We have an existing warning message to encourage moving away from the old
0.11-and-earlier style of redundantly wrapping standalone expressions in
templates, but due to the special rules for object keys the warning
message was giving misleading advice in that context: a user following the
advice as given would then encounter an error about the object key being
ambiguous.
To account for that, this introduces a special alternative version of the
warning just for that particular position, directing the user to replace
the template interpolation markers with parenthesis instead. That will
then get the same result as the former interpolation sequence, rather than
producing the ambiguity error.
Martin Atkins