Fixing a bug with template dump

commands/templates.go

@@ -5,6 +5,7 @@ import (
 	"fmt"
 	"io"
 	"os"
+	"path/filepath"
 
 	"github.com/spf13/cobra"
 	"github.com/voxpupuli/jig/internal/scaffold"
@@ -99,18 +100,44 @@ func explainTemplate(w io.Writer, src *templateSource, name string) error {
 	return nil
 }
 
+// isCwd reports whether destination resolves to the current working
+// directory. Backing up the destination is skipped in that case: renaming
+// the current directory out from under the process is unreliable across
+// platforms (fails outright when destination is "."), so templates are
+// written directly into the existing directory instead, overwriting only
+// the files jig manages.
+func isCwd(destination string) (bool, error) {
+	cwd, err := os.Getwd()
+	if err != nil {
+		return false, fmt.Errorf("failed to determine current directory: %w", err)
+	}
+
+	abs, err := filepath.Abs(destination)
+	if err != nil {
+		return false, fmt.Errorf("failed to resolve destination %s: %w", destination, err)
+	}
+
+	return abs == cwd, nil
+}
+
 func (a *App) templatesDumpCmd() *cobra.Command {
 	cmd := &cobra.Command{
 		Use:   "dump <destination>",
 		Short: "Dump all available templates to a directory",
 		Args:  cobra.ExactArgs(1),
 		RunE: func(cmd *cobra.Command, args []string) error {
 			destination := args[0]
-			if _, err := os.Stat(destination); err == nil {
-				if err := scaffold.BackupDir(destination); err != nil {
-					return fmt.Errorf("failed to back up existing directory: %w", err)
+			destinationIsCwd, err := isCwd(destination)
+			if err != nil {
+				return err
+			}
+			if !destinationIsCwd {
+				if _, err := os.Stat(destination); err == nil {
+					if err := scaffold.BackupDir(destination); err != nil {
+						return fmt.Errorf("failed to back up existing directory: %w", err)
+					}
+					fmt.Printf("backed up existing directory %s\n", destination)
 				}
-				fmt.Printf("backed up existing directory %s\n", destination)
 			}
 			return template.DumpTemplates(destination)
 		},

commands/templates_test.go

@@ -108,6 +108,81 @@ func TestTemplatesResolve_NotFound(t *testing.T) {
 	}
 }
 
+// runTemplatesDump executes `jig templates dump <destination>` and returns
+// the command output.
+func runTemplatesDump(t *testing.T, a *App, destination string) (string, error) {
+	t.Helper()
+	cmd := a.templatesCmd()
+	var buf bytes.Buffer
+	cmd.SetOut(&buf)
+	cmd.SetErr(&buf)
+	cmd.SetArgs([]string{"dump", destination})
+	err := cmd.Execute()
+	return buf.String(), err
+}
+
+// Dumping to "." must write into the current directory in place rather than
+// trying to rename it out of the way: renaming "." fails on every platform,
+// and dumping is expected to behave like unpacking an archive alongside
+// existing files. See https://github.com/voxpupuli/jig/issues/82.
+func TestTemplatesDump_CurrentDirectory(t *testing.T) {
+	dir := t.TempDir()
+	t.Chdir(dir)
+	if err := os.WriteFile(filepath.Join(dir, "another-file"), []byte("keep me"), 0o644); err != nil {
+		t.Fatal(err)
+	}
+
+	a := testApp(config.Config{})
+	if _, err := runTemplatesDump(t, a, "."); err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+
+	if _, err := os.Stat(filepath.Join(dir, "another-file")); err != nil {
+		t.Errorf("expected pre-existing file to survive the dump: %v", err)
+	}
+	if _, err := os.Stat(filepath.Join(dir, "class", "class.pp.tmpl")); err != nil {
+		t.Errorf("expected templates to be written into the current directory: %v", err)
+	}
+
+	entries, err := os.ReadDir(filepath.Dir(dir))
+	if err != nil {
+		t.Fatal(err)
+	}
+	for _, e := range entries {
+		if strings.Contains(e.Name(), ".bak.") {
+			t.Errorf("expected no backup directory to be created, found %q", e.Name())
+		}
+	}
+}
+
+// Dumping to a non-cwd destination that already exists must still back it up
+// with a timestamp suffix before writing.
+func TestTemplatesDump_BacksUpExistingDestination(t *testing.T) {
+	t.Chdir(t.TempDir())
+	if err := os.Mkdir("existing", 0o755); err != nil {
+		t.Fatal(err)
+	}
+
+	a := testApp(config.Config{})
+	if _, err := runTemplatesDump(t, a, "existing"); err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+
+	entries, err := os.ReadDir(".")
+	if err != nil {
+		t.Fatal(err)
+	}
+	var sawBackup bool
+	for _, e := range entries {
+		if strings.Contains(e.Name(), "existing.bak.") {
+			sawBackup = true
+		}
+	}
+	if !sawBackup {
+		t.Error("expected a backup directory to be created")
+	}
+}
+
 // Inside a module directory, the [template] section of jig.toml must feed
 // resolution, matching what component commands do.
 func TestTemplatesResolve_ModuleConfigURL(t *testing.T) {

docs/commands/templates.md

@@ -9,7 +9,9 @@ remote template repositories work.
 Extracts all embedded default templates to a directory on disk. This is
 useful as a starting point for creating your own custom templates. If the
 destination directory already exists it will be renamed with a timestamp
-suffix before writing.
+suffix before writing, unless the destination is the current directory (e.g.
+`.`), in which case templates are written into it in place alongside any
+existing files.
 
 ```
 jig templates dump <destination>