Require that a `<_ as Try>::Residual` implement the `Residual` trait by scottmcm · Pull Request #154451 · rust-lang/rust

scottmcm · 2026-03-27T04:11:03Z

The Residual trait was even more experimental than Try, but now that rust-lang/rfcs#3721 is merged, I think it would make sense to require this. Technically it's not strictly required, but without it something working on <T: Try> might need an extra bound even to use a homogeneous try block with the same output type as T::Output. (Another where will of course be needed to return a differentimpl Try type still.)

cc #154391

scottmcm · 2026-03-27T04:14:03Z

 /// "foo-ness" of the residual so other types need to opt-in to interconversion.
 #[unstable(feature = "try_trait_v2", issue = "84277", old_name = "try_trait")]
- type Residual;
+ type Residual: Residual<Self::Output>;


There's a more nuanced conversation about whether this should go further and also require
Suggested change
typeResidual:Residual<Self::Output>;
typeResidual:Residual<Self::Output,TryType = Self>;
but that has a variety of implications, so I'd rather leave it for another time rather than this PR.

@scottmcm Where is that further step being discussed? And what are those implications?

IIUC, this would force Residuals to be truly colored. It's not enforced now, so, e.g., Poll currently shares a Residual with Result (Result<Infallible, E>). Someone can ? a Poll in a function returning Result without a specific FromResidual<R> impl:
fnfoo() -> Result<u8,bool>{ core::task::Poll::<Result<u16,bool>>::Ready(Ok(0))?;Ok(1)}
I guess that's not desirable because it's unexpected. If Poll had its own Residual, it would take a deliberate impl FromResidual<Poll<Result<Infallible, E>>> for Result<T, E> for the above to work.
I'm also curious to see the discussions.

I made #155368 as a place to have the discussion.

rustbot · 2026-03-28T09:26:10Z

Some changes occurred in src/tools/clippy

cc @rust-lang/clippy

rustbot · 2026-03-28T09:26:12Z

r? @petrochenkov

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They will have a look at your PR within the next two weeks and either review your PR or reassign to another reviewer.

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petrochenkov · 2026-04-07T13:42:37Z

r? library

rustbot · 2026-04-07T13:42:41Z

Failed to set assignee to library: invalid assignee

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petrochenkov · 2026-04-07T13:42:51Z

r? libs

jhpratt · 2026-04-09T02:50:06Z

cc @rust-lang/libs-api

r=me on implementation, but it's a design decision for you. imo it's more than reasonable to add this bound.

nxsaken · 2026-04-11T08:53:03Z

 /// "foo-ness" of the residual so other types need to opt-in to interconversion.
 #[unstable(feature = "try_trait_v2", issue = "84277", old_name = "try_trait")]
- type Residual;
+ type Residual: Residual<Self::Output>;


View changes since the review
Suggested change
typeResidual:Residual<Self::Output>;
typeResidual:[const]Residual<Self::Output>;

This needs more changes than just this so I'll leave it for a follow-up.

nia-e · 2026-04-15T14:45:16Z

Per the discussion in the last @rust-lang/libs-api meeting, we're happy to defer to @scottmcm on the details here and the idea seems sound. Thanks ^^

The `Residual` trait was even more experimental than `Try`, but now that RFC3721 is merged, I think it would make sense to require this.

rustbot · 2026-04-16T01:10:08Z

This PR was rebased onto a different main commit. Here's a range-diff highlighting what actually changed.

Rebasing is a normal part of keeping PRs up to date, so no action is needed—this note is just to help reviewers.

scottmcm · 2026-04-16T04:35:26Z

@bors r=jhpratt

rust-bors · 2026-04-16T04:35:30Z

📌 Commit 3efcdbc has been approved by jhpratt

It is now in the queue for this repository.

Rollup of 18 pull requests Successful merges: - #154451 (Require that a `<_ as Try>::Residual` implement the `Residual` trait) - #154595 (Emit fatal on invalid const args with nested defs) - #154599 (report the `varargs_without_pattern` lint in deps) - #154699 (`core::unicode`: Replace `Cased` table with `Lt`) - #155353 (resolve: Remove `inaccessible_ctor_reexport` resolver field) - #155357 (Add `--remap-path-scope` as unstable in rustdoc) - #150649 (clippy fix: non_canonical_clone_impl) - #154604 (abort in core) - #154616 (Add `--quiet` flag to x.py and bootstrap to suppress output) - #155215 (Clean up `AttributeLintKind` and refactor diagnostic attribute linting) - #155228 (Check diagnostic output in incremental `cpass` and `rpass` revisions) - #155266 (Adjust release notes for post-merge feedback) - #155326 (Disallow ZST allocations with `TypedArena`.) - #155334 (docs: Use `0b1` instead of `NonZero::MIN` in `NonZero::bit_width` doctests) - #155340 (Handle nonnull pattern types in size skeleton) - #155347 (Add push_mut and new Layout methods to release notes) - #155356 (remove calls to AliasTyKind::def_id) - #155364 (Reduce diagnostic type visibilities.)

Rollup merge of #154451 - scottmcm:require-residual, r=jhpratt Require that a `<_ as Try>::Residual` implement the `Residual` trait The `Residual` trait was even more experimental than `Try`, but now that rust-lang/rfcs#3721 is merged, I think it would make sense to require this. Technically it's not strictly required, but without it something working on `<T: Try>` might need an extra bound even to use a homogeneous try block with the same output type as `T::Output`. (Another `where` will of course be needed to return a *different* `impl Try` type still.) cc #154391

Rollup of 18 pull requests Successful merges: - rust-lang/rust#154451 (Require that a `<_ as Try>::Residual` implement the `Residual` trait) - rust-lang/rust#154595 (Emit fatal on invalid const args with nested defs) - rust-lang/rust#154599 (report the `varargs_without_pattern` lint in deps) - rust-lang/rust#154699 (`core::unicode`: Replace `Cased` table with `Lt`) - rust-lang/rust#155353 (resolve: Remove `inaccessible_ctor_reexport` resolver field) - rust-lang/rust#155357 (Add `--remap-path-scope` as unstable in rustdoc) - rust-lang/rust#150649 (clippy fix: non_canonical_clone_impl) - rust-lang/rust#154604 (abort in core) - rust-lang/rust#154616 (Add `--quiet` flag to x.py and bootstrap to suppress output) - rust-lang/rust#155215 (Clean up `AttributeLintKind` and refactor diagnostic attribute linting) - rust-lang/rust#155228 (Check diagnostic output in incremental `cpass` and `rpass` revisions) - rust-lang/rust#155266 (Adjust release notes for post-merge feedback) - rust-lang/rust#155326 (Disallow ZST allocations with `TypedArena`.) - rust-lang/rust#155334 (docs: Use `0b1` instead of `NonZero::MIN` in `NonZero::bit_width` doctests) - rust-lang/rust#155340 (Handle nonnull pattern types in size skeleton) - rust-lang/rust#155347 (Add push_mut and new Layout methods to release notes) - rust-lang/rust#155356 (remove calls to AliasTyKind::def_id) - rust-lang/rust#155364 (Reduce diagnostic type visibilities.)

scottmcm · 2026-03-27T04:11:03Z

The Residual trait was even more experimental than Try, but now that rust-lang/rfcs#3721 is merged, I think it would make sense to require this. Technically it's not strictly required, but without it something working on <T: Try> might need an extra bound even to use a homogeneous try block with the same output type as T::Output. (Another where will of course be needed to return a differentimpl Try type still.)

cc #154391

scottmcm · 2026-03-27T04:14:03Z

 /// "foo-ness" of the residual so other types need to opt-in to interconversion.
 #[unstable(feature = "try_trait_v2", issue = "84277", old_name = "try_trait")]
- type Residual;
+ type Residual: Residual<Self::Output>;


There's a more nuanced conversation about whether this should go further and also require
Suggested change
typeResidual:Residual<Self::Output>;
typeResidual:Residual<Self::Output,TryType = Self>;
but that has a variety of implications, so I'd rather leave it for another time rather than this PR.

