Make `Default` const and add some `const Default` impls #134628

estebank · 2024-12-21T20:25:57Z

Full list of impl const Default types:

()
bool
char
std::ascii::Char
usize
u8
u16
u32
u64
u128
i8
i16
i32
i64
i128
f16
f32
f64
f128
std::marker::PhantomData
Option
std::iter::Empty
std::ptr::Alignment
&[T]
&mut [T]
&str
&mut str
String
Vec

rustbot · 2024-12-21T20:26:04Z

rustbot has assigned @wesleywiser.
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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estebank · 2024-12-21T20:26:35Z

Made this for some experiments with default field values, might as well put it somewhere visible as it seems like an obvious next step for the const traits effort.

compiler-errors · 2024-12-21T20:31:31Z

Please make sure this is assigned to someone on @rust-lang/project-const-traits if you take this out of draft.

tests/ui/const-generics/std/const-generics-alloc.rs

bors · 2024-12-24T07:04:27Z

☔ The latest upstream changes (presumably #134716) made this pull request unmergeable. Please resolve the merge conflicts.

estebank · 2024-12-25T00:14:50Z

r? @oli-obk

Let me know what would be needed to make this merge-ready.

fee1-dead · 2024-12-30T15:00:19Z

I'd like to block this on #133999.

rustbot · 2025-02-12T17:48:55Z

Some changes occurred in src/tools/clippy

cc @rust-lang/clippy

bors · 2025-03-02T02:10:52Z

☔ The latest upstream changes (presumably #137752) made this pull request unmergeable. Please resolve the merge conflicts.

apiraino · 2025-03-06T15:53:34Z

This was blocked on #133999 (comment) which is now closed.

@fee1-dead are you still interested in working on a follow-up to #133999 or are there other plans? Or no plans for now?

Just to get a clearer picture of the progress here :-) Thanks

cc @oli-obk

estebank · 2025-07-01T17:20:16Z

src/tools/clippy/tests/ui/or_fun_call.stderr

-error: function call inside of `unwrap_or`
-  --> tests/ui/or_fun_call.rs:409:21
-   |
-LL |     let _ = opt_foo.unwrap_or(Foo { val: String::default() });
-   |                     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `unwrap_or_else(|| Foo { val: String::default() })`


Should this clippy lint have a check that the value is const constructable in a stable way (which would revert this output change)?

yes, otherwise users get clippy lints they cannot address

Isn't it the other way around: users don't get a lint to do unwrap_or_else(NowConstThing) because NowConstThing is now detected as const by clippy, even if it isn't const in stable? So it's not that the users get unactionable feedback, but rather that they don't get feedback actionable under older versions of the std. Does rustc take advantage of things that are unstably const for const folding on stable?

Right. It's missing lint, not a false alarm. Unfortunate, but not the end of the world

library/core/src/cell.rs

oli-obk

r=me with clippy lint fixed and commit squashed

Full list of `impl const Default` types: - () - bool - char - Cell - std::ascii::Char - usize - u8 - u16 - u32 - u64 - u128 - i8 - i16 - i32 - i64 - i128 - f16 - f32 - f64 - f128 - std::marker::PhantomData<T> - Option<T> - std::iter::Empty<T> - std::ptr::Alignment - &[T] - &mut [T] - &str - &mut str - String - Vec<T>

oli-obk · 2025-07-08T05:16:23Z

@bors r+

bors · 2025-07-08T05:16:27Z

📌 Commit 8f8099f has been approved by oli-obk

It is now in the queue for this repository.

