Helped-by: Eric Sunshine <sunsh...@sunshineco.com>
Helped-by: Junio C Hamano <gits...@pobox.com>
Signed-off-by: Nguyễn Thái Ngọc Duy <pclo...@gmail.com>
---
 Documentation/git-update-index.txt |   6 ++
 builtin/update-index.c             | 168 +++++++++++++++++++++++++++++++++++++
 2 files changed, 174 insertions(+)

diff --git a/Documentation/git-update-index.txt 
b/Documentation/git-update-index.txt
index f9a35cd..ed32bae 100644
--- a/Documentation/git-update-index.txt
+++ b/Documentation/git-update-index.txt
@@ -180,6 +180,12 @@ may not support it yet.
        system must change `st_mtime` field of a directory if files
        are added or deleted in that directory.
 
+--force-untracked-cache::
+       For safety, `--untracked-cache` performs tests on the working
+       directory to make sure untracked cache can be used. These
+       tests can take a few seconds. `--force-untracked-cache` can be
+       used to skip the tests.
+
 \--::
        Do not interpret any more arguments as options.
 
diff --git a/builtin/update-index.c b/builtin/update-index.c
index 3d2dedd..f5f6689 100644
--- a/builtin/update-index.c
+++ b/builtin/update-index.c
@@ -32,6 +32,7 @@ static int mark_valid_only;
 static int mark_skip_worktree_only;
 #define MARK_FLAG 1
 #define UNMARK_FLAG 2
+static struct strbuf mtime_dir = STRBUF_INIT;
 
 __attribute__((format (printf, 1, 2)))
 static void report(const char *fmt, ...)
@@ -47,6 +48,166 @@ static void report(const char *fmt, ...)
        va_end(vp);
 }
 
