git-restore is different from git-checkout that it only restores the
worktree by default, not both worktree and index. add--interactive
needs some update to support this mode.
Signed-off-by: NNguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

Use a more specific option name to express its purpose. --force may come
back as an alias of --ignore-unmerged and possibly more. But since this
is a destructive operation, I don't see why we need to "force" anything
more. We already don't hold back.

When 'checkout --force' or 'restore --ignore-unmerged' is used, we may
also print warnings about unmerged entries being ignore. Since this is
not exactly warning (people tell us to do so), more informational, let
it be suppressed if --quiet is given. This is a behavior change for
git-checkout.

PS. The diff looks a bit iffy since --force is moved to
add_common_switch_branch_options() (i.e. for switching). But
git-checkout is also doing switching and inherits this --force.
Signed-off-by: NNguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

"git restore --staged" without --source does not make much sense since
by default we restore from the index.  Instead of copying the index to
itself, set the default source to HEAD in this case, yielding behavior
that matches "git reset -- <paths>".
Signed-off-by: NNguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

git-checkout rejects plenty of invalid option combinations. Since
git-checkout is equivalent of either

    git restore --source --staged --worktree

or

    git restore --worktree

that still leaves the new mode 'git restore --index' unprotected. Reject
some more invalid option combinations.

The other new mode 'restore --source --worktree' does not need anything
else.
Signed-off-by: NNguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

'git checkout <tree-ish> <pathspec>' updates both index and
worktree. But updating the index when you want to restore worktree
files is non-intuitive. The index contains the data ready for the next
commit, and there's no indication that the user will want to commit
the restored versions.

'git restore' therefore by default only touches worktree. The user has
the option to update either the index with

    git restore --staged --source=<tree> <path>  (1)

or update both with

    git restore --staged --worktree --source=<tree> <path> (2)

PS. Orignally I wanted to make worktree update default and form (1)
would add index update while also updating the worktree, and the user
would need to do "--staged --no-worktree" to update index only. But it
looks really confusing that "--staged" option alone updates both. So
now form (2) is used for both, which reads much more obvious.

PPS. Yes form (1) overlaps with "git reset <rev> <path>". I don't know
if we can ever turn "git reset" back to "_always_ reset HEAD and
optionally do something else".
Signed-off-by: NNguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

Signed-off-by: NNguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

Overlay mode is considered confusing when the command is about
restoring files on worktree. Disable it by default. The user can still
turn it on, or use 'git checkout' which still has overlay mode on by
default.

While at it, make the check in checkout_branch() stricter. Neither
--overlay or --no-overlay should be accepted in branch switching mode.
Signed-off-by: NNguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

"git restore" without arguments does not make much sense when
it's about restoring files (what files now?). We could default to
either

    git restore .

or

    git restore :/

Neither is intuitive. Make the user always give pathspec, force the
user to think the scope of restore they want because this is a
destructive operation.

"git restore -p" without pathspec is an exception to this
because it really is a separate mode. It will be treated as running
patch mode on the whole worktree.
Signed-off-by: NNguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

This is another departure from 'git checkout' syntax, which uses -- to
separate ref and pathspec. The observation is restore (or "git
checkout -- <pathspec>") is most often used to restore some files from
the index. If this is correct, we can simplify it by taking away the
ref, so that we can write

    git restore some-file

without worrying about some-file being a ref and whether we need to do

    git restore -- some-file

for safety. If the source of the restore comes from a tree, it will be
in the form of an option with value, e.g.

    git restore --source=this-tree some-file

This is of course longer to type than using "--". But hopefully it
will not be used as often, and it is clearly easier to understand.

dwim_new_local_branch is no longer set (or unset) in cmd_restore_files()
because it's irrelevant because we don't really care about dwim-ing.
With accept_ref being unset, dwim can't happen.
Signed-off-by: NNguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

Previously the switching branch business of 'git checkout' becomes a
new command 'switch'. This adds the restore command for the checking
out paths path.

Similar to git-switch, a new man page is added to describe what the
command will become. The implementation will be updated shortly to
match the man page.

A couple main differences from 'git checkout <paths>':

- 'restore' by default will only update worktree. This matters more
  when --source is specified ('checkout <tree> <paths>' updates both
  worktree and index).

- 'restore --staged' can be used to restore the index. This command
  overlaps with 'git reset <paths>'.

- both worktree and index could also be restored at the same time
  (from a tree) when both --staged and --worktree are specified. This
  overlaps with 'git checkout <tree> <paths>'

- default source for restoring worktree and index is the index and
  HEAD respectively. A different (tree) source could be specified as
  with --source (*).

- when both index and worktree are restored, --source must be
  specified since the default source for these two individual targets
  are different (**)

- --no-overlay is enabled by default, if an entry is missing in the
  source, restoring means deleting the entry

(*) I originally went with --from instead of --source. I still think
  --from is a better name. The short option -f however is already
  taken by force. And I do think short option is good to have, e.g. to
  write -s@ or -s@^ instead of --source=HEAD.