Make `Default` const and add some `const Default` impls Full list of `impl const Default` types: - () - bool - char - std::ascii::Char - usize - u8 - u16 - u32 - u64 - u128 - i8 - i16 - i32 - i64 - i128 - f16 - f32 - f64 - f128 - std::marker::PhantomData<T> - Option<T> - std::iter::Empty<T> - std::ptr::Alignment - &[T] - &mut [T] - &str - &mut str - String - Vec<T>

Rollup of 6 pull requests Successful merges: - #134628 (Make `Default` const and add some `const Default` impls) - #143555 (Don't mark `#[target_feature]` safe fns as unsafe in rustdoc JSON.) - #143600 (Update intro blurb in `wasm32-wasip1` docs) - #143603 (Clarify the meaning of `AttributeOrder::KeepFirst` and `AttributeOrder::KeepLast`) - #143620 (fix: Remove newline from multiple crate versions note) - #143622 (Add target maintainer information for mips64-unknown-linux-muslabi64) r? `@ghost` `@rustbot` modify labels: rollup

bors · 2025-07-08T14:04:44Z

⌛ Testing commit 8f8099f with merge f838cbc...

bors · 2025-07-08T17:12:10Z

☀️ Test successful - checks-actions
Approved by: oli-obk
Pushing f838cbc to master...

Rollup of 6 pull requests Successful merges: - #134628 (Make `Default` const and add some `const Default` impls) - #143555 (Don't mark `#[target_feature]` safe fns as unsafe in rustdoc JSON.) - #143600 (Update intro blurb in `wasm32-wasip1` docs) - #143603 (Clarify the meaning of `AttributeOrder::KeepFirst` and `AttributeOrder::KeepLast`) - #143620 (fix: Remove newline from multiple crate versions note) - #143622 (Add target maintainer information for mips64-unknown-linux-muslabi64) r? `@ghost` `@rustbot` modify labels: rollup

github-actions · 2025-07-08T17:15:18Z

What is this?

This is an experimental post-merge analysis report that shows differences in test outcomes between the merged PR and its parent PR.

Comparing 040e2f8 (parent) -> f838cbc (this PR)

Test differences

Show 204 test diffs

Stage 1

[ui] tests/ui/traits/const-traits/const-traits-alloc.rs: [missing] -> pass (J0)
[ui] tests/ui/traits/const-traits/const-traits-core.rs: [missing] -> pass (J0)

Stage 2

[ui] tests/ui/traits/const-traits/const-traits-alloc.rs: [missing] -> pass (J1)
[ui] tests/ui/traits/const-traits/const-traits-core.rs: [missing] -> pass (J1)

Additionally, 200 doctest diffs were found. These are ignored, as they are noisy.

Job group index

Test dashboard

Run

cargo run --manifest-path src/ci/citool/Cargo.toml -- \
    test-dashboard f838cbc06de60819faff3413f374706b74824ca2 --output-dir test-dashboard

And then open test-dashboard/index.html in your browser to see an overview of all executed tests.

Job duration changes

x86_64-apple-2: 3058.6s -> 3983.6s (30.2%)
dist-apple-various: 9552.8s -> 7546.0s (-21.0%)
x86_64-gnu-aux: 6004.0s -> 6809.0s (13.4%)
dist-x86_64-musl: 7212.6s -> 8115.8s (12.5%)
x86_64-apple-1: 7022.5s -> 7529.9s (7.2%)
dist-sparcv9-solaris: 5306.9s -> 4928.4s (-7.1%)
test-various: 4689.0s -> 5000.5s (6.6%)
dist-s390x-linux: 5116.6s -> 4780.2s (-6.6%)
aarch64-gnu: 6192.3s -> 6595.1s (6.5%)
tidy: 70.1s -> 74.6s (6.4%)

How to interpret the job duration changes?

Job durations can vary a lot, based on the actual runner instance
that executed the job, system noise, invalidated caches, etc. The table above is provided
mostly for t-infra members, for simpler debugging of potential CI slow-downs.

rust-timer · 2025-07-08T18:23:48Z

Finished benchmarking commit (f838cbc): comparison URL.

