Add and document "perf" features

[joshtriplett]

• docs(edit): Document the "perf" feature
• feat(toml): Add "perf" feature, forwarding to toml_parse?/simd

[epage]

I'm currently going through breaking changes and as part of that, I'm tempted to remove the perf feature and directly expose simd. Still trying to figure out what I want. I am a bit looser with what I expose in toml_edit because it is less likely to show up in public APIs so I can be more free in breaking it.

[joshtriplett]

@epage While you're making breaking changes, have you considered enabling simd by default, and letting people opt out of it if they really need to? I would expect far more people want the performance.

[epage]

Looking at #945, I was wondering if simd made enough of a difference to be worth keeping (along with unsafe).

At least with simd, it only makes a performance difference and in a way that it should be safe to make it a default feature without "breaking" anyone.

I'm also split on how much defaults should be minimal vs all the bells and whistles. Two very different users who can walk away with very different negative impressions based on the result.

[joshtriplett]

At least with simd, it only makes a performance difference and in a way that it should be safe to make it a default feature without "breaking" anyone.

That would be my reaction as well. I think there's a lot of value to defaulting to performance, rather than expecting people to opt in, when in practice the vast vast majority of people should have it enabled.

[epage]

On a similar note, I've been wondering if the display feature should be off by default for toml as most people likely don't write out TOML.

[coveralls]

Pull Request Test Coverage Report for Build 15641038728

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 69.35%

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Totals
Change from base Build 15621376400:	0.0%
Covered Lines:	6202
Relevant Lines:	8943

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💛 - Coveralls

[joshtriplett]

On a similar note, I've been wondering if the display feature should be off by default for toml as most people likely don't write out TOML.

On the theory that if you want to write out TOML you probably want toml_edit?

[epage]

For json, a common use cases is to read and write as you are transmitting and receiving data.

For machines, TOML tends to be read only. Yes, then there is also the number of ese cases left that need format preserving writes with toml_edit. That leaves very few use cases for writing with toml (like Cargo.lock, or cargo publish writing a new Cargo.toml) and so I wonder if we should trim that out.

[joshtriplett]

@epage Making the display feature no longer enabled by default, in toml, seems pretty reasonable by that argument. Along with a comment on that feature saying "if you're enabling this, you might want toml_edit instead".