JSUP parser silently accepts invalid input that is a single identifier then EOF

[philrz]

tl;dr

This shows no output, despite the fact that the naked foo is invalid ZSON input.

$ echo 'foo' | super -i jsup -z -c 'yield typeof(this)' -
[no output]

Details

Repro is with super commit 49b1add. I bumped into this while working on the docs updates in #5386.

If I mix the invalid input value among valid ones, I do get the syntax error I would expect.

$ super -version
Version: v1.18.0-71-g49b1addb

$ echo '1 foo 2' | super -i jsup -z -c 'yield typeof(this)' -
stdio:stdin: Super JSON syntax error

When reacting to this in #5386 comments, @mccanne said:

This is a bug in the jsup parser for any input that is a single identifier then EOF. It shouldn't be too hard to fix.