buildenv/envs.go - build - Git at Google

 // Copyright 2011 The Go Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.

 // Package buildenv contains definitions for the
 // environments the Go build system can run in.
 package buildenv

 import (
 	"context"
 	"flag"
 	"fmt"
 	"log"
 	"math/rand"
 	"os"
 	"path/filepath"
 	"strings"
 	"sync"

 	"golang.org/x/oauth2"
 	"golang.org/x/oauth2/google"
 	compute "google.golang.org/api/compute/v1"
 	oauth2api "google.golang.org/api/oauth2/v2"
 )

 const (
 	prefix = "https://www.googleapis.com/compute/v1/projects/"
 )

 // KubeConfig describes the configuration of a Kubernetes cluster.
 type KubeConfig struct {
 	// MinNodes is the minimum number of nodes in the Kubernetes cluster.
 	// The autoscaler will ensure that at least this many nodes is always
 	// running despite any scale-down decision.
 	MinNodes int64

 	// MaxNodes is the maximum number of nodes that the autoscaler can
 	// provision in the Kubernetes cluster.
 	// If MaxNodes is 0, Kubernetes is not used.
 	MaxNodes int64

 	// MachineType is the GCE machine type to use for the Kubernetes cluster nodes.
 	MachineType string

 	// Name is the name of the Kubernetes cluster that will be created.
 	Name string
 }

 // Environment describes the configuration of the infrastructure for a
 // coordinator and its buildlet resources running on Google Cloud Platform.
 // Staging and Production are the two common build environments.
 type Environment struct {
 	// The GCP project name that the build infrastructure will be provisioned in.
 	// This field may be overridden as necessary without impacting other fields.
 	ProjectName string

 	// ProjectNumber is the GCP project's number, as visible in the admin console.
 	// This is used for things such as constructing the "email" of the default
 	// service account.
 	ProjectNumber int64

 	// The IsProd flag indicates whether production functionality should be
 	// enabled. When true, GCE and Kubernetes builders are enabled and the
 	// coordinator serves on 443. Otherwise, GCE and Kubernetes builders are
 	// disabled and the coordinator serves on 8119.
 	IsProd bool

 	// ControlZone is the GCE zone that the coordinator instance and Kubernetes cluster
 	// will run in. This field may be overridden as necessary without impacting
 	// other fields.
 	ControlZone string

 	// VMZones are the GCE zones that the VMs will be deployed to. These
 	// GCE zones will be periodically cleaned by deleting old VMs. The zones
 	// should all exist within a single region.
 	VMZones []string

 	// StaticIP is the public, static IP address that will be attached to the
 	// coordinator instance. The zero value means the address will be looked
 	// up by name. This field is optional.
 	StaticIP string

 	// MachineType is the GCE machine type to use for the coordinator.
 	MachineType string

 	// KubeBuild is the Kubernetes config for the buildlet cluster.
 	KubeBuild KubeConfig
 	// KubeTools is the Kubernetes config for the tools cluster.
 	KubeTools KubeConfig

 	// PreferContainersOnCOS controls whether we do most builds on
 	// Google's Container-Optimized OS Linux image running on a VM
 	// rather than using Kubernetes for builds. This does not
 	// affect cross-compiled builds just running make.bash. Those
 	// still use Kubernetes for now.
 	// See https://golang.org/issue/25108.
 	PreferContainersOnCOS bool

 	// DashURL is the base URL of the build dashboard, ending in a slash.
 	DashURL string

 	// PerfDataURL is the base URL of the benchmark storage server.
 	PerfDataURL string

 	// CoordinatorName is the hostname of the coordinator instance.
 	CoordinatorName string

 	// BuildletBucket is the GCS bucket that stores buildlet binaries.
 	// TODO: rename. this is not just for buildlets; also for bootstrap.
 	BuildletBucket string

