Rebasing a branch including all its children

Question

I have the following Git repository topology:

A-B-F (master)
   \   D (feature-a)
    \ /
     C (feature)
      \
       E (feature-b)

By rebasing feature branch I expected to rebase the whole subtree (including child branches):

$ git rebase feature master

A-B-F (master)
     \   D (feature-a)
      \ /
       C (feature)
        \
         E (feature-b)

However, this is the actual result:

      C' (feature)
     /
A-B-F (master)
   \   D (feature-a)
    \ /
     C
      \
       E (feature-b)

I know I can easily fix it manually by executing:

$ git rebase --onto feature C feature-a
$ git rebase --onto feature C feature-b

But is there a way to automatically rebase branch including all its children/descendants?

Solution 1

git branch --format='%(refname:short)' --contains C | \
xargs -n 1 \
git rebase --committer-date-is-author-date --onto F C^

Solution 2

A couple years ago I wrote something to handle this sort of thing. (Comments for improvement are of course welcome, but don't judge too much - it was a long time ago! I didn't even know Perl yet!)

It's meant for more static situations - you configure it by setting config parameters of the form branch.<branch>.autorebaseparent. It won't touch any branches which don't have that config parameter set. If that's not what you want, you could probably hack it to where you want it without too much trouble. I haven't really used it much in the last year or two, but when I did use it, it always seemed to be quite safe and stable, insofar as that's possible with mass automated rebasing.

So here it is. Use it by saving it into a file called git-auto-rebase in your PATH. It's probably also a good idea to use the dry run (-n) option before you try it for real. It may be a little more detail than you really want, but it will show you what it's going to try to rebase, and onto what. Might save you some grief.

#!/bin/bash

CACHE_DIR=.git/auto-rebase
TODO=$CACHE_DIR/todo
TODO_BACKUP=$CACHE_DIR/todo.backup
COMPLETED=$CACHE_DIR/completed
ORIGINAL_BRANCH=$CACHE_DIR/original_branch
REF_NAMESPACE=refs/pre-auto-rebase

print_help() {
    echo "Usage:  git auto-rebase [opts]"
    echo "Options:"
    echo "    -n   dry run"
    echo "    -c   continue previous auto-rebase"
    echo "    -a   abort previous auto-rebase"
    echo "         (leaves completed rebases intact)"
}

cleanup_autorebase() {
    rm -rf $CACHE_DIR
    if [ -n "$dry_run" ]; then
        # The dry run should do nothing here. It doesn't create refs, and won't
        # run unless auto-rebase is empty. Leave this here to catch programming
        # errors, and for possible future -f option.
        git for-each-ref --format="%(refname)" $REF_NAMESPACE |
        while read ref; do
            echo git update-ref -d $ref
        done
    else
        git for-each-ref --format="%(refname)" $REF_NAMESPACE |
        while read ref; do
            git update-ref -d $ref
        done
    fi
}

# Get the rebase relationships from branch.*.autorebaseparent
get_config_relationships() {
    mkdir -p .git/auto-rebase
    # We cannot simply read the indicated parents and blindly follow their
    # instructions; they must form a directed acyclic graph (like git!) which
    # furthermore has no sources with two sinks (i.e. a branch may not be
    # rebased onto two others).
    # 
    # The awk script checks for cycles and double-parents, then sorts first by
    # depth of hierarchy (how many parents it takes to get to a top-level
    # parent), then by parent name. This means that all rebasing onto a given
    # parent happens in a row - convenient for removal of cached refs.
    IFS=$'\n'
    git config --get-regexp 'branch\..+\.autorebaseparent' | \
    awk '{
        child=$1
        sub("^branch[.]","",child)
        sub("[.]autorebaseparent$","",child)
        if (parent[child] != 0) {
            print "Error: branch "child" has more than one parent specified."
            error=1
            exit 1
        }
        parent[child]=$2
    }
    END {
        if ( error != 0 )
            exit error
        # check for cycles
        for (child in parent) {
            delete cache
            depth=0
            cache[child]=1
            cur=child
            while ( parent[cur] != 0 ) {
                depth++
                cur=parent[cur]
                if ( cache[cur] != 0 ) {
                    print "Error: cycle in branch."child".autorebaseparent hierarchy detected"
                    exit 1
                } else {
                    cache[cur]=1
                }
            }
            depths[child]=depth" "parent[child]" "child
        }
        n=asort(depths, children)
        for (i=1; i<=n; i++) {
            sub(".* ","",children[i])
        }
        for (i=1; i<=n; i++) {
            if (parent[children[i]] != 0)
                print parent[children[i]],children[i]
        }
    }' > $TODO

