The syntax for providing a message with the deprecated attribute is not documented on dlang.org. It is also not specified if this is valid when deprecated is used as a storage class.
http://dlang.org/attribute.html#deprecated
The correct syntax seems to be (in ANTLR grammar form):
deprecated: 'deprecated' ('(' assignExpression ')')?
;
Comment #1 by k.hara.pg — 2013-12-27T20:22:07Z
Grammar is currently defined as follows.
DeprecatedAttribute:
deprecated
deprecated ( StringLiteral )