 	// LogBucket is the GCS bucket to which logs are written.
 	LogBucket string

 	// SnapBucket is the GCS bucket to which snapshots of
 	// completed builds (after make.bash, before tests) are
 	// written.
 	SnapBucket string

 	// MaxBuilds is the maximum number of concurrent builds that
 	// can run. Zero means unlimited. This is typically only used
 	// in a development or staging environment.
 	MaxBuilds int

 	// AutoCertCacheBucket is the GCS bucket to use for the
 	// golang.org/x/crypto/acme/autocert (LetsEncrypt) cache.
 	// If empty, LetsEncrypt isn't used.
 	AutoCertCacheBucket string

 	// COSServiceAccount (Container Optimized OS) is the service
 	// account that will be assigned to a VM instance that hosts
 	// a container when the instance is created.
 	COSServiceAccount string
 }

 // ComputePrefix returns the URI prefix for Compute Engine resources in a project.
 func (e Environment) ComputePrefix() string {
 	return prefix + e.ProjectName
 }

 // RandomVMZone returns a randomly selected zone from the zones in VMZones.
 // The Zone value will be returned if VMZones is not set.
 func (e Environment) RandomVMZone() string {
 	if len(e.VMZones) == 0 {
 		return e.ControlZone
 	}
 	return e.VMZones[rand.Intn(len(e.VMZones))]
 }

 // Region returns the GCE region, derived from its zone.
 func (e Environment) Region() string {
 	return e.ControlZone[:strings.LastIndex(e.ControlZone, "-")]
 }

 // SnapshotURL returns the absolute URL of the .tar.gz containing a
 // built Go tree for the builderType and Go rev (40 character Git
 // commit hash). The tarball is suitable for passing to
 // (*buildlet.Client).PutTarFromURL.
 func (e Environment) SnapshotURL(builderType, rev string) string {
 	return fmt.Sprintf("https://storage.googleapis.com/%s/go/%s/%s.tar.gz", e.SnapBucket, builderType, rev)
 }

 // DashBase returns the base URL of the build dashboard, ending in a slash.
 func (e Environment) DashBase() string {
 	// TODO(quentin): Should we really default to production? That's what the old code did.
 	if e.DashURL != "" {
 		return e.DashURL
 	}
 	return Production.DashURL
 }

 // Credentials returns the credentials required to access the GCP environment
 // with the necessary scopes.
 func (e Environment) Credentials(ctx context.Context) (*google.Credentials, error) {
 	// TODO: this method used to do much more. maybe remove it
 	// when TODO below is addressed, pushing scopes to caller? Or
 	// add a Scopes func/method somewhere instead?
 	scopes := []string{
 		// Cloud Platform should include all others, but the
 		// old code duplicated compute and the storage full
 		// control scopes, so I leave them here for now. They
 		// predated the all-encompassing "cloud platform"
 		// scope anyway.
 		// TODO: remove compute and DevstorageFullControlScope once verified to work
 		// without.
 		compute.CloudPlatformScope,
 		compute.ComputeScope,
 		compute.DevstorageFullControlScope,

 		// The coordinator needed the userinfo email scope for
 		// reporting to the perf dashboard running on App
 		// Engine at one point. The perf dashboard is down at
 		// the moment, but when it's back up we'll need this,
 		// and if we do other authenticated requests to App
 		// Engine apps, this would be useful.
 		oauth2api.UserinfoEmailScope,
 	}
 	creds, err := google.FindDefaultCredentials(ctx, scopes...)
 	if err != nil {
 		CheckUserCredentials()
 		return nil, err
 	}
 	creds.TokenSource = diagnoseFailureTokenSource{creds.TokenSource}
 	return creds, nil
 }