+static void remove_test_directory(void)
+{
+       if (mtime_dir.len)
+               remove_dir_recursively(&mtime_dir, 0);
+}
+
+static const char *get_mtime_path(const char *path)
+{
+       static struct strbuf sb = STRBUF_INIT;
+       strbuf_reset(&sb);
+       strbuf_addf(&sb, "%s/%s", mtime_dir.buf, path);
+       return sb.buf;
+}
+
+static void xmkdir(const char *path)
+{
+       path = get_mtime_path(path);
+       if (mkdir(path, 0700))
+               die_errno(_("failed to create directory %s"), path);
+}
+
+static int xstat_mtime_dir(struct stat *st)
+{
+       if (stat(mtime_dir.buf, st))
+               die_errno(_("failed to stat %s"), mtime_dir.buf);
+       return 0;
+}
+
+static int create_file(const char *path)
+{
+       int fd;
+       path = get_mtime_path(path);
+       fd = open(path, O_CREAT | O_RDWR, 0644);
+       if (fd < 0)
+               die_errno(_("failed to create file %s"), path);
+       return fd;
+}
+
+static void xunlink(const char *path)
+{
+       path = get_mtime_path(path);
+       if (unlink(path))
+               die_errno(_("failed to delete file %s"), path);
+}
+
+static void xrmdir(const char *path)
+{
+       path = get_mtime_path(path);
+       if (rmdir(path))
+               die_errno(_("failed to delete directory %s"), path);
+}
+
+static void avoid_racy(void)
+{
+       /*
+        * not use if we could usleep(10) if USE_NSEC is defined. The
+        * field nsec could be there, but the OS could choose to
+        * ignore it?
+        */
+       sleep(1);
+}
+
+static int test_if_untracked_cache_is_supported(void)
+{
+       struct stat st;
+       struct stat_data base;
+       int fd, ret = 0;
+
+       strbuf_addstr(&mtime_dir, "mtime-test-XXXXXX");
+       if (!mkdtemp(mtime_dir.buf))
+               die_errno("Could not make temporary directory");
+
+       fprintf(stderr, _("Testing "));
+       atexit(remove_test_directory);
+       xstat_mtime_dir(&st);
+       fill_stat_data(&base, &st);
+       fputc('.', stderr);
+
+       avoid_racy();
+       fd = create_file("newfile");
+       xstat_mtime_dir(&st);
+       if (!match_stat_data(&base, &st)) {
+               close(fd);
+               fputc('\n', stderr);
+               fprintf_ln(stderr,_("directory stat info does not "
+                                   "change after adding a new file"));
+               goto done;
+       }
+       fill_stat_data(&base, &st);
+       fputc('.', stderr);
+
+       avoid_racy();
+       xmkdir("new-dir");
+       xstat_mtime_dir(&st);
+       if (!match_stat_data(&base, &st)) {
+               close(fd);
+               fputc('\n', stderr);
+               fprintf_ln(stderr, _("directory stat info does not change "
+                                    "after adding a new directory"));
+               goto done;
+       }
+       fill_stat_data(&base, &st);
+       fputc('.', stderr);
+
+       avoid_racy();
+       write_or_die(fd, "data", 4);
+       close(fd);
+       xstat_mtime_dir(&st);
+       if (match_stat_data(&base, &st)) {
+               fputc('\n', stderr);
+               fprintf_ln(stderr, _("directory stat info changes "
+                                    "after updating a file"));
+               goto done;
+       }
+       fputc('.', stderr);
+
+       avoid_racy();
+       close(create_file("new-dir/new"));
+       xstat_mtime_dir(&st);
+       if (match_stat_data(&base, &st)) {
+               fputc('\n', stderr);
+               fprintf_ln(stderr, _("directory stat info changes after "
+                                    "adding a file inside subdirectory"));
+               goto done;
+       }
+       fputc('.', stderr);
+
+       avoid_racy();
+       xunlink("newfile");
+       xstat_mtime_dir(&st);
+       if (!match_stat_data(&base, &st)) {
+               fputc('\n', stderr);
+               fprintf_ln(stderr, _("directory stat info does not "
+                                    "change after deleting a file"));
+               goto done;
+       }
+       fill_stat_data(&base, &st);
+       fputc('.', stderr);
+
+       avoid_racy();
+       xunlink("new-dir/new");
+       xrmdir("new-dir");
+       xstat_mtime_dir(&st);
+       if (!match_stat_data(&base, &st)) {
+               fputc('\n', stderr);
+               fprintf_ln(stderr, _("directory stat info does not "
+                                    "change after deleting a directory"));
+               goto done;
+       }
+
+       if (rmdir(mtime_dir.buf))
+               die_errno(_("failed to delete directory %s"), mtime_dir.buf);
+       fprintf_ln(stderr, _(" OK"));
+       ret = 1;
+
+done:
+       strbuf_release(&mtime_dir);
+       return ret;
+}
+
 static int mark_ce_flags(const char *path, int flag, int mark)
 {
        int namelen = strlen(path);
@@ -834,6 +995,8 @@ int cmd_update_index(int argc, const char **argv, const 
char *prefix)
                        N_("enable or disable split index")),
                OPT_BOOL(0, "untracked-cache", &untracked_cache,
                        N_("enable/disable untracked cache")),
+               OPT_SET_INT(0, "force-untracked-cache", &untracked_cache,
+                           N_("enable untracked cache without testing the 
filesystem"), 2),
                OPT_END()
        };
 
@@ -943,6 +1106,11 @@ int cmd_update_index(int argc, const char **argv, const 
char *prefix)
        if (untracked_cache > 0 && !the_index.untracked) {
                struct untracked_cache *uc;
 
+               if (untracked_cache < 2) {
+                       setup_work_tree();
+                       if (!test_if_untracked_cache_is_supported())
+                               return 1;
+               }
                uc = xcalloc(1, sizeof(*uc));
                uc->exclude_per_dir = ".gitignore";
                /* should be the same flags used by git-status */
-- 
2.3.0.rc1.137.g477eb31

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