Allow static members in interfaces to treat type parameters as invari…

…ant (#46141) dotnet/csharplang#3275 https://github.com/dotnet/csharplang/blob/master/meetings/2020/LDM-2020-06-24.md#interface-static-member-variance https://github.com/dotnet/csharplang/blob/master/proposals/variance-safety-for-static-interface-members.md
dotnet · Jul 22, 2020 · 6a5ba0a · 6a5ba0a
1 parent 1e511fa
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diff --git a/src/Compilers/CSharp/Portable/CSharpResources.resx b/src/Compilers/CSharp/Portable/CSharpResources.resx
@@ -3851,6 +3851,9 @@ You should consider suppressing the warning only if you're sure that you don't w
   <data name="ERR_UnexpectedVariance" xml:space="preserve">
     <value>Invalid variance: The type parameter '{1}' must be {3} valid on '{0}'. '{1}' is {2}.</value>
   </data>
+  <data name="ERR_UnexpectedVarianceStaticMember" xml:space="preserve">
+    <value>Invalid variance: The type parameter '{1}' must be {3} valid on '{0}' unless language version '{4}' or greater is used. '{1}' is {2}.</value>
+  </data>
   <data name="ERR_DeriveFromDynamic" xml:space="preserve">
     <value>'{0}': cannot derive from the dynamic type</value>
   </data>
@@ -6348,4 +6351,7 @@ To remove the warning, you can use /reference instead (set the Embed Interop Typ
   <data name="ERR_ModuleInitializerMethodMustBeOrdinary" xml:space="preserve">
     <value>A module initializer must be an ordinary member method</value>
   </data>
+  <data name="IDS_FeatureVarianceSafetyForStaticInterfaceMembers" xml:space="preserve">
+    <value>variance safety for static interface members</value>
+  </data>
 </root>
diff --git a/src/Compilers/CSharp/Portable/Errors/ErrorCode.cs b/src/Compilers/CSharp/Portable/Errors/ErrorCode.cs
@@ -1868,6 +1868,9 @@ internal enum ErrorCode
         ERR_NonPrivateAPIInRecord = 8879,
 
         #endregion diagnostics introduced for C# 9.0
+
+        ERR_UnexpectedVarianceStaticMember = 9100,
+
         // Note: you will need to re-generate compiler code after adding warnings (eng\generate-compiler-code.cmd)
     }
 }
diff --git a/src/Compilers/CSharp/Portable/Errors/MessageID.cs b/src/Compilers/CSharp/Portable/Errors/MessageID.cs
@@ -209,6 +209,7 @@ internal enum MessageID
         IDS_FeatureNullPointerConstantPattern = MessageBase + 12783,
         IDS_FeatureModuleInitializers = MessageBase + 12784,
         IDS_FeatureTargetTypedConditional = MessageBase + 12785,
+        IDS_FeatureVarianceSafetyForStaticInterfaceMembers = MessageBase + 12786,
     }
 
     // Message IDs may refer to strings that need to be localized.
@@ -336,6 +337,7 @@ internal static LanguageVersion RequiredVersion(this MessageID feature)
                 case MessageID.IDS_FeatureTargetTypedConditional:  // semantic check
                 case MessageID.IDS_FeatureStaticAnonymousFunction: // syntax check
                 case MessageID.IDS_FeatureModuleInitializers: // semantic check on method attribute
+                case MessageID.IDS_FeatureVarianceSafetyForStaticInterfaceMembers: //semantic check
                     return LanguageVersion.Preview;
 
                 // C# 8.0 features.

diff --git a/src/Compilers/CSharp/Portable/Symbols/VarianceSafety.cs b/src/Compilers/CSharp/Portable/Symbols/VarianceSafety.cs
@@ -145,6 +145,11 @@ private static void CheckMethodVarianceSafety(this MethodSymbol method, Diagnost
 
         private static void CheckMethodVarianceSafety(this MethodSymbol method, LocationProvider<MethodSymbol> returnTypeLocationProvider, DiagnosticBag diagnostics)
         {
+            if (SkipVarianceSafetyChecks(method))
+            {
+                return;
+            }
+
             // Spec 13.2.1: "Furthermore, each class type constraint, interface type constraint and
             // type parameter constraint on any type parameter of the method must be input-safe."
             CheckTypeParametersVarianceSafety(method.TypeParameters, method, diagnostics);
@@ -162,11 +167,26 @@ private static void CheckMethodVarianceSafety(this MethodSymbol method, Location
             CheckParametersVarianceSafety(method.Parameters, method, diagnostics);
         }
 
