How rustc mutate parent node AST

I am trying to design the data structure of an AST, I found that a lot of transform action(or visit) maybe need to access or change to the parent node of the current AST node, but have a mutate reference to the parent node in AST seems not a good idea (because lifetime). I want to know how rustc compiler handles the need for some transform needed to access to the parent node ?
I took a look into rustc source code, and it seems does not have a reference to the parent, and rustc_ast::visit module seems do not provide context for accessing parent node.

AFAIK rustc does not modify the AST after creating it.

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The AST is mutated by macro expansion. HIR is immutable though.

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