[RFC] Clarify (and improve) rules for projections and well-formedness #1214

nikomatsakis · 2015-07-17T21:04:14Z

RFC has been accepted and merged.

Current text: https://github.com/rust-lang/rfcs/blob/master/text/1214-projections-lifetimes-and-wf.md
Tracking issue: rust-lang/rust#27579

Type system changes to address the outlives relation with respect to projections, and to better enforce that all types are well-formed (meaning that they respect their declared bounds). The current implementation can be both unsound (rust-lang/rust#24622), inconvenient (rust-lang/rust#23442), and surprising (rust-lang/rust#21748, rust-lang/rust#25692). The changes are as follows:

Simplify the outlives relation to be syntactically based.
Specify improved rules for the outlives relation and projections.
Specify more specifically where WF bounds are enforced, covering several cases missing from the implementation.

The proposed changes here have been tested and found to cause only a modest number of regressions (about two dozen root regressions were previously found on crates.io; however, that run did not yet include all the provisions from this RFC; updated numbers coming soon). In order to minimize the impact on users, the plan is to first introduce the changes in two stages:

Initially, warnings will be issued for cases that violate the rules specified in this RFC. These warnings are not lints and cannot be silenced except by correcting the code such that it type-checks under the new rules.
After one release cycle, those warnings will become errors.

Note that although the changes do cause regressions, they also cause some code (like that in rust-lang/rust#23442) which currently gets errors to compile successfully.

cc @rust-lang/lang

Rendered

nikomatsakis · 2015-07-17T21:05:00Z

cc @arielb1

Ryman · 2015-07-17T22:05:32Z

@nikomatsakis I think the issue referenced for 'unsound' in your description should be rust-lang/rust#24622 which is mentioned in the RFC (also labelled wrong).

nikomatsakis · 2015-07-17T22:17:42Z

@Ryman thanks.

trait is object safe

Diggsey · 2015-07-18T00:25:28Z

text/0000-projections-lifetimes-and-wf.md

+      R ⊢ scalar: 'a
+
+    OutlivesNominalType:
+      ∀i. Pi: 'a


Should this be ∀i. R ⊢ Pi: 'a?

arielb1 · 2015-07-18T08:59:15Z

I think the [[T]] issue is a straight bug in rustc and shouldn't result in just a warning.

arielb1 · 2015-07-18T09:50:44Z

text/0000-projections-lifetimes-and-wf.md

+      R ⊢ T WF
+      R ⊢ T: Sized
+      --------------------------------------------------
+      [T] WF


There should also be a WfTuple - in fact in the form you use there should be a Wf rule for each type constructor.

@arielb1

There should also be a WfTuple - in fact in the form you use there should be a Wf rule for each type constructor.

Added.

nikomatsakis · 2015-07-20T19:58:31Z

@arielb1

I think the [[T]] issue is a straight bug in rustc and shouldn't result in just a warning.

Perhaps, but the issue is really not whether it's a bug or not, the question is about whether code is affected by the change. That said, I haven't observed any.

arielb1 · 2015-07-20T20:40:22Z

@nikomatsakis

[[T]] basically causes an ICE every time it is used, so it is relatively hard to abuse.

arielb1 · 2015-07-21T15:26:53Z

Could you also clarify which of Box<Foo<'a>+'static>, Box<Foo<'static>+'a> and Box<Foo<'a>+'b> are well-formed (assuming 'a and `'b' are unrelated free regions)? AFAICT the rules say that only the second of these is valid, but an example would always be helpful.

The following warnings appear: ``` src/lib.rs:73:5: 73:68 warning: the trait `core::marker::Sized` is not implemented for the type `Self` [E0277] src/lib.rs:73 unsafe fn call_block<R>(self, block: *mut Block<Self, R>) -> R; ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ src/lib.rs:73:5: 73:68 help: run `rustc --explain E0277` to see a detailed explanation src/lib.rs:73:5: 73:68 note: `Self` does not have a constant size known at compile-time src/lib.rs:73 unsafe fn call_block<R>(self, block: *mut Block<Self, R>) -> R; ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ src/lib.rs:73:5: 73:68 note: this warning results from recent bug fixes and clarifications; it will become a HARD ERROR in the next release. See RFC 1214 for details. src/lib.rs:73 unsafe fn call_block<R>(self, block: *mut Block<Self, R>) -> R; ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ src/lib.rs:73:5: 73:68 note: required by `Block` src/lib.rs:73 unsafe fn call_block<R>(self, block: *mut Block<Self, R>) -> R; ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ src/lib.rs:187:5: 187:71 warning: the trait `core::marker::Sized` is not implemented for the type `Self` [E0277] src/lib.rs:187 fn into_concrete_block(self) -> ConcreteBlock<A, Self::Ret, Self>; ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ src/lib.rs:187:5: 187:71 help: run `rustc --explain E0277` to see a detailed explanation src/lib.rs:187:5: 187:71 note: `Self` does not have a constant size known at compile-time src/lib.rs:187 fn into_concrete_block(self) -> ConcreteBlock<A, Self::Ret, Self>; ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ src/lib.rs:187:5: 187:71 note: this warning results from recent bug fixes and clarifications; it will become a HARD ERROR in the next release. See RFC 1214 for details. src/lib.rs:187 fn into_concrete_block(self) -> ConcreteBlock<A, Self::Ret, Self>; ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ src/lib.rs:187:5: 187:71 note: required by `ConcreteBlock` src/lib.rs:187 fn into_concrete_block(self) -> ConcreteBlock<A, Self::Ret, Self>; ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ``` ...because of: rust-lang/rfcs#1214

