t0410: make test description clearer

[git/gitster.git] / worktree.c

#define USE_THE_REPOSITORY_VARIABLE

#include "git-compat-util.h"
#include "abspath.h"
#include "environment.h"
#include "gettext.h"
#include "path.h"
#include "repository.h"
#include "refs.h"
#include "setup.h"
#include "strbuf.h"
#include "worktree.h"
#include "dir.h"
#include "wt-status.h"
#include "config.h"

void free_worktree(struct worktree *worktree)
{
        if (!worktree)
                return;
        free(worktree->path);
        free(worktree->id);
        free(worktree->head_ref);
        free(worktree->lock_reason);
        free(worktree->prune_reason);
        free(worktree);
}

void free_worktrees(struct worktree **worktrees)
{
        int i = 0;
        for (i = 0; worktrees[i]; i++)
                free_worktree(worktrees[i]);
        free (worktrees);
}

/**
 * Update head_oid, head_ref and is_detached of the given worktree
 */
static void add_head_info(struct worktree *wt)
{
        int flags;
        const char *target;

        target = refs_resolve_ref_unsafe(get_worktree_ref_store(wt),
                                         "HEAD",
                                         0,
                                         &wt->head_oid, &flags);
        if (!target)
                return;

        if (flags & REF_ISSYMREF)
                wt->head_ref = xstrdup(target);
        else
                wt->is_detached = 1;
}

static int is_current_worktree(struct worktree *wt)
{
        char *git_dir = absolute_pathdup(repo_get_git_dir(the_repository));
        const char *wt_git_dir = get_worktree_git_dir(wt);
        int is_current = !fspathcmp(git_dir, absolute_path(wt_git_dir));
        free(git_dir);
        return is_current;
}

/**
 * get the main worktree
 */
static struct worktree *get_main_worktree(int skip_reading_head)
{
        struct worktree *worktree = NULL;
        struct strbuf worktree_path = STRBUF_INIT;

        strbuf_add_real_path(&worktree_path, repo_get_common_dir(the_repository));
        strbuf_strip_suffix(&worktree_path, "/.git");

        CALLOC_ARRAY(worktree, 1);
        worktree->repo = the_repository;
        worktree->path = strbuf_detach(&worktree_path, NULL);
        /*
         * NEEDSWORK: If this function is called from a secondary worktree and
         * config.worktree is present, is_bare_repository_cfg will reflect the
         * contents of config.worktree, not the contents of the main worktree.
         * This means that worktree->is_bare may be set to 0 even if the main
         * worktree is configured to be bare.
         */
        worktree->is_bare = (is_bare_repository_cfg == 1) ||
                is_bare_repository();
        worktree->is_current = is_current_worktree(worktree);
        if (!skip_reading_head)
                add_head_info(worktree);
        return worktree;
}

struct worktree *get_linked_worktree(const char *id,
                                     int skip_reading_head)
{
        struct worktree *worktree = NULL;
        struct strbuf path = STRBUF_INIT;
        struct strbuf worktree_path = STRBUF_INIT;

        if (!id)
                die("Missing linked worktree name");

        strbuf_git_common_path(&path, the_repository, "worktrees/%s/gitdir", id);
        if (strbuf_read_file(&worktree_path, path.buf, 0) <= 0)
                /* invalid gitdir file */
                goto done;
        strbuf_rtrim(&worktree_path);
        strbuf_strip_suffix(&worktree_path, "/.git");

        if (!is_absolute_path(worktree_path.buf)) {
            strbuf_strip_suffix(&path, "gitdir");
            strbuf_addbuf(&path, &worktree_path);
            strbuf_realpath_forgiving(&worktree_path, path.buf, 0);
        }

        CALLOC_ARRAY(worktree, 1);
        worktree->repo = the_repository;
        worktree->path = strbuf_detach(&worktree_path, NULL);
        worktree->id = xstrdup(id);
        worktree->is_current = is_current_worktree(worktree);
        if (!skip_reading_head)
                add_head_info(worktree);

done:
        strbuf_release(&path);
        strbuf_release(&worktree_path);
        return worktree;
}

