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Compiler hangs when compiling mutually-defined enums #55625

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varkor opened this issue Nov 2, 2018 · 6 comments
Closed

Compiler hangs when compiling mutually-defined enums #55625

varkor opened this issue Nov 2, 2018 · 6 comments
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I-hang Issue: The compiler never terminates, due to infinite loops, deadlock, livelock, etc. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue.

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@varkor
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varkor commented Nov 2, 2018 

#[derive(Clone)]
enum A<T> {
    A1(B<T>),
    A2(B<Option<T>>),
}

#[derive(Clone)]
enum B<T> {
    B1(T),
    B2(Box<A<B<T>>>),
}

fn main() {}

The following fails to halt or emit any warnings or errors.
@pnkfelix
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pnkfelix commented Nov 2, 2018

Back in rustc 1.20.0, we would explicitly end the compilation with an overflow error, as illustrated in the details block below.

% rustc +1.20.0 issue-55625.rs
error[E0320]: overflow while adding drop-check rules for A<T>
 --> issue-55625.rs:1:10
  |
1 | #[derive(Clone)]
  |          ^^^^^
  |
  = note: overflowed on A<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::o\
ption::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Optio\
n<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::opt\
ion::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<\
B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::optio\
n::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<\
std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option:\
:Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<T>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>\
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>

error[E0320]: overflow while adding drop-check rules for A<T>
 --> issue-55625.rs:1:10
  |
1 | #[derive(Clone)]
  |          ^^^^^
  |
  = note: overflowed on A<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::o\
ption::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Optio\
n<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::opt\
ion::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<\
B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::optio\
n::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<\
std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option:\
:Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<T>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>\
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>

error[E0320]: overflow while adding drop-check rules for A<T>
 --> issue-55625.rs:1:10
  |
1 | #[derive(Clone)]
  |          ^^^^^
  |
  = note: overflowed on A<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::o\
ption::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Optio\
n<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::opt\
ion::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<\
B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::optio\
n::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<\
std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option:\
:Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<T>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>\
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
error[E0320]: overflow while adding drop-check rules for B<T>
 --> issue-55625.rs:3:8
  |
3 |     A1(B<T>),
  |        ^^^^^
  |
  = note: overflowed on A<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::o\
ption::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Optio\
n<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::opt\
ion::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<\
B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::optio\
n::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<\
std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option:\
:Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<T>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>\
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>

error[E0320]: overflow while adding drop-check rules for A<T>
 --> issue-55625.rs:1:10
  |
1 | #[derive(Clone)]
  |          ^^^^^
  |
  = note: overflowed on A<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::o\
ption::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Optio\
n<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::opt\
ion::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<\
B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::optio\
n::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<\
std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option:\
:Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<T>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>\
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>

error[E0320]: overflow while adding drop-check rules for B<std::option::Option<T>>
 --> issue-55625.rs:4:8
  |
4 |     A2(B<Option<T>>),
  |        ^^^^^^^^^^^^^
  |
  = note: overflowed on A<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::o\
ption::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Optio\
n<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::opt\
ion::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<\
B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::optio\
n::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<\
std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option:\
:Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<T>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>\
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
rror[E0320]: overflow while adding drop-check rules for B<T>
 --> issue-55625.rs:7:10
  |
7 | #[derive(Clone)]
  |          ^^^^^
  |
  = note: overflowed on A<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::o\
ption::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Optio\
n<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::opt\
ion::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<\
B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::optio\
n::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<\
std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option:\
:Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<T>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>\
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>

error[E0320]: overflow while adding drop-check rules for B<T>
 --> issue-55625.rs:7:10
  |
7 | #[derive(Clone)]
  |          ^^^^^
  |
  = note: overflowed on A<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::o\
ption::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Optio\
n<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::opt\
ion::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<\
B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::optio\
n::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<\
std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option:\
:Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<T>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>\
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>

error[E0320]: overflow while adding drop-check rules for B<T>
 --> issue-55625.rs:7:10
  |
7 | #[derive(Clone)]
  |          ^^^^^
  |
  = note: overflowed on A<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::o\
ption::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Optio\
n<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::opt\
ion::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<\
B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::optio\
n::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<\
std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option:\
:Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<T>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>\
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>

error[E0320]: overflow while adding drop-check rules for B<T>
 --> issue-55625.rs:7:10
  |
7 | #[derive(Clone)]
  |          ^^^^^
  |
  = note: overflowed on A<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::o\
ption::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Optio\
n<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::opt\
ion::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<\
B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::optio\
n::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<\
std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option:\
:Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<T>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>\
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>

error[E0320]: overflow while adding drop-check rules for std::boxed::Box<A<B<T>>>
  --> issue-55625.rs:10:8
   |
10 |     B2(Box<A<B<T>>>),
   |        ^^^^^^^^^^^^^
   |
   = note: overflowed on A<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::\
option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Opti\
on<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::op\
tion::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option\
<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::opti\
on::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B\
<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option\
::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<std::option::Option<B<T>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>\
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>

error: aborting due to 11 previous errors

@pnkfelix
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pnkfelix commented Nov 2, 2018 •
edited
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(Also, this might be an instance of a polymorphic recursion (#4287) in the types? Not 100% sure, I'd have to review the structure more carefully. I mention that mostly because we have historically had a less than stellar record in handling polymorphic recursion in an elegant manner...)

Update June 2019: it is polymorphic recursion

@varkor
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varkor commented Nov 2, 2018

If you make minor adjustments to the definitions (e.g. removing a variant), you get the overflow error. It seems to be very volatile.

@pnkfelix pnkfelix added the T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. label Nov 2, 2018
@varkor varkor added the I-hang Issue: The compiler never terminates, due to infinite loops, deadlock, livelock, etc. label Dec 20, 2018
@pnkfelix
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pnkfelix commented Jun 24, 2019 •
edited
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Inlining the definition of A into the definition of B yields this, which might be easier to reason about, as it more clearly shows that there is a nested datatype (aka non-regular recursion), and appears to exhibit the same behavior:

enum B<T> {
    B1(T),
    B2(Box<B<B<T>>>),
    B3(Box<B<Option<B<T>>>>),
}

Note also that to see the hang without using #[derive(Clone)], you can just make a function that has a local that might hold a B, like so (play):

fn main() {
    let b1: Option<B<&'static str>>;
}

That seems to be enough to cause the drop-check rules analysis to fire (and then get into trouble).

@pnkfelix
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(something a tiny bit worrisome: for some reason, the hang that I see with a let local definition does not occur if the same type is provided as a function's formal argument, like so (play):

fn boo(b: Option<B<&'static str>>) {
    // let b1 = b; // uncommenting this brings the hang back.
}

@Mark-Simulacrum
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Mark-Simulacrum commented Sep 18, 2019 •
edited
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I'm going to close in favor of #4287 which is the same bug (hang on dropck)

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I-hang Issue: The compiler never terminates, due to infinite loops, deadlock, livelock, etc. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue.
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@pnkfelix @varkor @Mark-Simulacrum