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merge: allow to pretend a merge is made into a different branch

When a series of patches for a topic-B depends on having topic-A,
the workflow to prepare the topic-B branch would look like this:

    $ git checkout -b topic-B main
    $ git merge --no-ff --no-edit topic-A
    $ git am <mbox-for-topic-B

When topic-A gets updated, recreating the first merge and rebasing
the rest of the topic-B, all on detached HEAD, is a useful
technique.  After updating topic-A with its new round of patches:

    $ git checkout topic-B
    $ prev=$(git rev-parse 'HEAD^{/^Merge branch .topic-A. into}')
    $ git checkout --detach $prev^1
    $ git merge --no-ff --no-edit topic-A
    $ git rebase --onto HEAD $prev @{-1}^0
    $ git checkout -B @{-1}

This will

 (0) check out the current topic-B.
 (1) find the previous merge of topic-A into topic-B.
 (2) detach the HEAD to the parent of the previous merge.
 (3) merge the updated topic-A to it.
 (4) reapply the patches to rebuild the rest of topic-B.
 (5) update topic-B with the result.

without contaminating the reflog of topic-B too much.  topic-B@{1}
is the "logically previous" state before topic-A got updated, for
example.  At (4), comparison (e.g. range-diff) between HEAD and
@{-1} is a meaningful way to sanity check the result, and the same
can be done at (5) by comparing topic-B and topic-B@{1}.

But there is one glitch.  The merge into the detached HEAD done in
the step (3) above gives us "Merge branch 'topic-A' into HEAD", and
does not say "into topic-B".

Teach the "--into-name=<branch>" option to "git merge" and its
underlying "git fmt-merge-message", to pretend as if we were merging
into <branch>, no matter what branch we are actually merging into,
when they prepare the merge message.  The pretend name honors the
usual "into <target>" suppression mechanism, which can be seen in
the tests added here.

Signed-off-by: Junio C Hamano <gitster@pobox.com>
pull/1178/head
Junio C Hamano 8 months ago
parent
commit
bd2bc94252
  1. 6
      Documentation/git-fmt-merge-msg.txt
  2. 8
      Documentation/git-merge.txt
  3. 4
      builtin/fmt-merge-msg.c
  4. 4
      builtin/merge.c
  5. 7
      fmt-merge-msg.c
  6. 1
      fmt-merge-msg.h
  7. 42
      t/t6200-fmt-merge-msg.sh

6
Documentation/git-fmt-merge-msg.txt

@ -9,7 +9,7 @@ git-fmt-merge-msg - Produce a merge commit message
SYNOPSIS
--------
[verse]
'git fmt-merge-msg' [-m <message>] [--log[=<n>] | --no-log]
'git fmt-merge-msg' [-m <message>] [--into-name <branch>] [--log[=<n>] | --no-log]
'git fmt-merge-msg' [-m <message>] [--log[=<n>] | --no-log] -F <file>
DESCRIPTION
@ -44,6 +44,10 @@ OPTIONS
Use <message> instead of the branch names for the first line
of the log message. For use with `--log`.
--into-name <branch>::
Prepare the merge message as if merging to the branch `<branch>`,
instead of the name of the real branch to which the merge is made.
-F <file>::
--file <file>::
Take the list of merged objects from <file> instead of

8
Documentation/git-merge.txt

@ -12,7 +12,8 @@ SYNOPSIS
'git merge' [-n] [--stat] [--no-commit] [--squash] [--[no-]edit]
[--no-verify] [-s <strategy>] [-X <strategy-option>] [-S[<keyid>]]
[--[no-]allow-unrelated-histories]
[--[no-]rerere-autoupdate] [-m <msg>] [-F <file>] [<commit>...]
[--[no-]rerere-autoupdate] [-m <msg>] [-F <file>]
[--into-name <branch>] [<commit>...]
'git merge' (--continue | --abort | --quit)
DESCRIPTION
@ -76,6 +77,11 @@ The 'git fmt-merge-msg' command can be
used to give a good default for automated 'git merge'
invocations. The automated message can include the branch description.
--into-name <branch>::
Prepare the default merge message as if merging to the branch
`<branch>`, instead of the name of the real branch to which
the merge is made.
-F <file>::
--file=<file>::
Read the commit message to be used for the merge commit (in

4
builtin/fmt-merge-msg.c

@ -12,6 +12,7 @@ int cmd_fmt_merge_msg(int argc, const char **argv, const char *prefix)
{
const char *inpath = NULL;
const char *message = NULL;
char *into_name = NULL;
int shortlog_len = -1;
struct option options[] = {
{ OPTION_INTEGER, 0, "log", &shortlog_len, N_("n"),
@ -23,6 +24,8 @@ int cmd_fmt_merge_msg(int argc, const char **argv, const char *prefix)
DEFAULT_MERGE_LOG_LEN },
OPT_STRING('m', "message", &message, N_("text"),
N_("use <text> as start of message")),
OPT_STRING(0, "into-name", &into_name, N_("name"),
N_("use <name> instead of the real target branch")),
OPT_FILENAME('F', "file", &inpath, N_("file to read from")),
OPT_END()
};
@ -56,6 +59,7 @@ int cmd_fmt_merge_msg(int argc, const char **argv, const char *prefix)
opts.add_title = !message;
opts.credit_people = 1;
opts.shortlog_len = shortlog_len;
opts.into_name = into_name;
ret = fmt_merge_msg(&input, &output, &opts);
if (ret)

