Named/optional arguments with constructor shorthand leaks impl details

[DartBot]

This issue was originally filed by [email protected]

---

What steps will reproduce the problem?

1. http://try.dartlang.org/s/Ilsl

When using the constructor argument shorthand (this.variable) with optional/named arguments, the fact that the argument is being assigned to a private variable is leaked when the constructor is called.

In the example above, anyone who creates a new "SomeClass" object with a named parameter now knows that the argument is being assigned to a private variable (due to the "_" on the argument name).

[DartBot]

This comment was originally written by [email protected]

---

Looking at the spec, under "Named Optional Formals", it says:
"It is a compile-time error if the name of a named optional parameter begins with an ‘_’ character."

It looks like the compiler isn't catching variable names starting with "this._".

[dgrove]

Added Area-Dartboard, Triaged labels.

[ghost]

Removed Area-Dartboard label.
Added Area-Language, Duplicate labels.
Marked as being merged into #434.