[PATCH v3] status: long status advice adapted to recent capabilities

From: Rudy Rigot <rudy.rigot@gmail.com>

Improve the advice displayed when `git status` is slow because of excessive numbers of untracked files. Update the `git status` man page to explain the various configuration options.

`git status` can be slow when there are a large number of untracked files and directories, because Git must search the entire worktree to enumerate them. Previously, Git would print an advice message with the elapsed search time and a suggestion to disable the search using the `-uno` option. This suggestion also carried a warning that might scare off some users.

Git can reduce the size and time of the untracked file search when the `core.untrackedCache` and `core.fsmonitor` features are enabled by caching results from previous `git status` invocations.

Update the advice to explain the various combinations of additional configuration options and refer to (new) documentation in the man page that explains it in more detail than what can be printed in an advice message.

Finally, add new tests to verify the new functionality.

Signed-off-by: Rudy Rigot <rudy.rigot@gmail.com>
---
    status: long status advice adapted to recent capabilities
    
    Here is version 3 for this patch.
    
    Changes since v2:
    
     * Replaced copy of the commit message with the better one suggested by
       Jeff.
     * Replaced copy of the doc and the default advice message with the
       better ones suggested by Jeff.
     * Fixed EOF.
     * Changed the approach for users who are already optimized, pending
       more conversation to see what makes most sense.

Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-1384%2Frudyrigot%2Fadvice_statusFsmonitor-v3
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-1384/rudyrigot/advice_statusFsmonitor-v3
Pull-Request: https://github.com/gitgitgadget/git/pull/1384

Range-diff vs v2:

 1:  9ef7f1834b7 ! 1:  3c98492cb82 status: long status advice adapted to recent capabilities
     @@ Metadata
       ## Commit message ##
          status: long status advice adapted to recent capabilities
      
     -    Currently, if git-status takes more than 2 seconds for enumerating untracked
     -    files, a piece of advice is given to the user to consider ignoring untracked
     -    files. But Git now offers more possibilities to resolve that situation
     -    (untracked cache, fsmonitor) with different downsides.
     +    Improve the advice displayed when `git status` is slow because
     +    of excessive numbers of untracked files.  Update the `git status`
     +    man page to explain the various configuration options.
      
     -    This change is about refreshing that advice message. A new section in the
     -    documentation is introduced to present the possibilities, and the advice
     -    message links to it. I'm also introducing tests for this advice message,
     -    which was untested so far.
     +    `git status` can be slow when there are a large number of untracked
     +    files and directories, because Git must search the entire worktree
     +    to enumerate them.  Previously, Git would print an advice message
     +    with the elapsed search time and a suggestion to disable the search
     +    using the `-uno` option.  This suggestion also carried a warning
     +    that might scare off some users.
      
     -    One of the downsides of untracked cache / fsmonitor, is that the first call
     -    may be long in order to generate the cache, but the user may not know what
     -    their current configuration is. When collecting feedback from users of our
     -    very large repo, that's the most common point of confusion that keeps coming
     -    back: people complain about git status being slow, but are satisfied when
     -    we inform them that it's being cached and they should run it again to check.
     -    As a result, the advice message tries to keep them informed of their current
     -    configuration.
     +    Git can reduce the size and time of the untracked file search when
     +    the `core.untrackedCache` and `core.fsmonitor` features are enabled
     +    by caching results from previous `git status` invocations.
     +
     +    Update the advice to explain the various combinations of additional
     +    configuration options and refer to (new) documentation in the man
     +    page that explains it in more detail than what can be printed in an
     +    advice message.
     +
     +    Finally, add new tests to verify the new functionality.
      
          Signed-off-by: Rudy Rigot <rudy.rigot@gmail.com>
      
     @@ Documentation/git-status.txt: during the write may conflict with other simultane
      +UNTRACKED FILES AND STATUS SPEED
      +--------------------------------
      +
     -+If your untracked files take an unusual amount of time to enumerate, your
     -+repository certainly has a lot of them, and an advice message will display
     -+about it. Here are some configurations to consider in order to improve the
     -+situation:
     -+
     -+* Setting the `core.untrackedCache` configuration as `true` will allow for
     -+`git status` to keep track of the mtime of folders, in order to cache past
     -+`status` results and be sure to only browse folders that changed on subsequent
     -+runs, for filesystems that can support it (see linkgit:git-update-index[1]
     -+for details).
     -+* Used in conjonction with `core.untrackedCache`, setting the `core.fsmonitor`
     -+configuration as `true` will allow for `git status` to keep track of what
     -+files recently changed, in order to cache past `status` results and be sure
     -+to only focus on those files on subsequent runs (see linkgit:git-update-index[1]
     -+for details).
     -+* If none of the above options are satisfactory, setting the
     -+`status.showUntrackedFiles` configuration as `no` will cause `git status`
     -+to not attempt to list untracked files anymore, in which case you have to be
     -+careful not to forget to add new files yourself.
     -+
     -+If none of the above solutions are satisfactory, and you are bothered with
     -+the advice message, you can disable it by setting the `advice.statusUoption`
     -+configuration to `false`.
     ++`git status` can be very slow in large worktrees if/when it
     ++needs to search for untracked files and directories.  There are
     ++many configuration options available to speed this up by either
     ++avoiding the work or making use of cached results from previous
     ++Git commands.  Since we all work in different ways, there is no
     ++single optimum set of settings right for everyone.  Here is a
     ++brief summary of the relevant options to help you choose which
     ++is right for you.  Each of these settings is independently
     ++documented elsewhere in more detail, so please refer to them
     ++for complete details.
     ++
     ++* `-uno` or `status.showUntrackedFiles=false` : just don't search
     ++    and don't report on untracked files.  This is the fastest.
     ++    `git status` will not list the untracked files, so you need
     ++    to be careful to remember if you create any new files and
     ++    manually `git add` them.
     ++
     ++* `advice.statusUoption=false` : search, but don't complain if it
     ++    takes too long.
     ++
     ++* `core.untrackedCache=true` : enable the untracked cache feature
     ++    and only search directories that have been modified since the
     ++    previous `git status` command.  Git remembers the set of
     ++    untracked files within each directory and assumes that if a
     ++    directory has not been modified, then the set of untracked
     ++    file within has not changed.  This is much faster than
     ++    enumerating the contents of every directory, but still not
     ++    without cost, because Git still has to search for the set of
     ++    modified directories.
     ++
     ++* `core.untrackedCache=true` and `core.fsmonitor=true` or
     ++    `core.fsmonitor=<hook_command_pathname>` : enable both the
     ++    untracked cache and FSMonitor features and only search
     ++    directories that have been modified since the previous
     ++    `git status` command.  This is faster than using just the
     ++    untracked cache alone because Git can also avoid searching
     ++    for modified directories.  Git only has to enumerate the
     ++    exact set of directories that have changed recently.
     ++
     ++Note that after you turn on the untracked cache and/or FSMonitor
     ++features it may take a few `git status` commands for the various
     ++caches to warm up before you see improved command times.  This is
     ++normal.
      +
       SEE ALSO
       --------
     @@ t/t7065-wtstatus-slow.sh (new)
      +'
      +
      +test_done
     - \ No newline at end of file
      