@scottmcm Where is that further step being discussed? And what are those implications?

IIUC, this would force Residuals to be truly colored. It's not enforced now, so, e.g., Poll currently shares a Residual with Result (Result<Infallible, E>). Someone can ? a Poll in a function returning Result without a specific FromResidual<R> impl:
fnfoo() -> Result<u8,bool>{ core::task::Poll::<Result<u16,bool>>::Ready(Ok(0))?;Ok(1)}
I guess that's not desirable because it's unexpected. If Poll had its own Residual, it would take a deliberate impl FromResidual<Poll<Result<Infallible, E>>> for Result<T, E> for the above to work.
I'm also curious to see the discussions.

I made #155368 as a place to have the discussion.

rustbot · 2026-03-28T09:26:10Z

Some changes occurred in src/tools/clippy

cc @rust-lang/clippy

rustbot · 2026-03-28T09:26:12Z

r? @petrochenkov

rustbot has assigned @petrochenkov.
They will have a look at your PR within the next two weeks and either review your PR or reassign to another reviewer.

Use r? to explicitly pick a reviewer

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petrochenkov · 2026-04-07T13:42:37Z

r? library

rustbot · 2026-04-07T13:42:41Z

Failed to set assignee to library: invalid assignee

Note: Only org members with at least the repository "read" role, users with write permissions, or people who have commented on the PR may be assigned.

petrochenkov · 2026-04-07T13:42:51Z

r? libs

jhpratt · 2026-04-09T02:50:06Z

cc @rust-lang/libs-api

r=me on implementation, but it's a design decision for you. imo it's more than reasonable to add this bound.

nxsaken · 2026-04-11T08:53:03Z

 /// "foo-ness" of the residual so other types need to opt-in to interconversion.
 #[unstable(feature = "try_trait_v2", issue = "84277", old_name = "try_trait")]
- type Residual;
+ type Residual: Residual<Self::Output>;


View changes since the review
Suggested change
typeResidual:Residual<Self::Output>;
typeResidual:[const]Residual<Self::Output>;

This needs more changes than just this so I'll leave it for a follow-up.

nia-e · 2026-04-15T14:45:16Z

Per the discussion in the last @rust-lang/libs-api meeting, we're happy to defer to @scottmcm on the details here and the idea seems sound. Thanks ^^

The `Residual` trait was even more experimental than `Try`, but now that RFC3721 is merged, I think it would make sense to require this.

rustbot · 2026-04-16T01:10:08Z

This PR was rebased onto a different main commit. Here's a range-diff highlighting what actually changed.

Rebasing is a normal part of keeping PRs up to date, so no action is needed—this note is just to help reviewers.

scottmcm · 2026-04-16T04:35:26Z

@bors r=jhpratt

rust-bors · 2026-04-16T04:35:30Z

📌 Commit 3efcdbc has been approved by jhpratt

It is now in the queue for this repository.

Rollup of 18 pull requests Successful merges: - #154451 (Require that a `<_ as Try>::Residual` implement the `Residual` trait) - #154595 (Emit fatal on invalid const args with nested defs) - #154599 (report the `varargs_without_pattern` lint in deps) - #154699 (`core::unicode`: Replace `Cased` table with `Lt`) - #155353 (resolve: Remove `inaccessible_ctor_reexport` resolver field) - #155357 (Add `--remap-path-scope` as unstable in rustdoc) - #150649 (clippy fix: non_canonical_clone_impl) - #154604 (abort in core) - #154616 (Add `--quiet` flag to x.py and bootstrap to suppress output) - #155215 (Clean up `AttributeLintKind` and refactor diagnostic attribute linting) - #155228 (Check diagnostic output in incremental `cpass` and `rpass` revisions) - #155266 (Adjust release notes for post-merge feedback) - #155326 (Disallow ZST allocations with `TypedArena`.) - #155334 (docs: Use `0b1` instead of `NonZero::MIN` in `NonZero::bit_width` doctests) - #155340 (Handle nonnull pattern types in size skeleton) - #155347 (Add push_mut and new Layout methods to release notes) - #155356 (remove calls to AliasTyKind::def_id) - #155364 (Reduce diagnostic type visibilities.)

Rollup merge of #154451 - scottmcm:require-residual, r=jhpratt Require that a `<_ as Try>::Residual` implement the `Residual` trait The `Residual` trait was even more experimental than `Try`, but now that rust-lang/rfcs#3721 is merged, I think it would make sense to require this. Technically it's not strictly required, but without it something working on `<T: Try>` might need an extra bound even to use a homogeneous try block with the same output type as `T::Output`. (Another `where` will of course be needed to return a *different* `impl Try` type still.) cc #154391

Rollup of 18 pull requests Successful merges: - rust-lang/rust#154451 (Require that a `<_ as Try>::Residual` implement the `Residual` trait) - rust-lang/rust#154595 (Emit fatal on invalid const args with nested defs) - rust-lang/rust#154599 (report the `varargs_without_pattern` lint in deps) - rust-lang/rust#154699 (`core::unicode`: Replace `Cased` table with `Lt`) - rust-lang/rust#155353 (resolve: Remove `inaccessible_ctor_reexport` resolver field) - rust-lang/rust#155357 (Add `--remap-path-scope` as unstable in rustdoc) - rust-lang/rust#150649 (clippy fix: non_canonical_clone_impl) - rust-lang/rust#154604 (abort in core) - rust-lang/rust#154616 (Add `--quiet` flag to x.py and bootstrap to suppress output) - rust-lang/rust#155215 (Clean up `AttributeLintKind` and refactor diagnostic attribute linting) - rust-lang/rust#155228 (Check diagnostic output in incremental `cpass` and `rpass` revisions) - rust-lang/rust#155266 (Adjust release notes for post-merge feedback) - rust-lang/rust#155326 (Disallow ZST allocations with `TypedArena`.) - rust-lang/rust#155334 (docs: Use `0b1` instead of `NonZero::MIN` in `NonZero::bit_width` doctests) - rust-lang/rust#155340 (Handle nonnull pattern types in size skeleton) - rust-lang/rust#155347 (Add push_mut and new Layout methods to release notes) - rust-lang/rust#155356 (remove calls to AliasTyKind::def_id) - rust-lang/rust#155364 (Reduce diagnostic type visibilities.)

scottmcm · 2026-03-27T04:11:03Z

The Residual trait was even more experimental than Try, but now that rust-lang/rfcs#3721 is merged, I think it would make sense to require this. Technically it's not strictly required, but without it something working on <T: Try> might need an extra bound even to use a homogeneous try block with the same output type as T::Output. (Another where will of course be needed to return a differentimpl Try type still.)

cc #154391

scottmcm · 2026-03-27T04:14:03Z

 /// "foo-ness" of the residual so other types need to opt-in to interconversion.
 #[unstable(feature = "try_trait_v2", issue = "84277", old_name = "try_trait")]
- type Residual;
+ type Residual: Residual<Self::Output>;


There's a more nuanced conversation about whether this should go further and also require
Suggested change
typeResidual:Residual<Self::Output>;
typeResidual:Residual<Self::Output,TryType = Self>;
but that has a variety of implications, so I'd rather leave it for another time rather than this PR.

