fix(schema): reject an empty-string namespace value (#145)

A namespace name must be a non-empty anyURI, so <schema targetNamespace=""> and
<import namespace=""> are invalid. Omitting the attribute (no target namespace,
or a no-namespace import) stays valid.

XSTS invalid-schemas-accepted 134 to 132, 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 namespace value may not be the empty string. `<schema targetNamespace="">` and `<import namespace="">` are rejected, since a namespace name must be a non-empty `anyURI` (omitting the attribute, for no target namespace or a no-namespace import, stays valid). Caught two invalid schemas: invalid-schemas-accepted 134 → 132, no other bucket moved.
+
 - XSTS invalid-schemas-accepted (#145): a wildcard restriction may not weaken `processContents`. When a complex type restricts another, a restricting `xs:any` must have a `processContents` at least as strong as the base wildcard's (`strict` > `lax` > `skip`; Wildcard Subset, §3.10.6), in addition to narrowing the namespace. Caught three invalid schemas: invalid-schemas-accepted 137 → 134, no other bucket moved.
 
 - XSTS invalid-schemas-accepted (#145): a `simpleContent` restriction's base must be a complex type. Restricting a built-in (`xs:integer`, `xs:anySimpleType`) or a user `simpleType` through `<simpleContent><restriction>` is rejected (`src-ct.2`); a complex type with simple content is built by extending a simple type, not by restricting one. Caught five invalid schemas: invalid-schemas-accepted 142 → 137, no other bucket moved.

Sources/Schema/SchemaStructure.swift

@@ -66,6 +66,7 @@ extension PureXML.Schema.XSDParser {
         append(topLevelDeclarationErrors(schema), at: schema, into: &findings)
         append(nestedNamedDefinitionErrors(schema), at: schema, into: &findings)
         append(anySimpleTypeRestrictionErrors(schema), at: schema, into: &findings)
+        append(emptyNamespaceErrors(schema), at: schema, into: &findings)
         return findings
     }
 

Sources/Schema/SchemaStructureHelpers.swift

@@ -224,4 +224,19 @@ extension PureXML.Schema.XSDParser {
         }
         return []
     }
+
+    /// A namespace value must be a non-empty `anyURI` (or absent): the empty string
+    /// is not a legal namespace name. So `<schema targetNamespace="">` and
+    /// `<import namespace="">` are invalid, while omitting the attribute (no target
+    /// namespace, a no-namespace import) stays valid.
+    static func emptyNamespaceErrors(_ schema: XSDTree) -> [String] {
+        var errors: [String] = []
+        if PureXML.Schema.XSDNode.attribute(schema, "targetNamespace") == "" {
+            errors.append("the 'targetNamespace' attribute may not be the empty string")
+        }
+        for importNode in descendants(schema, named: "import") where PureXML.Schema.XSDNode.attribute(importNode, "namespace") == "" {
+            errors.append("an 'import' namespace may not be the empty string")
+        }
+        return errors
+    }
 }

Tests/XSTSSuiteTests.swift

@@ -108,8 +108,11 @@ struct XSTSSuiteTests {
     /// Requiring a restricting wildcard's `processContents` to be at least as strong
     /// as the base's (strict > lax > skip; Wildcard Subset §3.10.6) then caught three
     /// more invalid schemas: invalid-schemas accepted 137 → 134, no other bucket moved.
+    /// Rejecting an empty-string namespace value (`targetNamespace=""`, `import
+    /// namespace=""`) then caught two more invalid schemas: invalid-schemas accepted
+    /// 134 → 132, no other bucket moved.
     private let knownSchemaValidRejected = 1
-    private let knownSchemaInvalidAccepted = 134
+    private let knownSchemaInvalidAccepted = 132
     private let knownInstanceValidRejected = 3
     private let knownInstanceInvalidAccepted = 132