       ## t/t7065/no_untrackedcache_no_fsmonitor (new) ##
      @@
     @@ t/t7065/no_untrackedcache_no_fsmonitor (new)
      +
      +
      +It took X seconds to enumerate untracked files.
     -+See https://git-scm.com/docs/git-status#_untracked_files_and_status_speed
     -+for configuration options that may improve that time.
     ++See 'git help status' for information on how to improve this.
      +
      +nothing to commit (create/copy files and use "git add" to track)
      
     @@ t/t7065/with_untrackedcache_no_fsmonitor (new)
      +No commits yet
      +
      +
     -+It took X seconds to enumerate untracked files,
     -+but this is currently being cached, with fsmonitor OFF.
     -+See https://git-scm.com/docs/git-status#_untracked_files_and_status_speed
     -+for configuration options that may improve that time.
     ++It took X seconds to enumerate untracked files.
     ++See 'git help status' for information on how to improve this.
      +
      +nothing to commit (create/copy files and use "git add" to track)
      
     @@ t/t7065/with_untrackedcache_with_fsmonitor (new)
      +
      +
      +It took X seconds to enumerate untracked files,
     -+but this is currently being cached, with fsmonitor ON.
     -+See https://git-scm.com/docs/git-status#_untracked_files_and_status_speed
     -+for configuration options that may improve that time.
     ++but this is currently being cached.
     ++See 'git help status' for information on how to improve this.
      +
      +nothing to commit (create/copy files and use "git add" to track)
      
     @@ wt-status.c: static void wt_longstatus_print(struct wt_status *s)
      +		if (uf_was_slow(s->untracked_in_ms)) {
      +			if (advice_enabled(ADVICE_STATUS_U_OPTION)) {
      +				status_printf_ln(s, GIT_COLOR_NORMAL, "%s", "");
     -+				if (s->repo->settings.core_untracked_cache == UNTRACKED_CACHE_WRITE) {
     ++				if (fsm_mode > FSMONITOR_MODE_DISABLED) {
      +					status_printf_ln(s, GIT_COLOR_NORMAL,
      +							_("It took %.2f seconds to enumerate untracked files,\n"
     -+							"but this is currently being cached, with fsmonitor %s."),
     -+							s->untracked_in_ms / 1000.0,
     -+							(fsm_mode > FSMONITOR_MODE_DISABLED) ? "ON" : "OFF");
     ++							"but this is currently being cached."),
     ++							s->untracked_in_ms / 1000.0);
      +				} else {
      +					status_printf_ln(s, GIT_COLOR_NORMAL,
      +							_("It took %.2f seconds to enumerate untracked files."),
      +							s->untracked_in_ms / 1000.0);
      +				}
      +				status_printf_ln(s, GIT_COLOR_NORMAL,
     -+						_("See https://git-scm.com/docs/git-status#_untracked_files_and_status_speed\n"
     -+						"for configuration options that may improve that time."));
     ++						_("See 'git help status' for information on how to improve this."));
      +				status_printf_ln(s, GIT_COLOR_NORMAL, "%s", "");
      +			}
       		}

 Documentation/git-status.txt               | 47 ++++++++++++++++++++++
 t/t7065-wtstatus-slow.sh                   | 40 ++++++++++++++++++
 t/t7065/no_untrackedcache_no_fsmonitor     |  9 +++++
 t/t7065/with_untrackedcache_no_fsmonitor   |  9 +++++
 t/t7065/with_untrackedcache_with_fsmonitor | 10 +++++
 wt-status.c                                | 38 +++++++++++++----
 6 files changed, 146 insertions(+), 7 deletions(-)
 create mode 100755 t/t7065-wtstatus-slow.sh
 create mode 100644 t/t7065/no_untrackedcache_no_fsmonitor
 create mode 100644 t/t7065/with_untrackedcache_no_fsmonitor
 create mode 100644 t/t7065/with_untrackedcache_with_fsmonitor