Previously, trailing closures would try to match the first parameter
of (possibly optional) function type that didn't seem to have an
argument already, but in practice this broke when there were
parameters with default arguments before the function parameter.
The new rule is far simpler: a trailing closure matches the last
parameter. Fixes rdar://problem/17965209.
Swift SVN r24898
Previously the "as" keyword could either represent coercion or or forced
downcasting. This change separates the two notions. "as" now only means
type conversion, while the new "as!" operator is used to perform forced
downcasting. If a program uses "as" where "as!" is called for, we emit a
diagnostic and fixit.
Internally, this change removes the UnresolvedCheckedCastExpr class, in
favor of directly instantiating CoerceExpr when parsing the "as"
operator, and ForcedCheckedCastExpr when parsing the "as!" operator.
Swift SVN r24253
