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* "git difftool" builtin command
* This is a wrapper around the GIT_EXTERNAL_DIFF-compatible
* git-difftool--helper script.
* This script exports GIT_EXTERNAL_DIFF and GIT_PAGER for use by git.
* The GIT_DIFF* variables are exported for use by git-difftool--helper.
* Any arguments that are unknown to this script are forwarded to 'git diff'.
* Copyright (C) 2016 Johannes Schindelin
#include "cache.h"
#include "config.h"
#include "builtin.h"
#include "run-command.h"
#include "exec-cmd.h"
#include "parse-options.h"
#include "strvec.h"
#include "strbuf.h"
#include "lockfile.h"
#include "object-store.h"
#include "dir.h"
#include "entry.h"
static int trust_exit_code;
static const char *const builtin_difftool_usage[] = {
N_("git difftool [<options>] [<commit> [<commit>]] [--] [<path>...]"),
static int difftool_config(const char *var, const char *value, void *cb)
if (!strcmp(var, "difftool.trustexitcode")) {
trust_exit_code = git_config_bool(var, value);
return 0;
return git_default_config(var, value, cb);
static int print_tool_help(void)
const char *argv[] = { "mergetool", "--tool-help=diff", NULL };
return run_command_v_opt(argv, RUN_GIT_CMD);
static int parse_index_info(char *p, int *mode1, int *mode2,
struct object_id *oid1, struct object_id *oid2,
char *status)
if (*p != ':')
return error("expected ':', got '%c'", *p);
*mode1 = (int)strtol(p + 1, &p, 8);
if (*p != ' ')
return error("expected ' ', got '%c'", *p);
*mode2 = (int)strtol(p + 1, &p, 8);
if (*p != ' ')
return error("expected ' ', got '%c'", *p);
if (parse_oid_hex(++p, oid1, (const char **)&p))
return error("expected object ID, got '%s'", p);
if (*p != ' ')
return error("expected ' ', got '%c'", *p);
if (parse_oid_hex(++p, oid2, (const char **)&p))
return error("expected object ID, got '%s'", p);
if (*p != ' ')
return error("expected ' ', got '%c'", *p);
*status = *++p;
if (!*status)
return error("missing status");
if (p[1] && !isdigit(p[1]))
return error("unexpected trailer: '%s'", p + 1);
return 0;
* Remove any trailing slash from $workdir
* before starting to avoid double slashes in symlink targets.
static void add_path(struct strbuf *buf, size_t base_len, const char *path)
strbuf_setlen(buf, base_len);
if (buf->len && buf->buf[buf->len - 1] != '/')
strbuf_addch(buf, '/');
strbuf_addstr(buf, path);
* Determine whether we can simply reuse the file in the worktree.
static int use_wt_file(const char *workdir, const char *name,
struct object_id *oid)
struct strbuf buf = STRBUF_INIT;
struct stat st;
int use = 0;
strbuf_addstr(&buf, workdir);
add_path(&buf, buf.len, name);
if (!lstat(buf.buf, &st) && !S_ISLNK(st.st_mode)) {
struct object_id wt_oid;
int fd = open(buf.buf, O_RDONLY);
if (fd >= 0 &&
!index_fd(&the_index, &wt_oid, fd, &st, OBJ_BLOB, name, 0)) {
if (is_null_oid(oid)) {
oidcpy(oid, &wt_oid);
use = 1;
} else if (oideq(oid, &wt_oid))
use = 1;
return use;
struct working_tree_entry {
struct hashmap_entry entry;
char path[FLEX_ARRAY];
static int working_tree_entry_cmp(const void *unused_cmp_data,
const struct hashmap_entry *eptr,
const struct hashmap_entry *entry_or_key,
const void *unused_keydata)
const struct working_tree_entry *a, *b;
a = container_of(eptr, const struct working_tree_entry, entry);
b = container_of(entry_or_key, const struct working_tree_entry, entry);
return strcmp(a->path, b->path);
* The `left` and `right` entries hold paths for the symlinks hashmap,
* and a SHA-1 surrounded by brief text for submodules.
