Move demandDirectoryRoot into kyaml/filesys (#4677)

* Move demandDirectoryRoot into kyaml/filesys

* Make root directory platform-agnostic

Support windows root directory. Dogfood own error package.

* Use cleaner windows support implementation

* Address feedback

* Address feedback x2

* Re-apply go.sum changes to avoid CI errors

kyaml/filesys/filesystem_test.go

@@ -5,16 +5,26 @@ package filesys
 
 import (
 	"os"
+	"path/filepath"
 	"testing"
 
 	"github.com/pkg/errors"
 	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+const (
+	disk        = "MakeFsOnDisk"
+	memoryAbs   = "MakeFsInMemory"
+	memoryEmpty = "MakeEmptyDirInMemory"
+
+	existMsg = "expected '%s' to exist"
 )
 
 var filesysBuilders = map[string]func() FileSystem{
-	"MakeFsInMemory":       MakeFsInMemory,
-	"MakeFsOnDisk":         MakeFsOnDisk,
-	"MakeEmptyDirInMemory": func() FileSystem { return MakeEmptyDirInMemory() },
+	memoryAbs:   MakeFsInMemory,
+	disk:        MakeFsOnDisk,
+	memoryEmpty: func() FileSystem { return MakeEmptyDirInMemory() },
 }
 
 func TestNotExistErr(t *testing.T) {
@@ -42,3 +52,89 @@ func testNotExistErr(t *testing.T, fs FileSystem) {
 	err = fs.Walk(path, func(_ string, _ os.FileInfo, err error) error { return err })
 	assert.Truef(t, errors.Is(err, os.ErrNotExist), "Walk should return ErrNotExist, got %v", err)
 }
+
+// setupFileSys returns file system, default directory to test in, and working directory
+func setupFileSys(t *testing.T, name string) (FileSystem, string, string) {
+	t.Helper()
+
+	switch name {
+	case disk:
+		fSys, testDir := makeTestDir(t)
+		return fSys, testDir, cleanWd(t)
+	case memoryAbs:
+		return filesysBuilders[name](), Separator, Separator
+	case memoryEmpty:
+		return filesysBuilders[name](), "", ""
+	default:
+		t.Fatalf("unexpected FileSystem implementation '%s'", name)
+		panic("unreachable point of execution")
+	}
+}
+
+func TestConfirmDir(t *testing.T) {
+	for name := range filesysBuilders {
+		name := name
+		t.Run(name, func(t *testing.T) {
+			fSys, prefixPath, wd := setupFileSys(t, name)
+
+			d1Path := filepath.Join(prefixPath, "d1")
+			d2Path := filepath.Join(d1Path, ".d2")
+			err := fSys.MkdirAll(d2Path)
+			require.NoError(t, err)
+			require.Truef(t, fSys.Exists(d2Path), existMsg, d2Path)
+
+			tests := map[string]*struct {
+				dir      string
+				expected string
+			}{
+				"Simple": {
+					d1Path,
+					d1Path,
+				},
+				"Hidden": {
+					d2Path,
+					d2Path,
+				},
+				"Relative": {
+					SelfDir,
+					wd,
+				},
+			}
+			for subName, test := range tests {
+				test := test
+				t.Run(subName, func(t *testing.T) {
+					cleanDir, err := ConfirmDir(fSys, test.dir)
+					require.NoError(t, err)
+					require.Equal(t, test.expected, cleanDir.String())
+				})
+			}
+		})
+	}
+}
+
+func TestConfirmDirErr(t *testing.T) {
+	for name := range filesysBuilders {
+		thisName := name
+		t.Run(thisName, func(t *testing.T) {
+			fSys, prefixPath, _ := setupFileSys(t, thisName)
+
+			fPath := filepath.Join(prefixPath, "foo")
+			err := fSys.WriteFile(fPath, []byte(`foo`))
+			require.NoError(t, err)
+			require.Truef(t, fSys.Exists(fPath), existMsg, fPath)
+
+			tests := map[string]string{
+				"Empty":        "",
+				"File":         fPath,
+				"Non-existent": filepath.Join(prefixPath, "bar"),
+			}
+			for subName, invalidPath := range tests {
+				invalidPath := invalidPath
+				t.Run(subName, func(t *testing.T) {
+					_, err := ConfirmDir(fSys, invalidPath)
+					require.Error(t, err)
+				})
+			}
+		})
+	}
+}