Add ForceWithLease Push Option

--force-with-lease allows a push to force push with some safety
measures. If the ref on the remote is what we expect, then the force
push is allowed to happen.
See https://git-scm.com/docs/git-push#Documentation/git-push.txt---force-with-leaseltrefnamegt
for more information

1 files changed, 37 insertions, 6 deletions

diff --git a/remote.go b/remote.go
index 426bde9..fecdebf 100644
--- a/remote.go
+++ b/remote.go
@@ -326,7 +326,7 @@ func (r *Remote) newReferenceUpdateRequest(
 		}
 	}
 
-	if err := r.addReferencesToUpdate(o.RefSpecs, localRefs, remoteRefs, req, o.Prune); err != nil {
+	if err := r.addReferencesToUpdate(o.RefSpecs, localRefs, remoteRefs, req, o.Prune, o.ForceWithLease); err != nil {
 		return nil, err
 	}
 
@@ -568,6 +568,7 @@ func (r *Remote) addReferencesToUpdate(
 	remoteRefs storer.ReferenceStorer,
 	req *packp.ReferenceUpdateRequest,
 	prune bool,
+	forceWithLease *ForceWithLease,
 ) error {
 	// This references dictionary will be used to search references by name.
 	refsDict := make(map[string]*plumbing.Reference)
@@ -581,7 +582,7 @@ func (r *Remote) addReferencesToUpdate(
 				return err
 			}
 		} else {
-			err := r.addOrUpdateReferences(rs, localRefs, refsDict, remoteRefs, req)
+			err := r.addOrUpdateReferences(rs, localRefs, refsDict, remoteRefs, req, forceWithLease)
 			if err != nil {
 				return err
 			}
@@ -603,6 +604,7 @@ func (r *Remote) addOrUpdateReferences(
 	refsDict map[string]*plumbing.Reference,
 	remoteRefs storer.ReferenceStorer,
 	req *packp.ReferenceUpdateRequest,
+	forceWithLease *ForceWithLease,
 ) error {
 	// If it is not a wilcard refspec we can directly search for the reference
 	// in the references dictionary.
@@ -616,11 +618,11 @@ func (r *Remote) addOrUpdateReferences(
 			return nil
 		}
 
-		return r.addReferenceIfRefSpecMatches(rs, remoteRefs, ref, req)
+		return r.addReferenceIfRefSpecMatches(rs, remoteRefs, ref, req, forceWithLease)
 	}
 
 	for _, ref := range localRefs {
-		err := r.addReferenceIfRefSpecMatches(rs, remoteRefs, ref, req)
+		err := r.addReferenceIfRefSpecMatches(rs, remoteRefs, ref, req, forceWithLease)
 		if err != nil {
 			return err
 		}
@@ -706,7 +708,7 @@ func (r *Remote) addCommit(rs config.RefSpec,
 
 func (r *Remote) addReferenceIfRefSpecMatches(rs config.RefSpec,
 	remoteRefs storer.ReferenceStorer, localRef *plumbing.Reference,
-	req *packp.ReferenceUpdateRequest) error {
+	req *packp.ReferenceUpdateRequest, forceWithLease *ForceWithLease) error {
 
 	if localRef.Type() != plumbing.HashReference {
 		return nil
@@ -738,7 +740,11 @@ func (r *Remote) addReferenceIfRefSpecMatches(rs config.RefSpec,
 		return nil
 	}
 
-	if !rs.IsForceUpdate() {
+	if forceWithLease != nil {
+		if err = r.checkForceWithLease(localRef, cmd, forceWithLease); err != nil {
+			return err
+		}
+	} else if !rs.IsForceUpdate() {
 		if err := checkFastForwardUpdate(r.s, remoteRefs, cmd); err != nil {
 			return err
 		}
@@ -748,6 +754,31 @@ func (r *Remote) addReferenceIfRefSpecMatches(rs config.RefSpec,
 	return nil
 }
 
+func (r *Remote) checkForceWithLease(localRef *plumbing.Reference, cmd *packp.Command, forceWithLease *ForceWithLease) error {
+	remotePrefix := fmt.Sprintf("refs/remotes/%s/", r.Config().Name)
+
+	ref, err := storer.ResolveReference(
+		r.s,
+		plumbing.ReferenceName(remotePrefix+strings.Replace(localRef.Name().String(), "refs/heads/", "", -1)))
+	if err != nil {
+		return err
+	}
+
+	if forceWithLease.RefName.String() == "" || (forceWithLease.RefName == cmd.Name) {
+		expectedOID := ref.Hash()
+
+		if !forceWithLease.Hash.IsZero() {
+			expectedOID = forceWithLease.Hash
+		}
+
+		if cmd.Old != expectedOID {
+			return fmt.Errorf("non-fast-forward update: %s", cmd.Name.String())
+		}
+	}
+
+	return nil
+}
+
 func (r *Remote) references() ([]*plumbing.Reference, error) {
 	var localRefs []*plumbing.Reference