struct pair_entry {
struct hashmap_entry entry;
char left[PATH_MAX], right[PATH_MAX];
const char path[FLEX_ARRAY];
static int pair_cmp(const void *unused_cmp_data,
const struct hashmap_entry *eptr,
const struct hashmap_entry *entry_or_key,
const void *unused_keydata)
const struct pair_entry *a, *b;
a = container_of(eptr, const struct pair_entry, entry);
b = container_of(entry_or_key, const struct pair_entry, entry);
return strcmp(a->path, b->path);
static void add_left_or_right(struct hashmap *map, const char *path,
const char *content, int is_right)
struct pair_entry *e, *existing;
FLEX_ALLOC_STR(e, path, path);
hashmap_entry_init(&e->entry, strhash(path));
existing = hashmap_get_entry(map, e, entry, NULL);
if (existing) {
e = existing;
} else {
e->left[0] = e->right[0] = '\0';
hashmap_add(map, &e->entry);
strlcpy(is_right ? e->right : e->left, content, PATH_MAX);
struct path_entry {
struct hashmap_entry entry;
char path[FLEX_ARRAY];
static int path_entry_cmp(const void *unused_cmp_data,
const struct hashmap_entry *eptr,
const struct hashmap_entry *entry_or_key,
const void *key)
const struct path_entry *a, *b;
a = container_of(eptr, const struct path_entry, entry);
b = container_of(entry_or_key, const struct path_entry, entry);
return strcmp(a->path, key ? key : b->path);
static void changed_files(struct hashmap *result, const char *index_path,
const char *workdir)
struct child_process update_index = CHILD_PROCESS_INIT;
struct child_process diff_files = CHILD_PROCESS_INIT;
struct strbuf buf = STRBUF_INIT;
const char *git_dir = absolute_path(get_git_dir());
FILE *fp;
"--git-dir", git_dir, "--work-tree", workdir,
"update-index", "--really-refresh", "-q",
"--unmerged", NULL);
update_index.no_stdin = 1;
update_index.no_stdout = 1;
update_index.no_stderr = 1;
update_index.git_cmd = 1;
update_index.use_shell = 0;
update_index.clean_on_exit = 1;
update_index.dir = workdir;
strvec_pushf(&update_index.env_array, "GIT_INDEX_FILE=%s", index_path);
/* Ignore any errors of update-index */
"--git-dir", git_dir, "--work-tree", workdir,
"diff-files", "--name-only", "-z", NULL);
diff_files.no_stdin = 1;
diff_files.git_cmd = 1;
diff_files.use_shell = 0;
diff_files.clean_on_exit = 1;
diff_files.out = -1;
diff_files.dir = workdir;
strvec_pushf(&diff_files.env_array, "GIT_INDEX_FILE=%s", index_path);
if (start_command(&diff_files))
die("could not obtain raw diff");
fp = xfdopen(diff_files.out, "r");
while (!strbuf_getline_nul(&buf, fp)) {
struct path_entry *entry;
FLEX_ALLOC_STR(entry, path, buf.buf);
hashmap_entry_init(&entry->entry, strhash(buf.buf));
hashmap_add(result, &entry->entry);
if (finish_command(&diff_files))
die("diff-files did not exit properly");
static int ensure_leading_directories(char *path)
switch (safe_create_leading_directories(path)) {
case SCLD_OK:
return 0;
return error(_("could not create leading directories "
"of '%s'"), path);
* Unconditional writing of a plain regular file is what
* "git difftool --dir-diff" wants to do for symlinks. We are preparing two
* temporary directories to be fed to a Git-unaware tool that knows how to
* show a diff of two directories (e.g. "diff -r A B").
* Because the tool is Git-unaware, if a symbolic link appears in either of
* these temporary directories, it will try to dereference and show the
* difference of the target of the symbolic link, which is not what we want,
* as the goal of the dir-diff mode is to produce an output that is logically
* equivalent to what "git diff" produces.