/*
 * NEEDSWORK: This function exists so that we can look up metadata of a
 * worktree without trying to access any of its internals like the refdb. It
 * would be preferable to instead have a corruption-tolerant function for
 * retrieving worktree metadata that could be used when the worktree is known
 * to not be in a healthy state, e.g. when creating or repairing it.
 */
static struct worktree **get_worktrees_internal(int skip_reading_head)
{
        struct worktree **list = NULL;
        struct strbuf path = STRBUF_INIT;
        DIR *dir;
        struct dirent *d;
        int counter = 0, alloc = 2;

        ALLOC_ARRAY(list, alloc);

        list[counter++] = get_main_worktree(skip_reading_head);

        strbuf_addf(&path, "%s/worktrees", repo_get_common_dir(the_repository));
        dir = opendir(path.buf);
        strbuf_release(&path);
        if (dir) {
                while ((d = readdir_skip_dot_and_dotdot(dir)) != NULL) {
                        struct worktree *linked = NULL;

                        if ((linked = get_linked_worktree(d->d_name, skip_reading_head))) {
                                ALLOC_GROW(list, counter + 1, alloc);
                                list[counter++] = linked;
                        }
                }
                closedir(dir);
        }
        ALLOC_GROW(list, counter + 1, alloc);
        list[counter] = NULL;

        return list;
}

struct worktree **get_worktrees(void)
{
        return get_worktrees_internal(0);
}

const char *get_worktree_git_dir(const struct worktree *wt)
{
        if (!wt)
                return repo_get_git_dir(the_repository);
        else if (!wt->id)
                return repo_get_common_dir(the_repository);
        else
                return git_common_path("worktrees/%s", wt->id);
}

static struct worktree *find_worktree_by_suffix(struct worktree **list,
                                                const char *suffix)
{
        struct worktree *found = NULL;
        int nr_found = 0, suffixlen;

        suffixlen = strlen(suffix);
        if (!suffixlen)
                return NULL;

        for (; *list && nr_found < 2; list++) {
                const char      *path    = (*list)->path;
                int              pathlen = strlen(path);
                int              start   = pathlen - suffixlen;

                /* suffix must start at directory boundary */
                if ((!start || (start > 0 && is_dir_sep(path[start - 1]))) &&
                    !fspathcmp(suffix, path + start)) {
                        found = *list;
                        nr_found++;
                }
        }
        return nr_found == 1 ? found : NULL;
}

struct worktree *find_worktree(struct worktree **list,
                               const char *prefix,
                               const char *arg)
{
        struct worktree *wt;
        char *to_free = NULL;

        if ((wt = find_worktree_by_suffix(list, arg)))
                return wt;

        if (prefix)
                arg = to_free = prefix_filename(prefix, arg);
        wt = find_worktree_by_path(list, arg);
        free(to_free);
        return wt;
}

struct worktree *find_worktree_by_path(struct worktree **list, const char *p)
{
        struct strbuf wt_path = STRBUF_INIT;
        char *path = real_pathdup(p, 0);

        if (!path)
                return NULL;
        for (; *list; list++) {
                if (!strbuf_realpath(&wt_path, (*list)->path, 0))
                        continue;

                if (!fspathcmp(path, wt_path.buf))
                        break;
        }
        free(path);
        strbuf_release(&wt_path);
        return *list;
}

int is_main_worktree(const struct worktree *wt)
{
        return !wt->id;
}

const char *worktree_lock_reason(struct worktree *wt)
{
        if (is_main_worktree(wt))
                return NULL;

        if (!wt->lock_reason_valid) {
                struct strbuf path = STRBUF_INIT;

                strbuf_addstr(&path, worktree_git_path(the_repository, wt, "locked"));
                if (file_exists(path.buf)) {
                        struct strbuf lock_reason = STRBUF_INIT;
                        if (strbuf_read_file(&lock_reason, path.buf, 0) < 0)
                                die_errno(_("failed to read '%s'"), path.buf);
                        strbuf_trim(&lock_reason);
                        wt->lock_reason = strbuf_detach(&lock_reason, NULL);
                } else
                        wt->lock_reason = NULL;
                wt->lock_reason_valid = 1;
                strbuf_release(&path);
        }

        return wt->lock_reason;
}

const char *worktree_prune_reason(struct worktree *wt, timestamp_t expire)
{
        struct strbuf reason = STRBUF_INIT;
        char *path = NULL;

        if (is_main_worktree(wt))
                return NULL;
        if (wt->prune_reason_valid)
                return wt->prune_reason;