    # Check for any errors. If the awk script's good, this should really check
    # exit codes.
    if grep -q '^Error:' $TODO; then
        cat $TODO
        rm -rf $CACHE_DIR
        exit 1
    fi

    cp $TODO $TODO_BACKUP
}

# Get relationships from config, or if continuing, verify validity of cache
get_relationships() {
    if [ -n "$continue" ]; then
        if [ ! -d $CACHE_DIR ]; then
            echo "Error: You requested to continue a previous auto-rebase, but"
            echo "$CACHE_DIR does not exist."
            exit 1
        fi
        if [ -f $TODO -a -f $TODO_BACKUP -a -f $ORIGINAL_BRANCH ]; then
            if ! cat $COMPLETED $TODO | diff - $TODO_BACKUP; then
                echo "Error: You requested to continue a previous auto-rebase, but the cache appears"
                echo "to be invalid (completed rebases + todo rebases != planned rebases)."
                echo "You may attempt to manually continue from what is stored in $CACHE_DIR"
                echo "or remove it with \"git auto-rebase -a\""
                exit 1
            fi
        else
            echo "Error: You requested to continue a previous auto-rebase, but some cached files"
            echo "are missing."
            echo "You may attempt to manually continue from what is stored in $CACHE_DIR"
            echo "or remove it with \"git auto-rebase -a\""
            exit 1
        fi
    elif [ -d $CACHE_DIR ]; then
        echo "A previous auto-rebase appears to have been left unfinished."
        echo "Either continue it with \"git auto-rebase -c\" or remove the cache with"
        echo "\"git auto-rebase -a\""
        exit 1
    else
        get_config_relationships
    fi
}

# Verify that desired branches exist, and pre-refs do not.
check_ref_existence() {
    local parent child
    for pair in "${pairs[@]}"; do
        parent="${pair% *}"
        if ! git show-ref -q --verify "refs/heads/$parent" > /dev/null ; then
            if ! git show-ref -q --verify "refs/remotes/$parent" > /dev/null; then
                child="${pair#* }"
                echo "Error: specified parent branch $parent of branch $child does not exist"
                exit 1
            fi
        fi
        if [ -z "$continue" ]; then
            if git show-ref -q --verify "$REF_NAMESPACE/$parent" > /dev/null; then
                echo "Error: ref $REF_NAMESPACE/$parent already exists"
                echo "Most likely a previous git-auto-rebase did not complete; if you have fixed all"
                echo "necessary rebases, you may try again after removing it with:"
                echo
                echo "git update-ref -d $REF_NAMESPACE/$parent"
                echo
                exit 1
            fi
        else
            if ! git show-ref -q --verify "$REF_NAMESPACE/$parent" > /dev/null; then
                echo "Error: You requested to continue a previous auto-rebase, but the required"
                echo "cached ref $REF_NAMESPACE/$parent is missing."
                echo "You may attempt to manually continue from the contents of $CACHE_DIR"
                echo "and whatever refs in refs/$REF_NAMESPACE still exist, or abort the previous"
                echo "auto-rebase with \"git auto-rebase -a\""
                exit 1
            fi
        fi
    done
}

# Create the pre-refs, storing original position of rebased parents
create_pre_refs() {
    local parent prev_parent
    for pair in "${pairs[@]}"; do
        parent="${pair% *}"
        if [ "$prev_parent" != "$parent" ]; then
            if [ -n "$dry_run" ]; then
                echo git update-ref "$REF_NAMESPACE/$parent" "$parent" \"\"
            else
                if ! git update-ref "$REF_NAMESPACE/$parent" "$parent" ""; then
                    echo "Error: cannot create ref $REF_NAMESPACE/$parent"
                    exit 1
                fi
            fi
        fi

        prev_parent="$parent"
    done
}

# Perform the rebases, updating todo/completed as we go
perform_rebases() {
    local prev_parent parent child
    for pair in "${pairs[@]}"; do
        parent="${pair% *}"
        child="${pair#* }"

