Readonly members more test coverage

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

@@ -1153,7 +1153,7 @@ ContainingMemberOrLambda is MethodSymbol containingMethod &&
                 !method.IsEffectivelyReadOnly &&
                 !method.IsStatic)
             {
-                Error(diagnostics, ErrorCode.WRN_ImplicitCopyInReadOnlyMember, receiver.Syntax, method.Name, ThisParameterSymbol.SymbolName);
+                Error(diagnostics, ErrorCode.WRN_ImplicitCopyInReadOnlyMember, receiver.Syntax, method, ThisParameterSymbol.SymbolName);
                 return false;
             }
 

src/Compilers/CSharp/Portable/CSharpResources.resx

@@ -5431,7 +5431,7 @@ To remove the warning, you can use /reference instead (set the Embed Interop Typ
     <value>Call to non-readonly member from a 'readonly' member results in an implicit copy.</value>
   </data>
   <data name="ERR_StaticMemberCantBeReadOnly" xml:space="preserve">
-    <value>Static member '{0}' cannot be marked 'readonly' because readonly members cannot modify 'this' and static members do not have a 'this' parameter.</value>
+    <value>Static member '{0}' cannot be marked 'readonly'.</value>
   </data>
   <data name="ERR_AutoSetterCantBeReadOnly" xml:space="preserve">
     <value>Auto-implemented 'set' accessor '{0}' cannot be marked 'readonly'.</value>
@@ -5451,6 +5451,9 @@ To remove the warning, you can use /reference instead (set the Embed Interop Typ
   <data name="ERR_PartialMethodReadOnlyDifference" xml:space="preserve">
     <value>Both partial method declarations must be readonly or neither may be readonly</value>
   </data>
+  <data name="ERR_ReadOnlyModMissingAccessor" xml:space="preserve">
+    <value>'{0}': 'readonly' can only be used on accessors if the property or indexer has both a get and a set accessor</value>
+  </data>
   <data name="WRN_NullabilityMismatchInArgument" xml:space="preserve">
     <value>Argument of type '{0}' cannot be used for parameter '{2}' of type '{1}' in '{3}' due to differences in the nullability of reference types.</value>
   </data>

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

@@ -1691,6 +1691,7 @@ internal enum ErrorCode
         ERR_DuplicatePropertyReadOnlyMods = 8660,
         ERR_FieldLikeEventCantBeReadOnly = 8661,
         ERR_PartialMethodReadOnlyDifference = 8662,
+        ERR_ReadOnlyModMissingAccessor = 8663
 
         #endregion diagnostics introduced for C# 8.0
 

src/Compilers/CSharp/Portable/Symbols/Source/SourceEventSymbol.cs

@@ -480,7 +480,7 @@ protected void CheckModifiersAndType(DiagnosticBag diagnostics)
             }
             else if (IsReadOnly && IsStatic)
             {
-                // Static member '{0}' cannot be marked 'readonly' because readonly members cannot modify 'this' and static members do not have a 'this' parameter.
+                // Static member '{0}' cannot be marked 'readonly'.
                 diagnostics.Add(ErrorCode.ERR_StaticMemberCantBeReadOnly, location, this);
             }
             else if (IsReadOnly && HasAssociatedField)

src/Compilers/CSharp/Portable/Symbols/Source/SourceOrdinaryMethodSymbol.cs

@@ -940,7 +940,7 @@ private void CheckModifiers(bool hasBody, Location location, DiagnosticBag diagn
             }
             else if (IsStatic && IsDeclaredReadOnly)
             {
-                // Static member '{0}' cannot be marked 'readonly' because readonly members cannot modify 'this' and static members do not have a 'this' parameter.
+                // Static member '{0}' cannot be marked 'readonly'.
                 diagnostics.Add(ErrorCode.ERR_StaticMemberCantBeReadOnly, location, this);
             }
             else if (IsAbstract && !ContainingType.IsAbstract && (ContainingType.TypeKind == TypeKind.Class || ContainingType.TypeKind == TypeKind.Submission))

src/Compilers/CSharp/Portable/Symbols/Source/SourcePropertyAccessorSymbol.cs

@@ -477,7 +477,7 @@ private void CheckModifiers(Location location, bool hasBody, bool isAutoProperty
             }
             else if (LocalDeclaredReadOnly && IsStatic)
             {
-                // Static member '{0}' cannot be marked 'readonly' because readonly members cannot modify 'this' and static members do not have a 'this' parameter.
+                // Static member '{0}' cannot be marked 'readonly'.
                 diagnostics.Add(ErrorCode.ERR_StaticMemberCantBeReadOnly, location, this);
             }
             else if (LocalDeclaredReadOnly && _isAutoPropertyAccessor && MethodKind == MethodKind.PropertySet)

