Use filer.Filer to write template instantiation (#1911)

## Changes

Prior to this change, the output directory was part of the `renderer`
type and passed down to every `file` it produced. Every file knew its
absolute destination path. This is incompatible with the use of a filer,
where all operations are automatically anchored to some base path.

To make this compatible, this change updates:
* the `file` type to only know its own path relative to the instantiation root,
* the `renderer` type to no longer require or pass along the output directory,
* the `persistToDisk` function to take a context and filer argument,
* the `filer.WriteMode` to represent permission bits

## Tests

* Existing tests pass.
* Manually confirmed template initialization works as expected.

libs/filer/filer.go

@@ -7,13 +7,24 @@ import (
 	"io/fs"
 )
 
+// WriteMode captures intent when writing a file.
+//
+// The first 9 bits are reserved for the [fs.FileMode] permission bits.
+// These are used only by the local filer implementation and have
+// no effect for the other implementations.
 type WriteMode int
 
+// writeModePerm is a mask to extract permission bits from a WriteMode.
+const writeModePerm = WriteMode(fs.ModePerm)
+
 const (
-	OverwriteIfExists WriteMode = 1 << iota
+	// Note: these constants are defined as powers of 2 to support combining them using a bit-wise OR.
+	// They starts from the 10th bit (permission mask + 1) to avoid conflicts with the permission bits.
+	OverwriteIfExists WriteMode = (writeModePerm + 1) << iota
 	CreateParentDirectories
 )
 
+// DeleteMode captures intent when deleting a file.
 type DeleteMode int
 
 const (

libs/filer/filer_test.go

@@ -0,0 +1,12 @@
+package filer
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestWriteMode(t *testing.T) {
+	assert.Equal(t, 512, int(OverwriteIfExists))
+	assert.Equal(t, 1024, int(CreateParentDirectories))
+}

libs/filer/local_client.go

@@ -28,22 +28,31 @@ func (w *LocalClient) Write(ctx context.Context, name string, reader io.Reader,
 		return err
 	}
 
+	// Retrieve permission mask from the [WriteMode], if present.
+	perm := fs.FileMode(0644)
+	for _, m := range mode {
+		bits := m & writeModePerm
+		if bits != 0 {
+			perm = fs.FileMode(bits)
+		}
+	}
+
 	flags := os.O_WRONLY | os.O_CREATE
 	if slices.Contains(mode, OverwriteIfExists) {
 		flags |= os.O_TRUNC
 	} else {
 		flags |= os.O_EXCL
 	}
 
-	f, err := os.OpenFile(absPath, flags, 0644)
+	f, err := os.OpenFile(absPath, flags, perm)
 	if errors.Is(err, fs.ErrNotExist) && slices.Contains(mode, CreateParentDirectories) {
 		// Create parent directories if they don't exist.
 		err = os.MkdirAll(filepath.Dir(absPath), 0755)
 		if err != nil {
 			return err
 		}
 		// Try again.
-		f, err = os.OpenFile(absPath, flags, 0644)
+		f, err = os.OpenFile(absPath, flags, perm)
 	}
 
 	if err != nil {

libs/template/config_test.go

@@ -83,7 +83,7 @@ func TestTemplateConfigAssignValuesFromDefaultValues(t *testing.T) {
 	c, err := newConfig(ctx, os.DirFS(testDir), "schema.json")
 	require.NoError(t, err)
 
-	r, err := newRenderer(ctx, nil, nil, os.DirFS("."), "./testdata/empty/template", "./testdata/empty/library", t.TempDir())
+	r, err := newRenderer(ctx, nil, nil, os.DirFS("."), "./testdata/empty/template", "./testdata/empty/library")
 	require.NoError(t, err)
 
 	err = c.assignDefaultValues(r)
@@ -102,7 +102,7 @@ func TestTemplateConfigAssignValuesFromTemplatedDefaultValues(t *testing.T) {
 	c, err := newConfig(ctx, os.DirFS(testDir), "schema.json")
 	require.NoError(t, err)
 
-	r, err := newRenderer(ctx, nil, nil, os.DirFS("."), path.Join(testDir, "template/template"), path.Join(testDir, "template/library"), t.TempDir())
+	r, err := newRenderer(ctx, nil, nil, os.DirFS("."), path.Join(testDir, "template/template"), path.Join(testDir, "template/library"))
 	require.NoError(t, err)
 
