fix(schema): hold an attributeGroup reference to (annotation?) content (#145)

A referencing attributeGroup (one with a ref) names a definition elsewhere; its
own content model is (annotation?), so it may not also declare attributes,
nested attributeGroup references, or an anyAttribute. Only a defining
attributeGroup (with a name) carries those.

XSTS invalid-schemas-accepted 210 to 207, no other bucket moved.

CHANGELOG.md

@@ -22,6 +22,8 @@ Second pre-release. Continues the W3C XSTS schema-validity campaign: **invalid-s
 
 ### Fixed
 
+- XSTS invalid-schemas-accepted (#145): a referencing `attributeGroup` (one carrying a `ref`) is held to its `(annotation?)` content model. It names a definition elsewhere, so it may not itself declare attributes, nested attributeGroup references, or an `anyAttribute`; only a defining `attributeGroup` (with `name`) carries those (`attgD`). Caught three invalid schemas: invalid-schemas-accepted 210 → 207, no other bucket moved.
+
 - XSTS invalid-schemas-accepted (#145): notation names are now part of the component-name uniqueness check. A notation has its own symbol space, so two notations sharing a name and target namespace are a duplicate just as two global types or elements would be (`notatB005`). Caught one invalid schema: invalid-schemas-accepted 211 → 210, no other bucket moved.
 
 - XSTS invalid-schemas-accepted (#145): an `xsd:notation` declaration is held to its `(annotation?)` content model. A notation may carry only an optional `annotation` child, so any other element child, or any non-whitespace character content, is now rejected (`notatG`). Caught three invalid schemas: invalid-schemas-accepted 214 → 211, no other bucket moved.

Sources/Schema/SchemaStructureHelpers.swift

@@ -169,7 +169,16 @@ extension PureXML.Schema.XSDParser {
         return errors
     }
 
-    static func attributeGroupChildrenErrors(_: XSDTree, names: [String]) -> [String] {
+    static func attributeGroupChildrenErrors(_ node: XSDTree, names: [String]) -> [String] {
+        // A referencing attributeGroup (one with `ref`) names a definition elsewhere;
+        // its own content model is (annotation?), so it may not also declare
+        // attributes, nested attributeGroup references, or an anyAttribute. Only a
+        // defining attributeGroup (with `name`) carries those.
+        if PureXML.Schema.XSDNode.attribute(node, "ref") != nil {
+            return names.contains { $0 != "annotation" }
+                ? ["an attributeGroup reference may contain only an optional annotation"]
+                : []
+        }
         var errors: [String] = []
         let anyAttributes = names.count { $0 == "anyAttribute" }
         if anyAttributes > 1 {

Tests/XSTSSuiteTests.swift

@@ -113,8 +113,12 @@ struct XSTSSuiteTests {
     /// symbol space; two notations of the same name and namespace clash) then caught
     /// one more invalid schema: invalid-schemas accepted 211 → 210, no other bucket
     /// moved.
+    /// Holding a referencing `attributeGroup` (one with `ref`) to its `(annotation?)`
+    /// content model, so it may not also declare attributes, nested attributeGroup
+    /// references, or an anyAttribute, then caught three more invalid schemas:
+    /// invalid-schemas accepted 210 → 207, no other bucket moved.
     private let knownSchemaValidRejected = 1
-    private let knownSchemaInvalidAccepted = 210
+    private let knownSchemaInvalidAccepted = 207
     private let knownInstanceValidRejected = 3
     private let knownInstanceInvalidAccepted = 132