Lifetime regression in kick 0.1.2

[brson]

Original report.

error[E0309]: the parameter type `T` may not live long enough

   --> src/signal/variable.rs:114:5

    |

114 |     fn listen<F>(&self, f: F) -> Self::Listen


    |     ^

    |

    = help: consider adding an explicit lifetime bound `T: 'a`...

note: ...so that the type `T` will meet its required lifetime bounds

   --> src/signal/variable.rs:114:5

    |

114 |     fn listen<F>(&self, f: F) -> Self::Listen


    |     ^


error: aborting due to previous error

It's not clear what the change was here but @nagisa remembers something about:

09:28 < nagisa> so, the error for kick seems legit to me
09:28 < acrichto> brson: ok kaws is benign
09:28 < acrichto> nondeterministic cargo crate graph resolution
09:28 < acrichto> first build just happened to get a working crate graph
09:28 < acrichto> second build didn't
09:28 < nagisa> it has `where F: Into<Slot<'a, 'a, T, Tr>>` and no `T:'a`
09:29 < acrichto> brson: tl;dr; kaws is a standard legit cargo error, no regression
09:29 < nagisa> I mildly remember a pr or something along the lines
09:29 <~brson> ugh
09:30 <~brson> nagisa: that's for kick?
09:30 < nagisa> yes
09:30 < nagisa> though I might be remembering incorrectly too
09:30 < nagisa> would be best to ask nmatsakis if he wasn’t on a vacation
09:31  * brson still filing bugs
09:32 < nagisa> I would fill a bug for kick too, pink nmatsakis and revisit a week later

cc @nikomatsakis @rust-lang/lang

[nagisa]

Namely the signature of failing function looks like this;

pub enum Slot<'a, 'b: 'a, T: 'a, Tr: Transaction<'b> + 'b> {
    Nothing,
    Ref(&'a SlotFn<'a, 'b, T, Tr>),
    SRef(Rc<SlotFn<'a, 'b, T, Tr>>),
    WRef(Weak<SlotFn<'a, 'b, T, Tr>>),
    Mut(&'a mut SlotFnMut<'a, 'b, T, Tr>),
    Boxed(Box<SlotFnMut<'a, 'b, T, Tr>>),

    #[cfg(feature="nightly")]
    Once(Box<SlotFnBox<'a, 'b, T, Tr>>),
}

impl<'a, T, Tr: Transaction<'a> + 'a> Stream<'a, Tr> for Variable<'a, T, Tr>
    where T: Clone
{
    type Output = T;
    type Listen = <Event<'a, T, Tr> as Stream<'a, Tr>>::Listen;

    fn listen<F>(&self, f: F) -> Self::Listen
        where F: Into<Slot<'a, 'a, T, Tr>>
    {
        self.updates.listen(f)
    }
}

Note the T:'a bound on Slot but lack of any such requirement for the listen bound (or I’m not seeing one, anyway).

[nikomatsakis]

triage: P-high

[nikomatsakis]

I'll investigate, but seems like it is likely expected behavior.

[nikomatsakis]

I agree with @nagisa that this is expected behavior, though I'm not sure what caused it to change.

[brson]

Seems like we just need to add the test case.

[nikomatsakis]

Yeah, I'll have to try and minimize it though.

[alexcrichton]

If this is expected behavior and just needs a test case, I'll also remove the regression tag.

[nikomatsakis]

Can anyone verify that this used to work? It seems like if we are going to make a test case, we'd also want to verify that the test case used to pass...