@scottmcm Where is that further step being discussed? And what are those implications?

IIUC, this would force Residuals to be truly colored. It's not enforced now, so, e.g., Poll currently shares a Residual with Result (Result<Infallible, E>). Someone can ? a Poll in a function returning Result without a specific FromResidual<R> impl:
fnfoo() -> Result<u8,bool>{ core::task::Poll::<Result<u16,bool>>::Ready(Ok(0))?;Ok(1)}
I guess that's not desirable because it's unexpected. If Poll had its own Residual, it would take a deliberate impl FromResidual<Poll<Result<Infallible, E>>> for Result<T, E> for the above to work.
I'm also curious to see the discussions.

I made #155368 as a place to have the discussion.

rustbot · 2026-03-28T09:26:10Z

Some changes occurred in src/tools/clippy

cc @rust-lang/clippy

rustbot · 2026-03-28T09:26:12Z

r? @petrochenkov

rustbot has assigned @petrochenkov.
They will have a look at your PR within the next two weeks and either review your PR or reassign to another reviewer.

Use r? to explicitly pick a reviewer

Why was this reviewer chosen?

The reviewer was selected based on:

Owners of files modified in this PR: compiler
compiler expanded to 69 candidates
Random selection from 12 candidates

petrochenkov · 2026-04-07T13:42:37Z

r? library

rustbot · 2026-04-07T13:42:41Z

Failed to set assignee to library: invalid assignee

Note: Only org members with at least the repository "read" role, users with write permissions, or people who have commented on the PR may be assigned.

petrochenkov · 2026-04-07T13:42:51Z

r? libs

jhpratt · 2026-04-09T02:50:06Z

cc @rust-lang/libs-api

r=me on implementation, but it's a design decision for you. imo it's more than reasonable to add this bound.

nxsaken · 2026-04-11T08:53:03Z

 /// "foo-ness" of the residual so other types need to opt-in to interconversion.
 #[unstable(feature = "try_trait_v2", issue = "84277", old_name = "try_trait")]
- type Residual;
+ type Residual: Residual<Self::Output>;


View changes since the review
Suggested change
typeResidual:Residual<Self::Output>;
typeResidual:[const]Residual<Self::Output>;

This needs more changes than just this so I'll leave it for a follow-up.

nia-e · 2026-04-15T14:45:16Z

Per the discussion in the last @rust-lang/libs-api meeting, we're happy to defer to @scottmcm on the details here and the idea seems sound. Thanks ^^

The `Residual` trait was even more experimental than `Try`, but now that RFC3721 is merged, I think it would make sense to require this.

rustbot · 2026-04-16T01:10:08Z

This PR was rebased onto a different main commit. Here's a range-diff highlighting what actually changed.

Rebasing is a normal part of keeping PRs up to date, so no action is needed—this note is just to help reviewers.

scottmcm · 2026-04-16T04:35:26Z

@bors r=jhpratt

rust-bors · 2026-04-16T04:35:30Z

📌 Commit 3efcdbc has been approved by jhpratt

It is now in the queue for this repository.

Rollup of 18 pull requests Successful merges: - #154451 (Require that a `<_ as Try>::Residual` implement the `Residual` trait) - #154595 (Emit fatal on invalid const args with nested defs) - #154599 (report the `varargs_without_pattern` lint in deps) - #154699 (`core::unicode`: Replace `Cased` table with `Lt`) - #155353 (resolve: Remove `inaccessible_ctor_reexport` resolver field) - #155357 (Add `--remap-path-scope` as unstable in rustdoc) - #150649 (clippy fix: non_canonical_clone_impl) - #154604 (abort in core) - #154616 (Add `--quiet` flag to x.py and bootstrap to suppress output) - #155215 (Clean up `AttributeLintKind` and refactor diagnostic attribute linting) - #155228 (Check diagnostic output in incremental `cpass` and `rpass` revisions) - #155266 (Adjust release notes for post-merge feedback) - #155326 (Disallow ZST allocations with `TypedArena`.) - #155334 (docs: Use `0b1` instead of `NonZero::MIN` in `NonZero::bit_width` doctests) - #155340 (Handle nonnull pattern types in size skeleton) - #155347 (Add push_mut and new Layout methods to release notes) - #155356 (remove calls to AliasTyKind::def_id) - #155364 (Reduce diagnostic type visibilities.)

Rollup merge of #154451 - scottmcm:require-residual, r=jhpratt Require that a `<_ as Try>::Residual` implement the `Residual` trait The `Residual` trait was even more experimental than `Try`, but now that rust-lang/rfcs#3721 is merged, I think it would make sense to require this. Technically it's not strictly required, but without it something working on `<T: Try>` might need an extra bound even to use a homogeneous try block with the same output type as `T::Output`. (Another `where` will of course be needed to return a *different* `impl Try` type still.) cc #154391

Rollup of 18 pull requests Successful merges: - rust-lang/rust#154451 (Require that a `<_ as Try>::Residual` implement the `Residual` trait) - rust-lang/rust#154595 (Emit fatal on invalid const args with nested defs) - rust-lang/rust#154599 (report the `varargs_without_pattern` lint in deps) - rust-lang/rust#154699 (`core::unicode`: Replace `Cased` table with `Lt`) - rust-lang/rust#155353 (resolve: Remove `inaccessible_ctor_reexport` resolver field) - rust-lang/rust#155357 (Add `--remap-path-scope` as unstable in rustdoc) - rust-lang/rust#150649 (clippy fix: non_canonical_clone_impl) - rust-lang/rust#154604 (abort in core) - rust-lang/rust#154616 (Add `--quiet` flag to x.py and bootstrap to suppress output) - rust-lang/rust#155215 (Clean up `AttributeLintKind` and refactor diagnostic attribute linting) - rust-lang/rust#155228 (Check diagnostic output in incremental `cpass` and `rpass` revisions) - rust-lang/rust#155266 (Adjust release notes for post-merge feedback) - rust-lang/rust#155326 (Disallow ZST allocations with `TypedArena`.) - rust-lang/rust#155334 (docs: Use `0b1` instead of `NonZero::MIN` in `NonZero::bit_width` doctests) - rust-lang/rust#155340 (Handle nonnull pattern types in size skeleton) - rust-lang/rust#155347 (Add push_mut and new Layout methods to release notes) - rust-lang/rust#155356 (remove calls to AliasTyKind::def_id) - rust-lang/rust#155364 (Reduce diagnostic type visibilities.)

scottmcm · 2026-03-27T04:11:03Z

The Residual trait was even more experimental than Try, but now that rust-lang/rfcs#3721 is merged, I think it would make sense to require this. Technically it's not strictly required, but without it something working on <T: Try> might need an extra bound even to use a homogeneous try block with the same output type as T::Output. (Another where will of course be needed to return a differentimpl Try type still.)

cc #154391

scottmcm · 2026-03-27T04:14:03Z

 /// "foo-ness" of the residual so other types need to opt-in to interconversion.
 #[unstable(feature = "try_trait_v2", issue = "84277", old_name = "try_trait")]
- type Residual;
+ type Residual: Residual<Self::Output>;


There's a more nuanced conversation about whether this should go further and also require
Suggested change
typeResidual:Residual<Self::Output>;
typeResidual:Residual<Self::Output,TryType = Self>;
but that has a variety of implications, so I'd rather leave it for another time rather than this PR.

