https://issues.dlang.org/show_bug.cgi?id=21377
--- Comment #2 from [email protected] --- I have a sneaking suspicion that this may be slightly related to one of the underlying problems for https://issues.dlang.org/show_bug.cgi?id=21496 which is where templated types that contain a template parameter into a struct member, will then implicitly become embedded within the struct itself. So the anonymous lambda inside of `S2` in the example is being "falsely" embedded into `S2` which is causing this error, likely because the lambda is lowered into a form of template. --
