allow cachedir override using env var

- main - Read and use env var `DEPCACHEDIR` for instantiating dep context.
- context
  - Add field `Cachedir` to struct `Ctx`. This holds the value of env var
    `DEPCACHEDIR`.
  - Use `Ctx.Cachedir` while instantiating `gps.SourceMgr` if present, fallback
    to `$GOPATH/pkg/dep` otherwise.
- source_manager - Add a getter func `Cachedir` to facilitate testing in
  `context_test.go`.
- context_test - Add test to check `gps.SourceMgr` is instantiated with
  appropriate `cachedir`.
- integration_test - Add test to check environment variable `DEPCACHEDIR` is
  loaded and used if present.

cmd/dep/integration_test.go

@@ -52,6 +52,46 @@ func TestIntegration(t *testing.T) {
 	})
 }
 
+func TestDepCachedir(t *testing.T) {
+	t.Parallel()
+
+	test.NeedsExternalNetwork(t)
+	test.NeedsGit(t)
+
+	wd, err := os.Getwd()
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	initPath := filepath.Join("testdata", "cachedir")
+
+	testProj := integration.NewTestProject(t, initPath, wd, runMain)
+	defer testProj.Cleanup()
+
+	testProj.TempDir("cachedir")
+	cachedir := testProj.Path("cachedir")
+	testProj.Setenv("DEPCACHEDIR", cachedir)
+
+	// Running `dep ensure` will pull in the dependency into cachedir.
+	err = testProj.DoRun([]string{"ensure"})
+	if err != nil {
+		// Log the error output from running `dep ensure`, could be useful.
+		t.Log(testProj.GetStderr())
+		t.Fatalf("got an unexpected error: %s", err.Error())
+	}
+
+	// Check that the cache was created in the cachedir. Our fixture has the dependency
+	// `github.com/sdboyer/deptest`
+	_, err = os.Stat(testProj.Path("cachedir", "sources", "https---github.com-sdboyer-deptest"))
+	if err != nil {
+		if os.IsNotExist(err) {
+			t.Fatal("Expected cachedir to have been populated but none was found")
+		} else {
+			t.Fatalf("Got unexpected error: %s", err)
+		}
+	}
+}
+
 // execCmd is a test.RunFunc which runs the program in another process.
 func execCmd(prog string, args []string, stdout, stderr io.Writer, dir string, env []string) error {
 	cmd := exec.Command(prog, args...)

cmd/dep/main.go

@@ -145,12 +145,17 @@ func (c *Config) Run() (exitCode int) {
 				return
 			}
 
+			// Cachedir is loaded from env if present. `$GOPATH/pkg/dep` is used as the
+			// fallback cache location.
+			cachedir := getEnv(c.Env, "DEPCACHEDIR")
+
 			// Set up dep context.
 			ctx := &dep.Ctx{
 				Out:            outLogger,
 				Err:            errLogger,
 				Verbose:        *verbose,
 				DisableLocking: getEnv(c.Env, "DEPNOLOCK") != "",
+				Cachedir:       cachedir,
 			}
 
 			GOPATHS := filepath.SplitList(getEnv(c.Env, "GOPATH"))

cmd/dep/testdata/cachedir/Gopkg.toml

@@ -0,0 +1,4 @@
+
+[[constraint]]
+  name = "github.com/sdboyer/deptest"
+  version = "1.0.0"

cmd/dep/testdata/cachedir/main.go

@@ -0,0 +1,12 @@
+// Copyright 2016 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package main
+
+import (
+	_ "github.com/sdboyer/deptest"
+)
+
+func main() {
+}

context.go

@@ -40,6 +40,7 @@ type Ctx struct {
 	Out, Err       *log.Logger // Required loggers.
 	Verbose        bool        // Enables more verbose logging.
 	DisableLocking bool        // When set, no lock file will be created to protect against simultaneous dep processes.
+	Cachedir       string      // Cache directory loaded from environment.
 }
 
 // SetPaths sets the WorkingDir and GOPATHs fields. If GOPATHs is empty, then
@@ -87,8 +88,14 @@ func defaultGOPATH() string {
 // SourceManager produces an instance of gps's built-in SourceManager
 // initialized to log to the receiver's logger.
 func (c *Ctx) SourceManager() (*gps.SourceMgr, error) {
+	cachedir := c.Cachedir
+	if cachedir == "" {
+		// When `DEPCACHEDIR` isn't set in the env, fallback to `$GOPATH/pkg/dep`.
+		cachedir = filepath.Join(c.GOPATH, "pkg", "dep")
+	}
+
 	return gps.NewSourceManager(gps.SourceManagerConfig{
-		Cachedir:       filepath.Join(c.GOPATH, "pkg", "dep"),
+		Cachedir:       cachedir,
 		Logger:         c.Out,
 		DisableLocking: c.DisableLocking,
 	})

context_test.go

@@ -485,3 +485,42 @@ func TestDetectGOPATH(t *testing.T) {
 		}
 	}
 }
+
+func TestDepCachedir(t *testing.T) {
+	h := test.NewHelper(t)
+	defer h.Cleanup()
+
+	h.TempDir("cache")
+	// Create the directory for fallback cachedir location.
+	h.TempDir(filepath.Join("go", "pkg", "dep"))
+
+	testCachedir := h.Path("cache")
+	gopath := h.Path("go")
+	discardLgr := discardLogger()
+
+	cases := []struct {
+		cachedir     string
+		wantCachedir string
+	}{
+		// If `Cachedir` is not set in the context, it should use `$GOPATH/pkg/dep`.
+		{cachedir: "", wantCachedir: h.Path(filepath.Join("go", "pkg", "dep"))},
+		// If `Cachedir` is set in the context, it should use that.
+		{cachedir: testCachedir, wantCachedir: testCachedir},
+	}
+
+	for _, c := range cases {
+		ctx := &Ctx{
+			GOPATH:   gopath,
+			Cachedir: c.cachedir,
+			Out:      discardLgr,
+			Err:      discardLgr,
+		}
+		sm, err := ctx.SourceManager()
+		h.Must(err)
+		defer sm.Release()
+
+		if sm.Cachedir() != c.wantCachedir {
+			t.Errorf("expected cachedir to be %s, got %s", c.wantCachedir, sm.Cachedir())
+		}
+	}
+}

internal/gps/source_manager.go

@@ -292,6 +292,11 @@ func NewSourceManager(c SourceManagerConfig) (*SourceMgr, error) {
 	return sm, nil
 }
 
+// Cachedir returns the location of the cache directory.
+func (sm *SourceMgr) Cachedir() string {
+	return sm.cachedir
+}
+
 // UseDefaultSignalHandling sets up typical os.Interrupt signal handling for a
 // SourceMgr.
 func (sm *SourceMgr) UseDefaultSignalHandling() {