Build application from a srv directory in Go App Engine gomod buildpack

This fixes an incompatiblity with the appengine package which expects files to be compiled from srv for go.mod apps: https://github.com/golang/appengine/blob/553959209a20f3be281c16dd5be5c740a893978f/delay/delay.go#L136.

All source code is moved from /workspace to <layer>/srv and `go build` is then invoked with the latter as the work directory. The resulting binary will correctly have /srv/ in the stored file paths.

PiperOrigin-RevId: 327901991
Change-Id: Ic08452e67af3f6c20741e6661931cec717460930

builders/gae/go111/acceptance/acceptance_test.go

@@ -66,7 +66,6 @@ func TestAcceptance(t *testing.T) {
 			Name: "gopath no dependencies",
 			App:  "gopath",
 		},
-
 		// Test that GOOGLE_BUILDABLE takes precedence over app.yaml and go-app-stager.
 		{
 			Name: "gomod GOOGLE_BUILDABLE vs go-app-stager vs app.yaml main package",
@@ -107,6 +106,10 @@ func TestAcceptance(t *testing.T) {
 			Name: "gomod no dependencies",
 			App:  "gomod",
 		},
+		{
+			Name: "gomod appengine",
+			App:  "gomod_appengine",
+		},
 	}
 	for _, tc := range testCases {
 		tc := tc

builders/testdata/go/gomod_appengine/_main-package-path

@@ -0,0 +1 @@
+.

builders/testdata/go/gomod_appengine/go.mod

@@ -0,0 +1,5 @@
+module example.com/package
+
+go 1.11
+
+require rsc.io/quote v1.5.2

builders/testdata/go/gomod_appengine/main.go

@@ -0,0 +1,56 @@
+// Copyright 2020 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// Package main tests building source that has a go.mod file without gomod dependencies.
+// It also tests compatiblity with the golang/appengine package.
+package main
+
+import (
+	"fmt"
+	"net/http"
+	"os"
+	"path/filepath"
+	"runtime"
+	"strings"
+
+	"rsc.io/quote"
+)
+
+func handler(w http.ResponseWriter, r *http.Request) {
+	if got, want := quote.Hello(), "Hello, world."; got != want {
+		fmt.Fprintf(w, "FAIL: quote.Hello() = %s, want %s\n", got, want)
+		return
+	}
+
+	// Check that the path at compile time includes /srv/. This is done for compatibility with the
+	// appengine package, which requires it for historical reasons. See the go/appengine_gomod
+	// buildpack.
+	_, file, _, ok := runtime.Caller(0)
+	if !ok {
+		fmt.Fprintln(w, "FAIL: runtime.Caller(0) not ok")
+		return
+	}
+	sep := string(filepath.Separator)
+	srv := sep + "srv" + sep
+	if !strings.Contains(file, srv) {
+		fmt.Fprintf(w, "FAIL: caller file path %s does not contain %s\n", file, srv)
+		return
+	}
+	fmt.Fprintln(w, "PASS")
+}
+
+func main() {
+	http.HandleFunc("/", handler)
+	http.ListenAndServe(":"+os.Getenv("PORT"), nil)
+}

cmd/go/appengine_gomod/BUILD.bazel

@@ -26,6 +26,7 @@ go_binary(
     deps = [
         "//pkg/env",
         "//pkg/gcpbuildpack",
+        "//pkg/golang",
     ],
 )
 

cmd/go/appengine_gomod/main.go

@@ -24,6 +24,7 @@ import (
 
 	"github.com/GoogleCloudPlatform/buildpacks/pkg/env"
 	gcp "github.com/GoogleCloudPlatform/buildpacks/pkg/gcpbuildpack"
+	"github.com/GoogleCloudPlatform/buildpacks/pkg/golang"
 )
 
 const (
@@ -66,6 +67,14 @@ func buildFn(ctx *gcp.Context) error {
 	l := ctx.Layer("main_env", gcp.BuildLayer)
 	l.BuildEnvironment.Override(env.Buildable, buildMainPath)
 
