@atrick, is this the thing you just fixed?

I'm afraid this is not something I fixed.

In this code:

func foo(test: TestRef?) {
if let t = test?.testAny {}
}

A function-type value is being returned from test?.testAny without any partial_apply or retain:

// function_ref main.TestAny.testAny <A where A: main.TestAny> (A) -> () -> ()
%11 = function_ref @TFP4main7TestAny7testAnyuRq_S0Fq_FT_T : $@convention(thin) <τ_0_0 where τ_0_0 : TestAny> (@in τ_0_0) -> @owned @callee_owned () -> () // user: %12
%12 = apply %11<@opened("0844AB78-C38F-11E5-A516-AC87A3215592") TestRef>(%9#1) : $@convention(thin) <τ_0_0 where τ_0_0 : TestAny> (@in τ_0_0) -> @owned @callee_owned () -> () // user: %15

Then a closure is being created via partial_apply from the function value:

// function_ref reabstraction thunk helper from @callee_owned () -> (@unowned ()) to @callee_owned (@in ()) -> (@out ())
%14 = function_ref @TTRXFodTXFo_iTiT_ : $@convention(thin) (@out (), @in (), @owned @callee_owned () -> ()) -> () // user: %15
%15 = partial_apply %14(%12) : $@convention(thin) (@out (), @in (), @owned @callee_owned () -> ()) -> () // user: %16

That closure is wrapped in an Optional:

%16 = enum $Optional&lt;() -&gt; ()&gt;, #Optional.Some!enumelt.1, %15 : $@callee_owned (@out (), @in ()) -> () // user: %18

Then another closure is created

bb4(%22 : $@callee_owned (@out (), @in ()) -> ()): // Preds: bb2
// function_ref reabstraction thunk helper from @callee_owned (@in ()) -> (@out ()) to @callee_owned () -> (@unowned ())
%23 = function_ref @TTRXFo_iTiTXFodT_ : $@convention(thin) (@owned @callee_owned (@out (), @in ()) -> ()) -> () // user: %24
%24 = partial_apply %23(%22) : $@convention(thin) (@owned @callee_owned (@out (), @in ()) -> ()) -> () // users: %25, %26

Then we release the dead closure which has closed over the test? reference...

strong_release %24 : $@callee_owned () -> () // id: %26

It may be that one of these closure/thunk calls is failing to retain the closed-over self. At any rate, when I enable optimization, the dead closure disappears and the crash goes away.

Comment by Nikita Ilyasov (JIRA)

It also can be reproduced like this:

let test: protocol<TestRef> = Test()

func take_block(block: () -> ()) {
    block();
}

take_block(test.testAny)

test.testAny()

but not like this:

take_block(test.testRef)

Comment by Nikita Ilyasov (JIRA)

It can be reproduced in Release build configuration, it's not `NotOptimizedOnly`

Ah, okay. I guess it was just that particular test case where it got optimized away. Label removed.

Testing a fix: #2316

Fix merged as 461c8e7.