How to use GDB Pretty Printer within other pointer/struct?

Question

I have a FileSystemNode struct with "pointers" to all children and the parent

struct FileSystemNode{
    current_directory_path: String,
    current_directory_name: String,
    //we need mutable and immutable access to a node
    // (from here to child and from child's child to parent)
    parent_directory: Option<Rc<RefCell<FileSystemNode>>>,
    children: Vec<Rc<RefCell<FileSystemNode>>>,
    //if size is 0, this is a directory
    size: usize
}

Due to this behaviour, GDB will recursively print every parent and child, thus going into an endless recursion.

To prevent this, I tried to start a pretty printer, which will simply skip (or replace by a member) the parents and/or children. My first try was to print a hardcoded string, just to make sure I was on the right track:

class FileSystemNodePrinter:
    def __init__(self, val):
        self.val = val
    
    def to_string(self):
        return 'test'
        
    def display_hint(self):
        return 'FileSystemNode'

However, this does absolutely nothing. The output is the same as it would be without the pretty printer. The printer is listed in the info pretty-printer output, but I cannot be sure it is using it. The output is:

$1 = Rc(strong=1, weak=0) = {value = RefCell(borrow=0) = {
    value = advent_of_code_2022::day7::FileSystemNode {
    current_directory_path: "/",
    current_directory_name: "", 
    parent_directory: core::option::Option<alloc::rc::Rc<core::cell::RefCell<advent_of_code_2022::day7::FileSystemNode>>>::none, 
    children: Vec(size=0), 
    size: 0},
    borrow = 0},
    strong = 1, weak = 0}

I assume however, the problem is FileSystemNode being within the Rc<RefCell>

Repro Steps

The rust code is:

use std::cell::RefCell;
use std::rc::Rc;

struct FileSystemNode{
    current_directory_path: String,
    current_directory_name: String,
    //we need mutable and immutable access to a node
    // (from here to child and from child's child to parent)
    parent_directory: Option<Rc<RefCell<FileSystemNode>>>,
    children: Vec<Rc<RefCell<FileSystemNode>>>,
    //if size is 0, this is a directory
    size: usize
}

impl FileSystemNode {
    pub fn new() -> FileSystemNode {
        return FileSystemNode {
            current_directory_path: String::from(""),
            current_directory_name: String::from(""),
            parent_directory: None,
            children: Vec::new(),
            size: 0
        };
    }
}

pub fn main(){
    let root = Rc::new(RefCell::new(FileSystemNode::new()));
    root.borrow_mut().current_directory_path = String::from("/");

    let node = Rc::new(RefCell::new(FileSystemNode::new()));
    node.borrow_mut().current_directory_path = String::from("/test/");
    node.borrow_mut().current_directory_name = String::from("test");
    node.borrow_mut().parent_directory = Some(Rc::clone(&root));

    root.borrow_mut().children.push(Rc::clone(&node));

    println!("");
}

My .gdbinit file is:

import sys

sys.path.insert(0, "/path/to/FileSystemNodePrettyPrinterParent")

from FileSystemNodePrettyPrinter import register_printer
register_printer(None)

end

layout next

and the full FileSystemPrettyPrinter.py is

#tmp easy pretty printer to fix endless recursion

import gdb

class FileSystemNodePrinter:
    def __init__(self, val):
        self.val = val
    
    def to_string(self):
        return 'test'
        
    def display_hint(self):
        return 'FileSystemNode'
        
        
        
        
def register_printer(objfile):
    if objfile == None:
        objfile = gdb.current_objfile()
    gdb.printing.register_pretty_printer(objfile, build_pretty_printer(), True)
    print("Registered pretty printers for UE classes")
    
def build_pretty_printer():
    pp = gdb.printing.RegexpCollectionPrettyPrinter("Custom")
    pp.add_printer("FileSystemNode", '^FileSystemNode$', FileSystemNodePrinter)
    return pp
    
register_printer(None)

(The registration process I have more or less copied from UE4).

Set the path in .gdbinit correctly, start the program and print root once it has been setup.

Answer 1

In order to match types you have to match the full path of the type with your RegEx. Something like "^yourcrate::module::path::FileSystemNode$" should work instead of the simple "^FileSystemNode$". This is to make sure you can match only the types you actually want to and not types from other crates that happen to have the same name.