Promote Certain Lints to Errors in Rust 2021 Edition #80165

m-ou-se · 2020-12-18T19:02:13Z

Tracking issue for turning lints into errors in Rust 2021.

BARE_TRAIT_OBJECTS
ELLIPSIS_INCLUSIVE_RANGE_PATTERNS

The text was updated successfully, but these errors were encountered:

camelid · 2020-12-18T22:05:20Z

MACRO_USE_EXTERN_CRATE

I'm not sure if this one should be deny-by-default; this is what the lint's page says:

This lint is "allow" by default because this is a stylistic choice that has not been settled, see issue #52043 for more information.

camelid · 2020-12-18T22:07:01Z

Also, MACRO_USE_EXTERN_CRATE is not warn-by-default – it's actually allow-by-default.

m-ou-se · 2020-12-18T22:10:19Z

@rylev GitHub won't let me assign you to this issue; you wanted to work on this, right? I think you can @rustbot claim to claim the issue.

camelid · 2020-12-18T22:13:08Z

@rustbot assign @rylev

camelid · 2020-12-18T22:20:44Z

Hmm, I wonder why GitHub won't let us assign rylev directly – they are an org member...

rylev · 2020-12-18T23:08:55Z

@rustbot claim

taiki-e · 2020-12-19T02:12:45Z

UNUSED_EXTERN_CRATES

EXPLICIT_OUTLIVES_REQUIREMENTS

UNREACHABLE_PUB

MACRO_USE_EXTERN_CRATE

I think these lints belong to a similar category as unused lint. I think it probably makes sense to warn by default, but I don't think we need to deny it by default.

ELLIPSIS_INCLUSIVE_RANGE_PATTERNS

ELIDED_LIFETIMES_IN_PATHS

The other two (ELLIPSIS_INCLUSIVE_RANGE_PATTERNS and ELIDED_LIFETIMES_IN_PATHS) are related to compatibility or deprecation, and it seems reasonable to deny them in the next edition. (ELIDED_LIFETIMES_IN_PATHS is actually already rejected on async functions.)

jyn514 · 2020-12-19T12:36:31Z

unreachable_pub still has bugs after three years: #64762. I don't think it should be even warn-by-default until the false positives are fixed.

rylev · 2020-12-30T14:16:06Z

Where we are now:

Promote to deny:

ELLIPSIS_INCLUSIVE_RANGE_PATTERNS
ELIDED_LIFETIMES_IN_PATHS

Do the above need discussion, or are the uncontroversial?

Needs more discussion:

MACRO_USE_EXTERN_CRATE: this is currently allow by default. More discussion needs to happen (likely in edition lint: migrating extern crate with #[macro_use] #52043) on whether this should be promoted to warn. This is likely to fall in the same category as other "unused" lints and thus might not be subject to an edition change.
BARE_TRAIT_OBJECTS: this is currently warn-by-default but it has not been settled whether this will be deny-by-default. There is currently discussion happening in rust-lang/lang-team#65
EXPLICIT_OUTLIVES_REQUIREMENTS and UNUSED_EXTERN_CRATES: Should this be promoted to warn, and do we need to do this on an edition boundary?

Needs implementation work:

UNREACHABLE_PUB: this lint gives false positives and so is not currently ready to be promoted.

camelid · 2021-01-06T04:48:00Z

There's also the mutable_borrow_reservation_conflict lint. There's a PR to turn it from warn-by-default to deny-by-default: #76104.

nikomatsakis · 2021-01-15T19:46:11Z

I'm nominated this for @rust-lang/lang discussion. I'd like us to review these lints and make sure we are happy with them.

m-ou-se · 2021-01-19T19:03:13Z

As discussed in the lang meeting: Let's have separate PRs to turn each of these lints into deny-by-default on 2021 (which should be trivial changes), such that each lint can have its down discussion on its own PR. Then we can use this issue as the tracking issue for tracking those PRs. (cc @rylev)

joshtriplett · 2021-01-19T19:06:06Z

👍

We should also discuss (on an appropriate issue once filed) whether bare_trait_objects should be a deny-by-default lint, or a hard error. The argument for the latter is in rust-lang/lang-team#65 : making bare_trait_objects a hard error in an edition will make it possible to give better error messages for const-generics in that edition and newer.

rylev · 2021-01-20T09:46:34Z

I will submit PRs for each of these lints. 👍

rylev · 2021-03-04T11:12:33Z

There are bugfix lints for which the question isn't "make them a hard error in all code or in new code"; the question is "make them a hard error in new code or not at all".

