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diff --git a/Documentation/gitfaq.txt b/Documentation/gitfaq.txt index 9cd7a592ac..afdaeab850 100644 --- a/Documentation/gitfaq.txt +++ b/Documentation/gitfaq.txt @@ -241,6 +241,59 @@ How do I know if I want to do a fetch or a pull?:: ignore the upstream changes. A pull consists of a fetch followed immediately by either a merge or rebase. See linkgit:git-pull[1]. +Merging and Rebasing +-------------------- + +[[long-running-squash-merge]] +What kinds of problems can occur when merging long-lived branches with squash merges?:: + In general, there are a variety of problems that can occur when using squash + merges to merge two branches multiple times. These can include seeing extra + commits in `git log` output, with a GUI, or when using the `...` notation to + express a range, as well as the possibility of needing to re-resolve conflicts + again and again. ++ +When Git does a normal merge between two branches, it considers exactly three +points: the two branches and a third commit, called the _merge base_, which is +usually the common ancestor of the commits. The result of the merge is the sum +of the changes between the merge base and each head. When you merge two +branches with a regular merge commit, this results in a new commit which will +end up as a merge base when they're merged again, because there is now a new +common ancestor. Git doesn't have to consider changes that occurred before the +merge base, so you don't have to re-resolve any conflicts you resolved before. ++ +When you perform a squash merge, a merge commit isn't created; instead, the +changes from one side are applied as a regular commit to the other side. This +means that the merge base for these branches won't have changed, and so when Git +goes to perform its next merge, it considers all of the changes that it +considered the last time plus the new changes. That means any conflicts may +need to be re-resolved. Similarly, anything using the `...` notation in `git +diff`, `git log`, or a GUI will result in showing all of the changes since the +original merge base. ++ +As a consequence, if you want to merge two long-lived branches repeatedly, it's +best to always use a regular merge commit. + +[[merge-two-revert-one]] +If I make a change on two branches but revert it on one, why does the merge of those branches include the change?:: + By default, when Git does a merge, it uses a strategy called the recursive + strategy, which does a fancy three-way merge. In such a case, when Git + performs the merge, it considers exactly three points: the two heads and a + third point, called the _merge base_, which is usually the common ancestor of + those commits. Git does not consider the history or the individual commits + that have happened on those branches at all. ++ +As a result, if both sides have a change and one side has reverted that change, +the result is to include the change. This is because the code has changed on +one side and there is no net change on the other, and in this scenario, Git +adopts the change. ++ +If this is a problem for you, you can do a rebase instead, rebasing the branch +with the revert onto the other branch. A rebase in this scenario will revert +the change, because a rebase applies each individual commit, including the +revert. Note that rebases rewrite history, so you should avoid rebasing +published branches unless you're sure you're comfortable with that. See the +NOTES section in linkgit:git-rebase[1] for more details. + Hooks ----- @@ -310,6 +363,39 @@ information about how to configure files as text or binary. You can also control this behavior with the `core.whitespace` setting if you don't wish to remove the carriage returns from your line endings. +[[always-modified-files-case]] +Why do I have a file that's always modified?:: + Internally, Git always stores file names as sequences of bytes and doesn't + perform any encoding or case folding. However, Windows and macOS by default + both perform case folding on file names. As a result, it's possible to end up + with multiple files or directories whose names differ only in case. Git can + handle this just fine, but the file system can store only one of these files, + so when Git reads the other file to see its contents, it looks modified. ++ +It's best to remove one of the files such that you only have one file. You can +do this with commands like the following (assuming two files `AFile.txt` and +`afile.txt`) on an otherwise clean working tree: ++ +---- +$ git rm --cached AFile.txt +$ git commit -m 'Remove files conflicting in case' +$ git checkout . +---- ++ +This avoids touching the disk, but removes the additional file. Your project +may prefer to adopt a naming convention, such as all-lowercase names, to avoid +this problem from occurring again; such a convention can be checked using a +`pre-receive` hook or as part of a continuous integration (CI) system. ++ +It is also possible for perpetually modified files to occur on any platform if a +smudge or clean filter is in use on your system but a file was previously +committed without running the smudge or clean filter. To fix this, run the +following on an otherwise clean working tree: ++ +---- +$ git add --renormalize . +---- + [[recommended-storage-settings]] What's the recommended way to store files in Git?:: While Git can store and handle any file of any type, there are some |