@scottmcm Where is that further step being discussed? And what are those implications?

IIUC, this would force Residuals to be truly colored. It's not enforced now, so, e.g., Poll currently shares a Residual with Result (Result<Infallible, E>). Someone can ? a Poll in a function returning Result without a specific FromResidual<R> impl:
fnfoo() -> Result<u8,bool>{ core::task::Poll::<Result<u16,bool>>::Ready(Ok(0))?;Ok(1)}
I guess that's not desirable because it's unexpected. If Poll had its own Residual, it would take a deliberate impl FromResidual<Poll<Result<Infallible, E>>> for Result<T, E> for the above to work.
I'm also curious to see the discussions.

I made #155368 as a place to have the discussion.

rustbot · 2026-03-28T09:26:10Z

Some changes occurred in src/tools/clippy

cc @rust-lang/clippy

rustbot · 2026-03-28T09:26:12Z

r? @petrochenkov

rustbot has assigned @petrochenkov.
They will have a look at your PR within the next two weeks and either review your PR or reassign to another reviewer.

Use r? to explicitly pick a reviewer

Why was this reviewer chosen?

The reviewer was selected based on:

Owners of files modified in this PR: compiler
compiler expanded to 69 candidates
Random selection from 12 candidates

petrochenkov · 2026-04-07T13:42:37Z

r? library

rustbot · 2026-04-07T13:42:41Z

Failed to set assignee to library: invalid assignee

Note: Only org members with at least the repository "read" role, users with write permissions, or people who have commented on the PR may be assigned.

petrochenkov · 2026-04-07T13:42:51Z

r? libs

jhpratt · 2026-04-09T02:50:06Z

cc @rust-lang/libs-api

r=me on implementation, but it's a design decision for you. imo it's more than reasonable to add this bound.

nxsaken · 2026-04-11T08:53:03Z

 /// "foo-ness" of the residual so other types need to opt-in to interconversion.
 #[unstable(feature = "try_trait_v2", issue = "84277", old_name = "try_trait")]
- type Residual;
+ type Residual: Residual<Self::Output>;


View changes since the review
Suggested change
typeResidual:Residual<Self::Output>;
typeResidual:[const]Residual<Self::Output>;

This needs more changes than just this so I'll leave it for a follow-up.

nia-e · 2026-04-15T14:45:16Z

Per the discussion in the last @rust-lang/libs-api meeting, we're happy to defer to @scottmcm on the details here and the idea seems sound. Thanks ^^

The `Residual` trait was even more experimental than `Try`, but now that RFC3721 is merged, I think it would make sense to require this.

rustbot · 2026-04-16T01:10:08Z

This PR was rebased onto a different main commit. Here's a range-diff highlighting what actually changed.

Rebasing is a normal part of keeping PRs up to date, so no action is needed—this note is just to help reviewers.

scottmcm · 2026-04-16T04:35:26Z

@bors r=jhpratt

rust-bors · 2026-04-16T04:35:30Z

📌 Commit 3efcdbc has been approved by jhpratt

It is now in the queue for this repository.

Rollup of 18 pull requests Successful merges: - #154451 (Require that a `<_ as Try>::Residual` implement the `Residual` trait) - #154595 (Emit fatal on invalid const args with nested defs) - #154599 (report the `varargs_without_pattern` lint in deps) - #154699 (`core::unicode`: Replace `Cased` table with `Lt`) - #155353 (resolve: Remove `inaccessible_ctor_reexport` resolver field) - #155357 (Add `--remap-path-scope` as unstable in rustdoc) - #150649 (clippy fix: non_canonical_clone_impl) - #154604 (abort in core) - #154616 (Add `--quiet` flag to x.py and bootstrap to suppress output) - #155215 (Clean up `AttributeLintKind` and refactor diagnostic attribute linting) - #155228 (Check diagnostic output in incremental `cpass` and `rpass` revisions) - #155266 (Adjust release notes for post-merge feedback) - #155326 (Disallow ZST allocations with `TypedArena`.) - #155334 (docs: Use `0b1` instead of `NonZero::MIN` in `NonZero::bit_width` doctests) - #155340 (Handle nonnull pattern types in size skeleton) - #155347 (Add push_mut and new Layout methods to release notes) - #155356 (remove calls to AliasTyKind::def_id) - #155364 (Reduce diagnostic type visibilities.)

Rollup merge of #154451 - scottmcm:require-residual, r=jhpratt Require that a `<_ as Try>::Residual` implement the `Residual` trait The `Residual` trait was even more experimental than `Try`, but now that rust-lang/rfcs#3721 is merged, I think it would make sense to require this. Technically it's not strictly required, but without it something working on `<T: Try>` might need an extra bound even to use a homogeneous try block with the same output type as `T::Output`. (Another `where` will of course be needed to return a *different* `impl Try` type still.) cc #154391

Rollup of 18 pull requests Successful merges: - rust-lang/rust#154451 (Require that a `<_ as Try>::Residual` implement the `Residual` trait) - rust-lang/rust#154595 (Emit fatal on invalid const args with nested defs) - rust-lang/rust#154599 (report the `varargs_without_pattern` lint in deps) - rust-lang/rust#154699 (`core::unicode`: Replace `Cased` table with `Lt`) - rust-lang/rust#155353 (resolve: Remove `inaccessible_ctor_reexport` resolver field) - rust-lang/rust#155357 (Add `--remap-path-scope` as unstable in rustdoc) - rust-lang/rust#150649 (clippy fix: non_canonical_clone_impl) - rust-lang/rust#154604 (abort in core) - rust-lang/rust#154616 (Add `--quiet` flag to x.py and bootstrap to suppress output) - rust-lang/rust#155215 (Clean up `AttributeLintKind` and refactor diagnostic attribute linting) - rust-lang/rust#155228 (Check diagnostic output in incremental `cpass` and `rpass` revisions) - rust-lang/rust#155266 (Adjust release notes for post-merge feedback) - rust-lang/rust#155326 (Disallow ZST allocations with `TypedArena`.) - rust-lang/rust#155334 (docs: Use `0b1` instead of `NonZero::MIN` in `NonZero::bit_width` doctests) - rust-lang/rust#155340 (Handle nonnull pattern types in size skeleton) - rust-lang/rust#155347 (Add push_mut and new Layout methods to release notes) - rust-lang/rust#155356 (remove calls to AliasTyKind::def_id) - rust-lang/rust#155364 (Reduce diagnostic type visibilities.)

scottmcm · 2026-03-27T04:11:03Z

The Residual trait was even more experimental than Try, but now that rust-lang/rfcs#3721 is merged, I think it would make sense to require this. Technically it's not strictly required, but without it something working on <T: Try> might need an extra bound even to use a homogeneous try block with the same output type as T::Output. (Another where will of course be needed to return a differentimpl Try type still.)

cc #154391

scottmcm · 2026-03-27T04:14:03Z

 /// "foo-ness" of the residual so other types need to opt-in to interconversion.
 #[unstable(feature = "try_trait_v2", issue = "84277", old_name = "try_trait")]
- type Residual;
+ type Residual: Residual<Self::Output>;


There's a more nuanced conversation about whether this should go further and also require
Suggested change
typeResidual:Residual<Self::Output>;
typeResidual:Residual<Self::Output,TryType = Self>;
but that has a variety of implications, so I'd rather leave it for another time rather than this PR.

