Support 'last_rc' in Bazelisk [Go-only] (bazelbuild#60)

* Support last_rc version in bazelisk.go

* Document 'last_rc' version

* Test 'last_rc' version feature

* Make test_bazel_last_rc a Go-only test

BUILD

@@ -9,13 +9,15 @@ sh_test(
     srcs = ["bazelisk_test.sh"],
     data = ["bazelisk.py", "releases_for_tests.json"],
     deps = ["@bazel_tools//tools/bash/runfiles"],
+    args = ["PY"]
 )
 
 sh_test(
     name = "go_bazelisk_test",
     srcs = ["bazelisk_test.sh"],
     data = [":bazelisk", "releases_for_tests.json"],
     deps = ["@bazel_tools//tools/bash/runfiles"],
+    args = ["GO"]
 )
 
 go_library(

README.md

@@ -29,9 +29,10 @@ Bazelisk currently understands the following formats for version labels:
   be a release candidate version like `0.20.0rc3`.
 - `last_green` refers to the Bazel binary that was built at the most recent commit that passed [Bazel CI](https://buildkite.com/bazel/bazel-bazel). Ideally this binary should be very close to Bazel-at-head.
 - `last_downstream_green` points to the most recent Bazel binary that builds and tests all [downstream projects](https://buildkite.com/bazel/bazel-at-head-plus-downstream) successfully.
+- `last_rc` points to the most recent release candidate. If there is no active release candidate, Bazelisk uses the latest Bazel release instead. Currently only the Go version of Bazelisk supports this value.
 
 
-In the future I will add support for release candidates and for building Bazel from source at a given commit.
+In the future I will add support for building Bazel from source at a given commit.
 
 ## Other features
 

bazelisk.go

@@ -165,22 +165,101 @@ func resolveLatestVersion(bazeliskHome string, offset int) (string, error) {
 		return "", fmt.Errorf("could not parse JSON into list of releases: %v", err)
 	}
 
-	var versions []*version.Version
+	var tags []string
 	for _, release := range releases {
 		if release.Prerelease {
 			continue
 		}
-		v, err := version.NewVersion(release.TagName)
+		tags = append(tags, release.TagName)
+	}
+	return getNthMostRecentVersion(tags, offset)
+}
+
+func getNthMostRecentVersion(versions []string, offset int) (string, error) {
+	if offset >= len(versions) {
+		return "", fmt.Errorf("cannot resolve version \"latest-%d\": There are only %d Bazel versions", offset, len(versions))
+	}
+
+	wrappers := make([]*version.Version, len(versions))
+	for i, v := range versions {
+		wrapper, err := version.NewVersion(v)
 		if err != nil {
-			log.Printf("WARN: Could not parse version: %s", release.TagName)
+			log.Printf("WARN: Could not parse version: %s", v)
 		}
-		versions = append(versions, v)
+		wrappers[i] = wrapper
 	}
-	sort.Sort(version.Collection(versions))
-	if offset >= len(versions) {
-		return "", fmt.Errorf("cannot resolve version \"latest-%d\": There are only %d Bazel releases", offset, len(versions))
+	sort.Sort(version.Collection(wrappers))
+	return wrappers[len(wrappers)-1-offset].Original(), nil
+}
+
+type gcsListResponse struct {
+	Prefixes []string `json:"prefixes"`
+}
+
+func resolveLatestRcVersion() (string, error) {
+	versions, err := listDirectoriesInReleaseBucket("")
+	if err != nil {
+		return "", fmt.Errorf("could not list Bazel versions in GCS bucket: %v", err)
+	}
+
+	latestVersion, err := getHighestBazelVersion(versions)
+	if err != nil {
+		return "", fmt.Errorf("got invalid version number: %v", err)
 	}
-	return versions[len(versions)-1-offset].Original(), nil
+
+	// Append slash to match directories
+	rcVersions, err := listDirectoriesInReleaseBucket(latestVersion + "/")
+	if err != nil {
+		return "", fmt.Errorf("could not list release candidates for latest release: %v", err)
+	}
+	return getHighestRcVersion(rcVersions)
+}
+
+func listDirectoriesInReleaseBucket(prefix string) ([]string, error) {
+	url := "https://www.googleapis.com/storage/v1/b/bazel/o?delimiter=/"
+	if prefix != "" {
+		url = fmt.Sprintf("%s&prefix=%s", url, prefix)
+	}
+	content, err := readRemoteFile(url)
+	if err != nil {
+		return nil, fmt.Errorf("could not list GCS objects at %s: %v", url, err)
+	}
+
+	var response gcsListResponse
+	if err := json.Unmarshal(content, &response); err != nil {
+		return nil, fmt.Errorf("could not parse GCS index JSON: %v", err)
+	}
+	return response.Prefixes, nil
+}
+
+func getHighestBazelVersion(versions []string) (string, error) {
+	for i, v := range versions {
+		versions[i] = strings.TrimSuffix(v, "/")
+	}
+	return getNthMostRecentVersion(versions, 0)
+}
+
+func getHighestRcVersion(versions []string) (string, error) {
+	var version string
+	var lastRc int
+	re := regexp.MustCompile(`(\d+.\d+.\d+)/rc(\d+)/`)
+	for _, v := range versions {
+		// Fallback: use latest release if there is no active RC.
+		if strings.Index(v, "release") > -1 {
+			return strings.Split(v, "/")[0], nil
+		}
+
+		m := re.FindStringSubmatch(v)
+		version = m[1]
+		rc, err := strconv.Atoi(m[2])
+		if err != nil {
+			return "", fmt.Errorf("Invalid version number %s: %v", strings.TrimSuffix(v, "/"), err)
+		}
+		if rc > lastRc {
+			lastRc = rc
+		}
+	}
+	return fmt.Sprintf("%src%d", version, lastRc), nil
 }
 
 func resolveVersionLabel(bazeliskHome, bazelVersion string) (string, bool, error) {
@@ -198,6 +277,11 @@ func resolveVersionLabel(bazeliskHome, bazelVersion string) (string, bool, error
 		return commit, true, nil
 	}
 
+	if bazelVersion == "last_rc" {
+		version, err := resolveLatestRcVersion()
+		return version, false, err
+	}
+
 	r := regexp.MustCompile(`^latest(?:-(?P<offset>\d+))?$`)
 
 	match := r.FindStringSubmatch(bazelVersion)

bazelisk_test.sh

@@ -36,6 +36,9 @@ else
 fi
 # --- end runfiles.bash initialization ---
 
+BAZELISK_VERSION=$1
+shift 1
+
 function setup() {
   BAZELISK_HOME="$(mktemp -d $TEST_TMPDIR/home.XXXXXX)"
 
@@ -127,6 +130,17 @@ function test_bazel_last_downstream_green() {
       (echo "FAIL: 'bazelisk version' of an unreleased binary must not print a build label."; exit 1)
 }
 
+function test_bazel_last_rc() {
+  setup
+
+  USE_BAZEL_VERSION="last_rc" \
+      BAZELISK_HOME="$BAZELISK_HOME" \
+      bazelisk version 2>&1 | tee log
+
+  grep "Build label:" log || \
+      (echo "FAIL: Expected to find 'Build label' in the output of 'bazelisk version'"; exit 1)
+}
+
 echo "# test_bazel_version"
 test_bazel_version
 echo
@@ -150,3 +164,9 @@ echo
 echo "# test_bazel_last_downstream_green"
 test_bazel_last_downstream_green
 echo
+
+if [[$BAZELISK_VERSION == "GO"]]; then
+echo "# test_bazel_last_rc"
+test_bazel_last_rc
+echo
+fi