git/Documentation/git-fmt-merge-msg.txt
Junio C Hamano bd2bc94252 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>
2021-12-20 14:55:02 -08:00

83 lines
1.9 KiB
Plaintext

git-fmt-merge-msg(1)
====================
NAME
----
git-fmt-merge-msg - Produce a merge commit message
SYNOPSIS
--------
[verse]
'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
-----------
Takes the list of merged objects on stdin and produces a suitable
commit message to be used for the merge commit, usually to be
passed as the '<merge-message>' argument of 'git merge'.
This command is intended mostly for internal use by scripts
automatically invoking 'git merge'.
OPTIONS
-------
--log[=<n>]::
In addition to branch names, populate the log message with
one-line descriptions from the actual commits that are being
merged. At most <n> commits from each merge parent will be
used (20 if <n> is omitted). This overrides the `merge.log`
configuration variable.
--no-log::
Do not list one-line descriptions from the actual commits being
merged.
--[no-]summary::
Synonyms to --log and --no-log; these are deprecated and will be
removed in the future.
-m <message>::
--message <message>::
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
stdin.
CONFIGURATION
-------------
include::config/fmt-merge-msg.txt[]
merge.summary::
Synonym to `merge.log`; this is deprecated and will be removed in
the future.
EXAMPLES
--------
---------
$ git fetch origin master
$ git fmt-merge-msg --log <$GIT_DIR/FETCH_HEAD
---------
Print a log message describing a merge of the "master" branch from
the "origin" remote.
SEE ALSO
--------
linkgit:git-merge[1]
GIT
---
Part of the linkgit:git[1] suite