mac119 opened a new pull request, #21868:
URL: https://github.com/apache/datafusion/pull/21868
## Which issue does this PR close?
Closes #10628
## Rationale for this change
Users have been asking how to walk and manipulate `LogicalPlan` trees
(as noted in #10628). The existing doc examples only cover `apply`
(closure-based
inspection) and `transform` (closure-based rewriting), but lack examples for
`TreeNodeVisitor`, `TreeNodeRewriter`, and `exists`.
## What changes are included in this PR?
1. **New example file**
`datafusion-examples/examples/query_planning/plan_walk.rs` with 5 demos:
- `TreeNode::apply` — collect all referenced table names
- `TreeNode::exists` — check for specific node types
- `TreeNodeVisitor` — structured inspection with depth tracking
- `TreeNode::transform` — rewrite filter predicates with a closure
- `TreeNodeRewriter` — structured rewrites with state tracking
2. **Enhanced LogicalPlan doc comments** with two new inline examples:
- `TreeNodeVisitor` example (node counting)
- `TreeNodeRewriter` example (filter removal)
3. **Registered** `plan_walk` in the `query_planning` example group
## Are these changes tested?
- All doc tests pass (`cargo test --doc -p datafusion-expr -- LogicalPlan`)
- Example runs successfully (`cargo run --example query_planning --
plan_walk`)
- Zero warnings on `cargo check`
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