Generating copy-on-rewrite logic

[systay]

Description

Adds a new syntax tree rewrite utility. It makes it possible to share parts of the syntax tree with the original, so it should decrease memory pressure somewhat during planning. It also traverses the tree only once to do both operations, before we first needed to clone the full tree and only after could we rewrite it.

Additionally, it can report back to the user which nodes got cloned, which makes it possible to copy semantic information between the two trees.

Related Issue(s)

Checklist

• "Backport to:" labels have been added if this change should be back-ported
• Tests were added or are not required
• Documentation was added or is not required

[vitess-bot]

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[systay]

comment

[systay]

Maybe we should use a recovered panic here instead of setting a boolean and checking it everywhere

[frouioui]

I thought that recover was a source of performance loss

[vmg]

Looks great. I discussed with @systay the unified interface for pre/post and I think this is a great design!