Overall result: ❌ regressions - no action needed

@rustbot label: -perf-regression

Instruction count

Our most reliable metric. Used to determine the overall result above. However, even this metric can be noisy.

	mean	range	count
Regressions ❌ (primary)	1.5%	[1.5%, 1.5%]	1
Regressions ❌ (secondary)	1.5%	[1.5%, 1.5%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	1.5%	[1.5%, 1.5%]	1

Max RSS (memory usage)

Results (primary -4.2%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-4.2%	[-4.2%, -4.2%]	1
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-4.2%	[-4.2%, -4.2%]	1

Cycles

Results (primary -0.4%, secondary -4.2%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

	mean	range	count
Regressions ❌ (primary)	2.3%	[2.3%, 2.3%]	1
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-3.0%	[-3.0%, -3.0%]	1
Improvements ✅ (secondary)	-4.2%	[-4.2%, -4.2%]	1
All ❌✅ (primary)	-0.4%	[-3.0%, 2.3%]	2

Binary size

Results (secondary 0.0%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	0.0%	[0.0%, 0.0%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-	-	0

Bootstrap: 467.351s -> 466.242s (-0.24%)
Artifact size: 372.36 MiB -> 372.32 MiB (-0.01%)

rustbot assigned wesleywiser Dec 21, 2024

rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. T-libs Relevant to the library team, which will review and decide on the PR/issue. labels Dec 21, 2024

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estebank force-pushed the const-default branch from f36f4d5 to 00b0c75 Compare December 22, 2024 01:59

oli-obk reviewed Dec 22, 2024

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tests/ui/const-generics/std/const-generics-alloc.rs Outdated Show resolved Hide resolved

estebank force-pushed the const-default branch from 00b0c75 to d7cfdf5 Compare December 22, 2024 20:30

estebank force-pushed the const-default branch from d7cfdf5 to 4f6558b Compare December 25, 2024 00:13

rustbot assigned oli-obk and unassigned wesleywiser Dec 25, 2024

fee1-dead mentioned this pull request Dec 30, 2024

Prepare const traits for stabilization rust-lang/rust-project-goals#106

Open

14 tasks

fee1-dead added the S-blocked Status: Blocked on something else such as an RFC or other implementation work. label Dec 30, 2024

This was referenced Jan 16, 2025

Breakage related to default field values (RFC 3681) obi1kenobi/cargo-semver-checks#993

Open

Tracking issue for RFC 3681: Default field values #132162

Open

estebank added F-const_trait_impl `#![feature(const_trait_impl)]` F-default_field_values `#![feature(default_field_values)]` labels Jan 18, 2025

compiler-errors mentioned this pull request Jan 19, 2025

[generic_assert] "Constify" the Debug trait #135712

Closed

estebank force-pushed the const-default branch from 3a03fb5 to 78db9d1 Compare February 12, 2025 02:39

estebank marked this pull request as ready for review February 12, 2025 02:39

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estebank force-pushed the const-default branch from 5deb7c8 to 37eb628 Compare July 1, 2025 17:15

estebank commented Jul 1, 2025

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fmease reviewed Jul 1, 2025

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estebank force-pushed the const-default branch from c8e3810 to a8848a5 Compare July 3, 2025 18:22

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estebank force-pushed the const-default branch from a8848a5 to 4069e12 Compare July 3, 2025 18:40

estebank added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. and removed S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. labels Jul 3, 2025

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estebank added 2 commits July 7, 2025 22:09

Account for const stability in clippy when checking constness

8f8099f

estebank force-pushed the const-default branch from 4069e12 to 8f8099f Compare July 7, 2025 23:07

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 Jul 8, 2025

matthiaskrgr mentioned this pull request Jul 8, 2025

Rollup of 6 pull requests #143627

Closed

oli-obk mentioned this pull request Jul 8, 2025

Implement Default for &Option #140808

Open

bors added the merged-by-bors This PR was explicitly merged by bors. label Jul 8, 2025

bors merged commit f838cbc into rust-lang:master Jul 8, 2025
12 checks passed

rustbot added this to the 1.90.0 milestone Jul 8, 2025

Make Default const and add some const Default impls #134628

Make Default const and add some const Default impls #134628

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Test differences

Stage 1

Stage 2

Job duration changes

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rust-timer commented Jul 8, 2025

Overall result: ❌ regressions - no action needed

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Make `Default` const and add some `const Default` impls #134628

Make `Default` const and add some `const Default` impls #134628