Mahmoud Al-Qudsi 2fe2169065 Make eval a decorator
`eval` has always been implemented as a function, which was always a bit
of a hack that caused some issues such as triggering the creation of a
new scope. This turns `eval` into a decorator.

The scoping issues with eval prevented it from being usable to actually
implement other shell components in fish script, such as the problems
described in #4442, which should now no longer be the case.

Closes #4443.
2019-04-11 10:36:49 -05:00
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2019-04-11 10:36:49 -05:00