+	// HACK: For backwards compatibility on App Engine Go 1.11:
+	// Copy all files to a layer directory that ends with /srv because the appengine package relies on the name:
+	// https://github.com/golang/appengine/blob/553959209a20f3be281c16dd5be5c740a893978f/delay/delay.go#L136
+	// We change the work directory instead of modifying env.Buildable, because the latter is not necessarily a filesystem path.
+	srvl := ctx.Layer("srv", gcp.BuildLayer)
+	srvl.BuildEnvironment.Override(golang.BuildDirEnv, srvl.Path)
+	ctx.Exec([]string{"cp", "--dereference", "-R", ".", srvl.Path}, gcp.WithUserTimingAttribution)
+
 	return nil
 }
 

cmd/go/appengine_gopath/main.go

@@ -84,13 +84,17 @@ func buildFn(ctx *gcp.Context) error {
 		l.BuildEnvironment.Override(env.Buildable, buildMainPath)
 	}
 
+	// Unlike in the appengine_gomod buildpack, we do not have to compile gopath apps from a path that ends in /srv/. There are two cases:
+	//  * _gopath/main-package-path exists and app source is put on GOPATH, which is handled by:
+	//			https://github.com/golang/appengine/blob/553959209a20f3be281c16dd5be5c740a893978f/delay/delay.go#L136.
+	//  * _gopath/main-package-path does not exist and the app is built from the current directory, which is handled by:
+	//			https://github.com/golang/appengine/blob/553959209a20f3be281c16dd5be5c740a893978f/delay/delay.go#L125-L127
+
 	// TODO(b/145608768): Investigate creating and caching a GOCACHE layer.
 	return nil
 }
 
 func copyDir(ctx *gcp.Context, src, dst string) {
-	ctx.Debugf("copying %q to %q", src, dst)
-
 	// Trailing "/." copies the contents of src directory, but not src itself.
 	src = filepath.Clean(src) + string(filepath.Separator) + "."
 	ctx.Exec([]string{"cp", "--dereference", "-R", src, dst}, gcp.WithUserTimingAttribution)

cmd/go/build/main.go

@@ -67,9 +67,14 @@ func buildFn(ctx *gcp.Context) error {
 	bld = append(bld, goBuildFlags()...)
 	bld = append(bld, "-o", outBin)
 	bld = append(bld, buildable)
-	ctx.Exec(bld, gcp.WithEnv("GOCACHE="+cl.Path), gcp.WithMessageProducer(printTipsAndKeepStderrTail(ctx)), gcp.WithUserAttribution)
+	// BuildDirEnv should only be set by App Engine buildpacks.
+	workdir := os.Getenv(golang.BuildDirEnv)
+	if workdir == "" {
+		workdir = ctx.ApplicationRoot()
+	}
+	ctx.Exec(bld, gcp.WithEnv("GOCACHE="+cl.Path), gcp.WithWorkDir(workdir), gcp.WithMessageProducer(printTipsAndKeepStderrTail(ctx)), gcp.WithUserAttribution)
 
-	// Configure the entrypoint for production.  Use the full path to save `skaffold debug`
+	// Configure the entrypoint for production. Use the full path to save `skaffold debug`
 	// from fetching the remote container image (tens to hundreds of megabytes), which is slow.
 	if !devmode.Enabled(ctx) {
 		ctx.AddWebProcess([]string{outBin})

pkg/golang/golang.go

@@ -26,6 +26,8 @@ import (
 const (
 	// OutBin is the name of the final compiled binary produced by Go buildpacks.
 	OutBin = "main"
+	// BuildDirEnv is an environment variable that buildpacks can use to communicate the working directory to `go build`.
+	BuildDirEnv = "GOOGLE_INTERNAL_BUILD_DIR"
 )
 
 var (