Issue 9415 - delegate inference should make function literal impure

[9rnsr]

http://d.puremagic.com/issues/show_bug.cgi?id=9415

[WalterBright]

shouldn't this line be typed as pure, instead of line 726 as impure?

[9rnsr]

In current, dg is declared as int delegate(int) pure nothrow @safe.
Because, inside typeof, pureness and safety inference is suppressed in temporary.

So this line is now pure, and line 726 is already impure. But it is a bug. This line should be impure.

Essentially, if a lambda literal contacts to the frame enclosing it, it should be impure.
But there is a few exceptions. In following, lambda literal is inferred to delegate but keeps its pureness.

Bar8751 foo8751b(const int x) pure
{
    return y => x > y; // pure delegate
}