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package reachability
import (
"errors"
commitgraphread "codeberg.org/lindenii/furgit/format/commitgraph/read"
"codeberg.org/lindenii/furgit/objectid"
)
// IsAncestor reports whether ancestor is reachable from descendant via commit
// parent edges.
//
// Both inputs are peeled through annotated tags before commit traversal.
func (r *Reachability) IsAncestor(ancestor, descendant objectid.ObjectID) (bool, error) {
ancestorCommit, err := r.peelRootToDomain(ancestor, DomainCommits)
if err != nil {
return false, err
}
descendantCommit, err := r.peelRootToDomain(descendant, DomainCommits)
if err != nil {
return false, err
}
if ancestorCommit == descendantCommit {
return true, nil
}
graphResult, graphUsed, err := r.isAncestorGraph(ancestorCommit, descendantCommit)
if err != nil {
return false, err
}
if graphUsed {
return graphResult, nil
}
walk := r.Walk(DomainCommits, nil, map[objectid.ObjectID]struct{}{descendantCommit: {}})
for id := range walk.Seq() {
if id == ancestorCommit {
return true, nil
}
}
err = walk.Err()
if err != nil {
return false, err
}
return false, nil
}
func (r *Reachability) isAncestorGraph(ancestor, descendant objectid.ObjectID) (bool, bool, error) {
if r.graph == nil {
return false, false, nil
}
ancestorPos, err := r.graph.Lookup(ancestor)
if err != nil {
var notFound *commitgraphread.ErrNotFound
if errors.As(err, ¬Found) {
return false, false, nil
}
return false, true, err
}
descendantPos, err := r.graph.Lookup(descendant)
if err != nil {
var notFound *commitgraphread.ErrNotFound
if errors.As(err, ¬Found) {
return false, false, nil
}
return false, true, err
}
ancestorCommit, err := r.graph.CommitAt(ancestorPos)
if err != nil {
return false, true, err
}
ancestorGeneration := ancestorCommit.GenerationV2
stack := []commitgraphread.Position{descendantPos}
visited := make(map[commitgraphread.Position]struct{}, 64)
for len(stack) > 0 {
pos := stack[len(stack)-1]
stack = stack[:len(stack)-1]
if _, ok := visited[pos]; ok {
continue
}
visited[pos] = struct{}{}
if pos == ancestorPos {
return true, true, nil
}
commit, err := r.graph.CommitAt(pos)
if err != nil {
return false, true, err
}
if commit.GenerationV2 < ancestorGeneration {
continue
}
if commit.Parent1.Valid {
stack = append(stack, commit.Parent1.Pos)
}
if commit.Parent2.Valid {
stack = append(stack, commit.Parent2.Pos)
}
stack = append(stack, commit.ExtraParents...)
}
return false, true, nil
}
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