4
builtin/merge.c

@ -87,6 +87,7 @@ static int signoff;
static const char *sign_commit;
static int autostash;
static int no_verify;
static char *into_name;
static struct strategy all_strategy[] = {
{ "recursive", NO_TRIVIAL },
@ -286,6 +287,8 @@ static struct option builtin_merge_options[] = {
{ OPTION_LOWLEVEL_CALLBACK, 'F', "file", &merge_msg, N_("path"),
N_("read message from file"), PARSE_OPT_NONEG,
NULL, 0, option_read_message },
OPT_STRING(0, "into-name", &into_name, N_("name"),
N_("use <name> instead of the real target")),
OPT__VERBOSITY(&verbosity),
OPT_BOOL(0, "abort", &abort_current_merge,
N_("abort the current in-progress merge")),
@ -1122,6 +1125,7 @@ static void prepare_merge_message(struct strbuf *merge_names, struct strbuf *mer
opts.add_title = !have_message;
opts.shortlog_len = shortlog_len;
opts.credit_people = (0 < option_edit);
opts.into_name = into_name;
fmt_merge_msg(merge_names, merge_msg, &opts);
if (merge_msg->len)

7
fmt-merge-msg.c

@ -649,12 +649,15 @@ int fmt_merge_msg(struct strbuf *in, struct strbuf *out,
memset(&merge_parents, 0, sizeof(merge_parents));
/* get current branch */
/* learn the commit that we merge into and the current branch name */
current_branch = current_branch_to_free =
resolve_refdup("HEAD", RESOLVE_REF_READING, &head_oid, NULL);
if (!current_branch)
die("No current branch");
if (starts_with(current_branch, "refs/heads/"))
if (opts->into_name)
current_branch = opts->into_name;
else if (starts_with(current_branch, "refs/heads/"))
current_branch += 11;
find_merge_parents(&merge_parents, in, &head_oid);

1
fmt-merge-msg.h

@ -9,6 +9,7 @@ struct fmt_merge_msg_opts {
unsigned add_title:1,
credit_people:1;
int shortlog_len;
const char *into_name;
};
extern int merge_log_config;

42
t/t6200-fmt-merge-msg.sh

@ -573,7 +573,35 @@ test_expect_success 'merge-msg with "merging" an annotated tag' '
test_cmp expected .git/MERGE_MSG
'
test_expect_success 'merge --into-name=<name>' '
test_when_finished "git checkout main" &&
git checkout -B side main &&
git commit --allow-empty -m "One step ahead" &&
git checkout --detach main &&
git merge --no-ff side &&
git show -s --format="%s" >full.0 &&
head -n1 full.0 >actual &&
# expect that HEAD is shown as-is
grep -e "Merge branch .side. into HEAD$" actual &&
git reset --hard main &&
git merge --no-ff --into-name=main side &&
git show -s --format="%s" >full.1 &&
head -n1 full.1 >actual &&
# expect that we pretend to be merging to main, that is suppressed
grep -e "Merge branch .side.$" actual &&
git checkout -b throwaway main &&
git merge --no-ff --into-name=main side &&
git show -s --format="%s" >full.2 &&
head -n1 full.2 >actual &&
# expect that we pretend to be merging to main, that is suppressed
grep -e "Merge branch .side.$" actual
'
test_expect_success 'merge.suppressDest configuration' '
test_when_finished "git checkout main" &&
git checkout -B side main &&
git commit --allow-empty -m "One step ahead" &&
git checkout main &&
@ -590,7 +618,19 @@ test_expect_success 'merge.suppressDest configuration' '
git -c merge.suppressDest="ma?*[rn]" fmt-merge-msg <.git/FETCH_HEAD >full.3 &&
head -n1 full.3 >actual &&
grep -e "Merge branch .side." actual &&
! grep -e " into main$" actual
! grep -e " into main$" actual &&
git checkout --detach HEAD &&
git -c merge.suppressDest="main" fmt-merge-msg <.git/FETCH_HEAD >full.4 &&
head -n1 full.4 >actual &&
grep -e "Merge branch .side. into HEAD$" actual &&
git -c merge.suppressDest="main" fmt-merge-msg \
--into-name=main <.git/FETCH_HEAD >full.5 &&
head -n1 full.5 >actual &&
grep -e "Merge branch .side." actual &&
! grep -e " into main$" actual &&
! grep -e " into HEAD$" actual
'
test_done

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