(**) If you sit down and think about it, moving worktree's source from
  the index to HEAD makes sense, but nobody is really thinking it
  through when they type the commands.
Signed-off-by: NNguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

The new command "git switch" is added to avoid the confusion of
one-command-do-all "git checkout" for new users. They are also helpful
to avoid ambiguation context.

For these reasons, promote it everywhere possible. This includes
documentation, suggestions/advice from other commands...

The "Checking out files" progress line in unpack-trees.c is also updated
to "Updating files" to be neutral to both git-checkout and git-switch.
Signed-off-by: NNguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

Completion support for --guess could be made better. If no --detach is
given, we should only provide a list of refs/heads/* and dwim ones,
not the entire ref space. But I still can't penetrate that
__git_refs() function yet.
Signed-off-by: NNguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

Signed-off-by: NNguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

Switching and creating branches always involves knowing the
<start-point> to begin the new branch from. Sometimes, people want to
create a new branch that does not have any commits yet; --orphan is a
flag to allow that.

--orphan overrides the default of HEAD for <start-point> instead causing
us to start from an empty history with all tracked files removed from
the index and working tree. The use of --orphan is incompatible with
specifying a <start-point>.

A note on the implementation. An alternative is just create a dummy
commit in-core with empty tree and switch to it. But there's a chance
the commit's SHA-1 may end up somewhere permanent like reflog. It's best
to make sure "commit" pointer is NULL to avoid it.
Signed-off-by: NNguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

Unless you know what you're doing, switching to another branch to do
something then switching back could be confusing. Worse, you may even
forget that you're in the middle of something. By the time you realize,
you may have done a ton of work and it gets harder to go back.

A new option --ignore-in-progress was considered but dropped because it
was not exactly clear what should happen. Sometimes you can switch away
and get back safely and resume the operation. Sometimes not. And the
git-checkout behavior is automatically clear merge/revert/cherry-pick,
which makes it a bit even more confusing [1].

We may revisit and add this option in the future. But for now play it
safe and not allow it (you can't even skip this check with --force). The
user is suggested to cancel the operation by themselves (and hopefully
they do consider the consequences, not blindly type the command), or to
create a separate worktree instead of switching. The third option is
the good old "git checkout", but it's not mentioned.

[1] CACsJy8Axa5WsLSjiscjnxVK6jQHkfs-gH959=YtUvQkWriAk5w@mail.gmail.com
Signed-off-by: NNguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

When we switch from one branch to another, it makes sense to show a
summary of local changes since there could be conflicts, or some files
left modified.... When switch is used solely for creating a new
branch (and "switch" to the same commit) or detaching, we don't really
need to show anything.

"git checkout" does it anyway for historical reasons. But we can start
with a clean slate with switch and don't have to.

This essentially reverts fa655d84 (checkout: optimize "git checkout
-b <new_branch>" - 2018-08-16) and make it default for switch,
but also for -B and --detach. Users of big repos are encouraged to
move to switch.
Signed-off-by: NNguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

This is already the default in git-checkout. The real change in here is
just minor cleanup. The main excuse is to explain why dwim is kept default.

Contrary to detach mode that is easy to get into and confusing to get
back out. Automatically creating a tracking branch often does not kick
in as often (you would need a branch of the same name on a remote). And
since the branch creation is reported clearly, the user should be able
to undo/delete it if it's unwanted.
Signed-off-by: NNguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

"git checkout" automatically detaches branches and --detach is not
that useful (--no-detach is more likely). But for "switch", you
may want to use it more often once you're used to detached HEAD. This
of course adds -d to git-checkout but it does not harm (yet?) to do it.
Signed-off-by: NNguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

"git checkout <commit>" will checkout the commit in question and
detach HEAD from the current branch. It is naturally a right thing to
do once you get git references. But detached HEAD is a scary concept
to new users because we show a lot of warnings and stuff, and it could
be hard to get out of (until you know better).

To keep switch a bit more friendly to new users, we only allow
entering detached HEAD mode when --detach is given. "git
switch" must take a branch (unless you create a new branch,
then of course switch can take any commit-ish)
Signed-off-by: NNguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

"git checkout" can be executed without any arguments. What it does is
not exactly great: it switches from HEAD to HEAD and shows worktree
modification as a side effect.

Make switch reject this case. Just use "git status" if you want
that side effect. For switch, you have to either

- really switch a branch
- (explicitly) detach from the current branch
- create a new branch
Signed-off-by: NNguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

This command is about switching branch (or creating a new one) and
should not accept pathspec. This helps simplify ambiguation
handling. The other two ("git checkout" and "git restore") of
course do accept pathspec as before.
Signed-off-by: NNguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

This option is ancient. Nowadays reflog is enabled by default and
automatically created for new branches. Keep it in git-checkout only.
Signed-off-by: NNguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

--discard-changes is a better name than --force for this option since
it's what really happens. --force is turned to an alias for
--discard-changes. But it's meant to be an alias for potentially more
force options in the future.

