Specification defines features in terms of function-literal applications which isn't always a valid rewrite in async contexts.

[lrhn]

Example, o?.m(a1, . . . , an, xn+1 : an+1, . . . , xn+k : an+k) is defined as equivalent to ((x) => x == null?null : x.m(a1, . . . , an, xn+1 : an+1, . . . , xn+k : an+k))(o).

This moves the expressions a1 .. an+k into a new non-async function. If the original expression is in an async function and any of these expressions contain an await, the resulting rewrite is incorrect.

The specification needs another way to introduce new expression-level bindings without resorting to function literals, perhaps let x = e1 in e2 which wouldn't change the scope.

[kmillikin]

Dart itself needs let x = e1 in e2, not just the spec :)

[lrhn]

I completely agree, but that's #25275 :)

[eernstg]

No milestone now: This is independent of Dart 2. Note that several changes to the language specification have already eliminated such function literals and applications thereof. The issue still pertains to any remaining ones.