Add a mutable visitor

[lovasoa]

Happy new year 🥳

This is a follow-up on #765 .

This adds the ability to mutate the AST as it is visited. I didn't remove the old immutable-only visitor trait.
Previously, only visitors taking an immutable reference to the visited structures were allowed.

[coveralls]

Pull Request Test Coverage Report for Build 3818810193

• 0 of 28 (0.0%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage decreased (-0.2%) to 85.875%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
src/ast/visitor.rs	0	28	0.0%

Totals
Change from base Build 3801061789:	-0.2%
Covered Lines:	13102
Relevant Lines:	15257

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💛 - Coveralls

[alamb]

Looks good to me -- thank you @lovasoa

Happy new year to you as well 🌟

cc @tustvold and @AugustoFKL

Prior to releasing this code, I think we need to bump the version of the derive crate (semantically compatible), and make sqlparser depend on that higher version (to get the new derive_mut visitor)

[lovasoa]

@alamb, I think taking the values by ownership would require a significant amount of work, and not bring performance gains.
For the version bumps, I'll make a new commit.

[alamb]

@alamb, I think taking the values by ownership would require a significant amount of work, and not bring performance gains.

I don't think I did a good job explaining the alternative

The idea is to use something like https://github.com/apache/arrow-datafusion/blob/master/datafusion/expr/src/expr_rewriter.rs

However, I don't feel strongly about it -- the mutation approach looks good to me.

For the version bumps, I'll make a new commit.

Thank you 3ac3c67 looks good

[alamb]

I made a small toy version to compare the two, the by-value version is 4x slower even with a small struct:

BTW I think the more appropriate comparison is with release mode, but even then the example is 2x slower with ownership

https://play.rust-lang.org/?version=stable&mode=release&edition=2021

[lovasoa]

Great, thanks for merging! I'll use that in sqlpage. Do you think you can release a new version on crates.io soon?

[alamb]

Great, thanks for merging! I'll use that in sqlpage. Do you think you can release a new version on crates.io soon?

Yes I will go make one now

[alamb]

Preparing one now: #786

[alamb]

https://crates.io/crates/sqlparser/0.30.0 ✅