The following warnings appear: ``` src/command.rs:344:5: 344:56 warning: the trait `core::marker::Sized` is not implemented for the type `Self` [E0277] src/command.rs:344 fn from_json(body: &Json) -> WebDriverResult<Self>; ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ src/command.rs:344:5: 344:56 help: run `rustc --explain E0277` to see a detailed explanation src/command.rs:344:5: 344:56 note: `Self` does not have a constant size known at compile-time src/command.rs:344 fn from_json(body: &Json) -> WebDriverResult<Self>; ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ src/command.rs:344:5: 344:56 note: this warning results from recent bug fixes and clarifications; it will become a HARD ERROR in the next release. See RFC 1214 for details. src/command.rs:344 fn from_json(body: &Json) -> WebDriverResult<Self>; ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ src/command.rs:344:5: 344:56 note: required by `core::result::Result` src/command.rs:344 fn from_json(body: &Json) -> WebDriverResult<Self>; ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ``` ...because of: rust-lang/rfcs#1214

The following warnings appear: ``` src/platform/mod.rs:7:5: 7:56 warning: the trait `core::marker::Sized` is not implemented for the type `Self` [E0277] src/platform/mod.rs:7 fn create_headless() -> Result<Self, &'static str>; ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ src/platform/mod.rs:7:5: 7:56 help: run `rustc --explain E0277` to see a detailed explanation src/platform/mod.rs:7:5: 7:56 note: `Self` does not have a constant size known at compile-time src/platform/mod.rs:7 fn create_headless() -> Result<Self, &'static str>; ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ src/platform/mod.rs:7:5: 7:56 note: this warning results from recent bug fixes and clarifications; it will become a HARD ERROR in the next release. See RFC 1214 for details. src/platform/mod.rs:7 fn create_headless() -> Result<Self, &'static str>; ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ src/platform/mod.rs:7:5: 7:56 note: required by `core::result::Result` src/platform/mod.rs:7 fn create_headless() -> Result<Self, &'static str>; ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ``` ...because of: rust-lang/rfcs#1214

