From 53b05b5ba6f8128f3b39c9f8db5a8f8106cf9782 Mon Sep 17 00:00:00 2001
From: Leon Mika <lmika@lmika.org>
Date: Mon, 19 May 2025 22:04:09 +1000
Subject: [PATCH] Added 'error' and 'assert' builtins

---
 ucl/builtins.go | 25 +++++++++++++++++++++++++
 ucl/inst.go     |  3 +++
 ucl/objs.go     |  8 ++++++++
 3 files changed, 36 insertions(+)

diff --git a/ucl/builtins.go b/ucl/builtins.go
index 88a796d..9a1ac62 100644
--- a/ucl/builtins.go
+++ b/ucl/builtins.go
@@ -1103,6 +1103,31 @@ func returnBuiltin(ctx context.Context, args invocationArgs) (Object, error) {
 	return nil, errReturn{ret: args.args[0]}
 }
 
+// TODO - add tests
+
+func errorBuiltin(ctx context.Context, args invocationArgs) (Object, error) {
+	if len(args.args) < 1 {
+		return nil, errors.New("need at least one arguments")
+	}
+	return nil, ErrRuntime{args.args[0].String()}
+}
+
+func assertBuiltin(ctx context.Context, args invocationArgs) (Object, error) {
+	if len(args.args) < 1 {
+		return nil, errors.New("need at least one arguments")
+	}
+
+	if isTruthy(args.args[0]) {
+		return nil, nil
+	}
+
+	if len(args.args) > 1 {
+		return nil, ErrRuntime{args.args[1].String()}
+	}
+
+	return nil, ErrRuntime{"assertion failed"}
+}
+
 func procBuiltin(ctx context.Context, args macroArgs) (Object, error) {
 	if args.nargs() < 1 {
 		return nil, errors.New("need at least one arguments")
diff --git a/ucl/inst.go b/ucl/inst.go
index e47873f..94c0353 100644
--- a/ucl/inst.go
+++ b/ucl/inst.go
@@ -96,6 +96,9 @@ func New(opts ...InstOption) *Inst {
 	rootEC.addCmd("continue", invokableFunc(continueBuiltin))
 	rootEC.addCmd("return", invokableFunc(returnBuiltin))
 
+	rootEC.addCmd("error", invokableFunc(errorBuiltin))
+	rootEC.addCmd("assert", invokableFunc(assertBuiltin))
+
 	rootEC.addMacro("if", macroFunc(ifBuiltin))
 	rootEC.addMacro("foreach", macroFunc(foreachBuiltin))
 	rootEC.addMacro("for", macroFunc(foreachBuiltin))
diff --git a/ucl/objs.go b/ucl/objs.go
index 827260e..8ca798d 100644
--- a/ucl/objs.go
+++ b/ucl/objs.go
@@ -643,6 +643,14 @@ func (p OpaqueObject) Truthy() bool {
 	return p.v != nil
 }
 
+type ErrRuntime struct {
+	errStr string
+}
+
+func (e ErrRuntime) Error() string {
+	return e.errStr
+}
+
 type errBreak struct {
 	isCont bool
 	ret    Object