src/Compilers/CSharp/Portable/Symbols/Source/SourcePropertySymbol.cs

@@ -385,6 +385,12 @@ private SourcePropertySymbol(
                             {
                                 diagnostics.Add(ErrorCode.ERR_AccessModMissingAccessor, location, this);
                             }
+
+                            // Check that 'readonly' is not set on the one accessor.
+                            if (accessor.LocalDeclaredReadOnly)
+                            {
+                                diagnostics.Add(ErrorCode.ERR_ReadOnlyModMissingAccessor, location, this);
+                            }
                         }
                     }
                 }
@@ -910,7 +916,7 @@ private void CheckModifiers(Location location, bool isIndexer, DiagnosticBag dia
             }
             else if (IsStatic && HasReadOnlyModifier)
             {
-                // Static member '{0}' cannot be marked 'readonly' because readonly members cannot modify 'this' and static members do not have a 'this' parameter.
+                // Static member '{0}' cannot be marked 'readonly'.
                 diagnostics.Add(ErrorCode.ERR_StaticMemberCantBeReadOnly, location, this);
             }
             else if (IsOverride && (IsNew || IsVirtual))

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

@@ -292,6 +292,11 @@
         <target state="translated">Dílčí vzor vlastnosti vyžaduje odkaz na vlastnost nebo pole k přiřazení, např. „{{ Name: {0} }}“.</target>
         <note />
       </trans-unit>
+      <trans-unit id="ERR_ReadOnlyModMissingAccessor">
+        <source>'{0}': 'readonly' can only be used on accessors if the property or indexer has both a get and a set accessor</source>
+        <target state="new">'{0}': 'readonly' can only be used on accessors if the property or indexer has both a get and a set accessor</target>
+        <note />
+      </trans-unit>
       <trans-unit id="ERR_RefAssignNarrower">
         <source>Cannot ref-assign '{1}' to '{0}' because '{1}' has a narrower escape scope than '{0}'.</source>
         <target state="translated">Přiřazení odkazu {1} k {0} nelze provést, protože {1} má užší řídicí obor než {0}.</target>
@@ -318,8 +323,8 @@
         <note />
       </trans-unit>
       <trans-unit id="ERR_StaticMemberCantBeReadOnly">
-        <source>Static member '{0}' cannot be marked 'readonly' because readonly members cannot modify 'this' and static members do not have a 'this' parameter.</source>
-        <target state="new">Static member '{0}' cannot be marked 'readonly' because readonly members cannot modify 'this' and static members do not have a 'this' parameter.</target>
+        <source>Static member '{0}' cannot be marked 'readonly'.</source>
+        <target state="new">Static member '{0}' cannot be marked 'readonly'.</target>
         <note />
       </trans-unit>
       <trans-unit id="ERR_SwitchArmSubsumed">

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

@@ -292,6 +292,11 @@
         <target state="translated">Ein Eigenschaftsteilmuster erfordert einen Verweis auf die abzugleichende Eigenschaft oder das abzugleichende Feld. Beispiel: "{{ Name: {0} }}"</target>
         <note />
       </trans-unit>
+      <trans-unit id="ERR_ReadOnlyModMissingAccessor">
+        <source>'{0}': 'readonly' can only be used on accessors if the property or indexer has both a get and a set accessor</source>
+        <target state="new">'{0}': 'readonly' can only be used on accessors if the property or indexer has both a get and a set accessor</target>
+        <note />
+      </trans-unit>
       <trans-unit id="ERR_RefAssignNarrower">
         <source>Cannot ref-assign '{1}' to '{0}' because '{1}' has a narrower escape scope than '{0}'.</source>
         <target state="translated">ref-assign von "{1}" zu "{0}" ist nicht möglich, weil "{1}" einen geringeren Escapebereich als "{0}" aufweist.</target>
@@ -318,8 +323,8 @@
         <note />
       </trans-unit>
       <trans-unit id="ERR_StaticMemberCantBeReadOnly">
-        <source>Static member '{0}' cannot be marked 'readonly' because readonly members cannot modify 'this' and static members do not have a 'this' parameter.</source>
-        <target state="new">Static member '{0}' cannot be marked 'readonly' because readonly members cannot modify 'this' and static members do not have a 'this' parameter.</target>
+        <source>Static member '{0}' cannot be marked 'readonly'.</source>
+        <target state="new">Static member '{0}' cannot be marked 'readonly'.</target>
         <note />
       </trans-unit>
       <trans-unit id="ERR_SwitchArmSubsumed">