The following warnings appear: ``` Compiling chrono v0.2.15 (file:///Users/coreyf/Development/rust/rust-chrono) src/lib.rs:504:5: 504:52 warning: the trait `core::marker::Sized` is not implemented for the type `Self` [E0277] src/lib.rs:504 fn with_year(&self, year: i32) -> Option<Self>; ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ src/lib.rs:504:5: 504:52 help: run `rustc --explain E0277` to see a detailed explanation src/lib.rs:504:5: 504:52 note: `Self` does not have a constant size known at compile-time src/lib.rs:504 fn with_year(&self, year: i32) -> Option<Self>; ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ src/lib.rs:504:5: 504:52 note: this warning results from recent bug fixes and clarifications; it will become a HARD ERROR in the next release. See RFC 1214 for details. src/lib.rs:504 fn with_year(&self, year: i32) -> Option<Self>; ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ src/lib.rs:504:5: 504:52 note: required by `core::option::Option` src/lib.rs:504 fn with_year(&self, year: i32) -> Option<Self>; ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ src/lib.rs:509:5: 509:54 warning: the trait `core::marker::Sized` is not implemented for the type `Self` [E0277] src/lib.rs:509 fn with_month(&self, month: u32) -> Option<Self>; ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ src/lib.rs:509:5: 509:54 help: run `rustc --explain E0277` to see a detailed explanation src/lib.rs:509:5: 509:54 note: `Self` does not have a constant size known at compile-time src/lib.rs:509 fn with_month(&self, month: u32) -> Option<Self>; ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ src/lib.rs:509:5: 509:54 note: this warning results from recent bug fixes and clarifications; it will become a HARD ERROR in the next release. See RFC 1214 for details. src/lib.rs:509 fn with_month(&self, month: u32) -> Option<Self>; ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ src/lib.rs:509:5: 509:54 note: required by `core::option::Option` src/lib.rs:509 fn with_month(&self, month: u32) -> Option<Self>; ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ src/lib.rs:514:5: 514:56 warning: the trait `core::marker::Sized` is not implemented for the type `Self` [E0277] src/lib.rs:514 fn with_month0(&self, month0: u32) -> Option<Self>; ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ src/lib.rs:514:5: 514:56 help: run `rustc --explain E0277` to see a detailed explanation src/lib.rs:514:5: 514:56 note: `Self` does not have a constant size known at compile-time src/lib.rs:514 fn with_month0(&self, month0: u32) -> Option<Self>; ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ src/lib.rs:514:5: 514:56 note: this warning results from recent bug fixes and clarifications; it will become a HARD ERROR in the next release. See RFC 1214 for details. src/lib.rs:514 fn with_month0(&self, month0: u32) -> Option<Self>; ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ src/lib.rs:514:5: 514:56 note: required by `core::option::Option` src/lib.rs:514 fn with_month0(&self, month0: u32) -> Option<Self>; ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ src/lib.rs:519:5: 519:50 warning: the trait `core::marker::Sized` is not implemented for the type `Self` [E0277] src/lib.rs:519 fn with_day(&self, day: u32) -> Option<Self>; ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ src/lib.rs:519:5: 519:50 help: run `rustc --explain E0277` to see a detailed explanation src/lib.rs:519:5: 519:50 note: `Self` does not have a constant size known at compile-time src/lib.rs:519 fn with_day(&self, day: u32) -> Option<Self>; ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ src/lib.rs:519:5: 519:50 note: this warning results from recent bug fixes and clarifications; it will become a HARD ERROR in the next release. See RFC 1214 for details. src/lib.rs:519 fn with_day(&self, day: u32) -> Option<Self>; ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ src/lib.rs:519:5: 519:50 note: required by `core::option::Option` src/lib.rs:519 fn with_day(&self, day: u32) -> Option<Self>; ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ src/lib.rs:524:5: 524:52 warning: the trait `core::marker::Sized` is not implemented for the type `Self` [E0277] src/lib.rs:524 fn with_day0(&self, day0: u32) -> Option<Self>; ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ src/lib.rs:524:5: 524:52 help: run `rustc --explain E0277` to see a detailed explanation src/lib.rs:524:5: 524:52 note: `Self` does not have a constant size known at compile-time src/lib.rs:524 fn with_day0(&self, day0: u32) -> Option<Self>; ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ src/lib.rs:524:5: 524:52 note: this warning results from recent bug fixes and clarifications; it will become a HARD ERROR in the next release. See RFC 1214 for details. src/lib.rs:524 fn with_day0(&self, day0: u32) -> Option<Self>; ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ src/lib.rs:524:5: 524:52 note: required by `core::option::Option` src/lib.rs:524 fn with_day0(&self, day0: u32) -> Option<Self>; ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ src/lib.rs:529:5: 529:58 warning: the trait `core::marker::Sized` is not implemented for the type `Self` [E0277] src/lib.rs:529 fn with_ordinal(&self, ordinal: u32) -> Option<Self>; ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ src/lib.rs:529:5: 529:58 help: run `rustc --explain E0277` to see a detailed explanation src/lib.rs:529:5: 529:58 note: `Self` does not have a constant size known at compile-time src/lib.rs:529 fn with_ordinal(&self, ordinal: u32) -> Option<Self>; ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ src/lib.rs:529:5: 529:58 note: this warning results from recent bug fixes and clarifications; it will become a HARD ERROR in the next release. See RFC 1214 for details. src/lib.rs:529 fn with_ordinal(&self, ordinal: u32) -> Option<Self>; ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ src/lib.rs:529:5: 529:58 note: required by `core::option::Option` src/lib.rs:529 fn with_ordinal(&self, ordinal: u32) -> Option<Self>; ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ src/lib.rs:534:5: 534:60 warning: the trait `core::marker::Sized` is not implemented for the type `Self` [E0277] src/lib.rs:534 fn with_ordinal0(&self, ordinal0: u32) -> Option<Self>; ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ src/lib.rs:534:5: 534:60 help: run `rustc --explain E0277` to see a detailed explanation src/lib.rs:534:5: 534:60 note: `Self` does not have a constant size known at compile-time src/lib.rs:534 fn with_ordinal0(&self, ordinal0: u32) -> Option<Self>; ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ src/lib.rs:534:5: 534:60 note: this warning results from recent bug fixes and clarifications; it will become a HARD ERROR in the next release. See RFC 1214 for details. src/lib.rs:534 fn with_ordinal0(&self, ordinal0: u32) -> Option<Self>; ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ src/lib.rs:534:5: 534:60 note: required by `core::option::Option` src/lib.rs:534 fn with_ordinal0(&self, ordinal0: u32) -> Option<Self>; ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ src/lib.rs:580:5: 580:52 warning: the trait `core::marker::Sized` is not implemented for the type `Self` [E0277] src/lib.rs:580 fn with_hour(&self, hour: u32) -> Option<Self>; ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ src/lib.rs:580:5: 580:52 help: run `rustc --explain E0277` to see a detailed explanation src/lib.rs:580:5: 580:52 note: `Self` does not have a constant size known at compile-time src/lib.rs:580 fn with_hour(&self, hour: u32) -> Option<Self>; ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ src/lib.rs:580:5: 580:52 note: this warning results from recent bug fixes and clarifications; it will become a HARD ERROR in the next release. See RFC 1214 for details. src/lib.rs:580 fn with_hour(&self, hour: u32) -> Option<Self>; ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ src/lib.rs:580:5: 580:52 note: required by `core::option::Option` src/lib.rs:580 fn with_hour(&self, hour: u32) -> Option<Self>; ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ src/lib.rs:585:5: 585:53 warning: the trait `core::marker::Sized` is not implemented for the type `Self` [E0277] src/lib.rs:585 fn with_minute(&self, min: u32) -> Option<Self>; ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ src/lib.rs:585:5: 585:53 help: run `rustc --explain E0277` to see a detailed explanation src/lib.rs:585:5: 585:53 note: `Self` does not have a constant size known at compile-time src/lib.rs:585 fn with_minute(&self, min: u32) -> Option<Self>; ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ src/lib.rs:585:5: 585:53 note: this warning results from recent bug fixes and clarifications; it will become a HARD ERROR in the next release. See RFC 1214 for details. src/lib.rs:585 fn with_minute(&self, min: u32) -> Option<Self>; ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ src/lib.rs:585:5: 585:53 note: required by `core::option::Option` src/lib.rs:585 fn with_minute(&self, min: u32) -> Option<Self>; ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ src/lib.rs:590:5: 590:53 warning: the trait `core::marker::Sized` is not implemented for the type `Self` [E0277] src/lib.rs:590 fn with_second(&self, sec: u32) -> Option<Self>; ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ src/lib.rs:590:5: 590:53 help: run `rustc --explain E0277` to see a detailed explanation src/lib.rs:590:5: 590:53 note: `Self` does not have a constant size known at compile-time src/lib.rs:590 fn with_second(&self, sec: u32) -> Option<Self>; ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ src/lib.rs:590:5: 590:53 note: this warning results from recent bug fixes and clarifications; it will become a HARD ERROR in the next release. See RFC 1214 for details. src/lib.rs:590 fn with_second(&self, sec: u32) -> Option<Self>; ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ src/lib.rs:590:5: 590:53 note: required by `core::option::Option` src/lib.rs:590 fn with_second(&self, sec: u32) -> Option<Self>; ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ src/lib.rs:595:5: 595:58 warning: the trait `core::marker::Sized` is not implemented for the type `Self` [E0277] src/lib.rs:595 fn with_nanosecond(&self, nano: u32) -> Option<Self>; ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ src/lib.rs:595:5: 595:58 help: run `rustc --explain E0277` to see a detailed explanation src/lib.rs:595:5: 595:58 note: `Self` does not have a constant size known at compile-time src/lib.rs:595 fn with_nanosecond(&self, nano: u32) -> Option<Self>; ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ src/lib.rs:595:5: 595:58 note: this warning results from recent bug fixes and clarifications; it will become a HARD ERROR in the next release. See RFC 1214 for details. src/lib.rs:595 fn with_nanosecond(&self, nano: u32) -> Option<Self>; ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ src/lib.rs:595:5: 595:58 note: required by `core::option::Option` src/lib.rs:595 fn with_nanosecond(&self, nano: u32) -> Option<Self>; ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ``` ...because of: rust-lang/rfcs#1214

