Convert non-string errors to string

interpreter.go

@@ -364,6 +364,12 @@ func (i *interpreter) evaluate(a ast.Node, tc tailCallStatus) (value, error) {
 			// error when evaluating error message
 			return nil, err
 		}
+		if msgVal.getType() != stringType {
+			msgVal, err = builtinToString(e, &readyValue{msgVal})
+			if err != nil {
+				return nil, err
+			}
+		}
 		msg, err := e.getString(msgVal)
 		if err != nil {
 			return nil, err

testdata/error_function_fail.golden

@@ -0,0 +1,10 @@
+RUNTIME ERROR: Couldn't manifest function in JSON output.
+-------------------------------------------------
+	testdata/error_function_fail:1:1-22	$
+
+error (function(x) 42)
+
+-------------------------------------------------
+	During evaluation	
+
+

testdata/error_function_fail.jsonnet

@@ -0,0 +1 @@
+error (function(x) 42)

testdata/error_object.golden

@@ -0,0 +1,10 @@
+RUNTIME ERROR: {"blah": 42}
+-------------------------------------------------
+	testdata/error_object:1:1-21	$
+
+error { "blah": 42 }
+
+-------------------------------------------------
+	During evaluation	
+
+

testdata/error_object.jsonnet

@@ -0,0 +1 @@
+error { "blah": 42 }