Checkout another branch when there are uncommitted changes on the current branch

Question

Most of the time when I try to checkout another existing branch  Git doesn t allow me if I have some uncommitted changes on the current branch  So I ll have to commit or stash those changes first    However  occasionally Git does allow me to checkout another branch without committing or stashing those changes  and it will carry those changes to the branch I checkout   What is the rule here  Does it matter whether the changes are staged or unstaged  Carrying the changes to another branch doesn t make any sense to me  why does git allow it sometimes  That is  is it helpful in some situations

User · Answer

I have faced the same question recently  What I understand is  if the branch you are checking in has a file which you modified and it happens to be also modified and committed by that branch  Then git will stop you from switching to the branch to keep your change safe before you commit or stash

User · Answer

Preliminary notes This answer is an attempt to explain why Git behaves the way it does   It is not a recommendation to engage in any particular workflows    My own preference is to just commit anyway  avoiding git stash and not trying to be too tricky  but others like other methods   The observation here is that  after you start working in branch1  forgetting or not realizing that it would be good to switch to a different branch branch2 first   you run  git checkout branch2  Sometimes Git says  quot OK  you re on branch2 now  quot   Sometimes  Git says  quot I can t do that  I d lose some of your changes  quot  If Git won t let you do it  you have to commit your changes  to save them somewhere permanent   You may want to use git stash to save them  this is one of the things it s designed for   Note that git stash save or git stash push actually means  quot Commit all the changes  but on no branch at all  then remove them from where I am now  quot   That makes it possible to switch  you now have no in-progress changes   You can then git stash apply them after switching   Sidebar  git stash save is the old syntax  git stash push was introduced in Git version 2 13  to fix up some problems with the arguments to git stash and allow for new options   Both do the same thing  when used in the basic ways   You can stop reading here  if you like  If Git won t let you switch  you already have a remedy  use git stash or git commit  or  if your changes are trivial to re-create  use git checkout -f to force it   This answer is all about when Git will let you git checkout branch2 even though you started making some changes   Why does it work sometimes  and not other times  The rule here is simple in one way  and complicated hard-to-explain in another  You may switch branches with uncommitted changes in the work-tree if and only if said switching does not require clobbering those changes  That is   and please note that this is still simplified  there are some extra-difficult corner cases with staged git adds  git rms and such   suppose you are on branch1   A git checkout branch2 would have to do this   For every file that is in branch1 and not in branch2 1 remove that file  For every file that is in branch2 and not in branch1  create that file  with appropriate contents   For every file that is in both branches  if the version in branch2 is different  update the working tree version   Each of these steps could clobber something in your work-tree   Removing a file is  quot safe quot  if the version in the work-tree is the same as the committed version in branch1  it s  quot unsafe quot  if you ve made changes  Creating a file the way it appears in branch2 is  quot safe quot  if it does not exist now 2  It s  quot unsafe quot  if it does exist now but has the  quot wrong quot  contents  And of course  replacing the work-tree version of a file with a different version is  quot safe quot  if the work-tree version is already committed to branch1   Creating a new branch  git checkout -b newbranch  is always considered  quot safe quot   no files will be added  removed  or altered in the work-tree as part of this process  and the index staging-area is also untouched    Caveat  it s safe when creating a new branch without changing the new branch s starting-point  but if you add another argument  e g   git checkout -b newbranch different-start-point  this might have to change things  to move to different-start-point   Git will then apply the checkout safety rules as usual    1This requires that we define what it means for a file to be in a branch  which in turn requires defining the word branch properly    See also What exactly do we mean by  quot branch quot     Here  what I really mean is the commit to which the branch-name resolves  a file whose path is P is in branch1 if git rev-parse branch1 P produces a hash   That file is not in branch1 if you get an error message instead   The existence of path P in your index or work-tree is not relevant when answering this particular question   Thus  the secret here is to examine the result of git rev-parse on each branch-name path   This either fails because the file is  quot in quot  at most one branch  or gives us two hash IDs   If the two hash IDs are the same  the file is the same in both branches   No changing is required   If the hash IDs differ  the file is different in the two branches  and must be changed to switch branches  The key notion here is that files in commits are frozen forever   Files you will edit are obviously not frozen   We are  at least initially  looking only at the mismatches between two frozen commits   Unfortunately  we   or Git   also have to deal with files that aren t in the commit you re going to switch away from and are in the commit you re going to switch to   This leads to the remaining complications  since files can also exist in the index and or in the work-tree  without having to exist these two particular frozen commits we re working with  2It might be considered  quot sort-of-safe quot  if it already