        if (should_prune_worktree(wt->id, &reason, &path, expire))
                wt->prune_reason = strbuf_detach(&reason, NULL);
        wt->prune_reason_valid = 1;

        strbuf_release(&reason);
        free(path);
        return wt->prune_reason;
}

/* convenient wrapper to deal with NULL strbuf */
__attribute__((format (printf, 2, 3)))
static void strbuf_addf_gently(struct strbuf *buf, const char *fmt, ...)
{
        va_list params;

        if (!buf)
                return;

        va_start(params, fmt);
        strbuf_vaddf(buf, fmt, params);
        va_end(params);
}

int validate_worktree(const struct worktree *wt, struct strbuf *errmsg,
                      unsigned flags)
{
        struct strbuf wt_path = STRBUF_INIT;
        struct strbuf realpath = STRBUF_INIT;
        char *path = NULL;
        int err, ret = -1;

        strbuf_addf(&wt_path, "%s/.git", wt->path);

        if (is_main_worktree(wt)) {
                if (is_directory(wt_path.buf)) {
                        ret = 0;
                        goto done;
                }
                /*
                 * Main worktree using .git file to point to the
                 * repository would make it impossible to know where
                 * the actual worktree is if this function is executed
                 * from another worktree. No .git file support for now.
                 */
                strbuf_addf_gently(errmsg,
                                   _("'%s' at main working tree is not the repository directory"),
                                   wt_path.buf);
                goto done;
        }

        /*
         * Make sure "gitdir" file points to a real .git file and that
         * file points back here.
         */
        if (!is_absolute_path(wt->path)) {
                strbuf_addf_gently(errmsg,
                                   _("'%s' file does not contain absolute path to the working tree location"),
                                   git_common_path("worktrees/%s/gitdir", wt->id));
                goto done;
        }

        if (flags & WT_VALIDATE_WORKTREE_MISSING_OK &&
            !file_exists(wt->path)) {
                ret = 0;
                goto done;
        }

        if (!file_exists(wt_path.buf)) {
                strbuf_addf_gently(errmsg, _("'%s' does not exist"), wt_path.buf);
                goto done;
        }

        path = xstrdup_or_null(read_gitfile_gently(wt_path.buf, &err));
        if (!path) {
                strbuf_addf_gently(errmsg, _("'%s' is not a .git file, error code %d"),
                                   wt_path.buf, err);
                goto done;
        }

        strbuf_realpath(&realpath, git_common_path("worktrees/%s", wt->id), 1);
        ret = fspathcmp(path, realpath.buf);

        if (ret)
                strbuf_addf_gently(errmsg, _("'%s' does not point back to '%s'"),
                                   wt->path, git_common_path("worktrees/%s", wt->id));
done:
        free(path);
        strbuf_release(&wt_path);
        strbuf_release(&realpath);
        return ret;
}

void update_worktree_location(struct worktree *wt, const char *path_)
{
        struct strbuf path = STRBUF_INIT;
        struct strbuf repo = STRBUF_INIT;
        struct strbuf file = STRBUF_INIT;
        struct strbuf tmp = STRBUF_INIT;

        if (is_main_worktree(wt))
                BUG("can't relocate main worktree");

        strbuf_realpath(&repo, git_common_path("worktrees/%s", wt->id), 1);
        strbuf_realpath(&path, path_, 1);
        if (fspathcmp(wt->path, path.buf)) {
                strbuf_addf(&file, "%s/gitdir", repo.buf);
                write_file(file.buf, "%s/.git", relative_path(path.buf, repo.buf, &tmp));
                strbuf_reset(&file);
                strbuf_addf(&file, "%s/.git", path.buf);
                write_file(file.buf, "gitdir: %s", relative_path(repo.buf, path.buf, &tmp));

                free(wt->path);
                wt->path = strbuf_detach(&path, NULL);
        }
        strbuf_release(&path);
        strbuf_release(&repo);
        strbuf_release(&file);
        strbuf_release(&tmp);
}

int is_worktree_being_rebased(const struct worktree *wt,
                              const char *target)
{
        struct wt_status_state state;
        int found_rebase;

        memset(&state, 0, sizeof(state));
        found_rebase = wt_status_check_rebase(wt, &state) &&
                       (state.rebase_in_progress ||
                        state.rebase_interactive_in_progress) &&
                       state.branch &&
                       skip_prefix(target, "refs/heads/", &target) &&
                       !strcmp(state.branch, target);
        wt_status_state_free_buffers(&state);
        return found_rebase;
}

int is_worktree_being_bisected(const struct worktree *wt,
                               const char *target)
{
        struct wt_status_state state;
        int found_bisect;

        memset(&state, 0, sizeof(state));
        found_bisect = wt_status_check_bisect(wt, &state) &&
                       state.bisecting_from &&
                       skip_prefix(target, "refs/heads/", &target) &&
                       !strcmp(state.bisecting_from, target);
        wt_status_state_free_buffers(&state);
        return found_bisect;
}