 // ByProjectID returns an Environment for the specified
 // project ID. It is currently limited to the symbolic-datum-552
 // and go-dashboard-dev projects.
 // ByProjectID will panic if the project ID is not known.
 func ByProjectID(projectID string) *Environment {
 	var envKeys []string

 	for k := range possibleEnvs {
 		envKeys = append(envKeys, k)
 	}

 	var env *Environment
 	env, ok := possibleEnvs[projectID]
 	if !ok {
 		panic(fmt.Sprintf("Can't get buildenv for unknown project %q. Possible envs are %s", projectID, envKeys))
 	}

 	return env
 }

 // Staging defines the environment that the coordinator and build
 // infrastructure is deployed to before it is released to production.
 // For local dev, override the project with the program's flag to set
 // a custom project.
 var Staging = &Environment{
 	ProjectName:           "go-dashboard-dev",
 	ProjectNumber:         302018677728,
 	IsProd:                true,
 	ControlZone:           "us-central1-f",
 	VMZones:               []string{"us-central1-a", "us-central1-b", "us-central1-c", "us-central1-f"},
 	StaticIP:              "104.154.113.235",
 	MachineType:           "n1-standard-1",
 	PreferContainersOnCOS: true,
 	KubeBuild: KubeConfig{
 		MinNodes:    1,
 		MaxNodes:    1, // auto-scaling disabled
 		Name:        "buildlets",
 		MachineType: "n1-standard-4", // only used for make.bash due to PreferContainersOnCOS
 	},
 	KubeTools: KubeConfig{
 		MinNodes:    3,
 		MaxNodes:    3,
 		Name:        "go",
 		MachineType: "n1-standard-4",
 	},
 	DashURL:           "https://go-dashboard-dev.appspot.com/",
 	PerfDataURL:       "https://perfdata.golang.org",
 	CoordinatorName:   "farmer",
 	BuildletBucket:    "dev-go-builder-data",
 	LogBucket:         "dev-go-build-log",
 	SnapBucket:        "dev-go-build-snap",
 	COSServiceAccount: "linux-cos-builders@go-dashboard-dev.iam.gserviceaccount.com",
 }

 // Production defines the environment that the coordinator and build
 // infrastructure is deployed to for production usage at build.golang.org.
 var Production = &Environment{
 	ProjectName:           "symbolic-datum-552",
 	ProjectNumber:         872405196845,
 	IsProd:                true,
 	ControlZone:           "us-central1-f",
 	VMZones:               []string{"us-central1-a", "us-central1-b", "us-central1-c", "us-central1-f"},
 	StaticIP:              "107.178.219.46",
 	MachineType:           "n1-standard-4",
 	PreferContainersOnCOS: true,
 	KubeBuild: KubeConfig{
 		MinNodes:    2,
 		MaxNodes:    2, // auto-scaling disabled
 		Name:        "buildlets",
 		MachineType: "n1-standard-4", // only used for make.bash due to PreferContainersOnCOS
 	},
 	KubeTools: KubeConfig{
 		MinNodes:    4,
 		MaxNodes:    4,
 		Name:        "go",
 		MachineType: "n1-standard-4",
 	},
 	DashURL:             "https://build.golang.org/",
 	PerfDataURL:         "https://perfdata.golang.org",
 	CoordinatorName:     "farmer",
 	BuildletBucket:      "go-builder-data",
 	LogBucket:           "go-build-log",
 	SnapBucket:          "go-build-snap",
 	AutoCertCacheBucket: "farmer-golang-org-autocert-cache",
 	COSServiceAccount:   "linux-cos-builders@symbolic-datum-552.iam.gserviceaccount.com",
 }

 var Development = &Environment{
 	IsProd:   false,
 	StaticIP: "127.0.0.1",
 }

 // possibleEnvs enumerate the known buildenv.Environment definitions.
 var possibleEnvs = map[string]*Environment{
 	"dev":                Development,
 	"symbolic-datum-552": Production,
 	"go-dashboard-dev":   Staging,
 }

 var (
 	stagingFlag     bool
 	localDevFlag    bool
 	registeredFlags bool
 )

