Add Feature Flags baseline (#192)

* Add Feature Flags baseline

This commit adds the service, ensures that the service gets instanciated
with the rest and provides the required types and method to list
features flags.

* Add SetFeatureFlag method to FeaturesService

This commit allows to create and modify feature flags by setting their
values

* Change doc urls and simplify use of values according to docs too

feature_flags.go

+package gitlab
+
+import (
+	"fmt"
+	"net/url"
+)
+
+// FeaturesService handles the communication with the application FeaturesService
+// related methods of the GitLab API.
+//
+// GitLab API docs:
+// https://docs.gitlab.com/ce/api/features.html
+type FeaturesService struct {
+	client *Client
+}
+
+// Feature represents a GitLab feature flag.
+//
+// GitLab API docs:
+// https://docs.gitlab.com/ce/api/features.html
+type Feature struct {
+	Name  string `json:"name"`
+	State string `json:"state"`
+	Gates []Gate
+}
+
+// Gate represents a gate of a GitLab feature flag.
+//
+// GitLab API docs:
+// https://docs.gitlab.com/ce/api/features.html
+type Gate struct {
+	Key   string      `json:"key"`
+	Value interface{} `json:"value"`
+}
+
+func (f Feature) String() string {
+	return Stringify(f)
+}
+
+// ListFeatures gets a list of feature flags
+//
+// GitLab API docs:
+// https://docs.gitlab.com/ce/api/features.html
+func (s *FeaturesService) ListFeatures(options ...OptionFunc) ([]*Feature, *Response, error) {
+	req, err := s.client.NewRequest("GET", "features", nil, options)
+	if err != nil {
+		return nil, nil, err
+	}
+
+	var f []*Feature
+	resp, err := s.client.Do(req, &f)
+	if err != nil {
+		return nil, resp, err
+	}
+	return f, resp, err
+}
+
+// SetFeatureFlag sets or creates a feature flag gate
+//
+// GitLab API docs:
+// https://docs.gitlab.com/ce/api/features.html
+func (s *FeaturesService) SetFeatureFlag(name string, value interface{}, options ...OptionFunc) (*Feature, *Response, error) {
+	u := fmt.Sprintf("features/%s", url.QueryEscape(name))
+
+	opt := struct {
+		Value interface{} `url:"value" json:"value"`
+	}{
+		value,
+	}
+
+	req, err := s.client.NewRequest("POST", u, opt, options)
+	if err != nil {
+		return nil, nil, err
+	}
+
+	f := &Feature{}
+	resp, err := s.client.Do(req, f)
+	if err != nil {
+		return nil, resp, err
+	}
+	return f, resp, err
+}

feature_flags_test.go

+package gitlab
+
+import (
+	"fmt"
+	"net/http"
+	"reflect"
+	"testing"
+)
+
+func TestListFeatureFlags(t *testing.T) {
+	mux, server, client := setup()
+	defer teardown(server)
+
+	mux.HandleFunc("/features", func(w http.ResponseWriter, r *http.Request) {
+		testMethod(t, r, "GET")
+		fmt.Fprint(w, `
+		[
+			{
+			  "name": "experimental_feature",
+			  "state": "off",
+			  "gates": [
+				{
+				  "key": "boolean",
+				  "value": false
+				}
+			  ]
+			},
+			{
+			  "name": "new_library",
+			  "state": "on"
+			}
+		  ]
+	`)
+	})
+
+	features, _, err := client.Features.ListFeatures()
+	if err != nil {
+		t.Errorf("Features.ListFeatures returned error: %v", err)
+	}
+
+	want := []*Feature{
+		{Name: "experimental_feature", State: "off", Gates: []Gate{
+			{Key: "boolean", Value: false},
+		}},
+		{Name: "new_library", State: "on"},
+	}
+	if !reflect.DeepEqual(want, features) {
+		t.Errorf("Features.ListFeatures returned %+v, want %+v", features, want)
+	}
+}
+
+func TestSetFeatureFlag(t *testing.T) {
+	mux, server, client := setup()
+	defer teardown(server)
+
+	mux.HandleFunc("/features/new_library", func(w http.ResponseWriter, r *http.Request) {
+		testMethod(t, r, "POST")
+		fmt.Fprint(w, `
+		{
+			"name": "new_library",
+			"state": "conditional",
+			"gates": [
+			  {
+				"key": "boolean",
+				"value": false
+			  },
+			  {
+				"key": "percentage_of_time",
+				"value": 30
+			  }
+			]
+		  }
+		`)
+	})
+
+	feature, _, err := client.Features.SetFeatureFlag("new_library", "30")
+	if err != nil {
+		t.Errorf("Features.SetFeatureFlag returned error: %v", err)
+	}
+
+	want := &Feature{
+		Name:  "new_library",
+		State: "conditional",
+		Gates: []Gate{
+			{Key: "boolean", Value: false},
+			{Key: "percentage_of_time", Value: 30.0},
+		},
+	}
+	if !reflect.DeepEqual(want, feature) {
+		t.Errorf("Features.SetFeatureFlag returned %+v, want %+v", feature, want)
+	}
+}

gitlab.go

@@ -165,6 +165,7 @@ type Client struct {
 	BuildVariables       *BuildVariablesService
 	Commits              *CommitsService
 	DeployKeys           *DeployKeysService
+	Features             *FeaturesService
 	Groups               *GroupsService
 	Issues               *IssuesService
 	Jobs                 *JobsService
@@ -230,6 +231,7 @@ func newClient(httpClient *http.Client, tokenType tokenType, token string) *Clie
 	c.BuildVariables = &BuildVariablesService{client: c}
 	c.Commits = &CommitsService{client: c}
 	c.DeployKeys = &DeployKeysService{client: c}
+	c.Features = &FeaturesService{client: c}
 	c.Groups = &GroupsService{client: c}
 	c.Issues = &IssuesService{client: c}
 	c.Jobs = &JobsService{client: c}