public class MemoryLeaker {
    var closure: () -> Void = { () }

    public init() {}

    public func doNothing() {}

    public func doSomethingThatLeaks() {
        self.closure = {
            // This will leak as it'll create a permanent reference cycle:
            //
            //     self -> self.closure -> self
            self.doNothing()
        }
    }
}

@inline(never) // just to be sure to get this in a stack trace
func myFunctionDoingTheAllocation() {
    let thing = MemoryLeaker()
    thing.doSomethingThatLeaks()
}

myFunctionDoingTheAllocation()

docker run -it --rm --privileged -w /tmp -v /tmp:/tmp swift:5.2 bash -c 'swiftc -sanitize=address -g test.swift &&  ./test'

/usr/bin/ld.gold: warning: Cannot export local symbol '__asan_extra_spill_area'

=================================================================
==1==ERROR: LeakSanitizer: detected memory leaks

Direct leak of 32 byte(s) in 1 object(s) allocated from:
    #​0 0x559e61100c8d  (/tmp/test+0x95c8d)
    #​1 0x7f2cb51446b1  (/usr/lib/swift/linux/libswiftCore.so+0x3cb6b1)
    #​2 0x559e611312ce  (/tmp/test+0xc62ce)
    #​3 0x559e611304c3  (/tmp/test+0xc54c3)
    #​4 0x7f2cb3dc8b96  (/lib/x86_64-linux-gnu/libc.so.6+0x21b96)

SUMMARY: AddressSanitizer: 32 byte(s) leaked in 1 allocation(s).