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Diffstat (limited to 'Documentation/git-merge-base.txt')
| -rw-r--r-- | Documentation/git-merge-base.txt | 100 |
1 files changed, 58 insertions, 42 deletions
diff --git a/Documentation/git-merge-base.txt b/Documentation/git-merge-base.txt index 9f07f4f6ed..2d944e0851 100644 --- a/Documentation/git-merge-base.txt +++ b/Documentation/git-merge-base.txt @@ -80,9 +80,11 @@ 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 +.... + o---o---o---B + / +---o---1---o---o---o---A +.... the merge base between 'A' and 'B' is '1'. @@ -90,21 +92,25 @@ 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 +.... + 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 +.... + 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, @@ -116,11 +122,13 @@ the best common ancestor of all commits. 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 +.... +---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, @@ -131,36 +139,42 @@ and B is (or at least used to be) to compute the merge base between A and B, and check if it is the same as A, in which case, A is an ancestor of B. You will see this idiom used often in older scripts. - A=$(git rev-parse --verify A) - if test "$A" = "$(git merge-base A B)" - then - ... A is an ancestor of B ... - fi +.... +A=$(git rev-parse --verify A) +if test "$A" = "$(git merge-base A B)" +then + ... A is an ancestor of B ... +fi +.... In modern git, you can say this in a more direct way: - if git merge-base --is-ancestor A B - then - ... A is an ancestor of B ... - fi +.... +if git merge-base --is-ancestor A B +then + ... A is an ancestor of B ... +fi +.... instead. Discussion on fork-point mode ----------------------------- -After working on the `topic` branch created with `git checkout -b +After working on the `topic` branch created with `git switch -c topic origin/master`, the history of remote-tracking branch `origin/master` may have been rewound and rebuilt, leading to a history of this shape: - o---B2 - / - ---o---o---B1--o---o---o---B (origin/master) - \ - B0 - \ - D0---D1---D (topic) +.... + o---B2 + / +---o---o---B1--o---o---o---B (origin/master) + \ + B0 + \ + D0---D1---D (topic) +.... where `origin/master` used to point at commits B0, B1, B2 and now it points at B, and your `topic` branch was started on top of it back @@ -193,13 +207,15 @@ will find B0, and will replay D0, D1 and D on top of B to create a new history of this shape: - o---B2 - / - ---o---o---B1--o---o---o---B (origin/master) - \ \ - B0 D0'--D1'--D' (topic - updated) - \ - D0---D1---D (topic - old) +.... + o---B2 + / +---o---o---B1--o---o---o---B (origin/master) + \ \ + B0 D0'--D1'--D' (topic - updated) + \ + D0---D1---D (topic - old) +.... A caveat is that older reflog entries in your repository may be expired by `git gc`. If B0 no longer appears in the reflog of the |