Re: Error: @nogc function 'test.func2' cannot call non-@nogc delegate 'msg'

[Shachar Shemesh via Digitalmars-d]

On 10/12/17 14:00, Shachar Shemesh wrote:
On 10/12/17 13:44, Jonathan M Davis wrote:
it sounds like the delegate that's
being generated isn't @nogc, so it can't be called within the function,
which would be a completely different issue from allocating a closure.

Here's the thing, though. There is no reason for the delegate to be 
called at all!

Since func1's msg is also lazy, I expected the lowering to look like this:

void func1(/*scope*/ string delegate() msg) @nogc {
}

void func2(/*scope*/ string delegate() msg) @nogc {
   func1(msg);
}

Even with scope commented out, the above compiles just fine. The fact 
that msg is not @nogc doesn't matter at all, simply because no one is 
evaluating the delegate.

I think I got it. I think the lowering is this:

void func1(/*scope*/ string delegate() msg) @nogc {
}

void func2(/*scope*/ string delegate() msg) @nogc {
  func1((){ return msg(); });
}

With "scope" commented out, this generates the following error:
test.d(15): Error: function test.func2 is @nogc yet allocates closures 
with the GC
test.d(16):        test.func2.__lambda2 closes over variable msg at 
test.d(15)

So there are two problems here. The first is that a "lazy" generated 
delegate does not get forwarded to a function, and instead gets wrapped 
by a completely useless temporary delegate. The second is that scope on 
lazy is not honored.

I'll file a bug report.

Shachar