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

@@ -292,6 +292,11 @@
         <target state="translated">El subpatrón de una propiedad requiere una referencia a la propiedad o al campo que debe coincidir; por ejemplo, "{{ Name: {0} }}"</target>
         <note />
       </trans-unit>
+      <trans-unit id="ERR_ReadOnlyModMissingAccessor">
+        <source>'{0}': 'readonly' can only be used on accessors if the property or indexer has both a get and a set accessor</source>
+        <target state="new">'{0}': 'readonly' can only be used on accessors if the property or indexer has both a get and a set accessor</target>
+        <note />
+      </trans-unit>
       <trans-unit id="ERR_RefAssignNarrower">
         <source>Cannot ref-assign '{1}' to '{0}' because '{1}' has a narrower escape scope than '{0}'.</source>
         <target state="translated">No se puede asignar referencia "{1}" a "{0}" porque "{1}" tiene un ámbito de escape más limitado que "{0}".</target>
@@ -318,8 +323,8 @@
         <note />
       </trans-unit>
       <trans-unit id="ERR_StaticMemberCantBeReadOnly">
-        <source>Static member '{0}' cannot be marked 'readonly' because readonly members cannot modify 'this' and static members do not have a 'this' parameter.</source>
-        <target state="new">Static member '{0}' cannot be marked 'readonly' because readonly members cannot modify 'this' and static members do not have a 'this' parameter.</target>
+        <source>Static member '{0}' cannot be marked 'readonly'.</source>
+        <target state="new">Static member '{0}' cannot be marked 'readonly'.</target>
         <note />
       </trans-unit>
       <trans-unit id="ERR_SwitchArmSubsumed">

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

@@ -292,6 +292,11 @@
         <target state="translated">Un sous-modèle de propriété nécessite une correspondance de la référence à la propriété ou au champ. Exemple : '{{ Nom: {0} }}'</target>
         <note />
       </trans-unit>
+      <trans-unit id="ERR_ReadOnlyModMissingAccessor">
+        <source>'{0}': 'readonly' can only be used on accessors if the property or indexer has both a get and a set accessor</source>
+        <target state="new">'{0}': 'readonly' can only be used on accessors if the property or indexer has both a get and a set accessor</target>
+        <note />
+      </trans-unit>
       <trans-unit id="ERR_RefAssignNarrower">
         <source>Cannot ref-assign '{1}' to '{0}' because '{1}' has a narrower escape scope than '{0}'.</source>
         <target state="translated">Impossible d'effectuer une assignation par référence de '{1}' vers '{0}', car '{1}' a une portée de sortie plus limitée que '{0}'.</target>
@@ -318,8 +323,8 @@
         <note />
       </trans-unit>
       <trans-unit id="ERR_StaticMemberCantBeReadOnly">
-        <source>Static member '{0}' cannot be marked 'readonly' because readonly members cannot modify 'this' and static members do not have a 'this' parameter.</source>
-        <target state="new">Static member '{0}' cannot be marked 'readonly' because readonly members cannot modify 'this' and static members do not have a 'this' parameter.</target>
+        <source>Static member '{0}' cannot be marked 'readonly'.</source>
+        <target state="new">Static member '{0}' cannot be marked 'readonly'.</target>
         <note />
       </trans-unit>
       <trans-unit id="ERR_SwitchArmSubsumed">

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

@@ -292,6 +292,11 @@
         <target state="translated">Con un criterio secondario di proprietà è richiesto un riferimento alla proprietà o al campo da abbinare, ad esempio '{{ Name: {0} }}'</target>
         <note />
       </trans-unit>
+      <trans-unit id="ERR_ReadOnlyModMissingAccessor">
+        <source>'{0}': 'readonly' can only be used on accessors if the property or indexer has both a get and a set accessor</source>
+        <target state="new">'{0}': 'readonly' can only be used on accessors if the property or indexer has both a get and a set accessor</target>
+        <note />
+      </trans-unit>
       <trans-unit id="ERR_RefAssignNarrower">
         <source>Cannot ref-assign '{1}' to '{0}' because '{1}' has a narrower escape scope than '{0}'.</source>
         <target state="translated">Non è possibile assegnare '{1}' a '{0}' come ref perché l'ambito di escape di '{1}' è ridotto rispetto a quello di '{0}'.</target>
@@ -318,8 +323,8 @@
         <note />
       </trans-unit>
       <trans-unit id="ERR_StaticMemberCantBeReadOnly">
-        <source>Static member '{0}' cannot be marked 'readonly' because readonly members cannot modify 'this' and static members do not have a 'this' parameter.</source>
-        <target state="new">Static member '{0}' cannot be marked 'readonly' because readonly members cannot modify 'this' and static members do not have a 'this' parameter.</target>
+        <source>Static member '{0}' cannot be marked 'readonly'.</source>
+        <target state="new">Static member '{0}' cannot be marked 'readonly'.</target>
         <note />
       </trans-unit>
       <trans-unit id="ERR_SwitchArmSubsumed">