* Most importantly, we want to get textual comparison of the result of the
* readlink(2). get_symlink() provides that---it returns the contents of
* the symlink that gets written to a regular file to force the external tool
* to compare the readlink(2) result as text, even on a filesystem that is
* capable of doing a symbolic link.
static char *get_symlink(const struct object_id *oid, const char *path)
char *data;
if (is_null_oid(oid)) {
/* The symlink is unknown to Git so read from the filesystem */
struct strbuf link = STRBUF_INIT;
if (has_symlinks) {
if (strbuf_readlink(&link, path, strlen(path)))
die(_("could not read symlink %s"), path);
} else if (strbuf_read_file(&link, path, 128))
die(_("could not read symlink file %s"), path);
data = strbuf_detach(&link, NULL);
} else {
enum object_type type;
unsigned long size;
data = read_object_file(oid, &type, &size);
if (!data)
die(_("could not read object %s for symlink %s"),
oid_to_hex(oid), path);
return data;
static int checkout_path(unsigned mode, struct object_id *oid,
const char *path, const struct checkout *state)
struct cache_entry *ce;
int ret;
ce = make_transient_cache_entry(mode, oid, path, 0, NULL);
ret = checkout_entry(ce, state, NULL, NULL);
return ret;
static void write_file_in_directory(struct strbuf *dir, size_t dir_len,
const char *path, const char *content)
add_path(dir, dir_len, path);
write_file(dir->buf, "%s", content);
/* Write the file contents for the left and right sides of the difftool
* dir-diff representation for submodules and symlinks. Symlinks and submodules
* are written as regular text files so that external diff tools can diff them
* as text files, resulting in behavior that is analogous to to what "git diff"
* displays for symlink and submodule diffs.
static void write_standin_files(struct pair_entry *entry,
struct strbuf *ldir, size_t ldir_len,
struct strbuf *rdir, size_t rdir_len)
if (*entry->left)
write_file_in_directory(ldir, ldir_len, entry->path, entry->left);
if (*entry->right)
write_file_in_directory(rdir, rdir_len, entry->path, entry->right);
static int run_dir_diff(const char *extcmd, int symlinks, const char *prefix,
struct child_process *child)
struct strbuf info = STRBUF_INIT, lpath = STRBUF_INIT;
struct strbuf rpath = STRBUF_INIT, buf = STRBUF_INIT;
struct strbuf ldir = STRBUF_INIT, rdir = STRBUF_INIT;
struct strbuf wtdir = STRBUF_INIT;
struct strbuf tmpdir = STRBUF_INIT;
char *lbase_dir = NULL, *rbase_dir = NULL;
size_t ldir_len, rdir_len, wtdir_len;
const char *workdir, *tmp;
int ret = 0, i;
FILE *fp = NULL;
struct hashmap working_tree_dups = HASHMAP_INIT(working_tree_entry_cmp,
struct hashmap submodules = HASHMAP_INIT(pair_cmp, NULL);
struct hashmap symlinks2 = HASHMAP_INIT(pair_cmp, NULL);
struct hashmap_iter iter;
struct pair_entry *entry;
struct index_state wtindex;
struct checkout lstate, rstate;
int flags = RUN_GIT_CMD, err = 0;
const char *helper_argv[] = { "difftool--helper", NULL, NULL, NULL };
struct hashmap wt_modified, tmp_modified;
int indices_loaded = 0;
workdir = get_git_work_tree();
/* Setup temp directories */
tmp = getenv("TMPDIR");
strbuf_add_absolute_path(&tmpdir, tmp ? tmp : "/tmp");
strbuf_addstr(&tmpdir, "/git-difftool.XXXXXX");
if (!mkdtemp(tmpdir.buf)) {
ret = error("could not create '%s'", tmpdir.buf);
goto finish;
strbuf_addf(&ldir, "%s/left/", tmpdir.buf);
strbuf_addf(&rdir, "%s/right/", tmpdir.buf);
strbuf_addstr(&wtdir, workdir);
if (!wtdir.len || !is_dir_sep(wtdir.buf[wtdir.len - 1]))