This is definitely something we should discuss. I don't think we had a frank discussion about future incompatibility lints that are so pervasive that changing them in older code would be too damaging to be practical.

Yes, with the caveat that not all future incompat lints can be automatically fixed with cargo fix

I'm not sure if you're implying that we can only make future imcompat lints errors on edition boundaries if they can be automatically fixed with rustfix, but if so, that's not the case. We don't guarantee that edition changes have to be 100% migratable with rustfix.

Manishearth · 2021-03-04T17:39:16Z

I'm not sure if you're implying that we can only make future imcompat lints errors on edition boundaries if they can be automatically fixed with rustfix, but if so, that's not the case. We don't guarantee that edition changes have to be 100% migratable with rustfix.

I am not implying this. However, I am implying that edition breakages need to have a proper analysis of what they break, whether those breakages need to be autofixed, and if so, how they will be autofixed. This is something we're working on clarifying in the 2021 edition RFC.

Which means that we cannot have a blanket policy of upgrading future incompat lints to edition breakages since this manual analysis must be done as well.

Aloso · 2021-03-05T13:08:27Z

I wouldn't want a lint to have to spend a whole edition as deny-by-default before it could be a hard error.

The problem is that deny-by-default lints can be #[allow]ed. If someone has allowed bare trait objects and then upgrades to an edition that makes them deny-by-default, their code doesn't break. However, if a new release or edition turns it into a hard error, it's a breaking change (with no prior warning, since the warning was silenced).

One possible remedy is to issue a warning when someone allows a deny-by-default lint that is supposed to become a hard error in a future release.

For the person that has allowed bare_trait_objects, this means:

If they migrate to edition_2021, they get a new warning: "bare trait objects will become a hard error in a future release in the 2021 edition. Please update your code to use the dyn Trait syntax and remove the #[allow(bare_trait_objects)] attribute"
If they stay on edition_2018, their code will continue to work
If they migrate to edition_2021 after bare_trait_objects has been made a hard error in the 2021 edition, they get errors, even though their code built without warnings before. But this seems acceptable to me.

Manishearth · 2021-03-05T17:56:04Z

Okay so after going through this discussion I feel like we are retreading a lot of the work done for migration/idiom lints in the last edition, and facing the same dillemmas. We already decided on a lot of this in 2018.

There's also some discussion here that seems to redecide lint policy that has been so far never tied to editions.

If I recall correctly:

Idiom lints are "allow in edition X, warn in edition X + 1"
- It is acceptable for idiom lints to be "allow in edition X, warn in X+1, deny in X+1 after a period of time" (we never implemented this)
Migration lints are "allow/warn in edition X, warn when migrating to X+1, hard error after migrating to X+1"
Future incompat lints can and often should be turned into migration lints (i.e. they become hard errors in that edition). Note that the edition allows for entirely new lints to be immediately made into a hard error, so this is, if anything, a weaker change.
Idiom lints from previous editions probably should be made into migration lints in the next edition (i.e. they become a hard error). bare_trait_objects is one of these
It is not a big deal to turn any lint, allow or warn, into an edition migration lint.
It is not a big deal to turn any lint, allow or warn, into deny by default, at any point in time, though we should be careful about blast radius.
The edition upgrade mechanism should itself include a lint for allow() on any lints that have been turned into migration lints, if we ever do this

For turning something into a migration lint I really do not see a need to go "one step at a time". The edition involves entirely new things -- never before linted -- being made into hard errors, it should be even less of a problem for things which have been linted for ages.

I'll point out, bare_trait_objects is an idiom lint from 2018, and there was a general feeling that it would probably be a migration lint (warn -> hard error) in 2021.

There is the future incompatible warning that explicitly states that a warning will become a hard error in a future edition. Is this a requirement before upgrading a warn-by-default lint to deny-by-default? Or is it acceptable for a lint to be promoted when it was not explicitly stated that promotion would happen?

There is already a stability policy for lints. It is acceptable for lints to randomly change default lint levels without it ever being considered breaking, due to cap-lint-level. It is unacceptable for lints to turn into hard, nonsilenceable errors.

