compiler error: lifetimes in associated types leading to a compiler error.

Hello!

I am getting a compiler error when trying to define the following trait:

trait Foo {
  type PublicKey<'a> : From<&'a [u8]>;
	     
}

fn main() {
  println!("hello, world!")
}

I would have expected my code to compile successfully, or to exit with some error explaining why static compilation failed.

Instead, I am getting a:

error: internal compiler error: src/librustc/ty/subst.rs:426: Region parameter out of range when substituting in region 'a (root type=Some(&'a [u8])) (index=1)

More specifically, I'm having troubles trying to define some type PublicKey that must implement AsRef<[u8]> and From<&[u8]>. If I try with lifetimes I get this compiler error; if I replace the from trait with From<[u8; N]> for some const N: usize (enabling generic_associated_types and const_generics) I get:

error: const generics in any position are currently unsupported
 --> foo.rs:4:24
  |
4 |   type PublicKey<const N: usize> : From<[u8; N]>;
  |                        ^

Am I doing something terribly stupid here or const generics for associated types are not yet ready and lifetimes on associated types lead to a compiler error?

Here's the full traceback

 --> foo.rs:3:3
  |
3 |   type PublicKey<'a> : From<&'a[u8]>;
  |   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  |
  = help: add #![feature(generic_associated_types)] to the crate attributes to enable

error: internal compiler error: src/librustc/ty/subst.rs:426: Region parameter out of range when substituting in region 'a (root type=Some(&'a [u8])) (index=1)

thread 'rustc' panicked at 'Box<Any>', src/librustc_errors/lib.rs:558:9
note: Run with `RUST_BACKTRACE=1` environment variable to display a backtrace.
error: aborting due to 2 previous errors

For more information about this error, try `rustc --explain E0658`.

note: the compiler unexpectedly panicked. this is a bug.

note: we would appreciate a bug report: https://github.com/rust-lang/rust/blob/master/CONTRIBUTING.md#bug-reports

note: rustc 1.34.0-nightly (aadbc459b 2019-02-23) running on x86_64-unknown-linux-gnu

type PublicKey<'a> defines a generic associated type, which aren't yet fully implemented.

type PublicKey<'a> defines a generic associated type, which aren't yet fully implemented.

That's correct, but even without enabled feature it crashes, which should not happen, or am I wrong? :/

cc @rust-lang/compiler @rust-lang/release

It's technically a stable-to-beta regression, but it goes from hard error to ICE so I don't think it's worth blocking the release on this.

(Also woops, mistakenly closed the issue)

As long as we're not breaking working code it's not really a breakage and so I agree we should not block a release on it.

Also +1 for not blocking the release on this.

This error does not only occur in code that is illegal, it (apparently) only occurs in code that has already triggered a visible, clear, feature-gate error. Therefore, it's not even a particularly-high risk for confusing users (unlike e.g. an ICE that occurs instead of a valid error message, or an ICE that occurs after an obscure error message).

@arielb1

triage: P-medium. Assigning to self for initial investigation.

(P-medium based on the reasons given by @arielb1 : the risks for end users here do seem quite low.)

This seems like it was fixed. Going to bisect and see if a corresponding test was already added at time it was fixed.

Fixed between nightly-2019-05-25 (dec4c52 2019-05-24) and nightly-2019-05-26 (f492693 2019-05-25)

Here's what landed in that time frame:

% git log --format=oneline --author=bors dec4c5201..f49269398
f492693982d1e252f5411ae3e4d560ab0dfea48a Auto merge of #59276 - oli-obk:cleanups, r=eddyb
02f5786a324c40b2d8b2d0df98456e48fb45d30c Auto merge of #61151 - Centril:rollup-5rpyhfo, r=Centril

    #61092 (Make sanitize_place iterate instead of recurse)
    #61093 (Make borrow_of_local_data iterate instead of recurse)
    #61094 (Make find_local iterate instead of recurse)
    #61099 (Make ignore_borrow iterate instead of recurse)
    #61103 (Make find iterate instead of recurse)
    #61104 (Make eval_place_to_op iterate instead of recurse)


315ab95a9c13cbb69ae8538fcd69b9f7b0c30f89 Auto merge of #61150 - Centril:rollup-wmm7qga, r=Centril


    #61026 (Tweak macro parse errors when reaching EOF during macro call parse)
    #61095 (Update cargo)
    #61096 (tidy: don't short-circuit on license error)
    #61107 (Fix a couple docs typos)
    #61110 (Revert edition-guide toolstate override)
    #61111 (Fixed type-alias-bounds lint doc)
    #61113 (Deprecate FnBox. Box<dyn FnOnce()> can be called directly, since 1.35)
    #61116 (Remove the incorrect warning from README.md)
    #61118 (Dont ICE on an attempt to use GAT without feature gate)
    #61121 (improve debug-printing of scalars)
    #61125 (Updated my mailmap entry)
    #61134 (Annotate each reverse_bits with #[must_use])
    #61138 (Move async/await tests to their own folder)

524580312039e4fa5ccf91e8f7093cd755bc1aad Auto merge of #60441 - vext01:try-to-kill-projection-params, r=oli-obk

Oh, I fixed this back in PR #61118 (to fix #60654), which was part of rollup #61150, but I didn't notice that #60654 was a duplicate of #58694.

@pnkfelix

@pnkfelix it is not really fixed. It doesn't crash anymore with the above code, but it still ICEs with the feature gate: playground

well, if the ICE is not occurring any more when the feature attribute is omitted and we're back to a hard error, then its not a regression-from-stable-to-stable.

I'm going to open a fresh issue to track the problem with the feature gate enabled, because the comments in #58694 and #60654 make it hard to tell which bug (the ICE without feature-gate vs the ICE with feature-gate) is being discussed.

(the remaining bug, when the feature gate is enabled, is tracked in issue #62521)

closing as fixed as remaining bug is in #62521

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compiler error: lifetimes in associated types leading to a compiler error. #58694

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compiler error: lifetimes in associated types leading to a compiler error. #58694

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jonas-schievink commented on Feb 24, 2019

hellow554 commented on Feb 25, 2019

emilyalbini commented on Feb 25, 2019

Centril commented on Feb 25, 2019

arielb1 commented on Feb 25, 2019

pnkfelix commented on Feb 28, 2019

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pnkfelix commented on Jul 9, 2019

pnkfelix commented on Jul 9, 2019

pnkfelix commented on Jul 9, 2019

hellow554 commented on Jul 9, 2019

pnkfelix commented on Jul 9, 2019

pnkfelix commented on Jul 9, 2019

pnkfelix commented on Jul 9, 2019

pnkfelix commented on Jul 9, 2019

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