+        private static bool SkipVarianceSafetyChecks(Symbol member)
+        {
+            if (member.IsStatic)
+            {
+                return MessageID.IDS_FeatureVarianceSafetyForStaticInterfaceMembers.RequiredVersion() <= member.DeclaringCompilation.LanguageVersion;
+            }
+
+            return false;
+        }
+
         /// <summary>
         /// Accumulate diagnostics related to the variance safety of an interface property.
         /// </summary>
         private static void CheckPropertyVarianceSafety(PropertySymbol property, DiagnosticBag diagnostics)
         {
+            if (SkipVarianceSafetyChecks(property))
+            {
+                return;
+            }
+
             bool hasGetter = (object)property.GetMethod != null;
             bool hasSetter = (object)property.SetMethod != null;
             if (hasGetter || hasSetter)
@@ -193,6 +213,11 @@ private static void CheckPropertyVarianceSafety(PropertySymbol property, Diagnos
         /// </summary>
         private static void CheckEventVarianceSafety(EventSymbol @event, DiagnosticBag diagnostics)
         {
+            if (SkipVarianceSafetyChecks(@event))
+            {
+                return;
+            }
+
             IsVarianceUnsafe(
                 @event.Type,
                 requireOutputSafety: false,
@@ -442,7 +467,15 @@ private static void AddVarianceError<T>(
             // "requires output-safe", and "requires input-safe and output-safe".  This would make the error codes much easier to document and
             // much more actionable.
             // UNDONE: related location for use is much more useful
-            diagnostics.Add(ErrorCode.ERR_UnexpectedVariance, location, context, unsafeTypeParameter, actualVariance.Localize(), expectedVariance.Localize());
+            if (!(context is TypeSymbol) && context.IsStatic)
+            {
+                diagnostics.Add(ErrorCode.ERR_UnexpectedVarianceStaticMember, location, context, unsafeTypeParameter, actualVariance.Localize(), expectedVariance.Localize(),
+                                new CSharpRequiredLanguageVersion(MessageID.IDS_FeatureVarianceSafetyForStaticInterfaceMembers.RequiredVersion()));
+            }
+            else
+            {
+                diagnostics.Add(ErrorCode.ERR_UnexpectedVariance, location, context, unsafeTypeParameter, actualVariance.Localize(), expectedVariance.Localize());
+            }
         }
 
         private static T GetDeclaringSyntax<T>(this Symbol symbol) where T : SyntaxNode

diff --git a/src/Compilers/CSharp/Portable/xlf/CSharpResources.cs.xlf b/src/Compilers/CSharp/Portable/xlf/CSharpResources.cs.xlf
@@ -862,6 +862,11 @@
         <target state="new">A constructor declared in a record with parameters must have 'this' constructor initializer.</target>
         <note />
       </trans-unit>
+      <trans-unit id="ERR_UnexpectedVarianceStaticMember">
+        <source>Invalid variance: The type parameter '{1}' must be {3} valid on '{0}' unless language version '{4}' or greater is used. '{1}' is {2}.</source>
+        <target state="new">Invalid variance: The type parameter '{1}' must be {3} valid on '{0}' unless language version '{4}' or greater is used. '{1}' is {2}.</target>
+        <note />
+      </trans-unit>
       <trans-unit id="ERR_UnmanagedBoundWithClass">
         <source>'{0}': cannot specify both a constraint class and the 'unmanaged' constraint</source>
         <target state="translated">{0}: Nejde zadat třídu omezení a zároveň omezení unmanaged.</target>
@@ -1486,6 +1491,11 @@
         <target state="translated">deklarace using</target>
         <note />
       </trans-unit>
+      <trans-unit id="IDS_FeatureVarianceSafetyForStaticInterfaceMembers">
+        <source>variance safety for static interface members</source>
+        <target state="new">variance safety for static interface members</target>
+        <note />
+      </trans-unit>
       <trans-unit id="IDS_NULL">
         <source>&lt;null&gt;</source>
         <target state="translated">&lt;null&gt;</target>

