Added in high level schema type ref #215

Missed capturing the high level schema. Added test to document to capture use case permanently.

Signed-off-by: quobix <dave@quobix.com>

datamodel/high/base/schema.go

@@ -113,6 +113,9 @@ func NewSchema(schema *base.Schema) *Schema {
 	s := new(Schema)
 	s.low = schema
 	s.Title = schema.Title.Value
+	if !schema.SchemaTypeRef.IsEmpty() {
+		s.SchemaTypeRef = schema.SchemaTypeRef.Value
+	}
 	if !schema.MultipleOf.IsEmpty() {
 		s.MultipleOf = &schema.MultipleOf.Value
 	}

document_test.go

@@ -1249,3 +1249,36 @@ func TestDocument_LoadDocTwice(t *testing.T) {
     _, errs = doc.BuildV3Model()
     require.Empty(t, errs)
 }
+
+func TestSchemaTypeRef_Issue215(t *testing.T) {
+    docBytes := []byte(`
+openapi: 3.1.0
+components:
+  schemas:
+    Foo:
+      $schema: https://example.com/custom-json-schema-dialect
+      type: string`)
+
+    doc, err := NewDocument(docBytes)
+    if err != nil {
+        panic(err)
+    }
+
+    model, errs := doc.BuildV3Model()
+    if len(errs) > 0 {
+        panic(errs)
+    }
+
+    schema := model.Model.Components.Schemas.GetOrZero("Foo").Schema()
+    schemaLow := schema.GoLow()
+
+    // works as expected
+    if v := schemaLow.SchemaTypeRef.Value; v != "https://example.com/custom-json-schema-dialect" {
+        t.Errorf("low model: expected $schema to be 'https://example.com/custom-json-schema-dialect', but got '%v'", v)
+    }
+
+    // high model: expected $schema to be 'https://example.com/custom-json-schema-dialect', but got ''
+    if v := schema.SchemaTypeRef; v != "https://example.com/custom-json-schema-dialect" {
+        t.Errorf("high model: expected $schema to be 'https://example.com/custom-json-schema-dialect', but got '%v'", v)
+    }
+}