 // RegisterFlags registers the "staging" and "localdev" flags.
 func RegisterFlags() {
 	if registeredFlags {
 		panic("duplicate call to RegisterFlags or RegisterStagingFlag")
 	}
 	flag.BoolVar(&localDevFlag, "localdev", false, "use the localhost in-development coordinator")
 	RegisterStagingFlag()
 	registeredFlags = true
 }

 // RegisterStagingFlag registers the "staging" flag.
 func RegisterStagingFlag() {
 	if registeredFlags {
 		panic("duplicate call to RegisterFlags or RegisterStagingFlag")
 	}
 	flag.BoolVar(&stagingFlag, "staging", false, "use the staging build coordinator and buildlets")
 	registeredFlags = true
 }

 // FromFlags returns the build environment specified from flags,
 // as registered by RegisterFlags or RegisterStagingFlag.
 // By default it returns the production environment.
 func FromFlags() *Environment {
 	if !registeredFlags {
 		panic("FromFlags called without RegisterFlags")
 	}
 	if localDevFlag {
 		return Development
 	}
 	if stagingFlag {
 		return Staging
 	}
 	return Production
 }

 // warnCredsOnce guards CheckUserCredentials spamming stderr. Once is enough.
 var warnCredsOnce sync.Once

 // CheckUserCredentials warns if the gcloud Application Default Credentials file doesn't exist
 // and says how to log in properly.
 func CheckUserCredentials() {
 	adcJSON := filepath.Join(os.Getenv("HOME"), ".config/gcloud/application_default_credentials.json")
 	if _, err := os.Stat(adcJSON); os.IsNotExist(err) {
 		warnCredsOnce.Do(func() {
 			log.Printf("warning: file %s does not exist; did you run 'gcloud auth application-default login' ? (The 'application-default' part matters, confusingly.)", adcJSON)
 		})
 	}
 }

 // diagnoseFailureTokenSource is an oauth2.TokenSource wrapper that,
 // upon failure, diagnoses why the token acquistion might've failed.
 type diagnoseFailureTokenSource struct {
 	ts oauth2.TokenSource
 }

 func (ts diagnoseFailureTokenSource) Token() (*oauth2.Token, error) {
 	t, err := ts.ts.Token()
 	if err != nil {
 		CheckUserCredentials()
 		return nil, err
 	}
 	return t, nil
 }
	// Copyright 2011 The Go Authors. All rights reserved.
	// Use of this source code is governed by a BSD-style
	// license that can be found in the LICENSE file.

	// Package buildenv contains definitions for the
	// environments the Go build system can run in.
	package buildenv

	import (
	"context"
	"flag"
	"fmt"
	"log"
	"math/rand"
	"os"
	"path/filepath"
	"strings"
	"sync"

	"golang.org/x/oauth2"
	"golang.org/x/oauth2/google"
	compute "google.golang.org/api/compute/v1"
	oauth2api "google.golang.org/api/oauth2/v2"
	)

	const (
	prefix = "https://www.googleapis.com/compute/v1/projects/"
	)

	// KubeConfig describes the configuration of a Kubernetes cluster.
	type KubeConfig struct {
	// MinNodes is the minimum number of nodes in the Kubernetes cluster.
	// The autoscaler will ensure that at least this many nodes is always
	// running despite any scale-down decision.
	MinNodes int64

	// MaxNodes is the maximum number of nodes that the autoscaler can
	// provision in the Kubernetes cluster.
	// If MaxNodes is 0, Kubernetes is not used.
	MaxNodes int64

	// MachineType is the GCE machine type to use for the Kubernetes cluster nodes.
	MachineType string

	// Name is the name of the Kubernetes cluster that will be created.
	Name string
	}

	// Environment describes the configuration of the infrastructure for a
	// coordinator and its buildlet resources running on Google Cloud Platform.
	// Staging and Production are the two common build environments.
	type Environment struct {
	// The GCP project name that the build infrastructure will be provisioned in.
	// This field may be overridden as necessary without impacting other fields.
	ProjectName string

