bad error message with list comprehension over object

[jarondl]

Somewhere deep in my nested object, a list got accidentally replaced with an object.
Minimal working example:

jsonnet -e '[a for a in {}]'

The error I get with go-jsonnet is:

RUNTIME ERROR: Unexpected type object, expected array
		builtin function <flatMap>
	During evaluation

Without telling me what happened or even where. After a while I gave up and tried the c++ version, which gave me:

RUNTIME ERROR: In comprehension, can only iterate over array.
	<cmdline>:1:1-16

[sbarzowski]

Thanks for reporting the problem. The location should definitely be shown.

[ghostsquad]

I would also like to understand more about why some errors report trace information, and others do not.

[sbarzowski]

All runtime errors will result in a stack trace. It's just empty in this case (which is a bug).

[sbarzowski]

It's better now. There is a stack trace entry for this error, which points at the right place.

The error message is still not ideal (std.flatMap second param must be array / string, got object) which might be confusing, because std.flatMap is an implementation detail of object comprehensions.