@scottmcm Where is that further step being discussed? And what are those implications?

IIUC, this would force Residuals to be truly colored. It's not enforced now, so, e.g., Poll currently shares a Residual with Result (Result<Infallible, E>). Someone can ? a Poll in a function returning Result without a specific FromResidual<R> impl:
fnfoo() -> Result<u8,bool>{ core::task::Poll::<Result<u16,bool>>::Ready(Ok(0))?;Ok(1)}
I guess that's not desirable because it's unexpected. If Poll had its own Residual, it would take a deliberate impl FromResidual<Poll<Result<Infallible, E>>> for Result<T, E> for the above to work.
I'm also curious to see the discussions.

I made #155368 as a place to have the discussion.

rustbot · 2026-03-28T09:26:10Z

Some changes occurred in src/tools/clippy

cc @rust-lang/clippy

rustbot · 2026-03-28T09:26:12Z

r? @petrochenkov

rustbot has assigned @petrochenkov.
They will have a look at your PR within the next two weeks and either review your PR or reassign to another reviewer.

Use r? to explicitly pick a reviewer

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petrochenkov · 2026-04-07T13:42:37Z

r? library

rustbot · 2026-04-07T13:42:41Z

Failed to set assignee to library: invalid assignee

Note: Only org members with at least the repository "read" role, users with write permissions, or people who have commented on the PR may be assigned.

petrochenkov · 2026-04-07T13:42:51Z

r? libs

jhpratt · 2026-04-09T02:50:06Z

cc @rust-lang/libs-api

r=me on implementation, but it's a design decision for you. imo it's more than reasonable to add this bound.

nxsaken · 2026-04-11T08:53:03Z

 /// "foo-ness" of the residual so other types need to opt-in to interconversion.
 #[unstable(feature = "try_trait_v2", issue = "84277", old_name = "try_trait")]
- type Residual;
+ type Residual: Residual<Self::Output>;


View changes since the review
Suggested change
typeResidual:Residual<Self::Output>;
typeResidual:[const]Residual<Self::Output>;

This needs more changes than just this so I'll leave it for a follow-up.

nia-e · 2026-04-15T14:45:16Z

Per the discussion in the last @rust-lang/libs-api meeting, we're happy to defer to @scottmcm on the details here and the idea seems sound. Thanks ^^

The `Residual` trait was even more experimental than `Try`, but now that RFC3721 is merged, I think it would make sense to require this.

rustbot · 2026-04-16T01:10:08Z

This PR was rebased onto a different main commit. Here's a range-diff highlighting what actually changed.

Rebasing is a normal part of keeping PRs up to date, so no action is needed—this note is just to help reviewers.

scottmcm · 2026-04-16T04:35:26Z

@bors r=jhpratt

rust-bors · 2026-04-16T04:35:30Z

📌 Commit 3efcdbc has been approved by jhpratt

It is now in the queue for this repository.

Rollup of 18 pull requests Successful merges: - #154451 (Require that a `<_ as Try>::Residual` implement the `Residual` trait) - #154595 (Emit fatal on invalid const args with nested defs) - #154599 (report the `varargs_without_pattern` lint in deps) - #154699 (`core::unicode`: Replace `Cased` table with `Lt`) - #155353 (resolve: Remove `inaccessible_ctor_reexport` resolver field) - #155357 (Add `--remap-path-scope` as unstable in rustdoc) - #150649 (clippy fix: non_canonical_clone_impl) - #154604 (abort in core) - #154616 (Add `--quiet` flag to x.py and bootstrap to suppress output) - #155215 (Clean up `AttributeLintKind` and refactor diagnostic attribute linting) - #155228 (Check diagnostic output in incremental `cpass` and `rpass` revisions) - #155266 (Adjust release notes for post-merge feedback) - #155326 (Disallow ZST allocations with `TypedArena`.) - #155334 (docs: Use `0b1` instead of `NonZero::MIN` in `NonZero::bit_width` doctests) - #155340 (Handle nonnull pattern types in size skeleton) - #155347 (Add push_mut and new Layout methods to release notes) - #155356 (remove calls to AliasTyKind::def_id) - #155364 (Reduce diagnostic type visibilities.)

Rollup merge of #154451 - scottmcm:require-residual, r=jhpratt Require that a `<_ as Try>::Residual` implement the `Residual` trait The `Residual` trait was even more experimental than `Try`, but now that rust-lang/rfcs#3721 is merged, I think it would make sense to require this. Technically it's not strictly required, but without it something working on `<T: Try>` might need an extra bound even to use a homogeneous try block with the same output type as `T::Output`. (Another `where` will of course be needed to return a *different* `impl Try` type still.) cc #154391

Rollup of 18 pull requests Successful merges: - rust-lang/rust#154451 (Require that a `<_ as Try>::Residual` implement the `Residual` trait) - rust-lang/rust#154595 (Emit fatal on invalid const args with nested defs) - rust-lang/rust#154599 (report the `varargs_without_pattern` lint in deps) - rust-lang/rust#154699 (`core::unicode`: Replace `Cased` table with `Lt`) - rust-lang/rust#155353 (resolve: Remove `inaccessible_ctor_reexport` resolver field) - rust-lang/rust#155357 (Add `--remap-path-scope` as unstable in rustdoc) - rust-lang/rust#150649 (clippy fix: non_canonical_clone_impl) - rust-lang/rust#154604 (abort in core) - rust-lang/rust#154616 (Add `--quiet` flag to x.py and bootstrap to suppress output) - rust-lang/rust#155215 (Clean up `AttributeLintKind` and refactor diagnostic attribute linting) - rust-lang/rust#155228 (Check diagnostic output in incremental `cpass` and `rpass` revisions) - rust-lang/rust#155266 (Adjust release notes for post-merge feedback) - rust-lang/rust#155326 (Disallow ZST allocations with `TypedArena`.) - rust-lang/rust#155334 (docs: Use `0b1` instead of `NonZero::MIN` in `NonZero::bit_width` doctests) - rust-lang/rust#155340 (Handle nonnull pattern types in size skeleton) - rust-lang/rust#155347 (Add push_mut and new Layout methods to release notes) - rust-lang/rust#155356 (remove calls to AliasTyKind::def_id) - rust-lang/rust#155364 (Reduce diagnostic type visibilities.)

scottmcm · 2026-03-27T04:11:03Z

The Residual trait was even more experimental than Try, but now that rust-lang/rfcs#3721 is merged, I think it would make sense to require this. Technically it's not strictly required, but without it something working on <T: Try> might need an extra bound even to use a homogeneous try block with the same output type as T::Output. (Another where will of course be needed to return a differentimpl Try type still.)

cc #154391

scottmcm · 2026-03-27T04:14:03Z

 /// "foo-ness" of the residual so other types need to opt-in to interconversion.
 #[unstable(feature = "try_trait_v2", issue = "84277", old_name = "try_trait")]
- type Residual;
+ type Residual: Residual<Self::Output>;


There's a more nuanced conversation about whether this should go further and also require
Suggested change
typeResidual:Residual<Self::Output>;
typeResidual:Residual<Self::Output,TryType = Self>;
but that has a variety of implications, so I'd rather leave it for another time rather than this PR.

