n.b.: { $__loc__: "foo" } is still not allowed.
$__loc__ cannot be overwritten, and it is always an object.
Using { $x: "foo" } where $x is not a string is an error, so there is
not much of a point in supporting that.
Previously, bindings were parsed as the combination of two tokens:
'$' IDENT
This meant that using a keyword as variable name (e.g. $then, $label)
did not work.
Attempts were made to allow $keyword to work by adding some '$' Keyword
rules in the parser, but this did not allow $keyword in all places:
jq --arg label foo -n '$label' # ok
jq -n '"foo" as $label | .' # error
Treating $foo as a single token is much simpler, in my opinion.
This patch also changes how LOC is lexed: "$__loc__" instead of as
"__loc__" that gets combined with '$' in the parser.
This patch also disallows having spaces after '$' when recalling a
variable `$ foo' since that was probably just an unintentional side
effect of the implementation, and it was not documented.
Fixes#2675
Emanuele Torre