func (s *SearchService) MergeRequestsByGroup(gid interface{}, query string, opt *SearchOptions, options ...OptionFunc) ([]*MergeRequest, *Response, error) {
	var ms []*MergeRequest
	resp, err := s.searchByGroup(gid, "merge_requests", query, &ms, opt, options...)
	return ms, resp, err
}
MergeRequestsByGroup searches the expression within merge requests for
the specified group

GitLab API docs:
https://docs.gitlab.com/ce/api/search.html#scope-merge_requests
package gitlab
import (
	"fmt"
)
type SearchService struct {
	client *Client
}
type SearchOptions ListOptions
type searchOptions struct {
	SearchOptions
	Scope  string `url:"scope" json:"scope"`
	Search string `url:"search" json:"search"`
}
func (s *SearchService) Projects(query string, opt *SearchOptions, options ...OptionFunc) ([]*Project, *Response, error) {
	var ps []*Project
	resp, err := s.search("projects", query, &ps, opt, options...)
	return ps, resp, err
}
func (s *SearchService) ProjectsByGroup(gid interface{}, query string, opt *SearchOptions, options ...OptionFunc) ([]*Project, *Response, error) {
	var ps []*Project
	resp, err := s.searchByGroup(gid, "projects", query, &ps, opt, options...)
	return ps, resp, err
}
func (s *SearchService) Issues(query string, opt *SearchOptions, options ...OptionFunc) ([]*Issue, *Response, error) {
	var is []*Issue
	resp, err := s.search("issues", query, &is, opt, options...)
	return is, resp, err
}
func (s *SearchService) IssuesByGroup(gid interface{}, query string, opt *SearchOptions, options ...OptionFunc) ([]*Issue, *Response, error) {
	var is []*Issue
	resp, err := s.searchByGroup(gid, "issues", query, &is, opt, options...)
	return is, resp, err
}
func (s *SearchService) IssuesByProject(pid interface{}, query string, opt *SearchOptions, options ...OptionFunc) ([]*Issue, *Response, error) {
	var is []*Issue
	resp, err := s.searchByProject(pid, "issues", query, &is, opt, options...)
	return is, resp, err
}
func (s *SearchService) MergeRequests(query string, opt *SearchOptions, options ...OptionFunc) ([]*MergeRequest, *Response, error) {
	var ms []*MergeRequest
	resp, err := s.search("merge_requests", query, &ms, opt, options...)
	return ms, resp, err
}