@scottmcm Where is that further step being discussed? And what are those implications?

IIUC, this would force Residuals to be truly colored. It's not enforced now, so, e.g., Poll currently shares a Residual with Result (Result<Infallible, E>). Someone can ? a Poll in a function returning Result without a specific FromResidual<R> impl:
fnfoo() -> Result<u8,bool>{ core::task::Poll::<Result<u16,bool>>::Ready(Ok(0))?;Ok(1)}
I guess that's not desirable because it's unexpected. If Poll had its own Residual, it would take a deliberate impl FromResidual<Poll<Result<Infallible, E>>> for Result<T, E> for the above to work.
I'm also curious to see the discussions.

I made #155368 as a place to have the discussion.

rustbot · 2026-03-28T09:26:10Z

Some changes occurred in src/tools/clippy

cc @rust-lang/clippy

rustbot · 2026-03-28T09:26:12Z

r? @petrochenkov

rustbot has assigned @petrochenkov.
They will have a look at your PR within the next two weeks and either review your PR or reassign to another reviewer.

Use r? to explicitly pick a reviewer

Why was this reviewer chosen?

The reviewer was selected based on:

Owners of files modified in this PR: compiler
compiler expanded to 69 candidates
Random selection from 12 candidates

petrochenkov · 2026-04-07T13:42:37Z

r? library

rustbot · 2026-04-07T13:42:41Z

Failed to set assignee to library: invalid assignee

Note: Only org members with at least the repository "read" role, users with write permissions, or people who have commented on the PR may be assigned.

petrochenkov · 2026-04-07T13:42:51Z

r? libs

jhpratt · 2026-04-09T02:50:06Z

cc @rust-lang/libs-api

r=me on implementation, but it's a design decision for you. imo it's more than reasonable to add this bound.

nxsaken · 2026-04-11T08:53:03Z

 /// "foo-ness" of the residual so other types need to opt-in to interconversion.
 #[unstable(feature = "try_trait_v2", issue = "84277", old_name = "try_trait")]
- type Residual;
+ type Residual: Residual<Self::Output>;


View changes since the review
Suggested change
typeResidual:Residual<Self::Output>;
typeResidual:[const]Residual<Self::Output>;

This needs more changes than just this so I'll leave it for a follow-up.

nia-e · 2026-04-15T14:45:16Z

Per the discussion in the last @rust-lang/libs-api meeting, we're happy to defer to @scottmcm on the details here and the idea seems sound. Thanks ^^

The `Residual` trait was even more experimental than `Try`, but now that RFC3721 is merged, I think it would make sense to require this.

rustbot · 2026-04-16T01:10:08Z

This PR was rebased onto a different main commit. Here's a range-diff highlighting what actually changed.

Rebasing is a normal part of keeping PRs up to date, so no action is needed—this note is just to help reviewers.

scottmcm · 2026-04-16T04:35:26Z

@bors r=jhpratt

rust-bors · 2026-04-16T04:35:30Z

📌 Commit 3efcdbc has been approved by jhpratt

It is now in the queue for this repository.

Rollup of 18 pull requests Successful merges: - #154451 (Require that a `<_ as Try>::Residual` implement the `Residual` trait) - #154595 (Emit fatal on invalid const args with nested defs) - #154599 (report the `varargs_without_pattern` lint in deps) - #154699 (`core::unicode`: Replace `Cased` table with `Lt`) - #155353 (resolve: Remove `inaccessible_ctor_reexport` resolver field) - #155357 (Add `--remap-path-scope` as unstable in rustdoc) - #150649 (clippy fix: non_canonical_clone_impl) - #154604 (abort in core) - #154616 (Add `--quiet` flag to x.py and bootstrap to suppress output) - #155215 (Clean up `AttributeLintKind` and refactor diagnostic attribute linting) - #155228 (Check diagnostic output in incremental `cpass` and `rpass` revisions) - #155266 (Adjust release notes for post-merge feedback) - #155326 (Disallow ZST allocations with `TypedArena`.) - #155334 (docs: Use `0b1` instead of `NonZero::MIN` in `NonZero::bit_width` doctests) - #155340 (Handle nonnull pattern types in size skeleton) - #155347 (Add push_mut and new Layout methods to release notes) - #155356 (remove calls to AliasTyKind::def_id) - #155364 (Reduce diagnostic type visibilities.)

Rollup merge of #154451 - scottmcm:require-residual, r=jhpratt Require that a `<_ as Try>::Residual` implement the `Residual` trait The `Residual` trait was even more experimental than `Try`, but now that rust-lang/rfcs#3721 is merged, I think it would make sense to require this. Technically it's not strictly required, but without it something working on `<T: Try>` might need an extra bound even to use a homogeneous try block with the same output type as `T::Output`. (Another `where` will of course be needed to return a *different* `impl Try` type still.) cc #154391

Rollup of 18 pull requests Successful merges: - rust-lang/rust#154451 (Require that a `<_ as Try>::Residual` implement the `Residual` trait) - rust-lang/rust#154595 (Emit fatal on invalid const args with nested defs) - rust-lang/rust#154599 (report the `varargs_without_pattern` lint in deps) - rust-lang/rust#154699 (`core::unicode`: Replace `Cased` table with `Lt`) - rust-lang/rust#155353 (resolve: Remove `inaccessible_ctor_reexport` resolver field) - rust-lang/rust#155357 (Add `--remap-path-scope` as unstable in rustdoc) - rust-lang/rust#150649 (clippy fix: non_canonical_clone_impl) - rust-lang/rust#154604 (abort in core) - rust-lang/rust#154616 (Add `--quiet` flag to x.py and bootstrap to suppress output) - rust-lang/rust#155215 (Clean up `AttributeLintKind` and refactor diagnostic attribute linting) - rust-lang/rust#155228 (Check diagnostic output in incremental `cpass` and `rpass` revisions) - rust-lang/rust#155266 (Adjust release notes for post-merge feedback) - rust-lang/rust#155326 (Disallow ZST allocations with `TypedArena`.) - rust-lang/rust#155334 (docs: Use `0b1` instead of `NonZero::MIN` in `NonZero::bit_width` doctests) - rust-lang/rust#155340 (Handle nonnull pattern types in size skeleton) - rust-lang/rust#155347 (Add push_mut and new Layout methods to release notes) - rust-lang/rust#155356 (remove calls to AliasTyKind::def_id) - rust-lang/rust#155364 (Reduce diagnostic type visibilities.)

scottmcm · 2026-03-27T04:11:03Z

The Residual trait was even more experimental than Try, but now that rust-lang/rfcs#3721 is merged, I think it would make sense to require this. Technically it's not strictly required, but without it something working on <T: Try> might need an extra bound even to use a homogeneous try block with the same output type as T::Output. (Another where will of course be needed to return a differentimpl Try type still.)

cc #154391

scottmcm · 2026-03-27T04:14:03Z

 /// "foo-ness" of the residual so other types need to opt-in to interconversion.
 #[unstable(feature = "try_trait_v2", issue = "84277", old_name = "try_trait")]
- type Residual;
+ type Residual: Residual<Self::Output>;


There's a more nuanced conversation about whether this should go further and also require
Suggested change
typeResidual:Residual<Self::Output>;
typeResidual:Residual<Self::Output,TryType = Self>;
but that has a variety of implications, so I'd rather leave it for another time rather than this PR.

