[Fusion] Updated source schema validation rule "ExternalOverrideCollisionRule" (#8785)

Author: glen-84

src/HotChocolate/Fusion-vnext/src/Fusion.Composition/Properties/CompositionResources.Designer.cs

@@ -214,7 +214,7 @@
     <value>The interface field '{0}' in schema '{1}' must not be marked as external.</value>
   </data>
   <data name="LogEntryHelper_ExternalOverrideCollision" xml:space="preserve">
-    <value>The external field '{0}' must not be annotated with the @override directive.</value>
+    <value>The external field '{0}' in schema '{1}' must not be annotated with the @override directive.</value>
   </data>
   <data name="LogEntryHelper_ExternalUnused" xml:space="preserve">
     <value>The external field '{0}' in schema '{1}' is not referenced by a @provides directive in the schema.</value>

src/HotChocolate/Fusion-vnext/src/Fusion.Composition/Properties/CompositionResources.resx

@@ -10,7 +10,8 @@ namespace HotChocolate.Fusion.SourceSchemaValidationRules;
 /// schema, and the current schema merely references it. Therefore, a field marked with
 /// <c>@external</c> must <b>not</b> simultaneously carry directives that assume local ownership or
 /// resolution responsibility, such as <c>@override</c>, which transfers ownership of the field’s
-/// definition from one schema to another.
+/// definition from one schema to another, and is incompatible with an already-external field
+/// definition.
 /// </summary>
 /// <seealso href="https://graphql.github.io/composite-schemas-spec/draft/#sec-External-Override-Collision">
 /// Specification

src/HotChocolate/Fusion-vnext/src/Fusion.Composition/SourceSchemaValidationRules/ExternalOverrideCollisionRule.cs

@@ -48,11 +48,20 @@ public static TheoryData<string[]> ValidExamplesData()
     {
         return new TheoryData<string[]>
         {
-            // In this scenario, "User.fullName" is overriding the field from schema A. Since
-            // @override is not combined with @external on the same field, no collision occurs.
+            // In this scenario, "User.fullName" is defined in Schema A, but overridden in Schema B.
+            // Since @override is not combined with @external on the same field, no collision
+            // occurs.
             {
                 [
                     """
+                    # Source Schema A
+                    type User {
+                        id: ID!
+                        fullName: String
+                    }
+                    """,
+                    """
+                    # Source Schema B
                     type User {
                         id: ID!
                         fullName: String @override(from: "A")
@@ -73,14 +82,23 @@ public static TheoryData<string[], string[]> InvalidExamplesData()
             {
                 [
                     """
+                    # Source Schema A
+                    type Payment {
+                        id: ID!
+                        amount: Int
+                    }
+                    """,
+                    """
+                    # Source Schema B
                     type Payment {
                         id: ID!
                         amount: Int @override(from: "A") @external
                     }
                     """
                 ],
                 [
-                    "The external field 'Payment.amount' must not be annotated with the @override directive."
+                    "The external field 'Payment.amount' in schema 'B' must not be annotated with "
+                    + "the @override directive."
                 ]
             }
         };