strbuf_addch(&wtdir, '/');
mkdir(ldir.buf, 0700);
mkdir(rdir.buf, 0700);
memset(&wtindex, 0, sizeof(wtindex));
memset(&lstate, 0, sizeof(lstate));
lstate.base_dir = lbase_dir = xstrdup(ldir.buf);
lstate.base_dir_len = ldir.len;
lstate.force = 1;
memset(&rstate, 0, sizeof(rstate));
rstate.base_dir = rbase_dir = xstrdup(rdir.buf);
rstate.base_dir_len = rdir.len;
rstate.force = 1;
ldir_len = ldir.len;
rdir_len = rdir.len;
wtdir_len = wtdir.len;
child->no_stdin = 1;
child->git_cmd = 1;
child->use_shell = 0;
child->clean_on_exit = 1;
child->dir = prefix;
child->out = -1;
if (start_command(child))
die("could not obtain raw diff");
fp = xfdopen(child->out, "r");
/* Build index info for left and right sides of the diff */
i = 0;
while (!strbuf_getline_nul(&info, fp)) {
int lmode, rmode;
struct object_id loid, roid;
char status;
const char *src_path, *dst_path;
if (starts_with(info.buf, "::"))
die(N_("combined diff formats ('-c' and '--cc') are "
"not supported in\n"
"directory diff mode ('-d' and '--dir-diff')."));
if (parse_index_info(info.buf, &lmode, &rmode, &loid, &roid,
if (strbuf_getline_nul(&lpath, fp))
src_path = lpath.buf;
if (status != 'C' && status != 'R') {
dst_path = src_path;
} else {
if (strbuf_getline_nul(&rpath, fp))
dst_path = rpath.buf;
if (S_ISGITLINK(lmode) || S_ISGITLINK(rmode)) {
strbuf_addf(&buf, "Subproject commit %s",
add_left_or_right(&submodules, src_path, buf.buf, 0);
strbuf_addf(&buf, "Subproject commit %s",
if (oideq(&loid, &roid))
strbuf_addstr(&buf, "-dirty");
add_left_or_right(&submodules, dst_path, buf.buf, 1);
if (S_ISLNK(lmode)) {
char *content = get_symlink(&loid, src_path);
add_left_or_right(&symlinks2, src_path, content, 0);
if (S_ISLNK(rmode)) {
char *content = get_symlink(&roid, dst_path);
add_left_or_right(&symlinks2, dst_path, content, 1);
if (lmode && status != 'C') {
if (checkout_path(lmode, &loid, src_path, &lstate)) {
ret = error("could not write '%s'", src_path);
goto finish;
if (rmode && !S_ISLNK(rmode)) {
struct working_tree_entry *entry;
/* Avoid duplicate working_tree entries */
FLEX_ALLOC_STR(entry, path, dst_path);
hashmap_entry_init(&entry->entry, strhash(dst_path));
if (hashmap_get(&working_tree_dups, &entry->entry,
NULL)) {
hashmap_add(&working_tree_dups, &entry->entry);
if (!use_wt_file(workdir, dst_path, &roid)) {
if (checkout_path(rmode, &roid, dst_path,
&rstate)) {
ret = error("could not write '%s'",
goto finish;
} else if (!is_null_oid(&roid)) {
* Changes in the working tree need special
* treatment since they are not part of the
* index.
struct cache_entry *ce2 =
make_cache_entry(&wtindex, rmode, &roid,
dst_path, 0, 0);
add_index_entry(&wtindex, ce2,
add_path(&rdir, rdir_len, dst_path);
if (ensure_leading_directories(rdir.buf)) {
ret = error("could not create "
"directory for '%s'",
goto finish;
add_path(&wtdir, wtdir_len, dst_path);
if (symlinks) {
if (symlink(wtdir.buf, rdir.buf)) {
ret = error_errno("could not symlink '%s' to '%s'", wtdir.buf, rdir.buf);
goto finish;
} else {
struct stat st;
if (stat(wtdir.buf, &st))
st.st_mode = 0644;
if (copy_file(rdir.buf, wtdir.buf,
st.st_mode)) {
ret = error("could not copy '%s' to '%s'", wtdir.buf, rdir.buf);
goto finish;
fp = NULL;
if (finish_command(child)) {
ret = error("error occurred running diff --raw");
goto finish;
if (!i)
goto finish;
* Changes to submodules require special treatment.This loop writes a
* temporary file to both the left and right directories to show the
* change in the recorded SHA1 for the submodule.