        # We do this *before* rebasing, assuming most likely any failures will be
        # fixed with rebase --continue, and therefore should not be attempted again
        head -n 1 $TODO >> $COMPLETED
        sed -i '1d' $TODO

        if [ -n "$dry_run" ]; then
            echo git rebase --onto "$parent" "$REF_NAMESPACE/$parent" "$child"
            echo "Successfully rebased $child onto $parent"
        else
            echo git rebase --onto "$parent" "$REF_NAMESPACE/$parent" "$child"
            if ( git merge-ff -q "$child" "$parent" 2> /dev/null && echo "Fast-forwarded $child to $parent." ) || \
                git rebase --onto "$parent" "$REF_NAMESPACE/$parent" "$child"; then
                echo "Successfully rebased $child onto $parent"
            else
                echo "Error rebasing $child onto $parent."
                echo 'You should either fix it (end with git rebase --continue) or abort it, then use'
                echo '"git auto-rebase -c" to continue. You may also use "git auto-rebase -a" to'
                echo 'abort the auto-rebase. Note that this will not undo already-completed rebases.'
                exit 1
            fi
        fi

        prev_parent="$parent"
    done
}

rebase_all_intelligent() {
    if ! git rev-parse --show-git-dir &> /dev/null; then
        echo "Error: git-auto-rebase must be run from inside a git repository"
        exit 1
    fi

    SUBDIRECTORY_OK=1
    . "$(git --exec-path | sed 's/:/\n/' | grep -m 1 git-core)"/git-sh-setup
    cd_to_toplevel


    # Figure out what we need to do (continue, or read from config)
    get_relationships

    # Read the resulting todo list
    OLDIFS="$IFS"
    IFS=$'\n'
    pairs=($(cat $TODO))
    IFS="$OLDIFS"

    # Store the original branch
    if [ -z "$continue" ]; then
        git symbolic-ref HEAD | sed 's@refs/heads/@@' > $ORIGINAL_BRANCH
    fi

    check_ref_existence
    # These three depend on the pairs array
    if [ -z "$continue" ]; then
        create_pre_refs
    fi
    perform_rebases

    echo "Returning to original branch"
    if [ -n "$dry_run" ]; then
        echo git checkout $(cat $ORIGINAL_BRANCH)
    else
        git checkout $(cat $ORIGINAL_BRANCH) > /dev/null
    fi

    if diff -q $COMPLETED $TODO_BACKUP ; then
        if [ "$(wc -l $TODO | cut -d" " -f1)" -eq 0 ]; then
            cleanup_autorebase
            echo "Auto-rebase complete"
        else
            echo "Error: todo-rebases not empty, but completed and planned rebases match."
            echo "This should not be possible, unless you hand-edited a cached file."
            echo "Examine $TODO, $TODO_BACKUP, and $COMPLETED to determine what went wrong."
            exit 1
        fi
    else
        echo "Error: completed rebases don't match planned rebases."
        echo "Examine $TODO_BACKUP and $COMPLETED to determine what went wrong."
        exit 1
    fi
}


while getopts "nca" opt; do
    case $opt in
        n ) dry_run=1;;
        c ) continue=1;;
        a ) abort=1;;
        * )
            echo "git-auto-rebase is too dangerous to run with invalid options; exiting"
            print_help
            exit 1
    esac
done
shift $((OPTIND-1))


case $# in
    0 )
        if [ -n "$abort" ]; then
            cleanup_autorebase
        else
            rebase_all_intelligent
        fi
        ;;

    * )
        print_help
        exit 1
        ;;
esac

One thing that I've found, since I originally addressed this, is that sometimes the answer is that you didn't actually want to rebase at all! There's something to be said for starting topic branches at the right common ancestor in the first place, and not trying to move them forward after that. But that's between you and your workflow.

Solution 3

Building up on Adam's answer to address multiple commits on either of the side branches as:

A-B-F (master)
   \
    O   D (feature-a)
     \ /
      C (feature)
       \
        T-E (feature-b)

here is a more stable approach:

[alias]
    # rebases branch with its sub-branches (one level down)
    # useage: git move <upstream> <branch>
    move = "!mv() { git rebase $1 $2; git branch --format='%(refname:short)' --contains $2@{1} | xargs -n 1 git rebase --onto $2 $2@{1}; }; mv"

so that git move master feature results in expected:

A-B-F (master)
     \
      O`   D` (feature-a)
       \ /
        C` (feature)
         \
          T`-E` (feature-b)

Breakdown of how this works:

• git rebase $1 $2 results in

A-B--------------------F (master)
   \                    \
    O   D (feature-a)    O`
     \ /                  \
      C                    C` (feature)
       \
        T-E (feature-b)

Note that feature is now at C` and not at C

• let's unpack git branch --format='%(refname:short)' --contains $2@{1} This will return list of branches that contain C as feature previous location and will format output as

feature-a
feature-b

The previous location of feature comes from reflogs $2@{1} that simply means "second parameter (feature branch) previous location".

• | xargs -n 1 git rebase --onto $2 $2@{1} this bit pipes above mentioned list of branches into separate rebase commands for each and really translates into git rebase --onto feature C feature-a; git rebase --onto feature C feature-b