diff --git a/src/Compilers/CSharp/Portable/xlf/CSharpResources.de.xlf b/src/Compilers/CSharp/Portable/xlf/CSharpResources.de.xlf
@@ -862,6 +862,11 @@
         <target state="new">A constructor declared in a record with parameters must have 'this' constructor initializer.</target>
         <note />
       </trans-unit>
+      <trans-unit id="ERR_UnexpectedVarianceStaticMember">
+        <source>Invalid variance: The type parameter '{1}' must be {3} valid on '{0}' unless language version '{4}' or greater is used. '{1}' is {2}.</source>
+        <target state="new">Invalid variance: The type parameter '{1}' must be {3} valid on '{0}' unless language version '{4}' or greater is used. '{1}' is {2}.</target>
+        <note />
+      </trans-unit>
       <trans-unit id="ERR_UnmanagedBoundWithClass">
         <source>'{0}': cannot specify both a constraint class and the 'unmanaged' constraint</source>
         <target state="translated">"{0}": Eine Einschränkungsklasse kann nicht gleichzeitig mit einer unmanaged-Einschränkung angegeben werden.</target>
@@ -1486,6 +1491,11 @@
         <target state="translated">Using-Deklarationen</target>
         <note />
       </trans-unit>
+      <trans-unit id="IDS_FeatureVarianceSafetyForStaticInterfaceMembers">
+        <source>variance safety for static interface members</source>
+        <target state="new">variance safety for static interface members</target>
+        <note />
+      </trans-unit>
       <trans-unit id="IDS_NULL">
         <source>&lt;null&gt;</source>
         <target state="translated">&lt;NULL&gt;</target>

diff --git a/src/Compilers/CSharp/Portable/xlf/CSharpResources.es.xlf b/src/Compilers/CSharp/Portable/xlf/CSharpResources.es.xlf
@@ -862,6 +862,11 @@
         <target state="new">A constructor declared in a record with parameters must have 'this' constructor initializer.</target>
         <note />
       </trans-unit>
+      <trans-unit id="ERR_UnexpectedVarianceStaticMember">
+        <source>Invalid variance: The type parameter '{1}' must be {3} valid on '{0}' unless language version '{4}' or greater is used. '{1}' is {2}.</source>
+        <target state="new">Invalid variance: The type parameter '{1}' must be {3} valid on '{0}' unless language version '{4}' or greater is used. '{1}' is {2}.</target>
+        <note />
+      </trans-unit>
       <trans-unit id="ERR_UnmanagedBoundWithClass">
         <source>'{0}': cannot specify both a constraint class and the 'unmanaged' constraint</source>
         <target state="translated">"{0}": no se puede especificar a la vez una clase de restricción y la restricción "unmanaged"</target>
@@ -1486,6 +1491,11 @@
         <target state="translated">declaraciones using</target>
         <note />
       </trans-unit>
+      <trans-unit id="IDS_FeatureVarianceSafetyForStaticInterfaceMembers">
+        <source>variance safety for static interface members</source>
+        <target state="new">variance safety for static interface members</target>
+        <note />
+      </trans-unit>
       <trans-unit id="IDS_NULL">
         <source>&lt;null&gt;</source>
         <target state="translated">&lt;NULL&gt;</target>

diff --git a/src/Compilers/CSharp/Portable/xlf/CSharpResources.fr.xlf b/src/Compilers/CSharp/Portable/xlf/CSharpResources.fr.xlf
@@ -862,6 +862,11 @@
         <target state="new">A constructor declared in a record with parameters must have 'this' constructor initializer.</target>
         <note />
       </trans-unit>
+      <trans-unit id="ERR_UnexpectedVarianceStaticMember">
+        <source>Invalid variance: The type parameter '{1}' must be {3} valid on '{0}' unless language version '{4}' or greater is used. '{1}' is {2}.</source>
+        <target state="new">Invalid variance: The type parameter '{1}' must be {3} valid on '{0}' unless language version '{4}' or greater is used. '{1}' is {2}.</target>
+        <note />
+      </trans-unit>
       <trans-unit id="ERR_UnmanagedBoundWithClass">
         <source>'{0}': cannot specify both a constraint class and the 'unmanaged' constraint</source>
         <target state="translated">'{0}' : impossible de spécifier à la fois une classe de contrainte et la contrainte 'unmanaged'</target>
@@ -1486,6 +1491,11 @@
         <target state="translated">Déclarations using</target>
         <note />
       </trans-unit>
+      <trans-unit id="IDS_FeatureVarianceSafetyForStaticInterfaceMembers">
+        <source>variance safety for static interface members</source>
+        <target state="new">variance safety for static interface members</target>
+        <note />
+      </trans-unit>
       <trans-unit id="IDS_NULL">
         <source>&lt;null&gt;</source>
         <target state="translated">&lt;Null&gt;</target>

