gerrit: delete GetProjects in favor of ListProjects

The ListProjects and GetProjects methods were added in CL 38717 and
CL 37252 at around the same time, and they're both exposing the same
GET /projects/ Gerrit API endpoint. The latter is hardcoded to provide
the 'b' query parameter, one of many that GET /projects/ offers.

Rewrite cmd/gitmirror and cmd/updatestd to use ListProjects and N calls
to GetBranch instead, and delete GetProjects since we no longer use it.

I considered deprecating GetProjects instead of deleting, but x/build
and x/build/gerrit specifically are both documented to be for internal
Go project needs and not subject to the Go 1 compatibility promise, so
skip the overhead of doing that. If it happens to cause a problem that
can't be worked around in a better way, we'll consider re-adding it in
deprecated form. Add a pkg.go.dev link to increase visibility to the
general-purpose Gerrit API clients written in Go.

Updates golang/go#18743.

Change-Id: I583356526af04e915bce5464004eb68a650221d5
Reviewed-on: https://go-review.googlesource.com/c/build/+/518676
Run-TryBot: Dmitri Shuralyov <[email protected]>
TryBot-Result: Gopher Robot <[email protected]>
Auto-Submit: Dmitri Shuralyov <[email protected]>
Reviewed-by: Heschi Kreinick <[email protected]>
Reviewed-by: Dmitri Shuralyov <[email protected]>

Author: dmitshur

cmd/gitmirror/gitmirror.go

@@ -11,6 +11,7 @@ package main
 import (
 	"bytes"
 	"context"
+	"errors"
 	"flag"
 	"fmt"
 	"io/ioutil"
@@ -696,15 +697,19 @@ func (m *gitMirror) subscribeToMaintnerAndTickle() error {
 func (m *gitMirror) gerritMetaMap() (map[string]string, error) {
 	ctx, cancel := context.WithTimeout(context.Background(), 30*time.Second)
 	defer cancel()
-	meta, err := m.gerritClient.GetProjects(ctx, "master")
+	projs, err := m.gerritClient.ListProjects(ctx)
 	if err != nil {
-		return nil, fmt.Errorf("gerritClient.GetProjects: %v", err)
+		return nil, fmt.Errorf("gerritClient.ListProjects: %v", err)
 	}
 	result := map[string]string{}
-	for repo, v := range meta {
-		if master, ok := v.Branches["master"]; ok {
-			result[repo] = master
+	for _, p := range projs {
+		b, err := m.gerritClient.GetBranch(ctx, p.Name, "master")
+		if errors.Is(err, gerrit.ErrResourceNotExist) {
+			continue
+		} else if err != nil {
+			return nil, fmt.Errorf(`gerritClient.GetBranch(ctx, %q, "master"): %v`, p.Name, err)
 		}
+		result[p.Name] = b.Revision
 	}
 	return result, nil
 }

cmd/updatestd/updatestd.go

@@ -70,7 +70,7 @@ func main() {
 	// Fetch latest hashes of Go projects from Gerrit,
 	// using the specified branch name.
 	//
-	// This gives us a consistent snapshot of all golang.org/x module versions
+	// We get a fairly consistent snapshot of all golang.org/x module versions
 	// at a given point in time. This ensures selection of latest available
 	// pseudo-versions is done without being subject to module mirror caching,
 	// and that selected pseudo-versions can be re-used across multiple modules.
@@ -79,18 +79,19 @@ func main() {
 	// commits that are selected and reporting if any of them have a failure.
 	//
 	cl := gerrit.NewClient("https://go-review.googlesource.com", gerrit.NoAuth)
-	projs, err := cl.GetProjects(context.Background(), *branch)
+	projs, err := cl.ListProjects(context.Background())
 	if err != nil {
 		log.Fatalln("failed to get a list of Gerrit projects:", err)
 	}
 	hashes := map[string]string{}
-	for name, p := range projs {
-		if p.State != "ACTIVE" {
+	for _, p := range projs {
+		b, err := cl.GetBranch(context.Background(), p.Name, *branch)
+		if errors.Is(err, gerrit.ErrResourceNotExist) {
 			continue
+		} else if err != nil {
+			log.Fatalf("failed to get the %q branch of Gerrit project %q: %v\n", *branch, p.Name, err)
 		}
-		if hash, ok := p.Branches[*branch]; ok {
-			hashes[name] = hash
-		}
+		hashes[p.Name] = b.Revision
 	}
 
 	w := Work{

gerrit/gerrit.go

@@ -4,8 +4,10 @@
 
 // Package gerrit contains code to interact with Gerrit servers.
 //
-// The API is not subject to the Go 1 compatibility promise and may change at
-// any time.
+// This package doesn't intend to provide complete coverage of the Gerrit API,
+// but only a small subset for the current needs of the Go project infrastructure.
+// Its API is not subject to the Go 1 compatibility promise and may change at any time.
+// For general-purpose Gerrit API clients, see https://pkg.go.dev/search?q=gerrit.
 package gerrit
 
 import (
@@ -732,7 +734,7 @@ type ProjectInfo struct {
 //
 // The returned slice is sorted by project ID and excludes the "All-Projects" and "All-Users" projects.
 //
-// See https://gerrit-review.googlesource.com/Documentation/rest-api-projects.html#list-projects
+// See https://gerrit-review.googlesource.com/Documentation/rest-api-projects.html#list-projects.
 func (c *Client) ListProjects(ctx context.Context) ([]ProjectInfo, error) {
 	var res map[string]ProjectInfo
 	err := c.do(ctx, &res, "GET", "/projects/")
@@ -1013,13 +1015,6 @@ func (c *Client) QueryAccounts(ctx context.Context, q string, opts ...QueryAccou
 	return changes, err
 }
 
-// GetProjects returns a map of all projects on the Gerrit server.
-func (c *Client) GetProjects(ctx context.Context, branch string) (map[string]*ProjectInfo, error) {
-	mp := make(map[string]*ProjectInfo)
-	err := c.do(ctx, &mp, "GET", fmt.Sprintf("/projects/?b=%s&format=JSON", branch))
-	return mp, err
-}
-
 type TimeStamp time.Time
 
 func (ts TimeStamp) Equal(v TimeStamp) bool {