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Make some Clone impls const #91804

Merged
merged 1 commit into from
Mar 10, 2022
Merged

Make some Clone impls const #91804

merged 1 commit into from
Mar 10, 2022

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lilasta
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@lilasta lilasta commented Dec 11, 2021 •
edited

Tracking issue: #91805
Clone::clone_from and some impls (Option, Result) bounded on ~const Drop.

// core::clone
impl const Clone for INTEGER
impl const Clone for FLOAT
impl const Clone for bool
impl const Clone for char
impl const Clone for !
impl<T: ?Sized> const Clone for *const T
impl<T: ?Sized> const Clone for *mut T
impl<T: ?Sized> const Clone for &T

// core::option
impl<T> const Clone for Option<T>
where
    T: ~const Clone + ~const Drop

// core::result
impl<T, E> const Clone for Result<T, E>
where
    T: ~const Clone + ~const Drop,
    E: ~const Clone + ~const Drop,

// core::convert
impl const Clone for Infallible

// core::ptr
impl<T: ?Sized> const Clone for NonNull<T>
impl<T: ?Sized> const Clone for Unique<T>

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r? @joshtriplett

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@rust-highfive rust-highfive added the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label Dec 11, 2021
@lilasta lilasta changed the title Make Clone impls const Make some Clone impls const Dec 11, 2021
@lilasta lilasta mentioned this pull request Dec 11, 2021
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@apiraino apiraino added the T-libs Relevant to the library team, which will review and decide on the PR/issue. label Dec 14, 2021
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camelid commented Jan 25, 2022

r? @oli-obk maybe?

oli-obk
oli-obk reviewed Jan 26, 2022
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library/core/src/option.rs
#[rustc_const_unstable(feature = "const_clone", issue = "91805")]
impl<T> const Clone for Option<T>
where
T: ~const Clone + ~const Drop,
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Does this change the way rustdoc renders it?

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Before:
image
After:
image

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ah yea, there's a pending fix for the missing space, but the additional Drop bound is really confusing for users and we should probably figure out out story there (both for documentation and explanation) before we expose it

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Will all such cases need to be explained in the future? It seems a bit hard... I think it would be nice if we could switch displaying of ~const (and ~const Drop) bound...

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Yea, I'm unsure about ~const bounds in general, we should probably talk to the rustdoc team to figure out how it should display.

For ~const Drop I think we should just hide it from rustdoc. That bound is pretty much useless to see for anyone. We could potentially add a small symbol to the generic param that has a ~const Drop bound. Otherwise I fear that the useful bounds may get drowned out

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@lilasta lilasta Jan 30, 2022 •
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T: ~const Drop seems to mean "T doesn't require non-const Drop to destruct the value", not "T implements ~const Drop". For example, primitive types don't implement const Drop but are destructible at compile-time. Anyway, the point is that this is mostly needed in code that destructs values at compile-time and is implemented using generics.

The determination seems to be implemented here:
https://github.com/rust-lang/rust/blob/master/compiler/rustc_const_eval/src/transform/check_consts/qualifs.rs#L140

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T: ~const Drop seems to mean "T doesn't require non-const Drop to destruct the value"

I'm a bit confused about what you mean. Do you mean "T must be able to be Droped at compile-time"?

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Yes. I'm sorry for confusing you.

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@camelid camelid Feb 3, 2022 •
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What does the ~ mean? I thought ~const meant "maybe const" rather than "definitely const", but I may have misunderstood.

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It means "const if whatever the bound is on is in a const context". So if it's on a generic param of a const fn, calling that const fn in a const item or other const context requires the generic param to implement the trait constly, in regular runtime code it just requires the trait to be implemented with no requirement about constness at all

@oli-obk oli-obk added S-blocked Status: Marked as blocked ❌ on something else such as an RFC or other implementation work. and removed S-blocked Status: Marked as blocked ❌ on something else such as an RFC or other implementation work. labels Mar 2, 2022
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oli-obk commented Mar 9, 2022

This should be hidden from rustdoc now, and it doesn't introduce any new bounds that would not be hidden, so

@bors r+ rollup

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bors commented Mar 9, 2022

📌 Commit 6620244 has been approved by oli-obk

@bors bors added S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Mar 9, 2022
matthiaskrgr added a commit to matthiaskrgr/rust that referenced this pull request Mar 9, 2022
@matthiaskrgr
Rollup merge of rust-lang#91804 - woppopo:const_clone, r=oli-obk
0301ee8 
Make some `Clone` impls `const`