	// ProjectNumber is the GCP project's number, as visible in the admin console.
	// This is used for things such as constructing the "email" of the default
	// service account.
	ProjectNumber int64

	// The IsProd flag indicates whether production functionality should be
	// enabled. When true, GCE and Kubernetes builders are enabled and the
	// coordinator serves on 443. Otherwise, GCE and Kubernetes builders are
	// disabled and the coordinator serves on 8119.
	IsProd bool

	// ControlZone is the GCE zone that the coordinator instance and Kubernetes cluster
	// will run in. This field may be overridden as necessary without impacting
	// other fields.
	ControlZone string

	// VMZones are the GCE zones that the VMs will be deployed to. These
	// GCE zones will be periodically cleaned by deleting old VMs. The zones
	// should all exist within a single region.
	VMZones []string

	// StaticIP is the public, static IP address that will be attached to the
	// coordinator instance. The zero value means the address will be looked
	// up by name. This field is optional.
	StaticIP string

	// MachineType is the GCE machine type to use for the coordinator.
	MachineType string

	// KubeBuild is the Kubernetes config for the buildlet cluster.
	KubeBuild KubeConfig
	// KubeTools is the Kubernetes config for the tools cluster.
	KubeTools KubeConfig

	// PreferContainersOnCOS controls whether we do most builds on
	// Google's Container-Optimized OS Linux image running on a VM
	// rather than using Kubernetes for builds. This does not
	// affect cross-compiled builds just running make.bash. Those
	// still use Kubernetes for now.
	// See https://golang.org/issue/25108.
	PreferContainersOnCOS bool

	// DashURL is the base URL of the build dashboard, ending in a slash.
	DashURL string

	// PerfDataURL is the base URL of the benchmark storage server.
	PerfDataURL string

	// CoordinatorName is the hostname of the coordinator instance.
	CoordinatorName string

	// BuildletBucket is the GCS bucket that stores buildlet binaries.
	// TODO: rename. this is not just for buildlets; also for bootstrap.
	BuildletBucket string

	// LogBucket is the GCS bucket to which logs are written.
	LogBucket string

	// SnapBucket is the GCS bucket to which snapshots of
	// completed builds (after make.bash, before tests) are
	// written.
	SnapBucket string

	// MaxBuilds is the maximum number of concurrent builds that
	// can run. Zero means unlimited. This is typically only used
	// in a development or staging environment.
	MaxBuilds int

	// AutoCertCacheBucket is the GCS bucket to use for the
	// golang.org/x/crypto/acme/autocert (LetsEncrypt) cache.
	// If empty, LetsEncrypt isn't used.
	AutoCertCacheBucket string

	// COSServiceAccount (Container Optimized OS) is the service
	// account that will be assigned to a VM instance that hosts
	// a container when the instance is created.
	COSServiceAccount string
	}

	// ComputePrefix returns the URI prefix for Compute Engine resources in a project.
	func (e Environment) ComputePrefix() string {
	return prefix + e.ProjectName
	}

	// RandomVMZone returns a randomly selected zone from the zones in VMZones.
	// The Zone value will be returned if VMZones is not set.
	func (e Environment) RandomVMZone() string {
	if len(e.VMZones) == 0 {
	return e.ControlZone
	}
	return e.VMZones[rand.Intn(len(e.VMZones))]
	}

	// Region returns the GCE region, derived from its zone.
	func (e Environment) Region() string {
	return e.ControlZone[:strings.LastIndex(e.ControlZone, "-")]
	}

	// SnapshotURL returns the absolute URL of the .tar.gz containing a
	// built Go tree for the builderType and Go rev (40 character Git
	// commit hash). The tarball is suitable for passing to
	// (*buildlet.Client).PutTarFromURL.
	func (e Environment) SnapshotURL(builderType, rev string) string {
	return fmt.Sprintf("https://storage.googleapis.com/%s/go/%s/%s.tar.gz", e.SnapBucket, builderType, rev)
	}