There is a strong distinction between deny-by-default and hard error that is being missed here. deny-by-default is silenceable, and does not break dependencies. On the other hand hard errors are not silenceable and always break dependencies. New hard errors for things which previously compiled or linted are always breaking changes, new deny lints for things which previously compiled or warn-linted are never breaking changes.

Turning a warn into a deny never need be tied to an edition, it can be for making people want to do it more. Turning a warn into a hard error almost always must be tied to an edition (or an argument should be made about why the breakage is acceptable and the blast radius should be surveyed -- this happens with future incompat stuff)

camelid · 2021-03-11T04:29:34Z

I'm not sure if we're including rustdoc lints in this list, but I wonder if it might be a good idea to promote rustdoc::broken_intra_doc_links and maybe rustdoc::private_intra_doc_links to deny-by-default lints.

jyn514 · 2021-03-11T04:36:49Z

I don't think those should be denied by default. The documentation still works fine even if the links are broken, and if people care they can always deny the lint themselves.

Manishearth · 2021-03-11T06:47:57Z

I'm not sure if we're including rustdoc lints in this list, but I wonder if it might be a good idea to promote rustdoc::broken_intra_doc_links and maybe rustdoc::private_intra_doc_links to deny-by-default lints.

Please no, these are not particularly bad, and are sometimes possible to trigger by accident. The bar for deny lints in rustc is pretty high, basically "this is very bad or deprecated"

nikomatsakis · 2021-05-10T15:14:45Z

Closing this as done! Thanks @rylev for pushing on this.

warning: trait objects without an explicit `dyn` are deprecated --> src/ignore.rs:48:12 | 48 | Ok(Visitor::ignore()) | ^^^^^^^ help: use `dyn`: `<dyn Visitor>` | = note: `#[warn(bare_trait_objects)]` on by default = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in the 2021 edition! = note: for more information, see issue #80165 <rust-lang/rust#80165> warning: trait objects without an explicit `dyn` are deprecated --> src/ignore.rs:58:12 | 58 | Ok(Visitor::ignore()) | ^^^^^^^ help: use `dyn`: `<dyn Visitor>` | = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in the 2021 edition! = note: for more information, see issue #80165 <rust-lang/rust#80165>

=== stdout === === stderr === warning: trait objects without an explicit `dyn` are deprecated --> /home/runner/work/glacier/glacier/ices/86132.rs:4:36 | 4 | const TRAIT_OBJ_UNALIGNED_VTABLE: &Trait = | ^^^^^ help: use `dyn`: `dyn Trait` | = note: `#[warn(bare_trait_objects)]` on by default = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in the 2021 edition! = note: for more information, see issue #80165 <rust-lang/rust#80165> warning: constant is never used: `TRAIT_OBJ_UNALIGNED_VTABLE` --> /home/runner/work/glacier/glacier/ices/86132.rs:4:1 | 4 | / const TRAIT_OBJ_UNALIGNED_VTABLE: &Trait = 5 | | unsafe { mem::transmute((&92u8, &[0b_______001_11i128; 128])) }; | |____________________________________________________________________^ | = note: `#[warn(dead_code)]` on by default error: any use of this value will cause an error --> /home/runner/work/glacier/glacier/ices/86132.rs:5:14 | 4 | / const TRAIT_OBJ_UNALIGNED_VTABLE: &Trait = 5 | | unsafe { mem::transmute((&92u8, &[0b_______001_11i128; 128])) }; | |______________^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^__- | | | invalid vtable: alignment `7` is not a power of 2 | = note: `#[deny(const_err)]` on by default = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release! = note: for more information, see issue #71800 <rust-lang/rust#71800> error: aborting due to previous error; 2 warnings emitted ==============

=== stdout === === stderr === warning: trait objects without an explicit `dyn` are deprecated --> /home/runner/work/glacier/glacier/ices/83630.rs:2:14 | 2 | static DATA: Iterator<Item = _> = "my string"; | ^^^^^^^^^^^^^^^^^^ help: use `dyn`: `dyn Iterator<Item = _>` | = note: `#[warn(bare_trait_objects)]` on by default = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in the 2021 edition! = note: for more information, see issue #80165 <rust-lang/rust#80165> error[E0121]: the type placeholder `_` is not allowed within types on item signatures --> /home/runner/work/glacier/glacier/ices/83630.rs:2:30 | 2 | static DATA: Iterator<Item = _> = "my string"; | ^ not allowed in type signatures error: aborting due to previous error; 1 warning emitted For more information about this error, try `rustc --explain E0121`. ==============