Tracking issue: rust-lang#91805
`Clone::clone_from` and some impls (Option, Result) bounded on `~const Drop`.

```rust
// core::clone
impl const Clone for INTEGER
impl const Clone for FLOAT
impl const Clone for bool
impl const Clone for char
impl const Clone for !
impl<T: ?Sized> const Clone for *const T
impl<T: ?Sized> const Clone for *mut T
impl<T: ?Sized> const Clone for &T

// core::option
impl<T> const Clone for Option<T>
where
    T: ~const Clone + ~const Drop

// core::result
impl<T, E> const Clone for Result<T, E>
where
    T: ~const Clone + ~const Drop,
    E: ~const Clone + ~const Drop,

// core::convert
impl const Clone for Infallible

// core::ptr
impl<T: ?Sized> const Clone for NonNull<T>
impl<T: ?Sized> const Clone for Unique<T>
```
@matthiaskrgr matthiaskrgr mentioned this pull request Mar 9, 2022
Closed
matthiaskrgr added a commit to matthiaskrgr/rust that referenced this pull request Mar 9, 2022
@matthiaskrgr
Rollup merge of rust-lang#91804 - woppopo:const_clone, r=oli-obk
fe6ad3c 
Make some `Clone` impls `const`

Tracking issue: rust-lang#91805
`Clone::clone_from` and some impls (Option, Result) bounded on `~const Drop`.

```rust
// core::clone
impl const Clone for INTEGER
impl const Clone for FLOAT
impl const Clone for bool
impl const Clone for char
impl const Clone for !
impl<T: ?Sized> const Clone for *const T
impl<T: ?Sized> const Clone for *mut T
impl<T: ?Sized> const Clone for &T

// core::option
impl<T> const Clone for Option<T>
where
    T: ~const Clone + ~const Drop

// core::result
impl<T, E> const Clone for Result<T, E>
where
    T: ~const Clone + ~const Drop,
    E: ~const Clone + ~const Drop,

// core::convert
impl const Clone for Infallible

// core::ptr
impl<T: ?Sized> const Clone for NonNull<T>
impl<T: ?Sized> const Clone for Unique<T>
```
@matthiaskrgr matthiaskrgr mentioned this pull request Mar 9, 2022
Closed
Dylan-DPC added a commit to Dylan-DPC/rust that referenced this pull request Mar 9, 2022
@Dylan-DPC
Rollup merge of rust-lang#91804 - woppopo:const_clone, r=oli-obk
ed0ed70 
Make some `Clone` impls `const`

Tracking issue: rust-lang#91805
`Clone::clone_from` and some impls (Option, Result) bounded on `~const Drop`.

```rust
// core::clone
impl const Clone for INTEGER
impl const Clone for FLOAT
impl const Clone for bool
impl const Clone for char
impl const Clone for !
impl<T: ?Sized> const Clone for *const T
impl<T: ?Sized> const Clone for *mut T
impl<T: ?Sized> const Clone for &T

// core::option
impl<T> const Clone for Option<T>
where
    T: ~const Clone + ~const Drop

// core::result
impl<T, E> const Clone for Result<T, E>
where
    T: ~const Clone + ~const Drop,
    E: ~const Clone + ~const Drop,

// core::convert
impl const Clone for Infallible

// core::ptr
impl<T: ?Sized> const Clone for NonNull<T>
impl<T: ?Sized> const Clone for Unique<T>
```
@Dylan-DPC Dylan-DPC mentioned this pull request Mar 9, 2022
Closed
@matthiaskrgr matthiaskrgr mentioned this pull request Mar 9, 2022
Merged
bors added a commit to rust-lang-ci/rust that referenced this pull request Mar 10, 2022
@bors
Auto merge of rust-lang#94787 - matthiaskrgr:rollup-yyou15f, r=matthi…
01ad0ad 
…askrgr

Rollup of 8 pull requests

Successful merges:

 - rust-lang#91804 (Make some `Clone` impls `const`)
 - rust-lang#92541 (Mention intent of `From` trait in its docs)
 - rust-lang#93057 (Add Iterator::collect_into)
 - rust-lang#94739 (Suggest `if let`/`let_else` for refutable pat in `let`)
 - rust-lang#94754 (Warn users about `||` in let chain expressions)
 - rust-lang#94763 (Add documentation about lifetimes to thread::scope.)
 - rust-lang#94768 (Ignore `close_read_wakes_up` test on SGX platform)
 - rust-lang#94772 (Add miri to the well known conditional compilation names and values)

Failed merges:

r? `@ghost`
`@rustbot` modify labels: rollup
@bors bors merged commit c025962 into rust-lang:master Mar 10, 2022
@rustbot rustbot added this to the 1.61.0 milestone Mar 10, 2022
@lilasta lilasta deleted the const_clone branch March 10, 2022 12:42
yvt added a commit to r3-os/r3 that referenced this pull request Mar 21, 2022
@yvt
refactor: use the default implementation of clone_from in `impl con…
388d3ce 
…st Clone`

`Clone::clone_from` gained `#[default_method_body_is_const]` in
[rust-lang/rust#91804][1].

n.b. `vec.rs` is shared by `r3_core` and `r3_kernel` (via a symbolic
link), hence the lack of a scope in the commit message headline.

[1]: rust-lang/rust#91804
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