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

[Shachar Shemesh]

Submitted
https://issues.dlang.org/show_bug.cgi?id=18058

On 10/12/17 14:07, Shachar Shemesh wrote:
> 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