Diagnose a static type used in an 'is' or 'as' expression. (#46240)

Fixes #30198

Author: Neal Gafter

docs/compilers/CSharp/Warnversion Warning Waves.md

@@ -19,4 +19,5 @@ The table below describes all of the warnings controlled by warning levels `5` o
 
 | Warning ID | warning level | Description |
 |------------|---------|-------------|
+| CS7023 | 5 | [A static type is used in an 'is' or 'as' expression](https://github.com/dotnet/roslyn/issues/30198) |
 | CS8073 | 5 | [Expression always true (or false) when comparing a struct to null](https://github.com/dotnet/roslyn/issues/45744) |

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

@@ -2875,12 +2875,11 @@ private bool IsOperatorErrors(CSharpSyntaxNode node, TypeSymbol operandType, Bou
             // The native compiler allows "x is C" where C is a static class. This
             // is strictly illegal according to the specification (see the section
             // called "Referencing Static Class Types".) To retain compatibility we
-            // allow it, but when /feature:strict is enabled we break with the native
-            // compiler and turn this into an error, as it should be.
-            if (targetType.IsStatic && Compilation.FeatureStrictEnabled)
+            // allow it, but when /warn:5 or higher we break with the native
+            // compiler and turn this into a warning.
+            if (targetType.IsStatic)
             {
-                Error(diagnostics, ErrorCode.ERR_StaticInAsOrIs, node, targetType);
-                return true;
+                Error(diagnostics, ErrorCode.WRN_StaticInAsOrIs, node, targetType);
             }
 
             if ((object)operandType != null && operandType.IsPointerOrFunctionPointer() || targetType.IsPointerOrFunctionPointer())
@@ -3401,12 +3400,11 @@ private BoundExpression BindAsOperator(BinaryExpressionSyntax node, DiagnosticBa
             // a static type C to be an expression of type C.
             // It also allows "someObject as C" if "someObject"
             // is of type object. To retain compatibility we
-            // allow it, but when /feature:strict is enabled we break with the native
-            // compiler and turn this into an error, as it should be.
-            if (targetType.IsStatic && Compilation.FeatureStrictEnabled)
+            // allow it, but when /warn:5 or higher we break with the native
+            // compiler and turn this into a warning.
+            if (targetType.IsStatic)
             {
-                Error(diagnostics, ErrorCode.ERR_StaticInAsOrIs, node, targetType);
-                return new BoundAsOperator(node, operand, typeExpression, Conversion.NoConversion, resultType, hasErrors: true);
+                Error(diagnostics, ErrorCode.WRN_StaticInAsOrIs, node, targetType);
             }
 
             if (operand.IsLiteralNull())

src/Compilers/CSharp/Portable/CSharpResources.resx

@@ -3896,9 +3896,12 @@ You should consider suppressing the warning only if you're sure that you don't w
   <data name="WRN_MainIgnored_Title" xml:space="preserve">
     <value>The entry point of the program is global code; ignoring entry point</value>
   </data>
-  <data name="ERR_StaticInAsOrIs" xml:space="preserve">
+  <data name="WRN_StaticInAsOrIs" xml:space="preserve">
     <value>The second operand of an 'is' or 'as' operator may not be static type '{0}'</value>
   </data>
+  <data name="WRN_StaticInAsOrIs_Title" xml:space="preserve">
+    <value>The second operand of an 'is' or 'as' operator may not be a static type</value>
+  </data>
   <data name="ERR_BadVisEventType" xml:space="preserve">
     <value>Inconsistent accessibility: event type '{1}' is less accessible than event '{0}'</value>
   </data>

src/Compilers/CSharp/Portable/Errors/ErrorCode.cs

@@ -1166,7 +1166,7 @@ internal enum ErrorCode
         ERR_YieldNotAllowedInScript = 7020,
         ERR_NamespaceNotAllowedInScript = 7021,
         WRN_MainIgnored = 7022,
-        ERR_StaticInAsOrIs = 7023,
+        WRN_StaticInAsOrIs = 7023,
         ERR_InvalidDelegateType = 7024,
         ERR_BadVisEventType = 7025,
         ERR_GlobalAttributesNotAllowed = 7026,

