1 files changed, 60 insertions, 0 deletions
diff --git a/util/syspolicy/setting/errors.go b/util/syspolicy/setting/errors.go
new file mode 100644
index 000000000..8d5e73754
--- /dev/null
+++ b/util/syspolicy/setting/errors.go
@@ -0,0 +1,60 @@
+// Copyright (c) Tailscale Inc & AUTHORS
+// SPDX-License-Identifier: BSD-3-Clause
+
+package setting
+
+import "errors"
+
+var (
+	// ErrNotConfigured is returned when the requested policy setting is not configured.
+	ErrNotConfigured = errors.New("not configured")
+	// ErrTypeMismatch is returned when there's a type mismatch between the actual type
+	// of the setting value and the expected type.
+	ErrTypeMismatch = errors.New("type mismatch")
+	// ErrNoSuchKey is returned by [DefinitionOf] when no policy setting
+	// has been registered with the specified key.
+	//
+	// Until 2024-08-02, this error was also returned by a [Handler] when the specified
+	// key did not have a value set. While the package maintains compatibility with this
+	// usage of ErrNoSuchKey, it is recommended to return [ErrNotConfigured] from newer
+	// [source.Store] implementations.
+	ErrNoSuchKey = errors.New("no such key")
+)
+
+// Error is an error when reading or parsing a policy setting.
+type Error struct {
+	text string
+}
+
+// NewError returns a [Error] with the specified error message.
+func NewError(text string) *Error {
+	return &Error{text}
+}
+
+// WrapError returns an [Error] with the text of the specified error,
+// or nil if err is nil, [ErrNotConfigured], or [ErrNoSuchKey].
+func WrapError(err error) *Error {
+	if err == nil || errors.Is(err, ErrNotConfigured) || errors.Is(err, ErrNoSuchKey) {
+		return nil
+	}
+	if err, ok := err.(*Error); ok {
+		return err
+	}
+	return &Error{err.Error()}
+}
+
+// Error implements error.
+func (e Error) Error() string {
+	return e.text
+}
+
+// MarshalText implements [encoding.TextMarshaler].
+func (e Error) MarshalText() (text []byte, err error) {
+	return []byte(e.Error()), nil
+}
+
+// UnmarshalText implements [encoding.TextUnmarshaler].
+func (e *Error) UnmarshalText(text []byte) error {
+	e.text = string(text)
+	return nil
+}