/*
 * note: this function should be able to detect shared symref even if
 * HEAD is temporarily detached (e.g. in the middle of rebase or
 * bisect). New commands that do similar things should update this
 * function as well.
 */
int is_shared_symref(const struct worktree *wt, const char *symref,
                     const char *target)
{
        const char *symref_target;
        struct ref_store *refs;
        int flags;

        if (wt->is_bare)
                return 0;

        if (wt->is_detached && !strcmp(symref, "HEAD")) {
                if (is_worktree_being_rebased(wt, target))
                        return 1;
                if (is_worktree_being_bisected(wt, target))
                        return 1;
        }

        refs = get_worktree_ref_store(wt);
        symref_target = refs_resolve_ref_unsafe(refs, symref, 0,
                                                NULL, &flags);
        if ((flags & REF_ISSYMREF) &&
            symref_target && !strcmp(symref_target, target))
                return 1;

        return 0;
}

const struct worktree *find_shared_symref(struct worktree **worktrees,
                                          const char *symref,
                                          const char *target)
{

        for (int i = 0; worktrees[i]; i++)
                if (is_shared_symref(worktrees[i], symref, target))
                        return worktrees[i];

        return NULL;
}

int submodule_uses_worktrees(const char *path)
{
        char *submodule_gitdir;
        struct strbuf sb = STRBUF_INIT, err = STRBUF_INIT;
        DIR *dir;
        struct dirent *d;
        int ret = 0;
        struct repository_format format = REPOSITORY_FORMAT_INIT;

        submodule_gitdir = git_pathdup_submodule(path, "%s", "");
        if (!submodule_gitdir)
                return 0;

        /* The env would be set for the superproject. */
        get_common_dir_noenv(&sb, submodule_gitdir);
        free(submodule_gitdir);

        strbuf_addstr(&sb, "/config");
        read_repository_format(&format, sb.buf);
        if (verify_repository_format(&format, &err)) {
                strbuf_release(&err);
                strbuf_release(&sb);
                clear_repository_format(&format);
                return 1;
        }
        clear_repository_format(&format);
        strbuf_release(&err);

        /* Replace config by worktrees. */
        strbuf_setlen(&sb, sb.len - strlen("config"));
        strbuf_addstr(&sb, "worktrees");

        /* See if there is any file inside the worktrees directory. */
        dir = opendir(sb.buf);
        strbuf_release(&sb);

        if (!dir)
                return 0;

        d = readdir_skip_dot_and_dotdot(dir);
        if (d)
                ret = 1;
        closedir(dir);
        return ret;
}

void strbuf_worktree_ref(const struct worktree *wt,
                         struct strbuf *sb,
                         const char *refname)
{
        if (parse_worktree_ref(refname, NULL, NULL, NULL) ==
                    REF_WORKTREE_CURRENT &&
            wt && !wt->is_current) {
                if (is_main_worktree(wt))
                        strbuf_addstr(sb, "main-worktree/");
                else
                        strbuf_addf(sb, "worktrees/%s/", wt->id);
        }
        strbuf_addstr(sb, refname);
}

int other_head_refs(each_ref_fn fn, void *cb_data)
{
        struct worktree **worktrees, **p;
        struct strbuf refname = STRBUF_INIT;
        int ret = 0;

        worktrees = get_worktrees();
        for (p = worktrees; *p; p++) {
                struct worktree *wt = *p;
                struct object_id oid;
                int flag;

                if (wt->is_current)
                        continue;

                strbuf_reset(&refname);
                strbuf_worktree_ref(wt, &refname, "HEAD");
                if (refs_resolve_ref_unsafe(get_main_ref_store(the_repository),
                                            refname.buf,
                                            RESOLVE_REF_READING,
                                            &oid, &flag))
                        ret = fn(refname.buf, NULL, &oid, flag, cb_data);
                if (ret)
                        break;
        }
        free_worktrees(worktrees);
        strbuf_release(&refname);
        return ret;
}

