Library guide / DiffMarkdown

Diff

Tree-to-tree and index-to-worktree diffs, blob patches, and the DiffEntry model the grit CLI renders.

grit_lib::diff grit_lib::diffing grit_lib::porcelain::status

Diffing in grit-lib centers on diff and the diffing module view. Results are DiffEntry rows with a DiffStatus letter (M, A, D, …), paths, modes, and object ids — the same shape grit diff and porcelain::status use before formatting output.

Tree-to-tree

diff_trees compares two tree objects recursively and returns changed paths. Pass None for either side to diff against an empty tree. diff_trees_show_tree_entries can emit tree objects themselves (Git’s diff-tree -t behavior).

Commit-to-commit diffs resolve each commit’s tree with parse_commit, then call diff_trees on the parent and child trees.

Index-to-worktree

diff_index_to_worktree compares the index to files on disk. diff_index_to_worktree_with_options adds index mtime, submodule/gitlink handling, broken-gitlink detection, and an optional repository git-dir override. porcelain::add::stage uses diff_index_to_worktree_for_staging internally so staging sees the same dirty paths as status.

Blob diffs

For a single modified file, read old and new bytes from Odb and pass them to unified_diff (histogram algorithm, Git-compatible hunks). The CLI builds human, --json, and --markdown views from DiffEntry lists plus optional unified bodies.

Porcelain models

Status — combines index vs HEAD and index vs worktree scans into structured sections (the CLI maps them to default / --json / --markdown output).
Add — uses diff results to decide which paths to hash and stage.
Diff command — tree-to-tree for commit ranges, index-to-worktree for uncommitted changes, then blob-level rendering for text files.

//! Tree-to-tree, index-to-worktree, and blob diffs used by porcelain and the CLI. //! //! Source for the library guide "Diff" page (included in the docs site). use grit_lib::diff::{diff_index_to_worktree, diff_trees, unified_diff, DiffEntry, DiffStatus}; use grit_lib::objects::{parse_commit, ObjectId}; use grit_lib::repo::Repository; use grit_lib::state::resolve_head; use std::path::{Path, PathBuf}; fn open_repo(root: &Path) -> Result<Repository, grit_lib::error::Error> { let git_dir = if root.join(".git").is_dir() { root.join(".git") } else { root.to_path_buf() }; let work_tree = if root.join(".git").is_dir() { Some(root) } else { None }; Repository::open(&git_dir, work_tree) } fn tree_oid(repo: &Repository, commit: &ObjectId) -> Result<ObjectId, grit_lib::error::Error> { let obj = repo.odb.read(commit)?; Ok(parse_commit(&obj.data)?.tree) } fn print_name_status(entries: &[DiffEntry]) { for entry in entries { let letter = entry.status.letter(); let path = entry.path(); if entry.status == DiffStatus::Renamed { if let (Some(old), Some(new)) = (&entry.old_path, &entry.new_path) { println!("{letter}\t{old}\t{new}"); continue; } } println!("{letter}\t{path}"); } } fn main() -> Result<(), grit_lib::error::Error> { let root = std::env::args() .nth(1) .map(PathBuf::from) .or_else(|| std::env::current_dir().ok()) .ok_or_else(|| grit_lib::error::Error::Message("missing repository path".into()))?; let repo = open_repo(&root)?; let head = resolve_head(&repo.git_dir)?; let new_commit = head .oid() .cloned() .ok_or_else(|| grit_lib::error::Error::Message("HEAD has no commit".into()))?; let new_obj = repo.odb.read(&new_commit)?; let new_commit_data = parse_commit(&new_obj.data)?; let parent = new_commit_data .parents .first() .copied() .ok_or_else(|| grit_lib::error::Error::Message("need a commit with a parent".into()))?; let old_tree = tree_oid(&repo, &parent)?; let new_tree = new_commit_data.tree; let tree_changes = diff_trees(&repo.odb, Some(&old_tree), Some(&new_tree), "")?; println!("tree_diff_begin"); print_name_status(&tree_changes); println!("tree_diff_end"); if let Some(wt) = repo.work_tree.as_deref() { let mut index = repo.load_index()?; let wt_changes = diff_index_to_worktree(&repo.odb, &mut index, wt, false, false)?; println!("index_worktree_dirty={}", !wt_changes.is_empty()); } if let (Some(entry),) = (tree_changes.first(),) { if entry.status == DiffStatus::Modified { let old_blob = repo.odb.read(&entry.old_oid)?.data; let new_blob = repo.odb.read(&entry.new_oid)?.data; let old_text = String::from_utf8_lossy(&old_blob); let new_text = String::from_utf8_lossy(&new_blob); let old_path = entry.old_path.as_deref().unwrap_or(entry.path()); let new_path = entry.new_path.as_deref().unwrap_or(entry.path()); let patch = unified_diff(&old_text, &new_text, old_path, new_path, 3, false, false); let hunk_lines = patch .lines() .filter(|l| l.starts_with('-') || l.starts_with('+')) .count(); println!("blob_unified_hunk_lines={hunk_lines}"); } } Ok(()) }