Side note. It's not obvious from the patch but --discard-changes also
affects submodules if --recurse-submodules is used. The knob to force
updating submodules is hidden behind unpack-trees.c
Signed-off-by: NNguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

The shortcut of these options do not make much sense when used with
switch. And their descriptions are also tied to checkout. Move -b/-B
to cmd_checkout() and new -c/-C with the same functionality in
cmd_switch_branch()
Signed-off-by: NNguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

"git checkout" doing too many things is a source of confusion for many
users (and it even bites old timers sometimes). To remedy that, the
command will be split into two new ones: switch and restore. The good
old "git checkout" command is still here and will be until all (or most
of users) are sick of it.

See the new man page for the final design of switch. The actual
implementation though is still pretty much the same as "git checkout"
and not completely aligned with the man page. Following patches will
adjust their behavior to match the man page.
Signed-off-by: NNguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

This is a preparation step for introducing new commands that do parts
of what checkout does. There will be two new commands, one is about
switching branches, detaching HEAD... one about checking out
paths. These share the a subset of command line options. The rest of
command line options are separate.
Signed-off-by: NNguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

These local variables are referenced by struct option[]. This struct
will soon be broken down, moved away and we can't rely on local
variables anymore. Move these two to struct checkout_opts in
preparation for that.
Signed-off-by: NNguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

"opts" will soon be moved out of cmd_checkout(). To keep changes in
that patch smaller, convert "opts" to a pointer and keep the real
thing behind "real_opts".
Signed-off-by: NNguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

This is in preparation for the new command restore, which also
needs to parse opts->source_tree but does not need all the
disambiguation logic.
Signed-off-by: NNguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

The include list becomes very long and frankly a bit unorganized. With
the exception of builtin.h, cache.h or git-compat-util.h which have to
come first, keep the rest sorted.
Signed-off-by: NNguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

After a successful switch, if a merge, cherry-pick or revert is ongoing,
it is canceled. This behavior has been with us from the very early
beginning, soon after git-merge was created but never actually
documented [1]. It may be a good idea to be transparent and tell the
user if some operation is canceled.

I consider this a better way of telling the user than just adding a
sentence or two in git-checkout.txt, which will be mostly ignored
anyway.

PS. Originally I wanted to print more details like

    warning: cancelling an in-progress merge from <SHA-1>

which may allow some level of undo if the user wants to. But that seems
a lot more work. Perhaps it can be improved later if people still want
that.

[1] ... and I will try not to argue whether it is a sensible behavior.
There is some more discussion here if people are interested:
CACsJy8Axa5WsLSjiscjnxVK6jQHkfs-gH959=YtUvQkWriAk5w@mail.gmail.com
Signed-off-by: NNguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

Detached HEAD mode is considered dangerous and confusing for newcomers
and we print a big block of warning how to move forward. But we should
also suggest the user the way to get out of it if they get into detached
HEAD by mistake.

While at there, I also suggest how to turn the advice off. This is
another thing I find annoying with advices and should be dealt with in a
more generic way. But that may require some refactoring in advice.c
first.
Signed-off-by: NNguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

The old name does not really say that this is about 'checkout -b'. See
49d833dc (Revert "checkout branch: prime cache-tree fully" -
2009-05-12) for more information
Signed-off-by: NNguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

Add backticks where we have none, replace single quotes with backticks
and replace double-quotes. Drop double-quotes from nested constructions
such as `"@{-1}"`.
Helped-by: NMartin Ågren <martin.agren@gmail.com>
Signed-off-by: NMartin Ågren <martin.agren@gmail.com>
Signed-off-by: NNguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

I added this option in git-checkout and git-merge in c1d7036b
(checkout,merge: disallow overwriting ignored files with
--no-overwrite-ignore - 2011-11-27) but did not remember to update
documentation. This completes that commit.
Signed-off-by: NNguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

<branch> can be omitted in this syntax, and it's actually documented a
few paragraphs down:

  You could omit <branch>, in which case the command degenerates to
  "check out the current branch", which is a glorified no-op with
  rather expensive side-effects to show only the tracking information,
  if exists, for the current branch.
Signed-off-by: NNguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

It's easier to search for and also less cryptic.
Signed-off-by: NNguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

Signed-off-by: NJunio C Hamano <gitster@pobox.com>

* maint:
  mingw: allow building with an MSYS2 runtime v3.x

Docfix.

* js/rebase-recreate-merge:
  rebase docs: fix "gitlink" typo