diff --git a/src/Compilers/CSharp/Portable/xlf/CSharpResources.it.xlf b/src/Compilers/CSharp/Portable/xlf/CSharpResources.it.xlf
@@ -862,6 +862,11 @@
         <target state="new">A constructor declared in a record with parameters must have 'this' constructor initializer.</target>
         <note />
       </trans-unit>
+      <trans-unit id="ERR_UnexpectedVarianceStaticMember">
+        <source>Invalid variance: The type parameter '{1}' must be {3} valid on '{0}' unless language version '{4}' or greater is used. '{1}' is {2}.</source>
+        <target state="new">Invalid variance: The type parameter '{1}' must be {3} valid on '{0}' unless language version '{4}' or greater is used. '{1}' is {2}.</target>
+        <note />
+      </trans-unit>
       <trans-unit id="ERR_UnmanagedBoundWithClass">
         <source>'{0}': cannot specify both a constraint class and the 'unmanaged' constraint</source>
         <target state="translated">'{0}': non è possibile specificare sia una classe constraint che il vincolo 'unmanaged'</target>
@@ -1486,6 +1491,11 @@
         <target state="translated">dichiarazioni using</target>
         <note />
       </trans-unit>
+      <trans-unit id="IDS_FeatureVarianceSafetyForStaticInterfaceMembers">
+        <source>variance safety for static interface members</source>
+        <target state="new">variance safety for static interface members</target>
+        <note />
+      </trans-unit>
       <trans-unit id="IDS_NULL">
         <source>&lt;null&gt;</source>
         <target state="translated">&lt;Null&gt;</target>

diff --git a/src/Compilers/CSharp/Portable/xlf/CSharpResources.ja.xlf b/src/Compilers/CSharp/Portable/xlf/CSharpResources.ja.xlf
@@ -862,6 +862,11 @@
         <target state="new">A constructor declared in a record with parameters must have 'this' constructor initializer.</target>
         <note />
       </trans-unit>
+      <trans-unit id="ERR_UnexpectedVarianceStaticMember">
+        <source>Invalid variance: The type parameter '{1}' must be {3} valid on '{0}' unless language version '{4}' or greater is used. '{1}' is {2}.</source>
+        <target state="new">Invalid variance: The type parameter '{1}' must be {3} valid on '{0}' unless language version '{4}' or greater is used. '{1}' is {2}.</target>
+        <note />
+      </trans-unit>
       <trans-unit id="ERR_UnmanagedBoundWithClass">
         <source>'{0}': cannot specify both a constraint class and the 'unmanaged' constraint</source>
         <target state="translated">'{0}': 制約クラスと 'unmanaged' 制約の両方を指定することはできません</target>
@@ -1486,6 +1491,11 @@
         <target state="translated">using 宣言</target>
         <note />
       </trans-unit>
+      <trans-unit id="IDS_FeatureVarianceSafetyForStaticInterfaceMembers">
+        <source>variance safety for static interface members</source>
+        <target state="new">variance safety for static interface members</target>
+        <note />
+      </trans-unit>
       <trans-unit id="IDS_NULL">
         <source>&lt;null&gt;</source>
         <target state="translated">&lt;null&gt;</target>

diff --git a/src/Compilers/CSharp/Portable/xlf/CSharpResources.ko.xlf b/src/Compilers/CSharp/Portable/xlf/CSharpResources.ko.xlf
@@ -862,6 +862,11 @@
         <target state="new">A constructor declared in a record with parameters must have 'this' constructor initializer.</target>
         <note />
       </trans-unit>
+      <trans-unit id="ERR_UnexpectedVarianceStaticMember">
+        <source>Invalid variance: The type parameter '{1}' must be {3} valid on '{0}' unless language version '{4}' or greater is used. '{1}' is {2}.</source>
+        <target state="new">Invalid variance: The type parameter '{1}' must be {3} valid on '{0}' unless language version '{4}' or greater is used. '{1}' is {2}.</target>
+        <note />
+      </trans-unit>
       <trans-unit id="ERR_UnmanagedBoundWithClass">
         <source>'{0}': cannot specify both a constraint class and the 'unmanaged' constraint</source>
         <target state="translated">'{0}': constraint 클래스와 'unmanaged' 제약 조건을 둘 다 지정할 수는 없습니다.</target>
@@ -1486,6 +1491,11 @@
         <target state="translated">using 선언</target>
         <note />
       </trans-unit>
+      <trans-unit id="IDS_FeatureVarianceSafetyForStaticInterfaceMembers">
+        <source>variance safety for static interface members</source>
+        <target state="new">variance safety for static interface members</target>
+        <note />
+      </trans-unit>
       <trans-unit id="IDS_NULL">
         <source>&lt;null&gt;</source>
         <target state="translated">&lt;null&gt;</target>

