Allow sharing the Go cache directory for crossbuilds

.circleci/config.yml

@@ -23,14 +23,24 @@ jobs:
     - run: git diff --exit-code
 
   build:
-    executor: golang
+    machine:
+      image: ubuntu-1604:201903-01
     working_directory: /home/circleci/.go_workspace/src/github.com/prometheus/promu
 
     steps:
-    - setup_remote_docker
     - checkout
-    - run: make promu
-    - run: promu crossbuild -v
+    - run: go install .
+    - restore_cache:
+        keys:
+        - v01-gocache-{{ checksum "go.mod" }}
+        - v01-gocache-
+    - run: mkdir -p /home/circleci/.cache/go-build
+    - run: promu crossbuild -v --gocache-path /home/circleci/.cache/go-build
+    - run: du -sh /home/circleci/.cache/go-build
+    - save_cache:
+        key: v01-gocache-{{ checksum "go.mod" }}
+        paths:
+        - /home/circleci/.cache/go-build
     - persist_to_workspace:
         root: .
         paths:

.promu.yml

@@ -5,7 +5,7 @@ go:
 repository:
     path: github.com/prometheus/promu
 build:
-    flags: -mod=vendor -a -tags 'netgo static_build'
+    flags: -mod=vendor -tags 'netgo static_build'
     ldflags: |
         -s
         -X github.com/prometheus/common/version.Version={{.Version}}
@@ -17,4 +17,3 @@ tarball:
     files:
         - LICENSE
         - NOTICE
-

cmd/crossbuild.go

@@ -78,14 +78,15 @@ var (
 			platformsFlagSet = true
 			return nil
 		}).Strings()
+	goCachePath = crossbuildcmd.Flag("gocache-path", "Path to a Go cache directory on the local machine").String()
 	// kingpin doesn't currently support using the crossbuild command and the
 	// crossbuild tarball subcommand at the same time, so we treat the
-	// tarball subcommand as an optional arg
+	// tarball subcommand as an optional arg.
 	tarballsSubcommand = crossbuildcmd.Arg("tarballs", "Optionally pass the string \"tarballs\" from cross-built binaries").String()
 )
 
 func runCrossbuild() {
-	//Check required configuration
+	// Check required configuration.
 	if len(strings.TrimSpace(config.Repository.Path)) == 0 {
 		log.Fatalf("missing required '%s' configuration", "repository.path")
 	}
@@ -149,7 +150,7 @@ func runCrossbuild() {
 	}
 
 	if !cgo {
-		// In non-CGO, use the base image without any crossbuild toolchain
+		// In non-CGO, use the base image without any crossbuild toolchain.
 		var allPlatforms []string
 		allPlatforms = append(allPlatforms, mainPlatforms[:]...)
 		allPlatforms = append(allPlatforms, armPlatforms[:]...)
@@ -158,7 +159,7 @@ func runCrossbuild() {
 		allPlatforms = append(allPlatforms, s390xPlatforms[:]...)
 
 		pg := &platformGroup{"base", dockerBaseBuilderImage, allPlatforms}
-		if err := pg.Build(repoPath); err != nil {
+		if err := pg.Build(repoPath, *goCachePath); err != nil {
 			fatal(errors.Wrapf(err, "The %s builder docker image exited unexpectedly", pg.Name))
 		}
 	} else {
@@ -169,7 +170,7 @@ func runCrossbuild() {
 			{"MIPS", dockerMIPSBuilderImage, mipsPlatforms},
 			{"s390x", dockerS390XBuilderImage, s390xPlatforms},
 		} {
-			if err := pg.Build(repoPath); err != nil {
+			if err := pg.Build(repoPath, *goCachePath); err != nil {
 				fatal(errors.Wrapf(err, "The %s builder docker image exited unexpectedly", pg.Name))
 			}
 		}
@@ -182,7 +183,9 @@ type platformGroup struct {
 	Platforms   []string
 }
 
-func (pg platformGroup) Build(repoPath string) error {
+const containerGoCacheDir = "/root/.cache/go-build"
+
+func (pg platformGroup) Build(repoPath string, goCachePath string) error {
 	platformsParam := strings.Join(pg.Platforms[:], " ")
 	if len(platformsParam) == 0 {
 		return nil
@@ -196,11 +199,22 @@ func (pg platformGroup) Build(repoPath string) error {
 	}
 
 	ctrName := "promu-crossbuild-" + pg.Name + strconv.FormatInt(time.Now().Unix(), 10)
-	err = sh.RunCommand("docker", "create", "-t",
+	args := []string{
+		"create", "-t",
 		"--name", ctrName,
+	}
+	if goCachePath != "" {
+		args = append(args,
+			"--env", fmt.Sprintf("GOCACHE=%s", containerGoCacheDir),
+			"-v", fmt.Sprintf("%s:%s", goCachePath, containerGoCacheDir),
+		)
+	}
+	args = append(args,
 		pg.DockerImage,
 		"-i", repoPath,
-		"-p", platformsParam)
+		"-p", platformsParam,
+	)
+	err = sh.RunCommand("docker", args...)
 	if err != nil {
 		return err
 	}