hashmap_for_each_entry(&submodules, &iter, entry,
entry /* member name */) {
write_standin_files(entry, &ldir, ldir_len, &rdir, rdir_len);
* Symbolic links require special treatment. The standard "git diff"
* shows only the link itself, not the contents of the link target.
* This loop replicates that behavior.
hashmap_for_each_entry(&symlinks2, &iter, entry,
entry /* member name */) {
write_standin_files(entry, &ldir, ldir_len, &rdir, rdir_len);
strbuf_setlen(&ldir, ldir_len);
helper_argv[1] = ldir.buf;
strbuf_setlen(&rdir, rdir_len);
helper_argv[2] = rdir.buf;
if (extcmd) {
helper_argv[0] = extcmd;
flags = 0;
} else
setenv("GIT_DIFFTOOL_DIRDIFF", "true", 1);
ret = run_command_v_opt(helper_argv, flags);
/* TODO: audit for interaction with sparse-index. */
* If the diff includes working copy files and those
* files were modified during the diff, then the changes
* should be copied back to the working tree.
* Do not copy back files when symlinks are used and the
* external tool did not replace the original link with a file.
* These hashes are loaded lazily since they aren't needed
* in the common case of --symlinks and the difftool updating
* files through the symlink.
hashmap_init(&wt_modified, path_entry_cmp, NULL, wtindex.cache_nr);
hashmap_init(&tmp_modified, path_entry_cmp, NULL, wtindex.cache_nr);
for (i = 0; i < wtindex.cache_nr; i++) {
struct hashmap_entry dummy;
const char *name = wtindex.cache[i]->name;
struct stat st;
add_path(&rdir, rdir_len, name);
if (lstat(rdir.buf, &st))
if ((symlinks && S_ISLNK(st.st_mode)) || !S_ISREG(st.st_mode))
if (!indices_loaded) {
struct lock_file lock = LOCK_INIT;
strbuf_addf(&buf, "%s/wtindex", tmpdir.buf);
if (hold_lock_file_for_update(&lock, buf.buf, 0) < 0 ||
write_locked_index(&wtindex, &lock, COMMIT_LOCK)) {
ret = error("could not write %s", buf.buf);
goto finish;
changed_files(&wt_modified, buf.buf, workdir);
strbuf_setlen(&rdir, rdir_len);
changed_files(&tmp_modified, buf.buf, rdir.buf);
add_path(&rdir, rdir_len, name);
indices_loaded = 1;
hashmap_entry_init(&dummy, strhash(name));
if (hashmap_get(&tmp_modified, &dummy, name)) {
add_path(&wtdir, wtdir_len, name);
if (hashmap_get(&wt_modified, &dummy, name)) {
warning(_("both files modified: '%s' and '%s'."),
wtdir.buf, rdir.buf);
warning(_("working tree file has been left."));
warning("%s", "");
err = 1;
} else if (unlink(wtdir.buf) ||
copy_file(wtdir.buf, rdir.buf, st.st_mode))
warning_errno(_("could not copy '%s' to '%s'"),
rdir.buf, wtdir.buf);
if (err) {
warning(_("temporary files exist in '%s'."), tmpdir.buf);
warning(_("you may want to cleanup or recover these."));
ret = 1;
} else {
remove_dir_recursively(&tmpdir, 0);
if (ret)
warning(_("failed: %d"), ret);
if (fp)
return (ret < 0) ? 1 : ret;
static int run_file_diff(int prompt, const char *prefix,
struct child_process *child)
const char *env[] = {
"GIT_PAGER=", "GIT_EXTERNAL_DIFF=git-difftool--helper", NULL,