 	// Note: only the string value is templated.

libs/template/file.go

@@ -1,53 +1,36 @@
 package template
 
 import (
+	"bytes"
 	"context"
-	"io"
 	"io/fs"
-	"os"
-	"path/filepath"
 	"slices"
+
+	"github.com/databricks/cli/libs/filer"
 )
 
 // Interface representing a file to be materialized from a template into a project
 // instance
 type file interface {
-	// Destination path for file. This is where the file will be created when
-	// PersistToDisk is called.
-	DstPath() *destinationPath
+	// Path of the file relative to the root of the instantiated template.
+	// This is where the file is written to when persisting the template to disk.
+	// Must be slash-separated.
+	RelPath() string
 
 	// Write file to disk at the destination path.
-	PersistToDisk() error
+	Write(ctx context.Context, out filer.Filer) error
 
 	// contents returns the file contents as a byte slice.
 	// This is used for testing purposes.
 	contents() ([]byte, error)
 }
 
-type destinationPath struct {
-	// Root path for the project instance. This path uses the system's default
-	// file separator. For example /foo/bar on Unix and C:\foo\bar on windows
-	root string
-
-	// Unix like file path relative to the "root" of the instantiated project. Is used to
-	// evaluate whether the file should be skipped by comparing it to a list of
-	// skip glob patterns.
-	relPath string
-}
-
-// Absolute path of the file, in the os native format. For example /foo/bar on
-// Unix and C:\foo\bar on windows
-func (f *destinationPath) absPath() string {
-	return filepath.Join(f.root, filepath.FromSlash(f.relPath))
-}
-
 type copyFile struct {
-	ctx context.Context
-
 	// Permissions bits for the destination file
 	perm fs.FileMode
 
-	dstPath *destinationPath
+	// Destination path for the file.
+	relPath string
 
 	// [fs.FS] rooted at template root. Used to read srcPath.
 	srcFS fs.FS
@@ -56,55 +39,40 @@ type copyFile struct {
 	srcPath string
 }
 
-func (f *copyFile) DstPath() *destinationPath {
-	return f.dstPath
+func (f *copyFile) RelPath() string {
+	return f.relPath
 }
 
-func (f *copyFile) PersistToDisk() error {
-	path := f.DstPath().absPath()
-	err := os.MkdirAll(filepath.Dir(path), 0755)
-	if err != nil {
-		return err
-	}
-	srcFile, err := f.srcFS.Open(f.srcPath)
-	if err != nil {
-		return err
-	}
-	defer srcFile.Close()
-	dstFile, err := os.OpenFile(path, os.O_CREATE|os.O_EXCL|os.O_WRONLY, f.perm)
+func (f *copyFile) Write(ctx context.Context, out filer.Filer) error {
+	src, err := f.srcFS.Open(f.srcPath)
 	if err != nil {
 		return err
 	}
-	defer dstFile.Close()
-	_, err = io.Copy(dstFile, srcFile)
-	return err
+	defer src.Close()
+	return out.Write(ctx, f.relPath, src, filer.CreateParentDirectories, filer.WriteMode(f.perm))
 }
 
 func (f *copyFile) contents() ([]byte, error) {
 	return fs.ReadFile(f.srcFS, f.srcPath)
 }
 
 type inMemoryFile struct {
-	dstPath *destinationPath
-
-	content []byte
-
 	// Permissions bits for the destination file
 	perm fs.FileMode
-}
 
-func (f *inMemoryFile) DstPath() *destinationPath {
-	return f.dstPath
+	// Destination path for the file.
+	relPath string
+
+	// Contents of the file.
+	content []byte
 }
 
-func (f *inMemoryFile) PersistToDisk() error {
-	path := f.DstPath().absPath()
+func (f *inMemoryFile) RelPath() string {
+	return f.relPath
+}
 
-	err := os.MkdirAll(filepath.Dir(path), 0755)
-	if err != nil {
-		return err
-	}
-	return os.WriteFile(path, f.content, f.perm)
+func (f *inMemoryFile) Write(ctx context.Context, out filer.Filer) error {
+	return out.Write(ctx, f.relPath, bytes.NewReader(f.content), filer.CreateParentDirectories, filer.WriteMode(f.perm))
 }
 
 func (f *inMemoryFile) contents() ([]byte, error) {

libs/template/file_test.go

@@ -8,77 +8,56 @@ import (
 	"runtime"
 	"testing"
 