src/Compilers/CSharp/Portable/Errors/ErrorFacts.cs

@@ -217,6 +217,7 @@ internal static int GetWarningLevel(ErrorCode code)
             switch (code)
             {
                 case ErrorCode.WRN_NubExprIsConstBool2:
+                case ErrorCode.WRN_StaticInAsOrIs:
                     // Warning level 5 is exclusively for warnings introduced in the compiler
                     // shipped with dotnet 5 (C# 9) and that can be reported for pre-existing code.
                     return 5;

src/Compilers/CSharp/Portable/Generated/ErrorFacts.Generated.cs

@@ -2416,6 +2416,16 @@
         <target state="translated">Metoda označená jako [DoesNotReturn] by se neměla ukončit standardním způsobem</target>
         <note />
       </trans-unit>
+      <trans-unit id="WRN_StaticInAsOrIs">
+        <source>The second operand of an 'is' or 'as' operator may not be static type '{0}'</source>
+        <target state="new">The second operand of an 'is' or 'as' operator may not be static type '{0}'</target>
+        <note />
+      </trans-unit>
+      <trans-unit id="WRN_StaticInAsOrIs_Title">
+        <source>The second operand of an 'is' or 'as' operator may not be a static type</source>
+        <target state="new">The second operand of an 'is' or 'as' operator may not be a static type</target>
+        <note />
+      </trans-unit>
       <trans-unit id="WRN_SwitchExpressionNotExhaustive">
         <source>The switch expression does not handle all possible values of its input type (it is not exhaustive). For example, the pattern '{0}' is not covered.</source>
         <target state="translated">Výraz switch nezachycuje všechny možné hodnoty vstupního typu (není úplný). Nezachycuje například vzor {0}.</target>
@@ -8289,11 +8299,6 @@ Potlačení upozornění zvažte jenom v případě, když určitě nechcete če
         <target state="translated">Vstupním bodem programu je globální kód. Vstupní bod se ignoruje</target>
         <note />
       </trans-unit>
-      <trans-unit id="ERR_StaticInAsOrIs">
-        <source>The second operand of an 'is' or 'as' operator may not be static type '{0}'</source>
-        <target state="translated">Druhý operand operátoru is nebo as nesmí být statického typu {0}.</target>
-        <note />
-      </trans-unit>
       <trans-unit id="ERR_BadVisEventType">
         <source>Inconsistent accessibility: event type '{1}' is less accessible than event '{0}'</source>
         <target state="translated">Nekonzistentní dostupnost: Typ události {1} je míň dostupný než událost {0}.</target>

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

@@ -2416,6 +2416,16 @@
         <target state="translated">Eine mit [DoesNotReturn] gekennzeichnete Methode darf nicht zurückgegeben werden.</target>
         <note />
       </trans-unit>
+      <trans-unit id="WRN_StaticInAsOrIs">
+        <source>The second operand of an 'is' or 'as' operator may not be static type '{0}'</source>
+        <target state="new">The second operand of an 'is' or 'as' operator may not be static type '{0}'</target>
+        <note />
+      </trans-unit>
+      <trans-unit id="WRN_StaticInAsOrIs_Title">
+        <source>The second operand of an 'is' or 'as' operator may not be a static type</source>
+        <target state="new">The second operand of an 'is' or 'as' operator may not be a static type</target>
+        <note />
+      </trans-unit>
       <trans-unit id="WRN_SwitchExpressionNotExhaustive">
         <source>The switch expression does not handle all possible values of its input type (it is not exhaustive). For example, the pattern '{0}' is not covered.</source>
         <target state="translated">Der switch-Ausdruck verarbeitet nicht alle möglichen Werte des zugehörigen Eingabetyps (nicht umfassender Ausdruck). Das Muster "{0}" wird beispielsweise nicht abgedeckt.</target>
@@ -8289,11 +8299,6 @@ Sie sollten das Unterdrücken der Warnung nur in Betracht ziehen, wenn Sie siche
         <target state="translated">Der Einstiegspunkt des Programms ist globaler Code. Der Einstiegspunkt wird ignoriert.</target>
         <note />
       </trans-unit>
-      <trans-unit id="ERR_StaticInAsOrIs">
-        <source>The second operand of an 'is' or 'as' operator may not be static type '{0}'</source>
-        <target state="translated">Der zweite Operand eines is- oder as-Operators darf nicht den statischen Typ "{0}" aufweisen.</target>
-        <note />
-      </trans-unit>
       <trans-unit id="ERR_BadVisEventType">
         <source>Inconsistent accessibility: event type '{1}' is less accessible than event '{0}'</source>
         <target state="translated">Inkonsistenter Zugriff: Ereignistyp "{1}" ist weniger zugreifbar als Ereignis "{0}".</target>