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

@@ -292,6 +292,11 @@
         <target state="translated">プロパティ サブパターンには、一致させるプロパティまたはフィールドへの参照が必要です。例: '{{ Name: {0} }}'</target>
         <note />
       </trans-unit>
+      <trans-unit id="ERR_ReadOnlyModMissingAccessor">
+        <source>'{0}': 'readonly' can only be used on accessors if the property or indexer has both a get and a set accessor</source>
+        <target state="new">'{0}': 'readonly' can only be used on accessors if the property or indexer has both a get and a set accessor</target>
+        <note />
+      </trans-unit>
       <trans-unit id="ERR_RefAssignNarrower">
         <source>Cannot ref-assign '{1}' to '{0}' because '{1}' has a narrower escape scope than '{0}'.</source>
         <target state="translated">'{1}' を '{0}' に ref 割り当てすることはできません。'{1}' のエスケープ スコープが '{0}' より狭いためです。</target>
@@ -318,8 +323,8 @@
         <note />
       </trans-unit>
       <trans-unit id="ERR_StaticMemberCantBeReadOnly">
-        <source>Static member '{0}' cannot be marked 'readonly' because readonly members cannot modify 'this' and static members do not have a 'this' parameter.</source>
-        <target state="new">Static member '{0}' cannot be marked 'readonly' because readonly members cannot modify 'this' and static members do not have a 'this' parameter.</target>
+        <source>Static member '{0}' cannot be marked 'readonly'.</source>
+        <target state="new">Static member '{0}' cannot be marked 'readonly'.</target>
         <note />
       </trans-unit>
       <trans-unit id="ERR_SwitchArmSubsumed">

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

@@ -292,6 +292,11 @@
         <target state="translated">속성 하위 패턴은 일치시킬 속성 또는 필드에 대한 참조가 필요합니다(예: '{{ Name: {0} }}')</target>
         <note />
       </trans-unit>
+      <trans-unit id="ERR_ReadOnlyModMissingAccessor">
+        <source>'{0}': 'readonly' can only be used on accessors if the property or indexer has both a get and a set accessor</source>
+        <target state="new">'{0}': 'readonly' can only be used on accessors if the property or indexer has both a get and a set accessor</target>
+        <note />
+      </trans-unit>
       <trans-unit id="ERR_RefAssignNarrower">
         <source>Cannot ref-assign '{1}' to '{0}' because '{1}' has a narrower escape scope than '{0}'.</source>
         <target state="translated">'{1}'을(를) '{0}'에 참조 할당할 수 없습니다. '{1}'이(가) '{0}'보다 이스케이프 범위가 좁기 때문입니다.</target>
@@ -318,8 +323,8 @@
         <note />
       </trans-unit>
       <trans-unit id="ERR_StaticMemberCantBeReadOnly">
-        <source>Static member '{0}' cannot be marked 'readonly' because readonly members cannot modify 'this' and static members do not have a 'this' parameter.</source>
-        <target state="new">Static member '{0}' cannot be marked 'readonly' because readonly members cannot modify 'this' and static members do not have a 'this' parameter.</target>
+        <source>Static member '{0}' cannot be marked 'readonly'.</source>
+        <target state="new">Static member '{0}' cannot be marked 'readonly'.</target>
         <note />
       </trans-unit>
       <trans-unit id="ERR_SwitchArmSubsumed">

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

@@ -292,6 +292,11 @@
         <target state="translated">Wzorzec podrzędny właściwości wymaga odwołania do właściwości lub pola, które należy dopasować, na przykład „{{ Name: {0} }}”</target>
         <note />
       </trans-unit>
+      <trans-unit id="ERR_ReadOnlyModMissingAccessor">
+        <source>'{0}': 'readonly' can only be used on accessors if the property or indexer has both a get and a set accessor</source>
+        <target state="new">'{0}': 'readonly' can only be used on accessors if the property or indexer has both a get and a set accessor</target>
+        <note />
+      </trans-unit>
       <trans-unit id="ERR_RefAssignNarrower">
         <source>Cannot ref-assign '{1}' to '{0}' because '{1}' has a narrower escape scope than '{0}'.</source>
         <target state="translated">Nie można przypisać odwołania elementu „{1}” do elementu „{0}”, ponieważ element „{1}” ma węższy zakres wyjścia niż element „{0}”.</target>
@@ -318,8 +323,8 @@
         <note />
       </trans-unit>
       <trans-unit id="ERR_StaticMemberCantBeReadOnly">
-        <source>Static member '{0}' cannot be marked 'readonly' because readonly members cannot modify 'this' and static members do not have a 'this' parameter.</source>
-        <target state="new">Static member '{0}' cannot be marked 'readonly' because readonly members cannot modify 'this' and static members do not have a 'this' parameter.</target>
+        <source>Static member '{0}' cannot be marked 'readonly'.</source>
+        <target state="new">Static member '{0}' cannot be marked 'readonly'.</target>
         <note />
       </trans-unit>
       <trans-unit id="ERR_SwitchArmSubsumed">