checkout: 'autostash' for branch switching

* Updated the git checkout and git switch docs to show the actual output when using -m to carry local changes across a branch switch, and changed "would carry" to "will carry".
* Rewrote the merge-conflict example in both docs to match the new, more concise message printed on autostash conflicts.
* Replaced the show_unpack_errors flag and old_commit parameter in merge_working_tree()/init_topts() with a plain quiet boolean, so the caller decides directly whether to suppress unpack errors.
* Tightened the 'checkout -m with dirty tree' test by replacing a printf with a heredoc.
* Made the 'checkout -m creates a recoverable stash on conflict' test also assert the reflog subject of the new stash entry.
* Replaced two test_grep calls in the 'checkout -m which would overwrite untracked file' test with a single test_cmp, which also catches a regression where the "would be overwritten" message could end up printed twice.

Harald Nordgren (5):
stash: add --label-ours, --label-theirs, --label-base for apply
sequencer: allow create_autostash to run silently
sequencer: teach autostash apply to take optional conflict marker
labels
checkout: rollback lock on early returns in merge_working_tree checkout -m: autostash when switching branches

 Documentation/git-checkout.adoc |  55 +++++------
 Documentation/git-stash.adoc    |  11 ++-
 Documentation/git-switch.adoc   |  36 ++++---
 builtin/checkout.c              | 166 +++++++++++++++-----------------
 builtin/commit.c                |   3 +-
 builtin/merge.c                 |  15 ++-
 builtin/stash.c                 |  28 ++++--
 sequencer.c                     |  69 +++++++++----
 sequencer.h                     |   7 +-
 t/t3420-rebase-autostash.sh     |  16 +--
 t/t3903-stash.sh                |  24 +++++
 t/t7201-co.sh                   |  71 +++++++++++++-
 t/t7600-merge.sh                |   3 +-
 xdiff-interface.c               |  12 +++
 xdiff-interface.h               |   1 +
 xdiff/xmerge.c                  |   6 +-
 16 files changed, 343 insertions(+), 180 deletions(-)

base-commit: 94f057755b7941b321fd11fec1b2e3ca5313a4e0
Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-git-2234%2FHaraldNordgren%2Fcheckout_autostash-v16
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-git-2234/HaraldNordgren/checkout_autostash-v16
Pull-Request: https://github.com/git/git/pull/2234

Range-diff vs v15:

 1:  aba8e6a9dc = 1:  aba8e6a9dc stash: add --label-ours, --label-theirs, --label-base for apply
 2:  89e0bfa803 = 2:  89e0bfa803 sequencer: allow create_autostash to run silently
 3:  a428ce7328 = 3:  a428ce7328 sequencer: teach autostash apply to take optional conflict marker labels
 4:  f358424085 = 4:  f358424085 checkout: rollback lock on early returns in merge_working_tree
 5:  96b14db827 ! 5:  07d25fda91 checkout -m: autostash when switching branches

@@ Documentation/git-checkout.adoc: $ git checkout mytopic

-You can give the -m flag to the command, which would try a -three-way merge:
-+You can give the -m flag to the command, which would carry your local ++You can give the -m flag to the command, which will carry your local
+changes to the new branch:

------------
$ git checkout -m mytopic
-Auto-merging frotz
++Applied autostash.
+Switched to branch 'mytopic'
++The following paths have local changes:
++M frotz
------------

-After this three-way merge, the local modifications are _not_
@@ Documentation/git-checkout.adoc: $ git checkout mytopic

-When a merge conflict happens during switching branches with -the -m option, you would see something like this:
-+When the --merge (-m) option is in effect and the locally -+modified files overlap with files that need to be updated by the -+branch switch, the changes are stashed and reapplied after the -+switch. If this process results in conflicts, a stash entry is saved -+and made available in git stash list:
++When the --merge (-m) option is given and the local changes ++overlap with the changes in the branch we're switching to, the ++changes are stashed and reapplied after the switch. If this ++process results in conflicts, the stash entry is saved and a ++message is printed:

------------
$ git checkout -m mytopic
@@ Documentation/git-checkout.adoc: $ git checkout mytopic
-ERROR: Merge conflict in frotz
-fatal: merge program failed
-------------
-+Your local changes are stashed, however, applying it to carry -+forward your local changes resulted in conflicts:
-
+-
-At this point, git diff shows the changes cleanly merged as in -the previous example, as well as the changes in the conflicted -files. Edit and resolve the conflict and mark it resolved with -git add as usual:
-+ - You can try resolving them now. If you resolved them
-+ successfully, discard the stash entry with "git stash drop".
-
-+ - Alternatively you can "git reset --hard" if you do not want
-+ to deal with them right now, and later "git stash pop" to
-+ recover your local changes.
- ------------
+-
+-------------
-$ edit frotz
-$ git add frotz
--------------
-+
-+You can try resolving the conflicts now. Edit the conflicting files -+and mark them resolved with git add as usual, then run git stash -+drop to discard the stash entry. Alternatively, you can clear the -+working tree with git reset --hard and recover your local changes -+later with git stash pop.
++Your local changes are stashed, however applying them ++resulted in conflicts. You can either resolve the conflicts ++and then discard the stash with "git stash drop", or, if you ++do not want to resolve them now, run "git reset --hard" and ++apply the local changes later by running "git stash pop".
+ ------------

CONFIGURATION
- -------------

## Documentation/git-switch.adoc ##
@@ Documentation/git-switch.adoc: variable.
@@ Documentation/git-switch.adoc: $ git switch mytopic

