
+                // (13,31): error CS1003: Syntax error, ':' expected
+                //         var t = o is string? _;
+                Diagnostic(ErrorCode.ERR_SyntaxError, ";").WithArguments(":", ";").WithLocation(13, 31),
+                // (13,31): error CS1525: Invalid expression term ';'
+                //         var t = o is string? _;
+                Diagnostic(ErrorCode.ERR_InvalidExprTerm, ";").WithArguments(";").WithLocation(13, 31),
+                // (16,22): error CS8129: No suitable 'Deconstruct' instance or extension method was found for type 'object', with 2 out parameters and a void return type.
+                //         var t = o is (string? _);
+                Diagnostic(ErrorCode.ERR_MissingDeconstruct, "(string? _)").WithArguments("object", "2").WithLocation(16, 22),
+                // (16,29): error CS1003: Syntax error, ',' expected
+                //         var t = o is (string? _);
+                Diagnostic(ErrorCode.ERR_SyntaxError, "?").WithArguments(",", "?").WithLocation(16, 29),
+                // (16,31): error CS1003: Syntax error, ',' expected
+                //         var t = o is (string? _);
+                Diagnostic(ErrorCode.ERR_SyntaxError, "_").WithArguments(",", "").WithLocation(16, 31)
+                );
+        }
+
         [Fact]
         public void IsAlwaysPatternKinds()
         {