Implement Copy, Clone, PartialEq and Eq for core::fmt::Alignment

[tmiasko]

Alignment is a fieldless exhaustive enum, so it is already possible to
clone and compare it by matching, but it is inconvenient to do so. For
example, if one would like to create a struct describing a formatter
configuration and provide a clone implementation:

pub struct Format {
    fill: char,
    width: Option<usize>,
    align: fmt::Alignment,
}

impl Clone for Format {
    fn clone(&self) -> Self {
        Format {
            align: match self.align {
                fmt::Alignment::Left => fmt::Alignment::Left,
                fmt::Alignment::Right => fmt::Alignment::Right,
                fmt::Alignment::Center => fmt::Alignment::Center,
            },
            .. *self
        }
    }
}

Derive Copy, Clone, PartialEq, and Eq for Alignment for convenience.

[rust-highfive]

r? @joshtriplett

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[joshtriplett]

Trait impls are insta-stable, so this would need an FCP.

What do folks on @rust-lang/libs-api think about this?

[yaahc]

Trait impls are insta-stable, so this would need an FCP.

What do folks on @rust-lang/libs-api think about this?

These seem reasonable, but I would the PR description to be updated with more detail including an example situation of when these impls would be useful.

[yaahc]

@rfcbot merge

[rfcbot]

Team member @yaahc has proposed to merge this. The next step is review by the rest of the tagged team members:

• @Amanieu
• @BurntSushi
• @dtolnay
• @joshtriplett
• @m-ou-se
• @yaahc

No concerns currently listed.

Once a majority of reviewers approve (and at most 2 approvals are outstanding), this will enter its final comment period. If you spot a major issue that hasn't been raised at any point in this process, please speak up!

See this document for info about what commands tagged team members can give me.

[rfcbot]

🔔 This is now entering its final comment period, as per the review above. 🔔

[rfcbot]

The final comment period, with a disposition to merge, as per the review above, is now complete.

As the automated representative of the governance process, I would like to thank the author for their work and everyone else who contributed.

This will be merged soon.

[dtolnay]

@bors r+

[bors]

📌 Commit a8acfa8 has been approved by dtolnay

[bors]

⌛ Testing commit a8acfa8 with merge 9257f5a...

[bors]

☀️ Test successful - checks-actions
Approved by: dtolnay
Pushing 9257f5a to master...

[rust-timer]

Finished benchmarking commit (9257f5a): comparison url.

Instruction count

This benchmark run did not return any relevant results for this metric.

Max RSS (memory usage)

Results

• Primary benchmarks: mixed results
• Secondary benchmarks: mixed results

	Regressions 😿 (primary)	Regressions 😿 (secondary)	Improvements 🎉 (primary)	Improvements 🎉 (secondary)	All 😿 🎉 (primary)
count1	1	2	1	2	2
mean2	1.2%	3.7%	-3.1%	-2.0%	-1.0%
max	1.2%	5.1%	-3.1%	-2.3%	-3.1%

Cycles

Results

• Primary benchmarks: 🎉 relevant improvements found
• Secondary benchmarks: mixed results

	Regressions 😿 (primary)	Regressions 😿 (secondary)	Improvements 🎉 (primary)	Improvements 🎉 (secondary)	All 😿 🎉 (primary)
count1	0	1	2	2	2
mean2	N/A	3.8%	-2.2%	-3.9%	-2.2%
max	N/A	3.8%	-2.9%	-4.0%	-2.9%

If you disagree with this performance assessment, please file an issue in rust-lang/rustc-perf.

@rustbot label: -perf-regression

Footnotes

1. number of relevant changes ↩ ↩²

2. the arithmetic mean of the percent change ↩ ↩²