/*
 * Repair worktree's /path/to/worktree/.git file if missing, corrupt, or not
 * pointing at <repo>/worktrees/<id>.
 */
static void repair_gitfile(struct worktree *wt,
                           worktree_repair_fn fn, void *cb_data)
{
        struct strbuf dotgit = STRBUF_INIT;
        struct strbuf repo = STRBUF_INIT;
        struct strbuf backlink = STRBUF_INIT;
        struct strbuf tmp = STRBUF_INIT;
        char *dotgit_contents = NULL;
        const char *repair = NULL;
        int err;

        /* missing worktree can't be repaired */
        if (!file_exists(wt->path))
                goto done;

        if (!is_directory(wt->path)) {
                fn(1, wt->path, _("not a directory"), cb_data);
                goto done;
        }

        strbuf_realpath(&repo, git_common_path("worktrees/%s", wt->id), 1);
        strbuf_addf(&dotgit, "%s/.git", wt->path);
        dotgit_contents = xstrdup_or_null(read_gitfile_gently(dotgit.buf, &err));

        if (dotgit_contents) {
                if (is_absolute_path(dotgit_contents)) {
                        strbuf_addstr(&backlink, dotgit_contents);
                } else {
                        strbuf_addf(&backlink, "%s/%s", wt->path, dotgit_contents);
                        strbuf_realpath_forgiving(&backlink, backlink.buf, 0);
                }
        }

        if (err == READ_GITFILE_ERR_NOT_A_FILE)
                fn(1, wt->path, _(".git is not a file"), cb_data);
        else if (err)
                repair = _(".git file broken");
        else if (fspathcmp(backlink.buf, repo.buf))
                repair = _(".git file incorrect");

        if (repair) {
                fn(0, wt->path, repair, cb_data);
                write_file(dotgit.buf, "gitdir: %s", relative_path(repo.buf, wt->path, &tmp));
        }

done:
        free(dotgit_contents);
        strbuf_release(&repo);
        strbuf_release(&dotgit);
        strbuf_release(&backlink);
        strbuf_release(&tmp);
}

static void repair_noop(int iserr UNUSED,
                        const char *path UNUSED,
                        const char *msg UNUSED,
                        void *cb_data UNUSED)
{
        /* nothing */
}

void repair_worktrees(worktree_repair_fn fn, void *cb_data)
{
        struct worktree **worktrees = get_worktrees_internal(1);
        struct worktree **wt = worktrees + 1; /* +1 skips main worktree */

        if (!fn)
                fn = repair_noop;
        for (; *wt; wt++)
                repair_gitfile(*wt, fn, cb_data);
        free_worktrees(worktrees);
}

void repair_worktree_after_gitdir_move(struct worktree *wt, const char *old_path)
{
        struct strbuf path = STRBUF_INIT;
        struct strbuf repo = STRBUF_INIT;
        struct strbuf gitdir = STRBUF_INIT;
        struct strbuf dotgit = STRBUF_INIT;
        struct strbuf olddotgit = STRBUF_INIT;
        struct strbuf tmp = STRBUF_INIT;

        if (is_main_worktree(wt))
                goto done;

        strbuf_realpath(&repo, git_common_path("worktrees/%s", wt->id), 1);
        strbuf_addf(&gitdir, "%s/gitdir", repo.buf);

        if (strbuf_read_file(&olddotgit, gitdir.buf, 0) < 0)
                goto done;

        strbuf_rtrim(&olddotgit);
        if (is_absolute_path(olddotgit.buf)) {
                strbuf_addbuf(&dotgit, &olddotgit);
        } else {
                strbuf_addf(&dotgit, "%s/worktrees/%s/%s", old_path, wt->id, olddotgit.buf);
                strbuf_realpath_forgiving(&dotgit, dotgit.buf, 0);
        }

        if (!file_exists(dotgit.buf))
                goto done;

        strbuf_addbuf(&path, &dotgit);
        strbuf_strip_suffix(&path, "/.git");

