From d291b5aad3fbd40407548dcd57af357175c72b54 Mon Sep 17 00:00:00 2001
From: Mike Danese <mikedanese@google.com>
Date: Wed, 9 Sep 2020 12:13:19 -0700
Subject: [PATCH] bazel: derive exec path of go binaries from action graph

Output paths are not a stable API and all our conditional path
construction here is fragile. This replaces the old path construction
with queries to the action graph.

Part of unblocking: kubernetes/kubernetes#94449
---
 .../nodeimage/internal/kube/builder_bazel.go  | 109 ++++++++++++------
 1 file changed, 75 insertions(+), 34 deletions(-)

diff --git a/pkg/build/nodeimage/internal/kube/builder_bazel.go b/pkg/build/nodeimage/internal/kube/builder_bazel.go
index c6ae72f982..1abe0bd1f8 100644
--- a/pkg/build/nodeimage/internal/kube/builder_bazel.go
+++ b/pkg/build/nodeimage/internal/kube/builder_bazel.go
@@ -17,10 +17,12 @@ limitations under the License.
 package kube
 
 import (
+	"encoding/json"
 	"fmt"
 	"os"
 	"path/filepath"
 
+	"sigs.k8s.io/kind/pkg/errors"
 	"sigs.k8s.io/kind/pkg/exec"
 	"sigs.k8s.io/kind/pkg/log"
 )
@@ -81,42 +83,27 @@ func (b *bazelBuilder) Build() (Bits, error) {
 		return nil, err
 	}
 
-	// https://docs.bazel.build/versions/master/output_directories.html
-	binDir := filepath.Join(b.kubeRoot, "bazel-bin")
-	buildDir := filepath.Join(binDir, "build")
-	bazelGoosGoarch := fmt.Sprintf("linux_%s", b.arch)
-
-	// helpers to get the binary paths which may or may not be "pure" (no cgo)
-	// Except for kubelet, these are pure in Kubernetes 1.14+
-	// kubelet is at bazel-bin/cmd/kubelet/kubelet since 1.14+
-	// TODO: do we care about building 1.13 from source once we add support
-	// for building from release binaries?
-	// https://github.com/kubernetes/kubernetes/pull/73930
-	strippedCommandPath := func(command string) string {
-		return filepath.Join(
-			binDir, "cmd", command,
-			fmt.Sprintf("%s_stripped", bazelGoosGoarch), command,
-		)
+	// This is a manual dereference of the alias created here:
+	//
+	// https://github.com/kubernetes/kubernetes/blob/b56d0acaf5bead31bd17d3b88d4a167fcbac7866/build/go.bzl#L45
+	kubeletPath, err := findGoBinary("//cmd/kubelet:_kubelet-cgo")
+	if err != nil {
+		return nil, errors.Wrap(err, "could not find kubelet")
 	}
-	commandPathPureOrNot := func(command string) string {
-		strippedPath := strippedCommandPath(command)
-		pureStrippedPath := filepath.Join(
-			binDir, "cmd", command,
-			fmt.Sprintf("%s_pure_stripped", bazelGoosGoarch), command,
-		)
-		// if the new path doesn't exist, do the old path
-		if _, err := os.Stat(pureStrippedPath); os.IsNotExist(err) {
-			return strippedPath
-		}
-		return pureStrippedPath
+
+	kubeadmPath, err := findGoBinary("//cmd/kubeadm:kubeadm")
+	if err != nil {
+		return nil, errors.Wrap(err, "could not find kubeadm")
 	}
-	//
-	kubeletPath := filepath.Join(binDir, "cmd", "kubelet", "kubelet")
-	oldKubeletPath := strippedCommandPath("kubelet")
-	if _, err := os.Stat(kubeletPath); os.IsNotExist(err) {
-		kubeletPath = oldKubeletPath
+
+	kubectlPath, err := findGoBinary("//cmd/kubectl:kubectl")
+	if err != nil {
+		return nil, errors.Wrap(err, "could not find kubectl")
 	}
 
+	// https://docs.bazel.build/versions/master/output_directories.html
+	buildDir := filepath.Join(b.kubeRoot, "bazel-bin/build")
+
 	// return the paths
 	return &bits{
 		imagePaths: []string{
@@ -127,9 +114,63 @@ func (b *bazelBuilder) Build() (Bits, error) {
 		},
 		binaryPaths: []string{
 			kubeletPath,
-			commandPathPureOrNot("kubeadm"),
-			commandPathPureOrNot("kubectl"),
+			kubeadmPath,
+			kubectlPath,
 		},
 		version: version,
 	}, nil
 }
+
+func findGoBinary(label string) (string, error) {
+	// This output of bazel aquery --output=jsonproto is an ActionGraphContainer
+	// as defined in:
+	//
+	// https://cs.opensource.google/bazel/bazel/+/master:src/main/protobuf/analysis.proto
+	type (
+		Action struct {
+			Mnemonic  string
+			OutputIds []string
+		}
+		Artifact struct {
+			Id       string
+			ExecPath string
+		}
+		ActionGraphContainer struct {
+			Artifacts []Artifact
+			Actions   []Action
+		}
+	)
+
+	cmd := exec.Command("bazel", "aquery", "--output=jsonproto", label)
+	actionBytes, err := exec.Output(cmd)
+	if err != nil {
+		return "", errors.Wrap(err, "failed to query action graph")
+	}
+	var agc ActionGraphContainer
+	if err := json.Unmarshal(actionBytes, &agc); err != nil {
+		return "", errors.Wrap(err, "failed to unpack action graph container")
+	}
+
+	var linkActions []Action
+	for _, action := range agc.Actions {
+		if action.Mnemonic == "GoLink" {
+			linkActions = append(linkActions, action)
+		}
+	}
+	if len(linkActions) != 1 {
+		return "", fmt.Errorf("unexpected number of link actions %d, wanted 1", len(linkActions))
+	}
+	linkAction := linkActions[0]
+	if len(linkAction.OutputIds) != 1 {
+		return "", fmt.Errorf("unexpected number of link action outputs %d, wanted 1", len(linkAction.OutputIds))
+	}
+	outputID := linkAction.OutputIds[0]
+
+	for _, artifact := range agc.Artifacts {
+		if artifact.Id == outputID {
+			return artifact.ExecPath, nil
+		}
+	}
+	// We really should never get here
+	return "", fmt.Errorf("could not find artifact corresponding to output id %q", outputID)
+}