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package object
import (
"fmt"
"sort"
"github.com/go-git/go-git/v5/plumbing"
"github.com/go-git/go-git/v5/plumbing/storer"
)
// errIsReachable is thrown when first commit is an ancestor of the second
var errIsReachable = fmt.Errorf("first is reachable from second")
// MergeBase mimics the behavior of `git merge-base actual other`, returning the
// best common ancestor between the actual and the passed one.
// The best common ancestors can not be reached from other common ancestors.
func (c *Commit) MergeBase(other *Commit) ([]*Commit, error) {
// use sortedByCommitDateDesc strategy
sorted := sortByCommitDateDesc(c, other)
newer := sorted[0]
older := sorted[1]
newerHistory, err := ancestorsIndex(older, newer)
if err == errIsReachable {
return []*Commit{older}, nil
}
if err != nil {
return nil, err
}
var res []*Commit
inNewerHistory := isInIndexCommitFilter(newerHistory)
resIter := NewFilterCommitIter(older, &inNewerHistory, &inNewerHistory)
_ = resIter.ForEach(func(commit *Commit) error {
res = append(res, commit)
return nil
})
return Independents(res)
}
// IsAncestor returns true if the actual commit is ancestor of the passed one.
// It returns an error if the history is not transversable
// It mimics the behavior of `git merge --is-ancestor actual other`
func (c *Commit) IsAncestor(other *Commit) (bool, error) {
found := false
iter := NewCommitPreorderIter(other, nil, nil)
err := iter.ForEach(func(comm *Commit) error {
if comm.Hash != c.Hash {
return nil
}
found = true
return storer.ErrStop
})
return found, err
}
// ancestorsIndex returns a map with the ancestors of the starting commit if the
// excluded one is not one of them. It returns errIsReachable if the excluded commit
// is ancestor of the starting, or another error if the history is not traversable.
func ancestorsIndex(excluded, starting *Commit) (map[plumbing.Hash]struct{}, error) {
if excluded.Hash.String() == starting.Hash.String() {
return nil, errIsReachable
}
startingHistory := map[plumbing.Hash]struct{}{}
startingIter := NewCommitIterBSF(starting, nil, nil)
err := startingIter.ForEach(func(commit *Commit) error {
if commit.Hash == excluded.Hash {
return errIsReachable
}
startingHistory[commit.Hash] = struct{}{}
return nil
})
if err != nil {
return nil, err
}
return startingHistory, nil
}
// Independents returns a subset of the passed commits, that are not reachable the others
// It mimics the behavior of `git merge-base --independent commit...`.
func Independents(commits []*Commit) ([]*Commit, error) {
// use sortedByCommitDateDesc strategy
candidates := sortByCommitDateDesc(commits...)
candidates = removeDuplicated(candidates)
seen := map[plumbing.Hash]struct{}{}
var isLimit CommitFilter = func(commit *Commit) bool {
_, ok := seen[commit.Hash]
return ok
}
if len(candidates) < 2 {
return candidates, nil
}
pos := 0
for {
from := candidates[pos]
others := remove(candidates, from)
fromHistoryIter := NewFilterCommitIter(from, nil, &isLimit)
err := fromHistoryIter.ForEach(func(fromAncestor *Commit) error {
for _, other := range others {
if fromAncestor.Hash == other.Hash {
candidates = remove(candidates, other)
others = remove(others, other)
}
}
if len(candidates) == 1 {
return storer.ErrStop
}
seen[fromAncestor.Hash] = struct{}{}
return nil
})
if err != nil {
return nil, err
}
nextPos := indexOf(candidates, from) + 1
if nextPos >= len(candidates) {
break
}
pos = nextPos
}
return candidates, nil
}
// sortByCommitDateDesc returns the passed commits, sorted by `committer.When desc`
//
// Following this strategy, it is tried to reduce the time needed when walking
// the history from one commit to reach the others. It is assumed that ancestors
// use to be committed before its descendant;
// That way `Independents(A^, A)` will be processed as being `Independents(A, A^)`;
// so starting by `A` it will be reached `A^` way sooner than walking from `A^`
// to the initial commit, and then from `A` to `A^`.
func sortByCommitDateDesc(commits ...*Commit) []*Commit {
sorted := make([]*Commit, len(commits))
copy(sorted, commits)
sort.Slice(sorted, func(i, j int) bool {
return sorted[i].Committer.When.After(sorted[j].Committer.When)
})
return sorted
}
// indexOf returns the first position where target was found in the passed commits
func indexOf(commits []*Commit, target *Commit) int {
for i, commit := range commits {
if target.Hash == commit.Hash {
return i
}
}
return -1
}
// remove returns the passed commits excluding the commit toDelete
func remove(commits []*Commit, toDelete *Commit) []*Commit {
res := make([]*Commit, len(commits))
j := 0
for _, commit := range commits {
if commit.Hash == toDelete.Hash {
continue
}
res[j] = commit
j++
}
return res[:j]
}
// removeDuplicated removes duplicated commits from the passed slice of commits
func removeDuplicated(commits []*Commit) []*Commit {
seen := make(map[plumbing.Hash]struct{}, len(commits))
res := make([]*Commit, len(commits))
j := 0
for _, commit := range commits {
if _, ok := seen[commit.Hash]; ok {
continue
}
seen[commit.Hash] = struct{}{}
res[j] = commit
j++
}
return res[:j]
}
// isInIndexCommitFilter returns a commitFilter that returns true
// if the commit is in the passed index.
func isInIndexCommitFilter(index map[plumbing.Hash]struct{}) CommitFilter {
return func(c *Commit) bool {
_, ok := index[c.Hash]
return ok
}
}
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