=== stdout === === stderr === warning: trait objects without an explicit `dyn` are deprecated --> /home/runner/work/glacier/glacier/ices/83630.rs:2:14 | 2 | static DATA: Iterator<Item = _> = "my string"; | ^^^^^^^^^^^^^^^^^^ help: use `dyn`: `dyn Iterator<Item = _>` | = note: `#[warn(bare_trait_objects)]` on by default = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in the 2021 edition! = note: for more information, see issue #80165 <rust-lang/rust#80165> error[E0121]: the type placeholder `_` is not allowed within types on item signatures --> /home/runner/work/glacier/glacier/ices/83630.rs:2:30 | 2 | static DATA: Iterator<Item = _> = "my string"; | ^ not allowed in type signatures error: aborting due to previous error; 1 warning emitted For more information about this error, try `rustc --explain E0121`. ============== Co-authored-by: rustbot <[email protected]>

=== stdout === === stderr === error: lifetime in trait object type must be followed by `+` --> /home/runner/work/glacier/glacier/ices/85350.rs:1:26 | 1 | impl FnMut(&Context) for 'tcx { | ^^^^ error[E0407]: method `print` is not a member of trait `FnMut` --> /home/runner/work/glacier/glacier/ices/85350.rs:2:5 | 2 | fn print () -> Self :: Output{ } | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ not a member of trait `FnMut` error[E0412]: cannot find type `Context` in this scope --> /home/runner/work/glacier/glacier/ices/85350.rs:1:13 | 1 | impl FnMut(&Context) for 'tcx { | ^^^^^^^ not found in this scope | help: consider importing one of these items | 1 | use core::task::Context; | 1 | use std::task::Context; | warning: trait objects without an explicit `dyn` are deprecated --> /home/runner/work/glacier/glacier/ices/85350.rs:1:26 | 1 | impl FnMut(&Context) for 'tcx { | ^^^^ help: use `dyn`: `dyn 'tcx` | = note: `#[warn(bare_trait_objects)]` on by default = warning: this is accepted in the current edition (Rust 2018) but is a hard error in Rust 2021! = note: for more information, see issue #80165 <rust-lang/rust#80165> error[E0601]: `main` function not found in crate `85350` --> /home/runner/work/glacier/glacier/ices/85350.rs:1:1 | 1 | / impl FnMut(&Context) for 'tcx { 2 | | fn print () -> Self :: Output{ } 3 | | } | |_^ consider adding a `main` function to `/home/runner/work/glacier/glacier/ices/85350.rs` error[E0224]: at least one trait is required for an object type --> /home/runner/work/glacier/glacier/ices/85350.rs:1:26 | 1 | impl FnMut(&Context) for 'tcx { | ^^^^ error[E0261]: use of undeclared lifetime name `'tcx` --> /home/runner/work/glacier/glacier/ices/85350.rs:1:26 | 1 | impl FnMut(&Context) for 'tcx { | - ^^^^ undeclared lifetime | | | help: consider introducing lifetime `'tcx` here: `<'tcx>` | = help: if you want to experiment with in-band lifetime bindings, add `#![feature(in_band_lifetimes)]` to the crate attributes error[E0229]: associated type bindings are not allowed here --> /home/runner/work/glacier/glacier/ices/85350.rs:1:6 | 1 | impl FnMut(&Context) for 'tcx { | ^^^^^^^^^^^^^^^ associated type not allowed here error[E0212]: cannot use the associated type of a trait with uninferred generic parameters --> /home/runner/work/glacier/glacier/ices/85350.rs:2:20 | 2 | fn print () -> Self :: Output{ } | ^^^^^^^^^^^^^^ help: use a fully qualified path with inferred lifetimes: `<[type error] as FnOnce<(&[type error],)>>::Output` error: aborting due to 8 previous errors; 1 warning emitted Some errors have detailed explanations: E0212, E0224, E0229, E0261, E0407, E0412, E0601. For more information about an error, try `rustc --explain E0212`. ==============