        write_file(dotgit.buf, "gitdir: %s", relative_path(repo.buf, path.buf, &tmp));
        write_file(gitdir.buf, "%s", relative_path(dotgit.buf, repo.buf, &tmp));
done:
        strbuf_release(&path);
        strbuf_release(&repo);
        strbuf_release(&gitdir);
        strbuf_release(&dotgit);
        strbuf_release(&olddotgit);
        strbuf_release(&tmp);
}

void repair_worktrees_after_gitdir_move(const char *old_path)
{
        struct worktree **worktrees = get_worktrees_internal(1);
        struct worktree **wt = worktrees + 1; /* +1 skips main worktree */

        for (; *wt; wt++)
                repair_worktree_after_gitdir_move(*wt, old_path);
        free_worktrees(worktrees);
}

static int is_main_worktree_path(const char *path)
{
        struct strbuf target = STRBUF_INIT;
        struct strbuf maindir = STRBUF_INIT;
        int cmp;

        strbuf_add_real_path(&target, path);
        strbuf_strip_suffix(&target, "/.git");
        strbuf_add_real_path(&maindir, repo_get_common_dir(the_repository));
        strbuf_strip_suffix(&maindir, "/.git");
        cmp = fspathcmp(maindir.buf, target.buf);

        strbuf_release(&maindir);
        strbuf_release(&target);
        return !cmp;
}

/*
 * If both the main worktree and linked worktree have been moved, then the
 * gitfile /path/to/worktree/.git won't point into the repository, thus we
 * won't know which <repo>/worktrees/<id>/gitdir to repair. However, we may
 * be able to infer the gitdir by manually reading /path/to/worktree/.git,
 * extracting the <id>, and checking if <repo>/worktrees/<id> exists.
 */
static int infer_backlink(const char *gitfile, struct strbuf *inferred)
{
        struct strbuf actual = STRBUF_INIT;
        const char *id;

        if (strbuf_read_file(&actual, gitfile, 0) < 0)
                goto error;
        if (!starts_with(actual.buf, "gitdir:"))
                goto error;
        if (!(id = find_last_dir_sep(actual.buf)))
                goto error;
        strbuf_trim(&actual);
        id++; /* advance past '/' to point at <id> */
        if (!*id)
                goto error;
        strbuf_reset(inferred);
        strbuf_git_common_path(inferred, the_repository, "worktrees/%s", id);
        if (!is_directory(inferred->buf))
                goto error;

        strbuf_release(&actual);
        return 1;

error:
        strbuf_release(&actual);
        strbuf_reset(inferred); /* clear invalid path */
        return 0;
}

/*
 * Repair <repo>/worktrees/<id>/gitdir if missing, corrupt, or not pointing at
 * the worktree's path.
 */
void repair_worktree_at_path(const char *path,
                             worktree_repair_fn fn, void *cb_data)
{
        struct strbuf dotgit = STRBUF_INIT;
        struct strbuf realdotgit = STRBUF_INIT;
        struct strbuf backlink = STRBUF_INIT;
        struct strbuf inferred_backlink = STRBUF_INIT;
        struct strbuf gitdir = STRBUF_INIT;
        struct strbuf olddotgit = STRBUF_INIT;
        struct strbuf realolddotgit = STRBUF_INIT;
        struct strbuf tmp = STRBUF_INIT;
        char *dotgit_contents = NULL;
        const char *repair = NULL;
        int err;

        if (!fn)
                fn = repair_noop;

        if (is_main_worktree_path(path))
                goto done;

        strbuf_addf(&dotgit, "%s/.git", path);
        if (!strbuf_realpath(&realdotgit, dotgit.buf, 0)) {
                fn(1, path, _("not a valid path"), cb_data);
                goto done;
        }

