Module diff 

Diff machinery — compare trees, index entries, and working tree files.

Overview

This module provides the core diffing infrastructure shared by diff, diff-index, status, log, show, commit, and merge.

Levels of comparison

1. Tree-to-tree — compare two tree objects (e.g. for log/show).
2. Tree-to-index — compare a tree (usually HEAD) against the index (staged changes, used by diff --cached and status).
3. Index-to-worktree — compare index against the working directory (unstaged changes, used by diff and status).

Content diff

Line-level diffing uses the similar crate (Myers, patience, minimal) and, for Git’s histogram algorithm, imara-diff for output compatible with upstream Git. Output formats: unified patch, raw (:old-mode new-mode ...), stat, numstat.

Structs

DiffEntry

A single diff entry representing one changed path.

DiffIndexToWorktreeOptions

Additional inputs for diff_index_to_worktree_with_options.

SubmodulePorcelainFlags

Submodule dirty bits aligned with Git’s DIRTY_SUBMODULE_* / porcelain v2 S??? token.

Enums

DiffStatus

The kind of change between two sides of a diff.

Constants

GIT_DIFF_DEFAULT_BREAK_SCORE

Default break threshold (DEFAULT_BREAK_SCORE in diffcore.h), internal 0–GIT_DIFF_MAX_SCORE scale.

GIT_DIFF_DEFAULT_MERGE_SCORE_AFTER_BREAK

Default merge threshold after a break (DEFAULT_MERGE_SCORE in diffcore.h): pairs broken for rename/copy but not consumed are merged back when deletion-weight is below this (60% by default).

GIT_DIFF_MAX_SCORE

Internal maximum diff score used by Git rename/break heuristics (MAX_SCORE in diffcore.h).

ZERO_OID

The zero (null) object ID used for “no object” in diff output.

Functions

anchored_unified_diff

Compute a unified diff with anchored lines.

count_changes

Count insertions and deletions between two strings.

count_changes_with_algorithm

Count insertions and deletions using the given line-diff algorithm.

count_git_lines

Line count for diffstat/--numstat, matching Git’s count_lines() in diff.c.

detect_copies

Detect copies among diff entries.

detect_renames

Detect renames by pairing Deleted and Added entries with similar content.

diff_index_to_tree

Compare the index against a tree (usually HEAD’s tree).

diff_index_to_worktree

Compare the index against the working tree.

diff_index_to_worktree_with_options

Compare the index against the working tree with optional racy-timestamp context.

diff_slice_ops_compacted

Line-diff ops for string slices after Git xdl_change_compact (and optional indent heuristic).

diff_tree_to_worktree

Compare a tree against the working tree.

diff_trees

Compare two trees and return the list of changed entries.

diff_trees_show_tree_entries

Like diff_trees but with show_trees flag: when true, emit entries for tree objects themselves in addition to their recursive contents (the -t flag of diff-tree).

diffcore_count_changes

Approximate copied vs added material between two blobs (Git diffcore_count_changes).

empty_blob_oid

Return the ObjectId for the empty blob object.

format_mode

Format a numeric mode as a zero-padded octal string.

format_raw

Format a diff entry in Git’s raw diff format.

format_raw_abbrev

Format a diff entry with abbreviated OIDs.

format_rename_path

Format a rename pair using Git’s compact path format.

format_stat_line

Generate diff stat output (file name + insertions/deletions).

format_stat_line_width

hash_worktree_file

head_path_states

Paths present in HEAD’s tree with mode and blob/commit OID (for status porcelain v2).

indent_heuristic_from_config

diff.indentHeuristic from config (Git defaults to true when unset).

map_new_to_old_lines_compacted

Map each line in new_joined to its origin in old_joined after Git-style compaction (for blame).

mode_from_metadata

Derive a Git file mode from filesystem metadata.

normalize_ignore_space_change

Normalise text like Git’s -b / --ignore-space-change: on each line, collapse runs of whitespace to a single ASCII space and trim trailing spaces.

normalize_ignore_space_change_line

Normalise one line like Git’s -b / --ignore-space-change.

parse_diff_rename_score_token

Parse a single Git parse_rename_score token (50, 50%, decimal forms) into internal 0–GIT_DIFF_MAX_SCORE units.

parse_indent_heuristic_cli_flags

Parse --indent-heuristic / --no-indent-heuristic from a plumbing argv slice (last occurrence wins).

read_submodule_head_for_checkout

Read the HEAD commit OID from a submodule checkout directory.

read_submodule_head_oid

Read the HEAD commit OID from a submodule working tree directory.

rename_similarity_score

Compute rename/copy similarity percentage (0–100) between two byte slices.

resolve_indent_heuristic

Resolve indent heuristic: --no-indent-heuristic and --indent-heuristic override config.

rewrite_dissimilarity_index_percent

Percentage shown in dissimilarity index N% for a rewrite (similarity_index in Git’s diff.c).

rewrite_merge_score

Git merge_score from diffcore-break.c when a pair is considered broken: how much of the source blob was removed (0–[DIFF_MAX_SCORE] scale). Used for dissimilarity index metadata.

should_break_rewrite_for_stat

Whether this modified blob pair should use Git’s “complete rewrite” diffstat path when --break-rewrites is in effect (should_break in diffcore-break.c).

should_break_rewrite_pair

Whether an in-place blob edit should be split into delete+create for rename/copy (should_break in diffcore-break.c). break_score is on the internal 0–GIT_DIFF_MAX_SCORE scale (default [DIFF_DEFAULT_BREAK_SCORE]).

stat_matches

status_apply_rename_copy_detection

Apply Git-style rename and optional copy detection for index↔worktree diffs.

submodule_commit_subject_line

First line of a commit’s message for git diff --submodule=log output.

submodule_embedded_git_dir

Resolve the embedded git directory for a submodule work tree (sub_dir/.git).

submodule_porcelain_flags

Inspect a checked-out submodule at rel_path (relative to super_worktree) and return flags used for git status --porcelain=v2 submodule tokens.

unified_diff

Generate a unified diff patch for two blobs.

unified_diff_histogram_hunks_only

Unified diff hunks for Git’s histogram algorithm (no --- / +++ lines).

unified_diff_histogram_with_prefix_and_funcname

Full unified diff (--- / +++ / hunks) using Git’s histogram algorithm.

unified_diff_with_prefix

Same as unified_diff but with configurable source/destination prefixes.

unified_diff_with_prefix_and_funcname

Same as unified_diff_with_prefix with optional custom hunk-header function-name matching.

unified_diff_with_prefix_and_funcname_and_algorithm

Same as unified_diff_with_prefix_and_funcname but allows callers to choose the line diff algorithm used for hunk generation.

worktree_differs_from_index_entry

Quick stat check: does the index entry’s cached stat data match the file? Returns true when the file at ie’s path differs from the index entry (mode or blob).

zero_oid

Return the zero ObjectId.