=== stdout === === stderr === error[E0403]: the name `T` is already used for a generic parameter in this item's generic parameters --> /home/runner/work/glacier/glacier/ices/86756.rs:1:14 | 1 | trait Foo<T, T = T> {} | - ^ already used | | | first use of `T` warning: trait objects without an explicit `dyn` are deprecated --> /home/runner/work/glacier/glacier/ices/86756.rs:3:15 | 3 | eq::<dyn, Foo> | ^^^ help: use `dyn`: `dyn Foo` | = note: `#[warn(bare_trait_objects)]` on by default = warning: this is accepted in the current edition (Rust 2018) but is a hard error in Rust 2021! = note: for more information, see issue #80165 <rust-lang/rust#80165> error[E0601]: `main` function not found in crate `86756` --> /home/runner/work/glacier/glacier/ices/86756.rs:1:1 | 1 | / trait Foo<T, T = T> {} 2 | | fn eq<A, B>() { 3 | | eq::<dyn, Foo> 4 | | } | |_^ consider adding a `main` function to `/home/runner/work/glacier/glacier/ices/86756.rs` error[E0224]: at least one trait is required for an object type --> /home/runner/work/glacier/glacier/ices/86756.rs:3:10 | 3 | eq::<dyn, Foo> | ^^^ error[E0107]: missing generics for trait `Foo` --> /home/runner/work/glacier/glacier/ices/86756.rs:3:15 | 3 | eq::<dyn, Foo> | ^^^ expected at least 1 generic argument | note: trait defined here, with at least 1 generic parameter: `T` --> /home/runner/work/glacier/glacier/ices/86756.rs:1:7 | 1 | trait Foo<T, T = T> {} | ^^^ - help: add missing generic argument | 3 | eq::<dyn, Foo<T>> | ^^^^^^ error: aborting due to 4 previous errors; 1 warning emitted Some errors have detailed explanations: E0107, E0224, E0403, E0601. For more information about an error, try `rustc --explain E0107`. ==============

auula · 2021-07-31T16:06:47Z

“dyn” this was previously accepted by the compiler but is being phased out; it will become a hard error in the 2021 edition!

m-ou-se added C-tracking-issue Category: An issue tracking the progress of sth. like the implementation of an RFC A-edition-2018-lints labels Dec 18, 2020

m-ou-se added this to the Rust 2021 milestone Dec 18, 2020

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nikomatsakis added T-lang Relevant to the language team, which will review and decide on the PR/issue. I-nominated labels Jan 15, 2021

rylev mentioned this issue Jan 21, 2021

Update BARE_TRAIT_OBJECTS lint to deny in 2021 edition #81244

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nikomatsakis removed the I-nominated label Feb 2, 2021

Manishearth mentioned this issue Mar 3, 2021

Tracking Issue for invalid_doc_attributes lint #82730

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ehuss mentioned this issue Mar 29, 2021

Update BARE_TRAIT_OBJECT and ELLIPSIS_INCLUSIVE_RANGE_PATTERNS to errors in Rust 2021 #83213

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danieleades mentioned this issue Mar 30, 2021

use 2018 edition idioms pop-os/upgrade#149

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ehuss added the A-edition-2021 Area: The 2021 edition label Apr 26, 2021

nikomatsakis closed this as completed May 10, 2021

djc mentioned this issue Jul 1, 2021

Implement destructoring nested tuples on "let" and "for" statement target rinja-rs/askama#506

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m-ou-se mentioned this issue Sep 3, 2021

🎉 Rust 2021 celebration and thanks #88623

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maciej-makowski mentioned this issue Sep 4, 2021

Fixing deprecated compiler constructs maciej-makowski/giphy-rs#29

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tmandry mentioned this issue Nov 15, 2023

Disallow future-incompatibility lints in the 2024 edition #117921

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fmease added A-edition-2018 Area: The 2018 edition A-lints Area: Lints (warnings about flaws in source code) such as unused_mut. and removed A-edition-2018-lints labels Dec 21, 2024

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Promote Certain Lints to Errors in Rust 2021 Edition #80165

Promote Certain Lints to Errors in Rust 2021 Edition #80165

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Promote Certain Lints to Errors in Rust 2021 Edition #80165

Promote Certain Lints to Errors in Rust 2021 Edition #80165

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