[PATCH] git log -p -m: Document, honor --first-parent
- From
Petr Baudis <pasky@suse.cz>
- Date
- Feb 10, 2010, 01:11 UTC
- Message-ID
- <20100210011149.GR9553@machine.or.cz>
- In-Reply-To
- <7v1vguuf8h.fsf@alter.siamese.dyndns.org>
On Tue, Feb 09, 2010 at 04:05:50PM -0800, Junio C Hamano wrote:
Show 22 quoted lines
> Petr Baudis <pasky@suse.cz> writes: > > > I'm not sure if there is any clever switch for this, but I usually > > just use one of > > > > git diff mergecommit^1 mergecommit > > git diff mergecommit^2 mergecommit > > > > depending on which parent I want the diff against. If you always do your > > merges as "on mainline, merging in a topic" without fast-forwarding, > > diff against the first parent will be probably the right one and you can > > simply use: > > > > git diff mergecommit^ mergecommit > > Frankly, we should make "git log --first-parent -p" DTRT, I think. > > The attitude towards merges we maintain officially is "all parents are > equal", but in practice, there often are cases where --first-parent > traversal makes a lot more sense when browsing the history (especially > "the official" one). The use of that option should be a clear enough sign > that diff between the first parent and the merge result is asked for.
I have also discovered -m while digging into this, which seems to have the effect of showing the merge TWICE, each time against a different parent; this is sort-of-almost what Christian also wanted.
This seems to be undocumented and does have this effect only in log, not in show - I have absolutely no idea why from cursory code examination.
I think making just --first-parent alone imply this behavior is wrong, IMHO first-parent alone does not warrant avoiding combined-diff behavior. I'm not really sure though, so feel free to add another
if (revs->diff && revs->follow_first_parent) revs->ignore_merges = 0;
test at the right place (whatever that is). At any rate, -m explicitly states the intent and the current behavior of not honoring --first-parent is IMHO a bug.
I think --first-parent documentation is still accurate with the new behavior, so I adjusted just -m documentation - also making the flag actually visible for non-diff-tree-stdin cases. Sorry that it's both conflated in a single patch, I'd rather avoid creating a patch queue out of this supposedly-5-minute hack.
--8<--
git log -p -m has a special magic behavior of showin one merge entry per parent, with an appropriate diff; this can be frequently useful when examining histories where full set of changes introduced by a merged branch is interesting, not only the conflicts.
This patch properly documents the -m switch, which has so far been mentioned only as a fairly special diff-tree flag. It also makes the code show full patch entry only for the first parent in case --first-parent is used. Thus,
git log -p -m --first-parent
will show the history from the "main branch perspective", while also including full diff of changes introduced by other merged in branches.
Signed-off-by: Petr Baudis <pasky@suse.cz>
---
diff --git a/Documentation/diff-generate-patch.txt b/Documentation/diff-generate-patch.txt index 0f25ba7..8f9a241 100644 --- a/Documentation/diff-generate-patch.txt +++ b/Documentation/diff-generate-patch.txt @@ -56,7 +56,8 @@ combined diff format "git-diff-tree", "git-diff-files" and "git-diff" can take '-c' or '--cc' option to produce 'combined diff'. For showing a merge commit -with "git log -p", this is the default format. +with "git log -p", this is the default format; you can force showing +full diff with the '-m' option. A 'combined diff' format looks like this: ------------ diff --git a/Documentation/git-log.txt b/Documentation/git-log.txt index 0e39bb6..a2a2d04 100644 --- a/Documentation/git-log.txt +++ b/Documentation/git-log.txt @@ -118,6 +118,15 @@ git log master --not --remotes=*/master:: Shows all commits that are in local master but not in any remote repository master branches. +git log -p -m --first-parent:: + + Shows the history including change diffs, but only from the + "main branch" perspective, skipping commits that come only from + merges, and showing full diffs of changes introduced by the merges. + This makes sense only when following a strict policy of merging all + topic branches when staying on a single integration branch and + making sure the merges are not fast-forwards. + Discussion ---------- diff --git a/Documentation/rev-list-options.txt b/Documentation/rev-list-options.txt index 6e9baf8..d7d0dee 100644 --- a/Documentation/rev-list-options.txt +++ b/Documentation/rev-list-options.txt @@ -108,8 +108,8 @@ options may be given. See linkgit:git-diff-files[1] for more options. -c:: - This flag changes the way a merge commit is displayed. It shows - the differences from each of the parents to the merge result + This flag forces the default way a merge commit is displayed. It + shows the differences from each of the parents to the merge result simultaneously instead of showing pairwise diff between a parent and the result one at a time. Furthermore, it lists only files which were modified from all parents. @@ -121,6 +121,15 @@ options may be given. See linkgit:git-diff-files[1] for more options. the parents have only two variants and the merge result picks one of them without modification. +-m:: + + This flag makes the merge commits show the full diff like + regular commits; for each merge parent, a separate log entry + and diff is generated. (An exception is made if '--first-parent' + option has been also passed; in that case, only diff against + the first parent is shown, representing the changes the merge + brought _into_ the then-current branch.) + -r:: Show recursive diffs. diff --git a/log-tree.c b/log-tree.c index 27afcf6..fb990a1 100644 --- a/log-tree.c +++ b/log-tree.c @@ -514,6 +514,14 @@ static int log_tree_diff(struct rev_info *opt, struct commit *commit, struct log return 0; else if (opt->combine_merges) return do_diff_combined(opt, commit); + else if (opt->first_parent_only) { + /* Generate merge log entry only for the first + * parent, showing summary diff of the others + * we merged _in_. */ + diff_tree_sha1(parents->item->object.sha1, sha1, "", &opt->diffopt); + log_tree_diff_flush(opt); + return !opt->loginfo; + } /* If we show individual diffs, show the parent info */ log->parent = parents->item;