@scottmcm Where is that further step being discussed? And what are those implications?

IIUC, this would force Residuals to be truly colored. It's not enforced now, so, e.g., Poll currently shares a Residual with Result (Result<Infallible, E>). Someone can ? a Poll in a function returning Result without a specific FromResidual<R> impl:
fnfoo() -> Result<u8,bool>{ core::task::Poll::<Result<u16,bool>>::Ready(Ok(0))?;Ok(1)}
I guess that's not desirable because it's unexpected. If Poll had its own Residual, it would take a deliberate impl FromResidual<Poll<Result<Infallible, E>>> for Result<T, E> for the above to work.
I'm also curious to see the discussions.

I made #155368 as a place to have the discussion.

rustbot · 2026-03-28T09:26:10Z

Some changes occurred in src/tools/clippy

cc @rust-lang/clippy

rustbot · 2026-03-28T09:26:12Z

r? @petrochenkov

rustbot has assigned @petrochenkov.
They will have a look at your PR within the next two weeks and either review your PR or reassign to another reviewer.

Use r? to explicitly pick a reviewer

Why was this reviewer chosen?

The reviewer was selected based on:

Owners of files modified in this PR: compiler
compiler expanded to 69 candidates
Random selection from 12 candidates

petrochenkov · 2026-04-07T13:42:37Z

r? library

rustbot · 2026-04-07T13:42:41Z

Failed to set assignee to library: invalid assignee

Note: Only org members with at least the repository "read" role, users with write permissions, or people who have commented on the PR may be assigned.

petrochenkov · 2026-04-07T13:42:51Z

r? libs

jhpratt · 2026-04-09T02:50:06Z

cc @rust-lang/libs-api

r=me on implementation, but it's a design decision for you. imo it's more than reasonable to add this bound.

nxsaken · 2026-04-11T08:53:03Z

 /// "foo-ness" of the residual so other types need to opt-in to interconversion.
 #[unstable(feature = "try_trait_v2", issue = "84277", old_name = "try_trait")]
- type Residual;
+ type Residual: Residual<Self::Output>;


View changes since the review
Suggested change
typeResidual:Residual<Self::Output>;
typeResidual:[const]Residual<Self::Output>;

This needs more changes than just this so I'll leave it for a follow-up.

nia-e · 2026-04-15T14:45:16Z

Per the discussion in the last @rust-lang/libs-api meeting, we're happy to defer to @scottmcm on the details here and the idea seems sound. Thanks ^^

The `Residual` trait was even more experimental than `Try`, but now that RFC3721 is merged, I think it would make sense to require this.

rustbot · 2026-04-16T01:10:08Z

This PR was rebased onto a different main commit. Here's a range-diff highlighting what actually changed.

Rebasing is a normal part of keeping PRs up to date, so no action is needed—this note is just to help reviewers.

scottmcm · 2026-04-16T04:35:26Z

@bors r=jhpratt

rust-bors · 2026-04-16T04:35:30Z

📌 Commit 3efcdbc has been approved by jhpratt

It is now in the queue for this repository.

Rollup of 18 pull requests Successful merges: - #154451 (Require that a `<_ as Try>::Residual` implement the `Residual` trait) - #154595 (Emit fatal on invalid const args with nested defs) - #154599 (report the `varargs_without_pattern` lint in deps) - #154699 (`core::unicode`: Replace `Cased` table with `Lt`) - #155353 (resolve: Remove `inaccessible_ctor_reexport` resolver field) - #155357 (Add `--remap-path-scope` as unstable in rustdoc) - #150649 (clippy fix: non_canonical_clone_impl) - #154604 (abort in core) - #154616 (Add `--quiet` flag to x.py and bootstrap to suppress output) - #155215 (Clean up `AttributeLintKind` and refactor diagnostic attribute linting) - #155228 (Check diagnostic output in incremental `cpass` and `rpass` revisions) - #155266 (Adjust release notes for post-merge feedback) - #155326 (Disallow ZST allocations with `TypedArena`.) - #155334 (docs: Use `0b1` instead of `NonZero::MIN` in `NonZero::bit_width` doctests) - #155340 (Handle nonnull pattern types in size skeleton) - #155347 (Add push_mut and new Layout methods to release notes) - #155356 (remove calls to AliasTyKind::def_id) - #155364 (Reduce diagnostic type visibilities.)

Rollup merge of #154451 - scottmcm:require-residual, r=jhpratt Require that a `<_ as Try>::Residual` implement the `Residual` trait The `Residual` trait was even more experimental than `Try`, but now that rust-lang/rfcs#3721 is merged, I think it would make sense to require this. Technically it's not strictly required, but without it something working on `<T: Try>` might need an extra bound even to use a homogeneous try block with the same output type as `T::Output`. (Another `where` will of course be needed to return a *different* `impl Try` type still.) cc #154391

Rollup of 18 pull requests Successful merges: - rust-lang/rust#154451 (Require that a `<_ as Try>::Residual` implement the `Residual` trait) - rust-lang/rust#154595 (Emit fatal on invalid const args with nested defs) - rust-lang/rust#154599 (report the `varargs_without_pattern` lint in deps) - rust-lang/rust#154699 (`core::unicode`: Replace `Cased` table with `Lt`) - rust-lang/rust#155353 (resolve: Remove `inaccessible_ctor_reexport` resolver field) - rust-lang/rust#155357 (Add `--remap-path-scope` as unstable in rustdoc) - rust-lang/rust#150649 (clippy fix: non_canonical_clone_impl) - rust-lang/rust#154604 (abort in core) - rust-lang/rust#154616 (Add `--quiet` flag to x.py and bootstrap to suppress output) - rust-lang/rust#155215 (Clean up `AttributeLintKind` and refactor diagnostic attribute linting) - rust-lang/rust#155228 (Check diagnostic output in incremental `cpass` and `rpass` revisions) - rust-lang/rust#155266 (Adjust release notes for post-merge feedback) - rust-lang/rust#155326 (Disallow ZST allocations with `TypedArena`.) - rust-lang/rust#155334 (docs: Use `0b1` instead of `NonZero::MIN` in `NonZero::bit_width` doctests) - rust-lang/rust#155340 (Handle nonnull pattern types in size skeleton) - rust-lang/rust#155347 (Add push_mut and new Layout methods to release notes) - rust-lang/rust#155356 (remove calls to AliasTyKind::def_id) - rust-lang/rust#155364 (Reduce diagnostic type visibilities.)

scottmcm · 2026-03-27T04:11:03Z

The Residual trait was even more experimental than Try, but now that rust-lang/rfcs#3721 is merged, I think it would make sense to require this. Technically it's not strictly required, but without it something working on <T: Try> might need an extra bound even to use a homogeneous try block with the same output type as T::Output. (Another where will of course be needed to return a differentimpl Try type still.)

cc #154391

scottmcm · 2026-03-27T04:14:03Z

 /// "foo-ness" of the residual so other types need to opt-in to interconversion.
 #[unstable(feature = "try_trait_v2", issue = "84277", old_name = "try_trait")]
- type Residual;
+ type Residual: Residual<Self::Output>;


There's a more nuanced conversation about whether this should go further and also require
Suggested change
typeResidual:Residual<Self::Output>;
typeResidual:Residual<Self::Output,TryType = Self>;
but that has a variety of implications, so I'd rather leave it for another time rather than this PR.