	// DashBase returns the base URL of the build dashboard, ending in a slash.
	func (e Environment) DashBase() string {
	// TODO(quentin): Should we really default to production? That's what the old code did.
	if e.DashURL != "" {
	return e.DashURL
	}
	return Production.DashURL
	}

	// Credentials returns the credentials required to access the GCP environment
	// with the necessary scopes.
	func (e Environment) Credentials(ctx context.Context) (*google.Credentials, error) {
	// TODO: this method used to do much more. maybe remove it
	// when TODO below is addressed, pushing scopes to caller? Or
	// add a Scopes func/method somewhere instead?
	scopes := []string{
	// Cloud Platform should include all others, but the
	// old code duplicated compute and the storage full
	// control scopes, so I leave them here for now. They
	// predated the all-encompassing "cloud platform"
	// scope anyway.
	// TODO: remove compute and DevstorageFullControlScope once verified to work
	// without.
	compute.CloudPlatformScope,
	compute.ComputeScope,
	compute.DevstorageFullControlScope,

	// The coordinator needed the userinfo email scope for
	// reporting to the perf dashboard running on App
	// Engine at one point. The perf dashboard is down at
	// the moment, but when it's back up we'll need this,
	// and if we do other authenticated requests to App
	// Engine apps, this would be useful.
	oauth2api.UserinfoEmailScope,
	}
	creds, err := google.FindDefaultCredentials(ctx, scopes...)
	if err != nil {
	CheckUserCredentials()
	return nil, err
	}
	creds.TokenSource = diagnoseFailureTokenSource{creds.TokenSource}
	return creds, nil
	}

	// ByProjectID returns an Environment for the specified
	// project ID. It is currently limited to the symbolic-datum-552
	// and go-dashboard-dev projects.
	// ByProjectID will panic if the project ID is not known.
	func ByProjectID(projectID string) *Environment {
	var envKeys []string

	for k := range possibleEnvs {
	envKeys = append(envKeys, k)
	}

	var env *Environment
	env, ok := possibleEnvs[projectID]
	if !ok {
	panic(fmt.Sprintf("Can't get buildenv for unknown project %q. Possible envs are %s", projectID, envKeys))
	}

	return env
	}

	// Staging defines the environment that the coordinator and build
	// infrastructure is deployed to before it is released to production.
	// For local dev, override the project with the program's flag to set
	// a custom project.
	var Staging = &Environment{
	ProjectName: "go-dashboard-dev",
	ProjectNumber: 302018677728,
	IsProd: true,
	ControlZone: "us-central1-f",
	VMZones: []string{"us-central1-a", "us-central1-b", "us-central1-c", "us-central1-f"},
	StaticIP: "104.154.113.235",
	MachineType: "n1-standard-1",
	PreferContainersOnCOS: true,
	KubeBuild: KubeConfig{
	MinNodes: 1,
	MaxNodes: 1, // auto-scaling disabled
	Name: "buildlets",
	MachineType: "n1-standard-4", // only used for make.bash due to PreferContainersOnCOS
	},
	KubeTools: KubeConfig{
	MinNodes: 3,
	MaxNodes: 3,
	Name: "go",
	MachineType: "n1-standard-4",
	},
	DashURL: "https://go-dashboard-dev.appspot.com/",
	PerfDataURL: "https://perfdata.golang.org",
	CoordinatorName: "farmer",
	BuildletBucket: "dev-go-builder-data",
	LogBucket: "dev-go-build-log",
	SnapBucket: "dev-go-build-snap",
	COSServiceAccount: "linux-cos-builders@go-dashboard-dev.iam.gserviceaccount.com",
	}

