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Tracking issue for future-incompatibility lint deref_into_dyn_supertrait #89460

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crlf0710 opened this issue Oct 2, 2021 · 5 comments · Fixed by #134367
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Tracking issue for future-incompatibility lint deref_into_dyn_supertrait #89460

crlf0710 opened this issue Oct 2, 2021 · 5 comments · Fixed by #134367
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A-dyn-trait Area: trait objects, vtable layout A-lints Area: Lints (warnings about flaws in source code) such as unused_mut. C-future-incompatibility Category: Future-incompatibility lints C-tracking-issue Category: An issue tracking the progress of sth. like the implementation of an RFC S-tracking-needs-summary Status: It's hard to tell what's been done and what hasn't! Someone should do some investigation. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. T-lang Relevant to the language team

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@crlf0710
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crlf0710 commented Oct 2, 2021 •
edited by pnkfelix
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What is this lint about

We're planning to add the dyn upcasting coercion language feature (see https://github.com/rust-lang/dyn-upcasting-coercion-initiative). Unfortunately this new coercion rule will take priority over certain other coercion rules, which will mean some behavior change. See #89190 for initial bug report.

How to fix this warning/error

Ensure your own Deref implementation is consistent with the trait_upcasting feature brings and allow this lint. Or avoid this code pattern altogether.

Current status

Implementation: #89461
@crlf0710 crlf0710 added A-lints Area: Lints (warnings about flaws in source code) such as unused_mut. T-lang Relevant to the language team T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. C-tracking-issue Category: An issue tracking the progress of sth. like the implementation of an RFC labels Oct 2, 2021
@crlf0710 crlf0710 mentioned this issue Oct 2, 2021
Merged
GuillaumeGomez added a commit to GuillaumeGomez/rust that referenced this issue Oct 7, 2021
@GuillaumeGomez
Rollup merge of rust-lang#89461 - crlf0710:dyn_upcasting_lint, r=niko…
ab276b8 
…matsakis

Add `deref_into_dyn_supertrait` lint.

Initial implementation of rust-lang#89460. Resolves rust-lang#89190.
Maybe also worth a beta backport if necessary.

r? `@nikomatsakis`
@joshtriplett joshtriplett added the S-tracking-needs-summary Status: It's hard to tell what's been done and what hasn't! Someone should do some investigation. label Jul 27, 2022
@joshtriplett
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Could we get a more detailed summary of the case this lint is addressing? dyn upcasting / coercion seems to have made a lot of progress, but this aspect of it doesn't seem to have gotten much discussion that I recall.

@Mark-Simulacrum Mark-Simulacrum mentioned this issue Jul 27, 2022
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@crlf0710
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crlf0710 commented Jul 28, 2022 •
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@joshtriplett Sure.

It is known that from user's perspective, coercions has "priorities", and dyn upcasting coercion has a higher priority than user defined Deref-based coercions. In the end, this coercion "shadows" a rare certain setup of user Deref implementation, which mimicks dyn upcasting coercion manually(see #89190 for an example).

For now we don't want to affect user's code, since dyn upcasting coercion might take a little while before it's stablized. Though, if user provided code decide to do other things in the Deref/DerefMut implementation, (even rarer, but possible, like running a hook or something), there will be a silent behavior change, when dyn upcasting gets stablized in the future. This lint emits a warning for this matter, to make sure that user doesn't write such code in their Deref/DerefMut implementations, then the future migration to dyn upcasting coercion will be smooth.

@crlf0710 crlf0710 mentioned this issue Sep 12, 2022
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@crlf0710 crlf0710 added the C-future-incompatibility Category: Future-incompatibility lints label Sep 12, 2022
@compiler-errors
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I'm curious -- why wasn't this implemented as a lint on the impl?

@crlf0710
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@compiler-errors It could be implemented that way, and thinking about it from current view, that would be a better way (No removal of the lint is needed with that approach)

@WaffleLapkin WaffleLapkin mentioned this issue Nov 22, 2022
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Dylan-DPC added a commit to Dylan-DPC/rust that referenced this issue Nov 24, 2022
@Dylan-DPC
Rollup merge of rust-lang#104742 - WaffleLapkin:forbidden-SUPER-deref…
b1aa7f5 
…, r=compiler-errors

Make `deref_into_dyn_supertrait` lint the impl and not the usage

Proposed by `@compiler-errors` in rust-lang#89460 (comment)
r? `@crlf0710`
matthiaskrgr added a commit to matthiaskrgr/rust that referenced this issue Nov 24, 2022
@matthiaskrgr
Rollup merge of rust-lang#104742 - WaffleLapkin:forbidden-SUPER-deref…
c08c57e 
…, r=compiler-errors