-You can give the -m flag to the command, which would try a three-way -merge:
-+You can give the -m flag to the command, which would carry your local ++You can give the -m flag to the command, which will carry your local
+changes to the new branch:

------------
$ git switch -m mytopic
-Auto-merging frotz
++Applied autostash.
+Switched to branch 'mytopic'
++The following paths have local changes:
++M frotz
------------

-After this three-way merge, the local modifications are _not_
@@ builtin/checkout.c: struct checkout_opts {
char *name; /* The short name used */
char *path; /* The full name of a real branch */
@@ builtin/checkout.c: static void setup_branch_path(struct branch_info *branch)
+ branch->path = strbuf_detach(&buf, NULL);
+ }

- static void init_topts(struct unpack_trees_options *topts, int merge, +-static void init_topts(struct unpack_trees_options *topts, int merge, ++static void init_topts(struct unpack_trees_options *topts,
int show_progress, int overwrite_ignore,
- struct commit *old_commit)
-+ struct commit *old_commit, bool show_unpack_errors)
++ bool quiet)
{
memset(topts, 0, sizeof(*topts));
topts->head_idx = -1;
@@ builtin/checkout.c: static void init_topts(struct unpack_trees_options *topts, i
topts->update = 1;
topts->merge = 1;
- topts->quiet = merge && old_commit;
-+ topts->quiet = merge && old_commit && !show_unpack_errors;
++ topts->quiet = quiet;
topts->verbose_update = show_progress;
topts->fn = twoway_merge;
topts->preserve_ignored = !overwrite_ignore;
@@ builtin/checkout.c: static void init_topts(struct unpack_trees_options *topts, i
static int merge_working_tree(const struct checkout_opts *opts,
struct branch_info *old_branch_info,
struct branch_info *new_branch_info,
-- int *writeout_error)
-+ int *writeout_error,
-+ bool show_unpack_errors)
++ bool quiet,
+ int *writeout_error)
{
int ret;
- struct lock_file lock_file = LOCK_INIT;
@@ builtin/checkout.c: static int merge_working_tree(const struct checkout_opts *opts,
+ }

/* 2-way merge to the new branch */
- init_topts(&topts, opts->merge, opts->show_progress,
+- init_topts(&topts, opts->merge, opts->show_progress,
- opts->overwrite_ignore, old_branch_info->commit);
-+ opts->overwrite_ignore, old_branch_info->commit,
-+ show_unpack_errors);
++ init_topts(&topts, opts->show_progress,
++ opts->overwrite_ignore, quiet);
init_checkout_metadata(&topts.meta, new_branch_info->refname,
new_branch_info->commit ? &new_branch_info->commit->object.oid :
@@ builtin/checkout.c: static int switch_branches(const struct checkout_opts *opts,
if (do_merge) {
- ret = merge_working_tree(opts, &old_branch_info, new_branch_info, &writeout_error);
+ ret = merge_working_tree(opts, &old_branch_info, new_branch_info,
-+ &writeout_error, false);
++ opts->merge, &writeout_error);
+ if (ret == MERGE_WORKING_TREE_UNPACK_FAILED && opts->merge) {
+ strbuf_addf(&autostash_msg,
+ "autostash while switching to '%s'",
@@ builtin/checkout.c: static int switch_branches(const struct checkout_opts *opts,
+ autostash_msg.buf, true);
+ created_autostash = 1;
+ ret = merge_working_tree(opts, &old_branch_info, new_branch_info,
-+ &writeout_error, true);
++ false, &writeout_error);
+ }
+ if (created_autostash) {
+ if (opts->conflict_style >= 0) {
@@ t/t7201-co.sh: test_expect_success 'checkout -m with dirty tree' '
test "$(git symbolic-ref HEAD)" = "refs/heads/side" &&

- printf "M\t%s\n" one >expect.messages &&
-+ printf "The following paths have local changes:\nM\t%s\n" one >expect.messages &&
++ cat >expect.messages <<-\EOF &&
++ The following paths have local changes:
++ M one
++ EOF
test_cmp expect.messages messages &&

fill "M one" "A three" "D two" >expect.main &&
@@ t/t7201-co.sh: test_expect_success 'checkout --merge --conflict=diff3 <branch>'
+ test_grep "git stash drop" actual &&
+ test_grep "git stash pop" actual &&
+ test_grep "The following paths have local changes" actual &&
-+ git show --format=%B --diff-merges=1 refs/stash >actual &&
++ git log -p -1 --format="%gs%n%B" -g --diff-merges=1 refs/stash >actual &&
+ sed /^index/d actual >actual.trimmed &&
+ cat >expect <<-EOF &&
++ autostash while switching to ${SQ}side${SQ}
+ On main: autostash while switching to ${SQ}side${SQ}
+
+ diff --git a/one b/one
@@ t/t7201-co.sh: test_expect_success 'checkout --merge --conflict=diff3 <branch>'
+ >another-file.t &&
+ fill 1 2 3 4 5 >one &&
+ test_must_fail git checkout -m @{-1} 2>err &&
-+ test_grep "would be overwritten by checkout" err &&
-+ test_grep "another-file.t" err
++ q_to_tab >expect <<-\EOF &&
++ error: The following untracked working tree files would be overwritten by checkout:
++ Qanother-file.t
++ Please move or remove them before you switch branches.
++ Aborting
++ Applied autostash.
++ EOF
++ test_cmp expect err
+'
+
test_expect_success 'switch to another branch while carrying a deletion' '

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