cargo-dry4rust 0.4.0

A cargo subcommand that detects duplicate and near-duplicate code blocks in Rust codebases using AST normalization
Documentation 
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// Copyright (c) 2026 Matjaz Domen Pecan
// Copyright 2026 Umberto Gotti <umberto.gotti@umbertogotti.dev>
// Licensed under the MIT License
// SPDX-License-Identifier: MIT

use std::collections::HashSet;

use crate::node::NodeKind;
use crate::node::NormalizedNode;
use crate::node::PlaceholderKind;

/// Gathers every placeholder occurrence in first-occurrence depth-first order,
/// deduplicating by (kind, old index) so a placeholder is recorded once.
pub struct PlaceholderOrderCollector {
    order: Vec<(PlaceholderKind, usize)>,
    seen: HashSet<(PlaceholderKind, usize)>,
}

impl PlaceholderOrderCollector {
    #[must_use]
    pub fn new() -> Self {
        Self {
            order: Vec::new(),
            seen: HashSet::new(),
        }
    }

    /// Visit `node` and its descendants, recording each placeholder the first
    /// time it is seen.
    pub fn collect(&mut self, node: &NormalizedNode) {
        if let NodeKind::Placeholder(kind, idx)
        | NodeKind::PatPlaceholder(kind, idx)
        | NodeKind::TypePlaceholder(kind, idx) = &node.kind
            && self.seen.insert((*kind, *idx))
        {
            self.order.push((*kind, *idx));
        }
        for child in &node.children {
            self.collect(child);
        }
    }

    #[must_use]
    pub fn into_order(self) -> Vec<(PlaceholderKind, usize)> {
        self.order
    }
}

impl Default for PlaceholderOrderCollector {
    fn default() -> Self {
        Self::new()
    }
}