        infer_backlink(realdotgit.buf, &inferred_backlink);
        strbuf_realpath_forgiving(&inferred_backlink, inferred_backlink.buf, 0);
        dotgit_contents = xstrdup_or_null(read_gitfile_gently(realdotgit.buf, &err));
        if (dotgit_contents) {
                if (is_absolute_path(dotgit_contents)) {
                        strbuf_addstr(&backlink, dotgit_contents);
                } else {
                        strbuf_addbuf(&backlink, &realdotgit);
                        strbuf_strip_suffix(&backlink, ".git");
                        strbuf_addstr(&backlink, dotgit_contents);
                        strbuf_realpath_forgiving(&backlink, backlink.buf, 0);
                }
        } else if (err == READ_GITFILE_ERR_NOT_A_FILE) {
                fn(1, realdotgit.buf, _("unable to locate repository; .git is not a file"), cb_data);
                goto done;
        } else if (err == READ_GITFILE_ERR_NOT_A_REPO) {
                if (inferred_backlink.len) {
                        /*
                         * Worktree's .git file does not point at a repository
                         * but we found a .git/worktrees/<id> in this
                         * repository with the same <id> as recorded in the
                         * worktree's .git file so make the worktree point at
                         * the discovered .git/worktrees/<id>.
                         */
                        strbuf_swap(&backlink, &inferred_backlink);
                } else {
                        fn(1, realdotgit.buf, _("unable to locate repository; .git file does not reference a repository"), cb_data);
                        goto done;
                }
        } else {
                fn(1, realdotgit.buf, _("unable to locate repository; .git file broken"), cb_data);
                goto done;
        }

        /*
         * If we got this far, either the worktree's .git file pointed at a
         * valid repository (i.e. read_gitfile_gently() returned success) or
         * the .git file did not point at a repository but we were able to
         * infer a suitable new value for the .git file by locating a
         * .git/worktrees/<id> in *this* repository corresponding to the <id>
         * recorded in the worktree's .git file.
         *
         * However, if, at this point, inferred_backlink is non-NULL (i.e. we
         * found a suitable .git/worktrees/<id> in *this* repository) *and* the
         * worktree's .git file points at a valid repository *and* those two
         * paths differ, then that indicates that the user probably *copied*
         * the main and linked worktrees to a new location as a unit rather
         * than *moving* them. Thus, the copied worktree's .git file actually
         * points at the .git/worktrees/<id> in the *original* repository, not
         * in the "copy" repository. In this case, point the "copy" worktree's
         * .git file at the "copy" repository.
         */
        if (inferred_backlink.len && fspathcmp(backlink.buf, inferred_backlink.buf)) {
                strbuf_swap(&backlink, &inferred_backlink);
        }

        strbuf_addf(&gitdir, "%s/gitdir", backlink.buf);
        if (strbuf_read_file(&olddotgit, gitdir.buf, 0) < 0)
                repair = _("gitdir unreadable");
        else {
                strbuf_rtrim(&olddotgit);
                if (is_absolute_path(olddotgit.buf)) {
                        strbuf_addbuf(&realolddotgit, &olddotgit);
                } else {
                        strbuf_addf(&realolddotgit, "%s/%s", backlink.buf, olddotgit.buf);
                        strbuf_realpath_forgiving(&realolddotgit, realolddotgit.buf, 0);
                }
                if (fspathcmp(realolddotgit.buf, realdotgit.buf))
                        repair = _("gitdir incorrect");
        }

        if (repair) {
                fn(0, gitdir.buf, repair, cb_data);
                write_file(gitdir.buf, "%s", relative_path(realdotgit.buf, backlink.buf, &tmp));
        }
done:
        free(dotgit_contents);
        strbuf_release(&olddotgit);
        strbuf_release(&realolddotgit);
        strbuf_release(&backlink);
        strbuf_release(&inferred_backlink);
        strbuf_release(&gitdir);
        strbuf_release(&realdotgit);
        strbuf_release(&dotgit);
        strbuf_release(&tmp);
}

int should_prune_worktree(const char *id, struct strbuf *reason, char **wtpath, timestamp_t expire)
{
        struct stat st;
        struct strbuf dotgit = STRBUF_INIT;
        struct strbuf gitdir = STRBUF_INIT;
        struct strbuf repo = STRBUF_INIT;
        struct strbuf file = STRBUF_INIT;
        char *path = NULL;
        int rc = 0;
        int fd;
        size_t len;
        ssize_t read_result;