diff --git a/src/Compilers/CSharp/Portable/xlf/CSharpResources.pl.xlf b/src/Compilers/CSharp/Portable/xlf/CSharpResources.pl.xlf
@@ -862,6 +862,11 @@
         <target state="new">A constructor declared in a record with parameters must have 'this' constructor initializer.</target>
         <note />
       </trans-unit>
+      <trans-unit id="ERR_UnexpectedVarianceStaticMember">
+        <source>Invalid variance: The type parameter '{1}' must be {3} valid on '{0}' unless language version '{4}' or greater is used. '{1}' is {2}.</source>
+        <target state="new">Invalid variance: The type parameter '{1}' must be {3} valid on '{0}' unless language version '{4}' or greater is used. '{1}' is {2}.</target>
+        <note />
+      </trans-unit>
       <trans-unit id="ERR_UnmanagedBoundWithClass">
         <source>'{0}': cannot specify both a constraint class and the 'unmanaged' constraint</source>
         <target state="translated">„{0}”: nie można jednocześnie określić klasy ograniczenia i ograniczenia „unmanaged”</target>
@@ -1486,6 +1491,11 @@
         <target state="translated">deklaracje using</target>
         <note />
       </trans-unit>
+      <trans-unit id="IDS_FeatureVarianceSafetyForStaticInterfaceMembers">
+        <source>variance safety for static interface members</source>
+        <target state="new">variance safety for static interface members</target>
+        <note />
+      </trans-unit>
       <trans-unit id="IDS_NULL">
         <source>&lt;null&gt;</source>
         <target state="translated">&lt;null&gt;</target>

diff --git a/src/Compilers/CSharp/Portable/xlf/CSharpResources.pt-BR.xlf b/src/Compilers/CSharp/Portable/xlf/CSharpResources.pt-BR.xlf
@@ -862,6 +862,11 @@
         <target state="new">A constructor declared in a record with parameters must have 'this' constructor initializer.</target>
         <note />
       </trans-unit>
+      <trans-unit id="ERR_UnexpectedVarianceStaticMember">
+        <source>Invalid variance: The type parameter '{1}' must be {3} valid on '{0}' unless language version '{4}' or greater is used. '{1}' is {2}.</source>
+        <target state="new">Invalid variance: The type parameter '{1}' must be {3} valid on '{0}' unless language version '{4}' or greater is used. '{1}' is {2}.</target>
+        <note />
+      </trans-unit>
       <trans-unit id="ERR_UnmanagedBoundWithClass">
         <source>'{0}': cannot specify both a constraint class and the 'unmanaged' constraint</source>
         <target state="translated">'{0}': não é possível especificar uma classe de restrição e a restrição 'unmanaged'</target>
@@ -1484,6 +1489,11 @@
         <target state="translated">declarações using</target>
         <note />
       </trans-unit>
+      <trans-unit id="IDS_FeatureVarianceSafetyForStaticInterfaceMembers">
+        <source>variance safety for static interface members</source>
+        <target state="new">variance safety for static interface members</target>
+        <note />
+      </trans-unit>
       <trans-unit id="IDS_NULL">
         <source>&lt;null&gt;</source>
         <target state="translated">&lt;nulo&gt;</target>

diff --git a/src/Compilers/CSharp/Portable/xlf/CSharpResources.ru.xlf b/src/Compilers/CSharp/Portable/xlf/CSharpResources.ru.xlf
@@ -862,6 +862,11 @@
         <target state="new">A constructor declared in a record with parameters must have 'this' constructor initializer.</target>
         <note />
       </trans-unit>
+      <trans-unit id="ERR_UnexpectedVarianceStaticMember">
+        <source>Invalid variance: The type parameter '{1}' must be {3} valid on '{0}' unless language version '{4}' or greater is used. '{1}' is {2}.</source>
+        <target state="new">Invalid variance: The type parameter '{1}' must be {3} valid on '{0}' unless language version '{4}' or greater is used. '{1}' is {2}.</target>
+        <note />
+      </trans-unit>
       <trans-unit id="ERR_UnmanagedBoundWithClass">
         <source>'{0}': cannot specify both a constraint class and the 'unmanaged' constraint</source>
         <target state="translated">"{0}": невозможно одновременно задать класс ограничения и ограничение "unmanaged"</target>
@@ -1486,6 +1491,11 @@
         <target state="translated">объявления using</target>
         <note />
       </trans-unit>
+      <trans-unit id="IDS_FeatureVarianceSafetyForStaticInterfaceMembers">
+        <source>variance safety for static interface members</source>
+        <target state="new">variance safety for static interface members</target>
+        <note />
+      </trans-unit>
       <trans-unit id="IDS_NULL">
         <source>&lt;null&gt;</source>
         <target state="translated">&lt;NULL&gt;</target>