@scottmcm Where is that further step being discussed? And what are those implications?

IIUC, this would force Residuals to be truly colored. It's not enforced now, so, e.g., Poll currently shares a Residual with Result (Result<Infallible, E>). Someone can ? a Poll in a function returning Result without a specific FromResidual<R> impl:
fnfoo() -> Result<u8,bool>{ core::task::Poll::<Result<u16,bool>>::Ready(Ok(0))?;Ok(1)}
I guess that's not desirable because it's unexpected. If Poll had its own Residual, it would take a deliberate impl FromResidual<Poll<Result<Infallible, E>>> for Result<T, E> for the above to work.
I'm also curious to see the discussions.

I made #155368 as a place to have the discussion.

rustbot · 2026-03-28T09:26:10Z

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rustbot · 2026-03-28T09:26:12Z

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petrochenkov · 2026-04-07T13:42:37Z

r? library

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petrochenkov · 2026-04-07T13:42:51Z

r? libs

jhpratt · 2026-04-09T02:50:06Z

cc @rust-lang/libs-api

r=me on implementation, but it's a design decision for you. imo it's more than reasonable to add this bound.

nxsaken · 2026-04-11T08:53:03Z

 /// "foo-ness" of the residual so other types need to opt-in to interconversion.
 #[unstable(feature = "try_trait_v2", issue = "84277", old_name = "try_trait")]
- type Residual;
+ type Residual: Residual<Self::Output>;


View changes since the review
Suggested change
typeResidual:Residual<Self::Output>;
typeResidual:[const]Residual<Self::Output>;

This needs more changes than just this so I'll leave it for a follow-up.

nia-e · 2026-04-15T14:45:16Z

Per the discussion in the last @rust-lang/libs-api meeting, we're happy to defer to @scottmcm on the details here and the idea seems sound. Thanks ^^

The `Residual` trait was even more experimental than `Try`, but now that RFC3721 is merged, I think it would make sense to require this.

rustbot · 2026-04-16T01:10:08Z

This PR was rebased onto a different main commit. Here's a range-diff highlighting what actually changed.

Rebasing is a normal part of keeping PRs up to date, so no action is needed—this note is just to help reviewers.

scottmcm · 2026-04-16T04:35:26Z

@bors r=jhpratt

rust-bors · 2026-04-16T04:35:30Z

📌 Commit 3efcdbc has been approved by jhpratt

It is now in the queue for this repository.

Rollup of 18 pull requests Successful merges: - #154451 (Require that a `<_ as Try>::Residual` implement the `Residual` trait) - #154595 (Emit fatal on invalid const args with nested defs) - #154599 (report the `varargs_without_pattern` lint in deps) - #154699 (`core::unicode`: Replace `Cased` table with `Lt`) - #155353 (resolve: Remove `inaccessible_ctor_reexport` resolver field) - #155357 (Add `--remap-path-scope` as unstable in rustdoc) - #150649 (clippy fix: non_canonical_clone_impl) - #154604 (abort in core) - #154616 (Add `--quiet` flag to x.py and bootstrap to suppress output) - #155215 (Clean up `AttributeLintKind` and refactor diagnostic attribute linting) - #155228 (Check diagnostic output in incremental `cpass` and `rpass` revisions) - #155266 (Adjust release notes for post-merge feedback) - #155326 (Disallow ZST allocations with `TypedArena`.) - #155334 (docs: Use `0b1` instead of `NonZero::MIN` in `NonZero::bit_width` doctests) - #155340 (Handle nonnull pattern types in size skeleton) - #155347 (Add push_mut and new Layout methods to release notes) - #155356 (remove calls to AliasTyKind::def_id) - #155364 (Reduce diagnostic type visibilities.)

Rollup merge of #154451 - scottmcm:require-residual, r=jhpratt Require that a `<_ as Try>::Residual` implement the `Residual` trait The `Residual` trait was even more experimental than `Try`, but now that rust-lang/rfcs#3721 is merged, I think it would make sense to require this. Technically it's not strictly required, but without it something working on `<T: Try>` might need an extra bound even to use a homogeneous try block with the same output type as `T::Output`. (Another `where` will of course be needed to return a *different* `impl Try` type still.) cc #154391

Rollup of 18 pull requests Successful merges: - rust-lang/rust#154451 (Require that a `<_ as Try>::Residual` implement the `Residual` trait) - rust-lang/rust#154595 (Emit fatal on invalid const args with nested defs) - rust-lang/rust#154599 (report the `varargs_without_pattern` lint in deps) - rust-lang/rust#154699 (`core::unicode`: Replace `Cased` table with `Lt`) - rust-lang/rust#155353 (resolve: Remove `inaccessible_ctor_reexport` resolver field) - rust-lang/rust#155357 (Add `--remap-path-scope` as unstable in rustdoc) - rust-lang/rust#150649 (clippy fix: non_canonical_clone_impl) - rust-lang/rust#154604 (abort in core) - rust-lang/rust#154616 (Add `--quiet` flag to x.py and bootstrap to suppress output) - rust-lang/rust#155215 (Clean up `AttributeLintKind` and refactor diagnostic attribute linting) - rust-lang/rust#155228 (Check diagnostic output in incremental `cpass` and `rpass` revisions) - rust-lang/rust#155266 (Adjust release notes for post-merge feedback) - rust-lang/rust#155326 (Disallow ZST allocations with `TypedArena`.) - rust-lang/rust#155334 (docs: Use `0b1` instead of `NonZero::MIN` in `NonZero::bit_width` doctests) - rust-lang/rust#155340 (Handle nonnull pattern types in size skeleton) - rust-lang/rust#155347 (Add push_mut and new Layout methods to release notes) - rust-lang/rust#155356 (remove calls to AliasTyKind::def_id) - rust-lang/rust#155364 (Reduce diagnostic type visibilities.)

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Require that a <_ as Try>::Residual implement Residual
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The `Residual` trait was even more experimental than `Try`, but now that RFC3721 is merged, I think it would make sense to require this.

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Require that a <_ as Try>::Residual implement Residual
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The `Residual` trait was even more experimental than `Try`, but now that RFC3721 is merged, I think it would make sense to require this.

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Require that a <_ as Try>::Residual implement Residual
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The `Residual` trait was even more experimental than `Try`, but now that RFC3721 is merged, I think it would make sense to require this.

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The `Residual` trait was even more experimental than `Try`, but now that RFC3721 is merged, I think it would make sense to require this.

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The `Residual` trait was even more experimental than `Try`, but now that RFC3721 is merged, I think it would make sense to require this.

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The `Residual` trait was even more experimental than `Try`, but now that RFC3721 is merged, I think it would make sense to require this.

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The `Residual` trait was even more experimental than `Try`, but now that RFC3721 is merged, I think it would make sense to require this.

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Require that a <_ as Try>::Residual implement Residual
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The `Residual` trait was even more experimental than `Try`, but now that RFC3721 is merged, I think it would make sense to require this.

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	typeResidual:Residual<Self::Output>;
	typeResidual:Residual<Self::Output,TryType = Self>;

	typeResidual:Residual<Self::Output>;
	typeResidual:[const]Residual<Self::Output>;

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