	// Production defines the environment that the coordinator and build
	// infrastructure is deployed to for production usage at build.golang.org.
	var Production = &Environment{
	ProjectName: "symbolic-datum-552",
	ProjectNumber: 872405196845,
	IsProd: true,
	ControlZone: "us-central1-f",
	VMZones: []string{"us-central1-a", "us-central1-b", "us-central1-c", "us-central1-f"},
	StaticIP: "107.178.219.46",
	MachineType: "n1-standard-4",
	PreferContainersOnCOS: true,
	KubeBuild: KubeConfig{
	MinNodes: 2,
	MaxNodes: 2, // auto-scaling disabled
	Name: "buildlets",
	MachineType: "n1-standard-4", // only used for make.bash due to PreferContainersOnCOS
	},
	KubeTools: KubeConfig{
	MinNodes: 4,
	MaxNodes: 4,
	Name: "go",
	MachineType: "n1-standard-4",
	},
	DashURL: "https://build.golang.org/",
	PerfDataURL: "https://perfdata.golang.org",
	CoordinatorName: "farmer",
	BuildletBucket: "go-builder-data",
	LogBucket: "go-build-log",
	SnapBucket: "go-build-snap",
	AutoCertCacheBucket: "farmer-golang-org-autocert-cache",
	COSServiceAccount: "linux-cos-builders@symbolic-datum-552.iam.gserviceaccount.com",
	}

	var Development = &Environment{
	IsProd: false,
	StaticIP: "127.0.0.1",
	}

	// possibleEnvs enumerate the known buildenv.Environment definitions.
	var possibleEnvs = map[string]*Environment{
	"dev": Development,
	"symbolic-datum-552": Production,
	"go-dashboard-dev": Staging,
	}

	var (
	stagingFlag bool
	localDevFlag bool
	registeredFlags bool
	)

	// RegisterFlags registers the "staging" and "localdev" flags.
	func RegisterFlags() {
	if registeredFlags {
	panic("duplicate call to RegisterFlags or RegisterStagingFlag")
	}
	flag.BoolVar(&localDevFlag, "localdev", false, "use the localhost in-development coordinator")
	RegisterStagingFlag()
	registeredFlags = true
	}

	// RegisterStagingFlag registers the "staging" flag.
	func RegisterStagingFlag() {
	if registeredFlags {
	panic("duplicate call to RegisterFlags or RegisterStagingFlag")
	}
	flag.BoolVar(&stagingFlag, "staging", false, "use the staging build coordinator and buildlets")
	registeredFlags = true
	}

	// FromFlags returns the build environment specified from flags,
	// as registered by RegisterFlags or RegisterStagingFlag.
	// By default it returns the production environment.
	func FromFlags() *Environment {
	if !registeredFlags {
	panic("FromFlags called without RegisterFlags")
	}
	if localDevFlag {
	return Development
	}
	if stagingFlag {
	return Staging
	}
	return Production
	}

	// warnCredsOnce guards CheckUserCredentials spamming stderr. Once is enough.
	var warnCredsOnce sync.Once

	// CheckUserCredentials warns if the gcloud Application Default Credentials file doesn't exist
	// and says how to log in properly.
	func CheckUserCredentials() {
	adcJSON := filepath.Join(os.Getenv("HOME"), ".config/gcloud/application_default_credentials.json")
	if _, err := os.Stat(adcJSON); os.IsNotExist(err) {
	warnCredsOnce.Do(func() {
	log.Printf("warning: file %s does not exist; did you run 'gcloud auth application-default login' ? (The 'application-default' part matters, confusingly.)", adcJSON)
	})
	}
	}

	// diagnoseFailureTokenSource is an oauth2.TokenSource wrapper that,
	// upon failure, diagnoses why the token acquistion might've failed.
	type diagnoseFailureTokenSource struct {
	ts oauth2.TokenSource
	}

	func (ts diagnoseFailureTokenSource) Token() (*oauth2.Token, error) {
	t, err := ts.ts.Token()
	if err != nil {
	CheckUserCredentials()
	return nil, err
	}
	return t, nil
	}