Make `deref_into_dyn_supertrait` lint the impl and not the usage

Proposed by ``@compiler-errors`` in rust-lang#89460 (comment)
r? ``@crlf0710``
flip1995 pushed a commit to flip1995/rust-clippy that referenced this issue Dec 1, 2022
@matthiaskrgr
Rollup merge of #104742 - WaffleLapkin:forbidden-SUPER-deref, r=compi…
ac6a77e 
…ler-errors

Make `deref_into_dyn_supertrait` lint the impl and not the usage

Proposed by ``@compiler-errors`` in rust-lang/rust#89460 (comment)
r? ``@crlf0710``
@WaffleLapkin
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For future reference: the lint change suggested by @compiler-errors was implemented in #104742 (I just tried to do that again because I forgor). The lint now lints against Deref impls for dyn Trait with type Target = dyn SupertraitOfTrait (instead of linting against the use of such Deref impl like it used to).

@lcnr lcnr mentioned this issue Nov 20, 2023
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matthiaskrgr added a commit to matthiaskrgr/rust that referenced this issue Nov 20, 2023
@matthiaskrgr
Rollup merge of rust-lang#118026 - compiler-errors:deref-into-dyn-reg…
ca246d3 
…ions, r=lcnr

Don't consider regions in `deref_into_dyn_supertrait` lint

I actually wonder if we should just warn on *any* deref impl with a target type that matches a supertrait by *def-id*.

cc rust-lang#89460

r? types
rust-timer added a commit to rust-lang-ci/rust that referenced this issue Nov 21, 2023
@rust-timer
Unrolled build for rust-lang#118026
41ff8aa 
Rollup merge of rust-lang#118026 - compiler-errors:deref-into-dyn-regions, r=lcnr

Don't consider regions in `deref_into_dyn_supertrait` lint

I actually wonder if we should just warn on *any* deref impl with a target type that matches a supertrait by *def-id*.

cc rust-lang#89460

r? types
@github-actions github-actions bot mentioned this issue Apr 9, 2024
Merged
@fmease fmease changed the title Tracking Issue for deref_into_dyn_supertrait compatibility lint Tracking issue for future-incompatibility lint deref_into_dyn_supertrait Sep 14, 2024
@fmease fmease added the A-dyn-trait Area: trait objects, vtable layout label Sep 14, 2024
@RalfJung RalfJung mentioned this issue Dec 19, 2024
Merged
matthiaskrgr added a commit to matthiaskrgr/rust that referenced this issue Feb 7, 2025
@matthiaskrgr
Rollup merge of rust-lang#134367 - WaffleLapkin:trait_upcasting_as_a_…
fcd67f1 
…treat, r=compiler-errors

Stabilize `feature(trait_upcasting)`

This feature was "done" for a while now, I think it's finally time to stabilize it! Stabilization report: rust-lang#134367 (comment).
cc reference PR: rust-lang/reference#1622.

Closes rust-lang#65991 (tracking issue), closes rust-lang#89460 (the lint is no longer future incompat).

r? compiler-errors
@bors bors closed this as completed in cbd44d7 Feb 7, 2025
rust-timer added a commit to rust-lang-ci/rust that referenced this issue Feb 7, 2025
@rust-timer
Unrolled build for rust-lang#134367
2406961 
Rollup merge of rust-lang#134367 - WaffleLapkin:trait_upcasting_as_a_treat, r=compiler-errors

Stabilize `feature(trait_upcasting)`

This feature was "done" for a while now, I think it's finally time to stabilize it! Stabilization report: rust-lang#134367 (comment).
cc reference PR: rust-lang/reference#1622.

Closes rust-lang#65991 (tracking issue), closes rust-lang#89460 (the lint is no longer future incompat).

r? compiler-errors
github-actions bot pushed a commit to tautschnig/verify-rust-std that referenced this issue Mar 11, 2025
@matthiaskrgr
Rollup merge of rust-lang#134367 - WaffleLapkin:trait_upcasting_as_a_…
faf1fa5 
…treat, r=compiler-errors

Stabilize `feature(trait_upcasting)`

This feature was "done" for a while now, I think it's finally time to stabilize it! Stabilization report: rust-lang#134367 (comment).
cc reference PR: rust-lang/reference#1622.

Closes rust-lang#65991 (tracking issue), closes rust-lang#89460 (the lint is no longer future incompat).

r? compiler-errors
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Labels
A-dyn-trait Area: trait objects, vtable layout A-lints Area: Lints (warnings about flaws in source code) such as unused_mut. C-future-incompatibility Category: Future-incompatibility lints C-tracking-issue Category: An issue tracking the progress of sth. like the implementation of an RFC S-tracking-needs-summary Status: It's hard to tell what's been done and what hasn't! Someone should do some investigation. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. T-lang Relevant to the language team
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@joshtriplett @crlf0710 @compiler-errors @fmease @WaffleLapkin