rustdoc failing to generate docs when returning impl Iterator

[SergioBenitez]

When a function returns an impl Iterator:

pub fn iter<'s>(&'s self) -> impl Iterator<Item=&'s Cookie<'static>> { ... }

rustdoc fails to build the docs with the following errors emitted in the console:

error[E0277]: the trait bound `!: std::iter::Iterator` is not satisfied
   --> src/http/cookies.rs:308:34
    |
308 |     pub fn iter<'s>(&'s self) -> impl Iterator<Item=&'s Cookie<'static>> {
    |                                  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ `!` is not an iterator; maybe try calling `.iter()` or a similar method
    |
    = help: the trait `std::iter::Iterator` is not implemented for `!`
    = note: the return type of a function must have a statically known size

---

Here's the full error log from building the docs for Rocket v0.3.2:

error[E0277]: the trait bound `!: std::iter::Iterator` is not satisfied
   --> src/http/cookies.rs:308:34
    |
308 |     pub fn iter<'s>(&'s self) -> impl Iterator<Item=&'s Cookie<'static>> {
    |                                  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ `!` is not an iterator; maybe try calling `.iter()` or a similar method
    |
    = help: the trait `std::iter::Iterator` is not implemented for `!`
    = note: the return type of a function must have a statically known size

error[E0277]: the trait bound `!: std::iter::Iterator` is not satisfied
   --> src/http/media_type.rs:384:36
    |
384 |     pub fn params<'a>(&'a self) -> impl Iterator<Item=(&'a str, &'a str)> + 'a {
    |                                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ `!` is not an iterator; maybe try calling `.iter()` or a similar method
    |
    = help: the trait `std::iter::Iterator` is not implemented for `!`
    = note: the return type of a function must have a statically known size

error[E0277]: the trait bound `!: std::iter::Iterator` is not satisfied
   --> src/http/header.rs:216:45
    |
216 |     pub fn get<'a>(&'a self, name: &str) -> impl Iterator<Item=&'a str> {
    |                                             ^^^^^^^^^^^^^^^^^^^^^^^^^^^ `!` is not an iterator; maybe try calling `.iter()` or a similar method
    |
    = help: the trait `std::iter::Iterator` is not implemented for `!`
    = note: the return type of a function must have a statically known size

error[E0277]: the trait bound `!: std::iter::Iterator` is not satisfied
   --> src/http/header.rs:541:34
    |
541 |     pub fn iter<'s>(&'s self) -> impl Iterator<Item=Header<'s>> {
    |                                  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ `!` is not an iterator; maybe try calling `.iter()` or a similar method
    |
    = help: the trait `std::iter::Iterator` is not implemented for `!`
    = note: the return type of a function must have a statically known size

error[E0277]: the trait bound `!: std::iter::Iterator` is not satisfied
   --> src/http/header.rs:587:31
    |
587 |     pub fn into_iter(self) -> impl Iterator<Item=Header<'h>> {
    |                               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ `!` is not an iterator; maybe try calling `.iter()` or a similar method
    |
    = help: the trait `std::iter::Iterator` is not implemented for `!`
    = note: the return type of a function must have a statically known size

error[E0277]: the trait bound `!: std::iter::Iterator` is not satisfied
   --> src/http/header.rs:603:16
    |
603 |             -> impl Iterator<Item=(Uncased<'h>, Vec<Cow<'h, str>>)> {
    |                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ `!` is not an iterator; maybe try calling `.iter()` or a similar method
    |
    = help: the trait `std::iter::Iterator` is not implemented for `!`
    = note: the return type of a function must have a statically known size

error[E0277]: the trait bound `!: std::iter::Iterator` is not satisfied
   --> src/http/accept.rs:294:34
    |
294 |     pub fn iter<'a>(&'a self) -> impl Iterator<Item=&'a QMediaType> + 'a {
    |                                  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ `!` is not an iterator; maybe try calling `.iter()` or a similar method
    |
    = help: the trait `std::iter::Iterator` is not implemented for `!`
    = note: the return type of a function must have a statically known size

error[E0277]: the trait bound `!: std::iter::Iterator` is not satisfied
   --> src/http/accept.rs:324:41
    |
324 |     pub fn media_types<'a>(&'a self) -> impl Iterator<Item=&'a MediaType> + 'a {
    |                                         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ `!` is not an iterator; maybe try calling `.iter()` or a similar method
    |
    = help: the trait `std::iter::Iterator` is not implemented for `!`
    = note: the return type of a function must have a statically known size

error[E0277]: the trait bound `!: std::iter::Iterator` is not satisfied
   --> src/config/config.rs:585:36
    |
585 |     pub fn extras<'a>(&'a self) -> impl Iterator<Item=(&'a str, &'a Value)> {
    |                                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ `!` is not an iterator; maybe try calling `.iter()` or a similar method
    |
    = help: the trait `std::iter::Iterator` is not implemented for `!`
    = note: the return type of a function must have a statically known size

error[E0277]: the trait bound `!: std::iter::Iterator` is not satisfied
  --> src/router/mod.rs:64:36
   |
64 |     pub fn routes<'a>(&'a self) -> impl Iterator<Item=&'a Route> + 'a {
   |                                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ `!` is not an iterator; maybe try calling `.iter()` or a similar method
   |
   = help: the trait `std::iter::Iterator` is not implemented for `!`
   = note: the return type of a function must have a statically known size

error[E0277]: the trait bound `!: std::iter::Iterator` is not satisfied
   --> src/rocket.rs:726:36
    |
726 |     pub fn routes<'a>(&'a self) -> impl Iterator<Item=&'a Route> + 'a {
    |                                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ `!` is not an iterator; maybe try calling `.iter()` or a similar method
    |
    = help: the trait `std::iter::Iterator` is not implemented for `!`
    = note: the return type of a function must have a statically known size

error: Compilation failed, aborting rustdoc

[steveklabnik]

is this a dup of #43869 ?

[SergioBenitez]

@steveklabnik Looks really similar, but that one errors with () not implementing Iterator, while this one remarks about !. May be the same root cause though.

[lilith]

rust doc is giving me E0282 on Result<Box<impl Trait>> with nightly-2017-08-30. It's a regression from 2017-07-31. Seems related?

[lilith]

Is there any known workaround?

[SergioBenitez]

This seems to have been fixed in a recent nightly. Closing this out.