Difference in map/set collection inference between analyzer and CFE

[lrhn]

Example code:

int foo(bool something) =>
   {if (something) ...throw "Badness" else 1: 2}.length;

The CFE accepts the code as a map literal, and either throws or returns 1.

The analyzer reports:

This literal must be either a map or a set, but the elements don't have enough information for type inference to work.

The specification should end up in the case:

• If leaf elements has at least one mapEntry and no expressionElement elements, then e is a map literal with unknown static type. The static type will be filled in by type inference, defined below.

In those steps, the context type, S, is empty, ?, and there are no type arguments. There is precisely one leaf element, 1: 2, and the ... throw "Badness" spread element won't be looked at until we reach type inference.