fix(gitlab): use diff_stats instead of changes_count for correct MR s…

backend/plugins/gitlab/models/migrationscripts/add_additions_deletions_to_mr.go

@@ -0,0 +1,32 @@
+package migrationscripts
+
+import (
+	"github.com/apache/incubator-devlake/core/context"
+	"github.com/apache/incubator-devlake/core/errors"
+	"github.com/apache/incubator-devlake/core/plugin"
+)
+
+var _ plugin.MigrationScript = (*addAdditionsDeletionsToMr)(nil)
+
+type mrAdditionsDeletions struct {
+	Additions int
+	Deletions int
+}
+
+func (mrAdditionsDeletions) TableName() string {
+	return "_tool_gitlab_merge_requests"
+}
+
+type addAdditionsDeletionsToMr struct{}
+
+func (*addAdditionsDeletionsToMr) Up(basicRes context.BasicRes) errors.Error {
+	return errors.Convert(basicRes.GetDal().AutoMigrate(&mrAdditionsDeletions{}))
+}
+
+func (*addAdditionsDeletionsToMr) Version() uint64 {
+	return 20260615000001
+}
+
+func (*addAdditionsDeletionsToMr) Name() string {
+	return "gitlab: add additions and deletions to merge requests"
+}

backend/plugins/gitlab/models/migrationscripts/register.go

@@ -53,5 +53,6 @@ func All() []plugin.MigrationScript {
 		new(changeIssueComponentType),
 		new(addIsChildToPipelines240906),
 		new(addPrSizeExcludedFileExtensions),
+		new(addAdditionsDeletionsToMr),
 	}
 }

backend/plugins/gitlab/models/mr.go

@@ -51,6 +51,8 @@ type GitlabMergeRequest struct {
 	AuthorUsername   string `gorm:"type:varchar(255)"`
 	AuthorUserId     int
 	Component        string `gorm:"type:varchar(255)"`
+	Additions         int        `gorm:"comment:Lines added in this MR diff only"`
+	Deletions         int        `gorm:"comment:Lines deleted in this MR diff only"`
 	common.NoPKModel
 }
 

backend/plugins/gitlab/tasks/mr_detail_collector.go

@@ -62,6 +62,7 @@ func CollectApiMergeRequestDetails(taskCtx plugin.SubTaskContext) errors.Error {
 		Query: func(reqData *helper.RequestData) (url.Values, errors.Error) {
 			query := url.Values{}
 			query.Set("with_stats", "true")
+			query.Set("include_diff_stats", "true")
 			return query, nil
 		},
 		ResponseParser: GetOneRawMessageFromResponse,

backend/plugins/gitlab/tasks/mr_extractor.go

@@ -65,6 +65,11 @@ type MergeRequestRes struct {
 	Assignees        []Assignee
 	FirstCommentTime common.Iso8601Time
 	Labels           []string `json:"labels"`
+	DiffStats *struct {
+		Additions int `json:"additions"`
+		Deletions int `json:"deletions"`
+	} `json:"diff_stats"`
+	ChangesCount string `json:"changes_count"`
 }
 
 type Reviewer struct {
@@ -246,6 +251,19 @@ func convertMergeRequest(mr *MergeRequestRes) (*models.GitlabMergeRequest, error
 		AuthorUsername:   mr.Author.Username,
 		AuthorUserId:     mr.Author.Id,
 	}
+	// Use diff_stats when available (GitLab 13.0+); fall back to changes_count
+	// for older self-managed instances that don't support include_diff_stats
+	if mr.DiffStats != nil && (mr.DiffStats.Additions > 0 || mr.DiffStats.Deletions > 0) {
+		gitlabMergeRequest.Additions = mr.DiffStats.Additions
+		gitlabMergeRequest.Deletions = mr.DiffStats.Deletions
+	}
+	else if mr.ChangesCount != "" && mr.ChangesCount != "0" {
+		count, err := strconv.Atoi(mr.ChangesCount)
+		if err == nil {
+			// changes_count is cumulative (bug source), but better than zero
+			gitlabMergeRequest.Additions = count
+		}
+	}
 	return gitlabMergeRequest, nil
 }