        *wtpath = NULL;
        strbuf_realpath(&repo, git_common_path("worktrees/%s", id), 1);
        strbuf_addf(&gitdir, "%s/gitdir", repo.buf);
        if (!is_directory(repo.buf)) {
                strbuf_addstr(reason, _("not a valid directory"));
                rc = 1;
                goto done;
        }
        strbuf_addf(&file, "%s/locked", repo.buf);
        if (file_exists(file.buf)) {
                goto done;
        }
        if (stat(gitdir.buf, &st)) {
                strbuf_addstr(reason, _("gitdir file does not exist"));
                rc = 1;
                goto done;
        }
        fd = open(gitdir.buf, O_RDONLY);
        if (fd < 0) {
                strbuf_addf(reason, _("unable to read gitdir file (%s)"),
                            strerror(errno));
                rc = 1;
                goto done;
        }
        len = xsize_t(st.st_size);
        path = xmallocz(len);

        read_result = read_in_full(fd, path, len);
        close(fd);
        if (read_result < 0) {
                strbuf_addf(reason, _("unable to read gitdir file (%s)"),
                            strerror(errno));
                rc = 1;
                goto done;
        } else if (read_result != len) {
                strbuf_addf(reason,
                            _("short read (expected %"PRIuMAX" bytes, read %"PRIuMAX")"),
                            (uintmax_t)len, (uintmax_t)read_result);
                rc = 1;
                goto done;
        }
        while (len && (path[len - 1] == '\n' || path[len - 1] == '\r'))
                len--;
        if (!len) {
                strbuf_addstr(reason, _("invalid gitdir file"));
                rc = 1;
                goto done;
        }
        path[len] = '\0';
        if (is_absolute_path(path)) {
                strbuf_addstr(&dotgit, path);
        } else {
                strbuf_addf(&dotgit, "%s/%s", repo.buf, path);
                strbuf_realpath_forgiving(&dotgit, dotgit.buf, 0);
        }
        if (!file_exists(dotgit.buf)) {
                strbuf_reset(&file);
                strbuf_addf(&file, "%s/index", repo.buf);
                if (stat(file.buf, &st) || st.st_mtime <= expire) {
                        strbuf_addstr(reason, _("gitdir file points to non-existent location"));
                        rc = 1;
                        goto done;
                }
        }
        *wtpath = strbuf_detach(&dotgit, NULL);
done:
        free(path);
        strbuf_release(&dotgit);
        strbuf_release(&gitdir);
        strbuf_release(&repo);
        strbuf_release(&file);
        return rc;
}

static int move_config_setting(const char *key, const char *value,
                               const char *from_file, const char *to_file)
{
        if (git_config_set_in_file_gently(to_file, key, NULL, value))
                return error(_("unable to set %s in '%s'"), key, to_file);
        if (git_config_set_in_file_gently(from_file, key, NULL, NULL))
                return error(_("unable to unset %s in '%s'"), key, from_file);
        return 0;
}

int init_worktree_config(struct repository *r)
{
        int res = 0;
        int bare = 0;
        struct config_set cs = { { 0 } };
        const char *core_worktree;
        char *common_config_file;
        char *main_worktree_file;

        /*
         * If the extension is already enabled, then we can skip the
         * upgrade process.
         */
        if (r->repository_format_worktree_config)
                return 0;
        if ((res = git_config_set_gently("extensions.worktreeConfig", "true")))
                return error(_("failed to set extensions.worktreeConfig setting"));

        common_config_file = xstrfmt("%s/config", r->commondir);
        main_worktree_file = xstrfmt("%s/config.worktree", r->commondir);

        git_configset_init(&cs);
        git_configset_add_file(&cs, common_config_file);

        /*
         * If core.bare is true in the common config file, then we need to
         * move it to the main worktree's config file or it will break all
         * worktrees. If it is false, then leave it in place because it
         * _could_ be negating a global core.bare=true.
         */
        if (!git_configset_get_bool(&cs, "core.bare", &bare) && bare) {
                if ((res = move_config_setting("core.bare", "true",
                                               common_config_file,
                                               main_worktree_file)))
                        goto cleanup;
        }
        /*
         * If core.worktree is set, then the main worktree is located
         * somewhere different than the parent of the common Git dir.
         * Relocate that value to avoid breaking all worktrees with this
         * upgrade to worktree config.
         */
        if (!git_configset_get_value(&cs, "core.worktree", &core_worktree, NULL)) {
                if ((res = move_config_setting("core.worktree", core_worktree,
                                               common_config_file,
                                               main_worktree_file)))
                        goto cleanup;
        }

        /*
         * Ensure that we use worktree config for the remaining lifetime
         * of the current process.
         */
        r->repository_format_worktree_config = 1;

cleanup:
        git_configset_clear(&cs);
        free(common_config_file);
        free(main_worktree_file);
        return res;
}