exists with the  quot right contents quot   so that Git does not have to create it after all   I recall at least some versions of Git allowing this  but testing just now shows it to be considered  quot unsafe quot  in Git 1 8 5 4   The same argument would apply to a modified file that happens to be modified to match the to-be-switch-to branch   Again  1 8 5 4 just says  quot would be overwritten quot   though   See the end of the technical notes as well  my memory may be faulty as I don t think the read-tree rules have changed since I first started using Git at version 1 5 something   Does it matter whether the changes are staged or unstaged  Yes  in some ways   In particular  you can stage a change  then  quot de-modify quot  the work tree file   Here s a file in two branches  that s different in branch1 and branch2    git show branch1 inboth this file is in both branches   git show branch2 inboth this file is in both branches but it has more stuff in branch2 now   git checkout branch1 Switched to branch  branch1    echo  but it has more stuff in branch2 now   gt  gt  inboth  At this point  the working tree file inboth matches the one in branch2  even though we re on branch1   This change is not staged for commit  which is what git status --short shows here    git status --short  M inboth  The space-then-M means  quot modified but not staged quot   or more precisely  working-tree copy differs from staged index copy     git checkout branch2 error  Your local changes      OK  now let s stage the working-tree copy  which we already know also matches the copy in branch2    git add inboth   git status --short M  inboth   git checkout branch2 Switched to branch  branch2   Here the staged-and-working copies both matched what was in branch2  so the checkout was allowed  Let s try another step    git checkout branch1 Switched to branch  branch1    cat inboth this file is in both branches  The change I made is lost from the staging area now  because checkout writes through the staging area    This is a bit of a corner case   The change is not gone  but the fact that I had staged it  is gone  Let s stage a third variant of the file  different from either branch-copy  then set the working copy to match the current branch version    echo  staged version different from all   gt  inboth   git add inboth   git show branch1 inboth  gt  inboth   git status --short MM inboth  The two Ms here mean  staged file differs from HEAD file  and  working-tree file differs from staged file   The working-tree version does match the branch1  aka HEAD  version    git diff HEAD    But git checkout won t allow the checkout    git checkout branch2 error  Your local changes      Let s set the branch2 version as the working version    git show branch2 inboth  gt  inboth   git status --short MM inboth   git diff HEAD diff --git a inboth b inboth index ecb07f7  aee20fb 100644 --- a inboth     b inboth    -1  1 2     this file is in both branches  but it has more stuff in branch2 now   git diff branch2 -- inboth   git checkout branch2 error  Your local changes      Even though the current working copy matches the one in branch2  the staged file does not  so a git checkout would lose that copy  and the git checkout is rejected  Technical notes   only for the insanely curious  -  The underlying implementation mechanism for all of this is Git s index   The index  also called the  quot staging area quot   is where you build the next commit  it starts out matching the current commit  i e   whatever you have checked-out now  and then each time you git add a file  you replace the index version with whatever you have in your work-tree  Remember  the work-tree is where you work on your files   Here  they have their normal form  rather than some special only-useful-to-Git form like they do in commits and in the index   So you extract a file from a commit  through the index  and then on into the work-tree   After changing it  you git add it to the index   So there are in fact three places for each file  the current commit  the index  and the work-tree  When you run git checkout branch2  what Git does underneath the covers is to compare the tip commit of branch2 to whatever is in both the current commit and the index now   Any file that matches what s there now  Git can leave alone   It s all untouched   Any file that s the same in both commits  Git can also leave alone   and these are the ones that let you switch branches  Much of Git  including commit-switching  is relatively fast because of this index   What s actually in the index is not each file itself  but rather each file s hash   The copy of the file itself is stored as what Git calls a blob object  in the repository   This is similar to how the files are stored in commits as well  commits don t actually contain the files  they just lead Git to the hash ID of each file   So Git can compare hash IDs   currently 160-bit-long strings   to decide if commits X and Y have the same file or not   It can then compare those hash IDs to the hash ID in the index  too  This is what leads to all the oddball corner cases above   We have commits X and Y that both have file path to name txt  and we have an index entry for path to name txt   Maybe all three hashes match   Maybe two of them match and one doesn t   Maybe all three are different   And  we might also have another file txt that s only in X or only in Y and is or is not in the index now   Each of these various cases requires its own separate consideration  does Git need to copy the file out from commit to index  or remove it from index  to switch from X to Y   If so  it also has to copy the file to the work-tree  or remove it from the work-tree   And if that s the case  the index and work-tree versions had better match at least one of the committed versions  otherwise Git will be clobbering some data   The complete rules for all of this are described in  not the git checkout documentation as you might expect  but rather the git read-tree documentation  under the section titled  quot Two Tree Merge quot