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

@@ -2416,6 +2416,16 @@
         <target state="translated">Un método marcado como [DoesNotReturn] no debe devolver nada.</target>
         <note />
       </trans-unit>
+      <trans-unit id="WRN_StaticInAsOrIs">
+        <source>The second operand of an 'is' or 'as' operator may not be static type '{0}'</source>
+        <target state="new">The second operand of an 'is' or 'as' operator may not be static type '{0}'</target>
+        <note />
+      </trans-unit>
+      <trans-unit id="WRN_StaticInAsOrIs_Title">
+        <source>The second operand of an 'is' or 'as' operator may not be a static type</source>
+        <target state="new">The second operand of an 'is' or 'as' operator may not be a static type</target>
+        <note />
+      </trans-unit>
       <trans-unit id="WRN_SwitchExpressionNotExhaustive">
         <source>The switch expression does not handle all possible values of its input type (it is not exhaustive). For example, the pattern '{0}' is not covered.</source>
         <target state="translated">La expresión switch no controla todos los valores posibles de su tipo de entrada (no es exhaustivo). Por ejemplo, el patrón "{0}" no está incluido.</target>
@@ -8289,11 +8299,6 @@ Considere la posibilidad de suprimir la advertencia solo si tiene la seguridad d
         <target state="translated">El punto de entrada del programa es código global; se ignora el punto de entrada.</target>
         <note />
       </trans-unit>
-      <trans-unit id="ERR_StaticInAsOrIs">
-        <source>The second operand of an 'is' or 'as' operator may not be static type '{0}'</source>
-        <target state="translated">El segundo operando de un operador 'is' o 'as' no puede ser el tipo estático '{0}'</target>
-        <note />
-      </trans-unit>
       <trans-unit id="ERR_BadVisEventType">
         <source>Inconsistent accessibility: event type '{1}' is less accessible than event '{0}'</source>
         <target state="translated">Incoherencia de accesibilidad: el tipo de evento '{1}' es menos accesible que el evento '{0}'</target>

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

@@ -2416,6 +2416,16 @@
         <target state="translated">Une méthode marquée [DoesNotReturn] ne doit pas être retournée.</target>
         <note />
       </trans-unit>
+      <trans-unit id="WRN_StaticInAsOrIs">
+        <source>The second operand of an 'is' or 'as' operator may not be static type '{0}'</source>
+        <target state="new">The second operand of an 'is' or 'as' operator may not be static type '{0}'</target>
+        <note />
+      </trans-unit>
+      <trans-unit id="WRN_StaticInAsOrIs_Title">
+        <source>The second operand of an 'is' or 'as' operator may not be a static type</source>
+        <target state="new">The second operand of an 'is' or 'as' operator may not be a static type</target>
+        <note />
+      </trans-unit>
       <trans-unit id="WRN_SwitchExpressionNotExhaustive">
         <source>The switch expression does not handle all possible values of its input type (it is not exhaustive). For example, the pattern '{0}' is not covered.</source>
         <target state="translated">L'expression switch ne prend pas en charge toutes les valeurs possibles de son type d'entrée (elle n'est pas exhaustive). Par exemple, le modèle '{0}' n'est pas couvert.</target>
@@ -8289,11 +8299,6 @@ Supprimez l'avertissement seulement si vous êtes sûr de ne pas vouloir attendr
         <target state="translated">Le point d'entrée du programme est du code global ; ce point d'entrée est ignoré</target>
         <note />
       </trans-unit>
-      <trans-unit id="ERR_StaticInAsOrIs">
-        <source>The second operand of an 'is' or 'as' operator may not be static type '{0}'</source>
-        <target state="translated">Le second opérande d'un opérateur 'is' ou 'as' ne peut pas être du type static '{0}'</target>
-        <note />
-      </trans-unit>
       <trans-unit id="ERR_BadVisEventType">
         <source>Inconsistent accessibility: event type '{1}' is less accessible than event '{0}'</source>
         <target state="translated">Accessibilité incohérente : le type d'événement '{1}' est moins accessible que l'événement '{0}'</target>