alamb commented on code in PR #20346:
URL: https://github.com/apache/datafusion/pull/20346#discussion_r2847432128
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datafusion/optimizer/src/optimizer.rs:
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@@ -88,8 +88,35 @@ pub trait OptimizerRule: Debug {
true
}
- /// Try to rewrite `plan` to an optimized form, returning
`Transformed::yes`
- /// if the plan was rewritten and `Transformed::no` if it was not.
+ /// Try to rewrite `plan` to an optimized form, returning
[`Transformed::yes`]
+ /// if the plan was rewritten and [`Transformed::no`] if it was not.
+ ///
+ /// # Notes for implementations:
+ ///
+ /// ## Return the same plan if no changes were made
+ ///
+ /// If there are no suitable transformations for the input plan,
+ /// the optimizer should simply return it unmodified.
+ ///
+ /// The optimizer will call `rewrite` several times until a fixed point is
+ /// reached, so it is important that `rewrite` return [`Transformed::no`]
if
+ /// the output is the same.
+ ///
+ /// ## Matching on functions
+ ///
+ /// The rule should avoid function-specific transformations, and instead
use
+ /// methods on [`ScalarUDFImpl`] and [`AggregateUDFImpl`]. Specifically,
the
Review Comment:
This is a great call -- added in 05f8ca177
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