command: Update "terraform get" to use the new module installer

We missed this on the initial update pass because this was calling
directly into the module package API rather than going through the Meta
methods that we updated for the new config loader.

m.installModules here is the same method that "terraform init" is using
for this purpose, ensuring the two will behave the same way. This changes
the output a little compared to the old installer, but it still includes
the important information about where each module is coming from.

command/get.go

@@ -1,10 +1,9 @@
 package command
 
 import (
-	"fmt"
 	"strings"
 
-	"github.com/hashicorp/terraform/config/module"
+	"github.com/hashicorp/terraform/tfdiags"
 )
 
 // GetCommand is a Command implementation that takes a Terraform
@@ -34,13 +33,11 @@ func (c *GetCommand) Run(args []string) int {
 		return 1
 	}
 
-	mode := module.GetModeGet
-	if update {
-		mode = module.GetModeUpdate
-	}
+	path = c.normalizePath(path)
 
-	if err := getModules(&c.Meta, path, mode); err != nil {
-		c.Ui.Error(err.Error())
+	diags := getModules(&c.Meta, path, update)
+	c.showDiagnostics(diags)
+	if diags.HasErrors() {
 		return 1
 	}
 
@@ -61,10 +58,10 @@ Usage: terraform get [options] PATH
 
 Options:
 
-  -update=false       If true, modules already downloaded will be checked
-                      for updates and updated if necessary.
+  -update             Check already-downloaded modules for available updates
+                      and install the newest versions available.
 
-  -no-color           If specified, output won't contain any color.
+  -no-color           Disable text coloring in the output.
 
 `
 	return strings.TrimSpace(helpText)
@@ -74,16 +71,10 @@ func (c *GetCommand) Synopsis() string {
 	return "Download and install modules for the configuration"
 }
 
-func getModules(m *Meta, path string, mode module.GetMode) error {
-	mod, err := module.NewTreeModule("", path)
-	if err != nil {
-		return fmt.Errorf("Error loading configuration: %s", err)
+func getModules(m *Meta, path string, upgrade bool) tfdiags.Diagnostics {
+	hooks := uiModuleInstallHooks{
+		Ui:             m.Ui,
+		ShowLocalPaths: true,
 	}
-
-	err = mod.Load(m.moduleStorage(m.DataDir(), mode))
-	if err != nil {
-		return fmt.Errorf("Error loading modules: %s", err)
-	}
-
-	return nil
+	return m.installModules(path, upgrade, hooks)
 }

command/get_test.go

@@ -30,10 +30,7 @@ func TestGet(t *testing.T) {
 	}
 
 	output := ui.OutputWriter.String()
-	if !strings.Contains(output, "module.foo") {
-		t.Fatalf("doesn't look like get: %s", output)
-	}
-	if strings.Contains(output, "(update)") {
+	if !strings.Contains(output, "- foo in") {
 		t.Fatalf("doesn't look like get: %s", output)
 	}
 }
@@ -78,10 +75,7 @@ func TestGet_noArgs(t *testing.T) {
 	}
 
 	output := ui.OutputWriter.String()
-	if !strings.Contains(output, "module.foo") {
-		t.Fatalf("doesn't look like get: %s", output)
-	}
-	if strings.Contains(output, "(update)") {
+	if !strings.Contains(output, "- foo in") {
 		t.Fatalf("doesn't look like get: %s", output)
 	}
 }
@@ -108,7 +102,7 @@ func TestGet_update(t *testing.T) {
 	}
 
 	output := ui.OutputWriter.String()
-	if !strings.Contains(output, `Updating source "./foo"`) {
+	if !strings.Contains(output, `- foo in`) {
 		t.Fatalf("doesn't look like get: %s", output)
 	}
 }