Prepare sequence registration preflight

internal/engine/sequence_registration.go

@@ -0,0 +1,38 @@
+package engine
+
+type sequenceRegistration struct {
+	path          Path
+	identityField string
+}
+
+type sequencePolicy struct {
+	identityFields map[string]string
+}
+
+func compileSequencePolicy(registrations []sequenceRegistration) (sequencePolicy, []Diagnostic) {
+	policy := sequencePolicy{identityFields: make(map[string]string, len(registrations))}
+	var diagnostics []Diagnostic
+	for _, registration := range registrations {
+		path, err := normalizeDestination(registration.path)
+		if err != nil {
+			diagnostics = append(diagnostics, Diagnostic{
+				Code: CodeOptionsInvalid, Severity: SeverityError,
+				Path: registration.path.clone(), Message: "sequence registration path must contain only non-reserved mapping keys",
+			})
+			continue
+		}
+
+		key := path.String()
+		if current, ok := policy.identityFields[key]; ok {
+			if current != registration.identityField {
+				diagnostics = append(diagnostics, Diagnostic{
+					Code: CodeOptionsInvalid, Severity: SeverityError,
+					Path: path, Message: "sequence registrations at one path must use the same identity field",
+				})
+			}
+			continue
+		}
+		policy.identityFields[key] = registration.identityField
+	}
+	return policy, canonicalDiagnostics(diagnostics)
+}