command: terraform get -upgrade

As of this commit this just upgrades modules, but this option will also
later upgrade plugins and indeed anything else that's being downloaded and
installed as part of the init.

command/init.go

@@ -31,7 +31,7 @@ type InitCommand struct {
 }
 
 func (c *InitCommand) Run(args []string) int {
-	var flagBackend, flagGet, flagGetPlugins bool
+	var flagBackend, flagGet, flagGetPlugins, flagUpgrade bool
 	var flagConfigExtra map[string]interface{}
 
 	args = c.Meta.process(args, false)
@@ -44,6 +44,7 @@ func (c *InitCommand) Run(args []string) int {
 	cmdFlags.BoolVar(&c.Meta.stateLock, "lock", true, "lock state")
 	cmdFlags.DurationVar(&c.Meta.stateLockTimeout, "lock-timeout", 0, "lock timeout")
 	cmdFlags.BoolVar(&c.reconfigure, "reconfigure", false, "reconfigure")
+	cmdFlags.BoolVar(&flagUpgrade, "upgrade", false, "")
 
 	cmdFlags.Usage = func() { c.Ui.Error(c.Help()) }
 	if err := cmdFlags.Parse(args); err != nil {
@@ -112,10 +113,17 @@ func (c *InitCommand) Run(args []string) int {
 		if flagGet && len(conf.Modules) > 0 {
 			header = true
 
-			c.Ui.Output(c.Colorize().Color(fmt.Sprintf(
-				"[reset][bold]" +
-					"Downloading modules (if any)...")))
-			if err := getModules(&c.Meta, path, module.GetModeGet); err != nil {
+			getMode := module.GetModeGet
+			if flagUpgrade {
+				getMode = module.GetModeUpdate
+				c.Ui.Output(c.Colorize().Color(fmt.Sprintf(
+					"[reset][bold]Upgrading modules...")))
+			} else {
+				c.Ui.Output(c.Colorize().Color(fmt.Sprintf(
+					"[reset][bold]Downloading modules...")))
+			}
+
+			if err := getModules(&c.Meta, path, getMode); err != nil {
 				c.Ui.Error(fmt.Sprintf(
 					"Error downloading modules: %s", err))
 				return 1
@@ -324,7 +332,11 @@ Options:
 
   -no-color            If specified, output won't contain any color.
 
-  -reconfigure          Reconfigure the backend, ignoring any saved configuration.
+  -reconfigure         Reconfigure the backend, ignoring any saved configuration.
+
+  -upgrade=false       If installing modules (-get) or plugins (-get-plugins),
+                       ignore previously-downloaded objects and install the
+                       latest version allowed within configured constraints.
 `
 	return strings.TrimSpace(helpText)
 }

command/init_test.go

@@ -80,6 +80,39 @@ func TestInit_get(t *testing.T) {
 	}
 }
 
+func TestInit_getUpgradeModules(t *testing.T) {
+	// Create a temporary working directory that is empty
+	td := tempDir(t)
+	os.MkdirAll(td, 0755)
+	// copy.CopyDir(testFixturePath("init-get"), td)
+	defer os.RemoveAll(td)
+	defer testChdir(t, td)()
+
+	ui := new(cli.MockUi)
+	c := &InitCommand{
+		Meta: Meta{
+			testingOverrides: metaOverridesForProvider(testProvider()),
+			Ui:               ui,
+		},
+	}
+
+	args := []string{
+		"-get=true",
+		"-get-plugins=false",
+		"-upgrade",
+		testFixturePath("init-get"),
+	}
+	if code := c.Run(args); code != 0 {
+		t.Fatalf("command did not complete successfully:\n%s", ui.ErrorWriter.String())
+	}
+
+	// Check output
+	output := ui.OutputWriter.String()
+	if !strings.Contains(output, "(update)") {
+		t.Fatalf("doesn't look like get upgrade: %s", output)
+	}
+}
+
 func TestInit_backend(t *testing.T) {
 	// Create a temporary working directory that is empty
 	td := tempDir(t)