User · Answer

In case you don t want this changes to be committed at all do  git reset --hard   Next you can checkout to wanted branch  but remember that uncommitted changes will be lost

User · Answer

If the new branch contains edits that are different from the current branch for that particular changed file  then it will not allow you to switch branches until the change is committed or stashed  If the changed file is the same on both branches  that is  the committed version of that file   then you can switch freely   Example     echo  hello world   gt  file txt   git add file txt   git commit -m  adding file txt     git checkout -b experiment   echo  goodbye world   gt  gt  file txt   git add file txt   git commit -m  added text         experiment now contains changes that master doesn t have        any future changes to this file will keep you from changing branches        until the changes are stashed or committed    echo  and we re back   gt  gt  file txt    making additional changes   git checkout master error  Your local changes to the following files would be overwritten by checkout      file txt Please  commit your changes or stash them before you can switch branches  Aborting   This goes for untracked files as well as tracked files  Here s an example for an untracked file   Example     git checkout -b experimental    creates new branch  experimental    echo  hello world   gt  file txt   git add file txt   git commit -m  added file txt     git checkout master   master does not have file txt   echo  goodbye world   gt  file txt   git checkout experimental error  The following untracked working tree files would be overwritten by checkout      file txt Please move or remove them before you can switch branches  Aborting   A good example of why you WOULD want to move between branches while making changes would be if you were performing some experiments on master  wanted to commit them  but not to master just yet       echo  experimental change   gt  gt  file txt   change to existing tracked file      I want to save these  but not on master    git checkout -b experiment M       file txt Switched to branch  experiment    git add file txt   git commit -m  possible modification for file txt

User · Answer

The correct answer is   git checkout -m origin master  It merges changes from the origin master branch with your local even uncommitted changes

User · Answer

You have two choices  stash your changes   git stash   then later to get them back   git stash apply   or put your changes on a branch so you can get the remote branch and then merge your changes onto it  That s one of the greatest things about git  you can make a branch  commit to it  then fetch other changes on to the branch you were on   You say it doesn t make any sense  but you are only doing it so you can merge them at will after doing the pull  Obviously your other choice is to commit on your copy of the branch and then do the pull  The presumption is you either don t want to do that  in which case I am puzzled that you don t want a branch  or you are afraid of conflicts

[git] Checkout another branch when there are uncommitted changes on the current branch

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