MBons · 2015-09-22T02:05:37Z

Ran into this error using an associated const on a trait. On IRC it was suggested that this is likely a compiler bug.

pub trait IterableEnum<T> {
    const ENUM_VARIANTS: &'static [T];
}

arielb1 · 2015-09-22T10:22:19Z

@Zalastra

Just add T: 'static. Not a bug.

bluss · 2015-09-22T10:47:17Z

It outputs two warnings (playpen)

warning: the trait core::marker::Sized is not implemented for the type T
warning: the parameter type T may not live long enough

The first one must be a bug.

eddyb · 2015-09-22T12:14:30Z

@bluss it's odd because it seems like it doesn't take actual bounds into account - see fixed version (the Sized bound is unnecessary, but it's there to show the issue).

nikomatsakis · 2015-09-30T20:16:27Z

I agree that the T: Sized message is a bug. Did anyone file an issue?

On Tue, Sep 22, 2015 at 8:14 AM, Eduard-Mihai Burtescu <
notifications@github.com> wrote:

@bluss https://github.com/bluss it's odd because it seems like it
doesn't take actual bounds into account - see fixed version
https://play.rust-lang.org/?gist=343add7244bd4b210961&version=nightly&run=1
(the Sized bound is unnecessary, but it's there to show the issue).

—
Reply to this email directly or view it on GitHub
#1214 (comment).

Initial version.

7902a6d

nikomatsakis added the T-lang Relevant to the language team, which will review and decide on the RFC. label Jul 17, 2015

nikomatsakis self-assigned this Jul 17, 2015

nikomatsakis added 3 commits July 17, 2015 18:18

Correct issue #.

bcc727f

add clause that says that an object type is WF only if the

6b07c20

trait is object safe

discuss type aliases a bit more

ffeccfd

Diggsey reviewed Jul 18, 2015
View reviewed changes

arielb1 reviewed Jul 18, 2015
View reviewed changes

Apply various clarifications based on suggestions

fb3ef33

crumblingstatue mentioned this pull request Aug 24, 2015

Put Sized bound on LoadSurface trait xsleonard/rust-sdl2_image#48

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arielb1 mentioned this pull request Aug 29, 2015

Inconsistency in type checking where clauses in trait definition rust-lang/rust#28055

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frewsxcv mentioned this pull request Sep 2, 2015

Fix nightly warnings related to lifetimes SSheldon/rust-block#1

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frewsxcv mentioned this pull request Sep 2, 2015

Fix nightly warnings related to lifetimes mozilla/webdriver-rust#17

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frewsxcv mentioned this pull request Sep 2, 2015

Fix nightly warnings related to lifetimes servo/surfman#27

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frewsxcv mentioned this pull request Sep 5, 2015

Fix nightly warnings related to lifetimes chronotope/chrono#46

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nikomatsakis mentioned this pull request Sep 30, 2015

Implied bounds on nested references + variance = soundness hole rust-lang/rust#25860

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nikomatsakis mentioned this pull request Oct 7, 2015

Generic type defaults should not be allowed if they don’t satisfy type constraints rust-lang/rust#28024

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aturon mentioned this pull request Oct 9, 2015

Nightly regression around HRTBs, likely connected to wf changes rust-lang/rust#28934

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Api updates brendanzab/gl-rs#387

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Ericson2314 mentioned this pull request Dec 4, 2015

Dropck Eyepatch RFC. #1327

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Tracking issue for unsized types within tuples rust-lang/rust#33242

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{Result,Option}::expect() hurt the readability of Rust code rust-lang/rust#35083

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RFC: Constant generics (restricted Π types) for Rust, core RFC (v2) #1931

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Document all features rust-lang/reference#9

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rustc: trait-level where clauses are mistakenly imposed when bounding by the trait rust-lang/rust#50792

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Centril added A-typesystem Type system related proposals & ideas A-lifetimes Lifetime related proposals. A-associated-types Proposals relating to associated types labels Nov 23, 2018

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region checking in intercrate mode rust-lang/trait-system-refactor-initiative#64

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[RFC] Clarify (and improve) rules for projections and well-formedness #1214

[RFC] Clarify (and improve) rules for projections and well-formedness #1214

nikomatsakis commented Jul 17, 2015 •

edited by traviscross

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nikomatsakis commented Jul 20, 2015

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MBons commented Sep 22, 2015

arielb1 commented Sep 22, 2015

bluss commented Sep 22, 2015

eddyb commented Sep 22, 2015

nikomatsakis commented Sep 30, 2015

[RFC] Clarify (and improve) rules for projections and well-formedness #1214

[RFC] Clarify (and improve) rules for projections and well-formedness #1214

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