Building out schema comparison mechanism

Which has led to a new wider hashing capability for the low level API. hashing makes it very easy to determine changes quickly, without having to run comparisons to discover changes, could really speed things up moving forward.

datamodel/low/base/schema_proxy.go

@@ -42,11 +42,13 @@ import (
 // it's not actually JSONSchema until 3.1, so lots of times a bad schema will break parsing. Errors are only found
 // when a schema is needed, so the rest of the document is parsed and ready to use.
 type SchemaProxy struct {
-	kn         *yaml.Node
-	vn         *yaml.Node
-	idx        *index.SpecIndex
-	rendered   *Schema
-	buildError error
+	kn              *yaml.Node
+	vn              *yaml.Node
+	idx             *index.SpecIndex
+	rendered        *Schema
+	buildError      error
+	isReference     bool   // Is the schema underneath originally a $ref?
+	referenceLookup string // If the schema is a $ref, what's its name?
 }
 
 // Build will prepare the SchemaProxy for rendering, it does not build the Schema, only sets up internal state.
@@ -87,3 +89,18 @@ func (sp *SchemaProxy) Schema() *Schema {
 func (sp *SchemaProxy) GetBuildError() error {
 	return sp.buildError
 }
+
+// IsSchemaReference returns true if the Schema that this SchemaProxy represents, is actually a reference to
+// a Schema contained within Components or Definitions. There is no difference in the mechanism used to resolve the
+// Schema when calling Schema(), however if we want to know if this schema was originally a reference, we won't
+// be able to determine that from the model, without this bit.
+func (sp *SchemaProxy) IsSchemaReference() bool {
+	return sp.isReference
+}
+
+// GetSchemaReference will return the lookup defined by the $ref that this schema points to. If the schema
+// is inline, and not a reference, then this method returns an empty string. Only useful when combined with
+// IsSchemaReference()
+func (sp *SchemaProxy) GetSchemaReference() string {
+	return sp.referenceLookup
+}