if (prompt > 0)
env[2] = "GIT_DIFFTOOL_PROMPT=true";
else if (!prompt)
env[2] = "GIT_DIFFTOOL_NO_PROMPT=true";
child->git_cmd = 1;
child->dir = prefix;
strvec_pushv(&child->env_array, env);
return run_command(child);
int cmd_difftool(int argc, const char **argv, const char *prefix)
int use_gui_tool = 0, dir_diff = 0, prompt = -1, symlinks = 0,
tool_help = 0, no_index = 0;
static char *difftool_cmd = NULL, *extcmd = NULL;
struct option builtin_difftool_options[] = {
OPT_BOOL('g', "gui", &use_gui_tool,
N_("use `diff.guitool` instead of `diff.tool`")),
OPT_BOOL('d', "dir-diff", &dir_diff,
N_("perform a full-directory diff")),
OPT_SET_INT_F('y', "no-prompt", &prompt,
N_("do not prompt before launching a diff tool"),
OPT_SET_INT_F(0, "prompt", &prompt, NULL,
OPT_BOOL(0, "symlinks", &symlinks,
N_("use symlinks in dir-diff mode")),
OPT_STRING('t', "tool", &difftool_cmd, N_("tool"),
N_("use the specified diff tool")),
OPT_BOOL(0, "tool-help", &tool_help,
N_("print a list of diff tools that may be used with "
OPT_BOOL(0, "trust-exit-code", &trust_exit_code,
N_("make 'git-difftool' exit when an invoked diff "
"tool returns a non-zero exit code")),
OPT_STRING('x', "extcmd", &extcmd, N_("command"),
N_("specify a custom command for viewing diffs")),
OPT_BOOL(0, "no-index", &no_index, N_("passed to `diff`")),
struct child_process child = CHILD_PROCESS_INIT;
git_config(difftool_config, NULL);
symlinks = has_symlinks;
argc = parse_options(argc, argv, prefix, builtin_difftool_options,
builtin_difftool_usage, PARSE_OPT_KEEP_UNKNOWN |
if (tool_help)
return print_tool_help();
if (!no_index && !startup_info->have_repository)
die(_("difftool requires worktree or --no-index"));
if (!no_index){
setenv(GIT_DIR_ENVIRONMENT, absolute_path(get_git_dir()), 1);
setenv(GIT_WORK_TREE_ENVIRONMENT, absolute_path(get_git_work_tree()), 1);
} else if (dir_diff)
die(_("options '%s' and '%s' cannot be used together"), "--dir-diff", "--no-index");
die_for_incompatible_opt3(use_gui_tool, "--gui",
!!difftool_cmd, "--tool",
!!extcmd, "--extcmd");
if (use_gui_tool)
setenv("GIT_MERGETOOL_GUI", "true", 1);
else if (difftool_cmd) {
if (*difftool_cmd)
setenv("GIT_DIFF_TOOL", difftool_cmd, 1);
die(_("no <tool> given for --tool=<tool>"));
if (extcmd) {
if (*extcmd)
setenv("GIT_DIFFTOOL_EXTCMD", extcmd, 1);
die(_("no <cmd> given for --extcmd=<cmd>"));
trust_exit_code ? "true" : "false", 1);
* In directory diff mode, 'git-difftool--helper' is called once
* to compare the a / b directories. In file diff mode, 'git diff'
* will invoke a separate instance of 'git-difftool--helper' for
* each file that changed.
strvec_push(&child.args, "diff");
if (no_index)
strvec_push(&child.args, "--no-index");
if (dir_diff)
strvec_pushl(&child.args, "--raw", "--no-abbrev", "-z", NULL);
strvec_pushv(&child.args, argv);
if (dir_diff)
return run_dir_diff(extcmd, symlinks, prefix, &child);
return run_file_diff(prompt, prefix, &child);