Throw better exception when attempting to map a read-only collection as a primitive collection

src/EFCore/Infrastructure/ModelValidator.cs

@@ -1023,14 +1023,21 @@ static void Validate(ITypeBase typeBase, IDiagnosticsLogger<DbLoggerCategory.Mod
             foreach (var property in typeBase.GetDeclaredProperties())
             {
                 var elementClrType = property.GetElementType()?.ClrType;
-                if (property is { IsPrimitiveCollection: true, ClrType.IsArray: false, ClrType.IsSealed: true }
-                    && elementClrType is { IsSealed: true }
-                    && elementClrType.TryGetElementType(typeof(IList<>)) == null)
+                if (property is { IsPrimitiveCollection: true, ClrType.IsArray: false })
                 {
-                    throw new InvalidOperationException(
-                        CoreStrings.BadListType(
-                            property.ClrType.ShortDisplayName(),
-                            typeof(IList<>).MakeGenericType(elementClrType).ShortDisplayName()));
+                    if (property.ClrType.IsSealed && property.ClrType.TryGetElementType(typeof(IList<>)) == null)
+                    {
+                        throw new InvalidOperationException(
+                            CoreStrings.BadListType(
+                                property.ClrType.ShortDisplayName(),
+                                typeof(IList<>).MakeGenericType(elementClrType!).ShortDisplayName()));
+                    }
+
+                    if (property.ClrType.GetGenericTypeDefinition() == typeof(IReadOnlyCollection<>)
+                        || property.ClrType.GetGenericTypeDefinition() == typeof(IReadOnlyList<>))
+                    {
+                        throw new InvalidOperationException(CoreStrings.ReadOnlyListType(property.ClrType.ShortDisplayName()));
+                    }
                 }
             }
 

src/EFCore/Properties/CoreStrings.resx

@@ -1381,6 +1381,9 @@
   <data name="QueryUnhandledQueryRootExpression" xml:space="preserve">
     <value>Query root of type '{type}' wasn't handled by provider code. This issue happens when using a provider specific method on a different provider where it is not supported.</value>
   </data>
+  <data name="ReadOnlyListType" xml:space="preserve">
+    <value>The type '{givenType}' cannot be used as a primitive collection because it is read-only. Read-only collections of primitive types are not supported.</value>
+  </data>
   <data name="RecursiveOnConfiguring" xml:space="preserve">
     <value>An attempt was made to use the context instance while it is being configured. A DbContext instance cannot be used inside 'OnConfiguring' since it is still being configured at this point. This can happen if a second operation is started on this context instance before a previous operation completed. Any instance members are not guaranteed to be thread safe.</value>
   </data>

test/EFCore.Tests/Infrastructure/ModelValidatorTest.cs

@@ -204,6 +204,52 @@ protected class WithStringCollection
         public string SomeString { get; set; }
     }
 
+    [ConditionalFact]
+    public virtual void Throws_when_mapping_an_IReadOnlyCollection()
+    {
+        var modelBuilder = CreateConventionModelBuilder();
+
+        modelBuilder.Entity<WithReadOnlyCollection>(
+            eb =>
+            {
+                eb.Property(e => e.Id);
+                eb.PrimitiveCollection(e => e.Tags);
+            });
+
+        VerifyError(
+            CoreStrings.ReadOnlyListType("IReadOnlyCollection<int>"),
+            modelBuilder, sensitiveDataLoggingEnabled: false);
+    }
+
+    protected class WithReadOnlyCollection
+    {
+        public int Id { get; set; }
+        public IReadOnlyCollection<int> Tags { get; set; }
+    }
+
+    [ConditionalFact]
+    public virtual void Throws_when_mapping_an_IReadOnlyList()
+    {
+        var modelBuilder = CreateConventionModelBuilder();
+
+        modelBuilder.Entity<WithReadOnlyList>(
+            eb =>
+            {
+                eb.Property(e => e.Id);
+                eb.PrimitiveCollection(e => e.Tags);
+            });
+
+        VerifyError(
+            CoreStrings.ReadOnlyListType("IReadOnlyList<char>"),
+            modelBuilder, sensitiveDataLoggingEnabled: false);
+    }
+
+    protected class WithReadOnlyList
+    {
+        public int Id { get; set; }
+        public IReadOnlyList<char> Tags { get; set; }
+    }
+
     [ConditionalFact]
     public virtual void Ignores_binary_keys_and_strings_without_custom_comparer()
     {