Add "squash merge" support to merge API

api/swagger.yml

@@ -686,7 +686,14 @@ components:
           type: boolean
           default: false
           description: Allow merge when the branches have the same content
-
+        squash_merge:
+          type: boolean
+          default: true
+          description: |
+            If set, set only the destination branch as a parent, which "squashes" the merge to
+            appear as a single commit on the destination branch.  The source commit is no longer
+            a part of the merge commit; consider adding it to the 'metadata' or 'message'
+            fields.
     BranchCreation:
       type: object
       required:

docs/assets/js/swagger.yml

@@ -686,7 +686,14 @@ components:
           type: boolean
           default: false
           description: Allow merge when the branches have the same content
-
+        squash_merge:
+          type: boolean
+          default: true
+          description: |
+            If set, set only the destination branch as a parent, which "squashes" the merge to
+            appear as a single commit on the destination branch.  The source commit is no longer
+            a part of the merge commit; consider adding it to the 'metadata' or 'message'
+            fields.
     BranchCreation:
       type: object
       required:

pkg/api/controller.go

@@ -4809,6 +4809,7 @@ func (c *Controller) MergeIntoBranch(w http.ResponseWriter, r *http.Request, bod
 		swag.StringValue(body.Strategy),
 		graveler.WithForce(swag.BoolValue(body.Force)),
 		graveler.WithAllowEmpty(swag.BoolValue(body.AllowEmpty)),
+		graveler.WithSquashMerge(swag.BoolValue(body.SquashMerge)),
 	)
 
 	if errors.Is(err, graveler.ErrConflictFound) {

pkg/api/controller_test.go

@@ -3797,6 +3797,77 @@ func TestController_MergeIntoExplicitBranch(t *testing.T) {
 	}
 }
 
+func namer(number int) func(name string) string {
+	return func(name string) string {
+		return fmt.Sprint(name, number)
+	}
+}
+
+func TestController_MergeSquashing(t *testing.T) {
+	const numCommits = 3
+	clt, deps := setupClientWithAdmin(t)
+	ctx := context.Background()
+
+	// setup env
+	repo := testUniqueRepoName()
+	_, err := deps.catalog.CreateRepository(ctx, repo, onBlock(deps, repo), "main", false)
+	testutil.Must(t, err)
+	base, err := deps.catalog.CreateBranch(ctx, repo, "branch", "main")
+	testutil.Must(t, err)
+	baseCommit := base.Reference
+
+	for commitNumber := 1; commitNumber <= numCommits; commitNumber++ {
+		n := namer(commitNumber)
+		err = deps.catalog.CreateEntry(ctx, repo, "branch", catalog.DBEntry{Path: n("foo/bar"), PhysicalAddress: n("bar-addr"), CreationDate: time.Now(), Size: 1, Checksum: n("checksum")})
+		testutil.Must(t, err)
+		_, err = deps.catalog.Commit(ctx, repo, "branch", "some message", DefaultUserID, nil, nil, nil, false)
+		testutil.Must(t, err)
+	}
+
+	cases := []struct {
+		Name               string
+		Squash             bool
+		ExpectedNumCommits int
+	}{{
+		Name:   "regular",
+		Squash: false,
+		// Commits: 1 "created repository", numCommits on branch, 1 merge.
+		ExpectedNumCommits: numCommits + 2,
+	}, {
+		Name:   "squash",
+		Squash: true,
+		// Commits: 1 "created repository", 1 merge.
+		ExpectedNumCommits: 2,
+	}}
+	for _, tc := range cases {
+		t.Run(tc.Name, func(t *testing.T) {
+			destinationBranch := "main-" + tc.Name
+
+			_, err := deps.catalog.CreateBranch(ctx, repo, destinationBranch, "main")
+			testutil.Must(t, err)
+
+			mergeResp, err := clt.MergeIntoBranchWithResponse(ctx, repo, "branch", destinationBranch, apigen.MergeIntoBranchJSONRequestBody{SquashMerge: &tc.Squash})
+			testutil.MustDo(t, "perform merge into branch", err)
+			if !apiutil.IsStatusCodeOK(mergeResp.StatusCode()) {
+				t.Fatal("merge request failed", mergeResp.Status())
+			}
+
+			commits, hasMore, err := deps.catalog.ListCommits(ctx, repo, destinationBranch, catalog.LogParams{Amount: numCommits + 5, StopAt: baseCommit})
+			testutil.MustDo(t, "log from merged commit", err)
+			if hasMore {
+				t.Errorf("Got pagination after %d results when no pagination expected", len(commits))
+			}
+
+			if len(commits) != tc.ExpectedNumCommits {
+				for i, commit := range commits {
+					t.Log(i, "  ", commit)
+				}
+				t.Errorf("Got %d commits when expecting %d", len(commits), tc.ExpectedNumCommits)
+			}
+		})
+	}
+}
+
 func TestController_MergeDirtyBranch(t *testing.T) {
 	clt, deps := setupClientWithAdmin(t)
 	ctx := context.Background()

pkg/graveler/graveler.go

@@ -196,6 +196,9 @@ type SetOptions struct {
 	AllowEmpty bool
 	// Hidden Will create the branch with the hidden property
 	Hidden bool
+	// SquashMerge causes merge commits to be "squashed", losing parent
+	// information about the merged-from branch.
+	SquashMerge bool
 }
 
 type SetOptionsFunc func(opts *SetOptions)
@@ -232,6 +235,12 @@ func WithHidden(v bool) SetOptionsFunc {
 	}
 }
 
+func WithSquashMerge(v bool) SetOptionsFunc {
+	return func(opts *SetOptions) {
+		opts.SquashMerge = v
+	}
+}
+
 // ListOptions controls list request defaults
 type ListOptions struct {
 	// Shows entities marked as hidden
@@ -2926,7 +2935,11 @@ func (g *Graveler) Merge(ctx context.Context, repository *RepositoryRecord, dest
 		commit.Committer = commitParams.Committer
 		commit.Message = commitParams.Message
 		commit.MetaRangeID = metaRangeID
-		commit.Parents = []CommitID{toCommit.CommitID, fromCommit.CommitID}
+		if options.SquashMerge {
+			commit.Parents = []CommitID{toCommit.CommitID}
+		} else {
+			commit.Parents = []CommitID{toCommit.CommitID, fromCommit.CommitID}
+		}
 		if toCommit.Generation > fromCommit.Generation {
 			commit.Generation = toCommit.Generation + 1
 		} else {