+	"github.com/databricks/cli/libs/filer"
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
 )
 
-func testInMemoryFile(t *testing.T, perm fs.FileMode) {
+func testInMemoryFile(t *testing.T, ctx context.Context, perm fs.FileMode) {
 	tmpDir := t.TempDir()
 
 	f := &inMemoryFile{
-		dstPath: &destinationPath{
-			root:    tmpDir,
-			relPath: "a/b/c",
-		},
 		perm:    perm,
+		relPath: "a/b/c",
 		content: []byte("123"),
 	}
-	err := f.PersistToDisk()
+
+	out, err := filer.NewLocalClient(tmpDir)
+	require.NoError(t, err)
+	err = f.Write(ctx, out)
 	assert.NoError(t, err)
 
 	assertFileContent(t, filepath.Join(tmpDir, "a/b/c"), "123")
 	assertFilePermissions(t, filepath.Join(tmpDir, "a/b/c"), perm)
 }
 
-func testCopyFile(t *testing.T, perm fs.FileMode) {
+func testCopyFile(t *testing.T, ctx context.Context, perm fs.FileMode) {
 	tmpDir := t.TempDir()
 	err := os.WriteFile(filepath.Join(tmpDir, "source"), []byte("qwerty"), perm)
 	require.NoError(t, err)
 
 	f := &copyFile{
-		ctx: context.Background(),
-		dstPath: &destinationPath{
-			root:    tmpDir,
-			relPath: "a/b/c",
-		},
 		perm:    perm,
-		srcPath: "source",
+		relPath: "a/b/c",
 		srcFS:   os.DirFS(tmpDir),
+		srcPath: "source",
 	}
-	err = f.PersistToDisk()
+
+	out, err := filer.NewLocalClient(tmpDir)
+	require.NoError(t, err)
+	err = f.Write(ctx, out)
 	assert.NoError(t, err)
 
 	assertFileContent(t, filepath.Join(tmpDir, "a/b/c"), "qwerty")
 	assertFilePermissions(t, filepath.Join(tmpDir, "a/b/c"), perm)
 }
 
-func TestTemplateFileDestinationPath(t *testing.T) {
-	if runtime.GOOS == "windows" {
-		t.SkipNow()
-	}
-	f := &destinationPath{
-		root:    `a/b/c`,
-		relPath: "d/e",
-	}
-	assert.Equal(t, `a/b/c/d/e`, f.absPath())
-}
-
-func TestTemplateFileDestinationPathForWindows(t *testing.T) {
-	if runtime.GOOS != "windows" {
-		t.SkipNow()
-	}
-	f := &destinationPath{
-		root:    `c:\a\b\c`,
-		relPath: "d/e",
-	}
-	assert.Equal(t, `c:\a\b\c\d\e`, f.absPath())
-}
-
 func TestTemplateInMemoryFilePersistToDisk(t *testing.T) {
 	if runtime.GOOS == "windows" {
 		t.SkipNow()
 	}
-	testInMemoryFile(t, 0755)
+	ctx := context.Background()
+	testInMemoryFile(t, ctx, 0755)
 }
 
 func TestTemplateInMemoryFilePersistToDiskForWindows(t *testing.T) {
@@ -87,14 +66,16 @@ func TestTemplateInMemoryFilePersistToDiskForWindows(t *testing.T) {
 	}
 	// we have separate tests for windows because of differences in valid
 	// fs.FileMode values we can use for different operating systems.
-	testInMemoryFile(t, 0666)
+	ctx := context.Background()
+	testInMemoryFile(t, ctx, 0666)
 }
 
 func TestTemplateCopyFilePersistToDisk(t *testing.T) {
 	if runtime.GOOS == "windows" {
 		t.SkipNow()
 	}
-	testCopyFile(t, 0644)
+	ctx := context.Background()
+	testCopyFile(t, ctx, 0644)
 }
 
 func TestTemplateCopyFilePersistToDiskForWindows(t *testing.T) {
@@ -103,5 +84,6 @@ func TestTemplateCopyFilePersistToDiskForWindows(t *testing.T) {
 	}
 	// we have separate tests for windows because of differences in valid
 	// fs.FileMode values we can use for different operating systems.
-	testCopyFile(t, 0666)
+	ctx := context.Background()
+	testCopyFile(t, ctx, 0666)
 }