//! Auxiliary types used by graph verification methods.use std::{    cmp::{max, min},    collections::BTreeMap,}; use gix_error::{message, ErrorExt, Exn, Message, ResultExt}; use crate::{    file::{self},    Graph, Position, GENERATION_NUMBER_MAX,}; /// Statistics gathered while verifying the integrity of the graph as returned by [`Graph::verify_integrity()`].#[derive(Clone, Debug, Eq, PartialEq)]#[cfg_attr(feature = "serde", derive(serde::Deserialize, serde::Serialize))]pub struct Outcome {    /// The length of the longest path between any two commits in this graph.    ///    /// For example, this will be `Some(9)` for a commit graph containing 10 linear commits.    /// This will be `Some(0)` for a commit graph containing 0 or 1 commits.    /// If the longest path length is too large to fit in a [u32], then this will be [None].    pub longest_path_length: Option<u32>,    /// The total number of commits traversed.    pub num_commits: u32,    /// A mapping of `N -> number of commits with N parents`.    pub parent_counts: BTreeMap<u32, u32>,} impl Graph {    /// Traverse all commits in the graph and call `processor(&commit) -> Result<(), E>` on it while verifying checksums.    ///    /// When `processor` returns an error, the entire verification is stopped and the error returned.    pub fn verify_integrity<E>(        &self,        mut processor: impl FnMut(&file::Commit<'_>) -> Result<(), E>,    ) -> Result<Outcome, Exn<Message>>    where        E: std::error::Error + Send + Sync + 'static,    {        if self.files.len() > 256 {            // A file in a split chain can only have up to 255 base files.            return Err(message!(                "Commit-graph should be composed of at most 256 files but actually contains {} files",                self.files.len()            )            .raise());        }         let mut stats = Outcome {            longest_path_length: None,            num_commits: 0,            parent_counts: BTreeMap::new(),        };        let mut max_generation = 0u32;         // TODO: Detect duplicate commit IDs across different files. Not sure how to do this without        //   a separate loop, e.g. self.iter_sorted_ids().         let mut file_start_pos = Position(0);        for (file_index, file) in self.files.iter().enumerate() {            if usize::from(file.base_graph_count()) != file_index {                return Err(message!(                    "'{}' should have {} base graphs, but claims {} base graphs",                    file.path().display(),                    file_index,                    file.base_graph_count()                )                .raise());            }             for (base_graph_index, (expected, actual)) in self                .files                .iter()                .take(file_index)                .map(crate::File::checksum)                .zip(file.iter_base_graph_ids())                .enumerate()            {                if actual != expected {                    return Err(message!(                        "'{}' base graph at index {} should have ID {} but is {}",                        file.path().display(),                        base_graph_index,                        expected,                        actual                    )                    .raise());                }            }             let next_file_start_pos = Position(file_start_pos.0 + file.num_commits());            let file_stats = file.traverse(|commit| {                let mut max_parent_generation = 0u32;                for parent_pos in commit.iter_parents() {                    let parent_pos = parent_pos.map_err(|err| err.raise_erased())?;                    if parent_pos >= next_file_start_pos {                        return Err(message!(                            "Commit {} has parent position {parent_pos} that is out of range (should be in range 0-{})",                            commit.id(),                            Position(next_file_start_pos.0 - 1)                        )                        .raise_erased());                    }                    let parent = self.commit_at(parent_pos);                    max_parent_generation = max(max_parent_generation, parent.generation());                }                 // If the max parent generation is GENERATION_NUMBER_MAX, then this commit's                // generation should be GENERATION_NUMBER_MAX too.                let expected_generation = min(max_parent_generation + 1, GENERATION_NUMBER_MAX);                if commit.generation() != expected_generation {                    return Err(message!(                        "Commit {}'s generation should be {expected_generation} but is {}",                        commit.id(),                        commit.generation()                    )                    .raise_erased());                }                 processor(commit).or_raise_erased(|| message!("processor failed on commit {id}", id = commit.id()))?;                 Ok(())            })?;             max_generation = max(max_generation, file_stats.max_generation);            stats.num_commits += file_stats.num_commits;            for (key, value) in file_stats.parent_counts.into_iter() {                *stats.parent_counts.entry(key).or_insert(0) += value;            }            file_start_pos = next_file_start_pos;        }         stats.longest_path_length = if max_generation < GENERATION_NUMBER_MAX {            Some(max_generation.saturating_sub(1))        } else {            None        };        Ok(stats)    }}