Types of lambda parameters are lost in some cases

[Juuxel]

See also: #308

This seemingly happens when the outside context (such as a local variable or parameter type) doesn't require the more specific type provided in the original source code. Dropping the types does, however, lead to compilation errors and silent behaviour changes.

Example

(from the test added in #308)

Input code:

Function<?, ?> f2a = (String x) -> x;
Function<?, ?> f2b = (String x) -> x.length() + 1;

// g(Function<?, ?>)
g((String x) -> x);
g((String x) -> x.length() + 1);

Decompiled output:

Function<?, ?> f2a = x -> x; // behaviour change
Function<?, ?> f2b = x -> x.length() + 1; // compilation error
this.g(x -> x); // behaviour change
this.g(x -> x.length() + 1); // compilation error

// The behaviour change is that the lambda now accepts any object, instead of throwing
// a ClassCastException if a non-String value is passed to it.
// The compilation error comes from trying to use String methods on a general Object instance.