Storage.GetModule

Add GetModule for the cli to initialize from a regisry module source.

Storage.GetModule fetches a module using the same detection and
discovery as used by the normal module loading. The final copy is still
done by module.GetCopy to remove vcs files.

config/module/storage.go

@@ -243,6 +243,41 @@ func (s Storage) findModule(key string) (string, error) {
 	return s.moduleDir(key)
 }
 
+// GetModule fetches a module source into the specified directory. This is used
+// as a convenience function by the CLI to initialize a configuration.
+func (s Storage) GetModule(dst, src string) error {
+	// reset this in case the caller was going to re-use it
+	mode := s.Mode
+	s.Mode = GetModeUpdate
+	defer func() {
+		s.Mode = mode
+	}()
+
+	rec, err := s.findRegistryModule(src, anyVersion)
+	if err != nil {
+		return err
+	}
+
+	pwd, err := os.Getwd()
+	if err != nil {
+		return err
+	}
+
+	source := rec.url
+	if source == "" {
+		source, err = getter.Detect(src, pwd, getter.Detectors)
+		if err != nil {
+			return fmt.Errorf("module %s: %s", src, err)
+		}
+	}
+
+	if source == "" {
+		return fmt.Errorf("module %q not found", src)
+	}
+
+	return GetCopy(dst, source)
+}
+
 // find a registry module
 func (s Storage) findRegistryModule(mSource, constraint string) (moduleRecord, error) {
 	rec := moduleRecord{

config/module/storage_test.go

@@ -0,0 +1,49 @@
+package module
+
+import (
+	"io/ioutil"
+	"os"
+	"path/filepath"
+	"testing"
+)
+
+func TestGetModule(t *testing.T) {
+	server := mockRegistry()
+	defer server.Close()
+	disco := testDisco(server)
+
+	td, err := ioutil.TempDir("", "tf")
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer os.RemoveAll(td)
+	storage := NewStorage(td, disco, nil)
+
+	// this module exists in a test fixture, and is known by the mockRegistry
+	// relative to our cwd.
+	err = storage.GetModule(filepath.Join(td, "foo"), "registry/local/sub")
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	// list everything to make sure nothing else got unpacked in here
+	ls, err := ioutil.ReadDir(td)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	var names []string
+	for _, info := range ls {
+		names = append(names, info.Name())
+	}
+
+	if !(len(names) == 1 && names[0] == "foo") {
+		t.Fatalf("expected only directory 'foo', found entries %q", names)
+	}
+
+	_, err = os.Stat(filepath.Join(td, "foo", "main.tf"))
+	if err != nil {
+		t.Fatal(err)
+	}
+
+}