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Diffstat (limited to 'Documentation/git-merge-base.txt')
| -rw-r--r-- | Documentation/git-merge-base.txt | 99 |
1 files changed, 89 insertions, 10 deletions
diff --git a/Documentation/git-merge-base.txt b/Documentation/git-merge-base.txt index 1a7ecbf8f3..eedef1bb1a 100644 --- a/Documentation/git-merge-base.txt +++ b/Documentation/git-merge-base.txt @@ -8,26 +8,99 @@ git-merge-base - Find as good common ancestors as possible for a merge SYNOPSIS -------- -'git merge-base' [--all] <commit> <commit> +[verse] +'git merge-base' [-a|--all] [--octopus] <commit> <commit>... +'git merge-base' --independent <commit>... DESCRIPTION ----------- -'git-merge-base' finds as good a common ancestor as possible between -the two commits. That is, given two commits A and B, `git merge-base A -B` will output a commit which is reachable from both A and B through -the parent relationship. +'git merge-base' finds best common ancestor(s) between two commits to use +in a three-way merge. One common ancestor is 'better' than another common +ancestor if the latter is an ancestor of the former. A common ancestor +that does not have any better common ancestor is a 'best common +ancestor', i.e. a 'merge base'. Note that there can be more than one +merge base for a pair of commits. -Given a selection of equally good common ancestors it should not be -relied on to decide in any particular way. +Unless `--octopus` is given, among the two commits to compute the merge +base from, one is specified by the first commit argument on the command +line; the other commit is a (possibly hypothetical) commit that is a merge +across all the remaining commits on the command line. As the most common +special case, specifying only two commits on the command line means +computing the merge base between the given two commits. -The 'git-merge-base' algorithm is still in flux - use the source... +As a consequence, the 'merge base' is not necessarily contained in each of the +commit arguments if more than two commits are specified. This is different +from linkgit:git-show-branch[1] when used with the `--merge-base` option. OPTIONS ------- +-a:: --all:: - Output all common ancestors for the two commits instead of - just one. + Output all merge bases for the commits, instead of just one. + +--octopus:: + Compute the best common ancestors of all supplied commits, + in preparation for an n-way merge. This mimics the behavior + of 'git show-branch --merge-base'. + +--independent:: + Instead of printing merge bases, print a minimal subset of + the supplied commits with the same ancestors. In other words, + among the commits given, list those which cannot be reached + from any other. This mimics the behavior of 'git show-branch + --independent'. + +DISCUSSION +---------- + +Given two commits 'A' and 'B', `git merge-base A B` will output a commit +which is reachable from both 'A' and 'B' through the parent relationship. + +For example, with this topology: + + o---o---o---B + / + ---o---1---o---o---o---A + +the merge base between 'A' and 'B' is '1'. + +Given three commits 'A', 'B' and 'C', `git merge-base A B C` will compute the +merge base between 'A' and a hypothetical commit 'M', which is a merge +between 'B' and 'C'. For example, with this topology: + + o---o---o---o---C + / + / o---o---o---B + / / + ---2---1---o---o---o---A + +the result of `git merge-base A B C` is '1'. This is because the +equivalent topology with a merge commit 'M' between 'B' and 'C' is: + + + o---o---o---o---o + / \ + / o---o---o---o---M + / / + ---2---1---o---o---o---A + +and the result of `git merge-base A M` is '1'. Commit '2' is also a +common ancestor between 'A' and 'M', but '1' is a better common ancestor, +because '2' is an ancestor of '1'. Hence, '2' is not a merge base. + +When the history involves criss-cross merges, there can be more than one +'best' common ancestor for two commits. For example, with this topology: + + ---1---o---A + \ / + X + / \ + ---2---o---o---B + +both '1' and '2' are merge-bases of A and B. Neither one is better than +the other (both are 'best' merge bases). When the `--all` option is not given, +it is unspecified which best one is output. Author ------ @@ -37,6 +110,12 @@ Documentation -------------- Documentation by David Greaves, Junio C Hamano and the git-list <git@vger.kernel.org>. +See also +-------- +linkgit:git-rev-list[1], +linkgit:git-show-branch[1], +linkgit:git-merge[1] + GIT --- Part of the linkgit:git[1] suite |