[nix] Don't indent output in ensure mode (#546)

## Summary

Makes output nicer in ensure mode

## How was it tested?

Added a package to devbox.json and ran `devbox shell`

Author: mikeland73

devbox.json

@@ -17,4 +17,4 @@
   "nixpkgs": {
     "commit": "3954218cf613eba8e0dcefa9abe337d26bc48fd0"
   }
-}
+}

internal/impl/devbox.go

@@ -607,7 +607,7 @@ func (d *Devbox) ensurePackagesAreInstalled(mode installMode) error {
 	}
 
 	// We need to re-install the packages
-	if err := d.installNixProfile(); err != nil {
+	if err := d.installNixProfile(mode); err != nil {
 		fmt.Fprintln(d.writer)
 		return errors.Wrap(err, "apply Nix derivation")
 	}
@@ -667,7 +667,7 @@ func (d *Devbox) printPackageUpdateMessage(
 
 // installNixProfile installs or uninstalls packages to or from this
 // devbox's Nix profile so that it matches what's in development.nix or flake.nix
-func (d *Devbox) installNixProfile() (err error) {
+func (d *Devbox) installNixProfile(mode installMode) (err error) {
 	profileDir, err := d.profileDir()
 	if err != nil {
 		return err
@@ -691,7 +691,10 @@ func (d *Devbox) installNixProfile() (err error) {
 	}
 
 	cmd.Env = nix.DefaultEnv()
-	cmd.Stdout = &nixPackageInstallWriter{d.writer}
+	cmd.Stdout = &nixPackageInstallWriter{
+		d.writer,
+		lo.Ternary(mode != ensure, "\t", ""),
+	}
 
 	cmd.Stderr = cmd.Stdout
 

internal/impl/writer.go

@@ -11,14 +11,15 @@ var nixPackageInstallIgnore = []string{
 }
 
 type nixPackageInstallWriter struct {
-	w io.Writer
+	w      io.Writer
+	indent string
 }
 
 func (fw *nixPackageInstallWriter) Write(p []byte) (n int, err error) {
 	lines := strings.Split(string(p), "\n")
 	for _, line := range lines {
 		if line != "" && !fw.ignore(line) {
-			_, err = io.WriteString(fw.w, "\t"+line+"\n")
+			_, err = io.WriteString(fw.w, fw.indent+line+"\n")
 			if err != nil {
 				return
 			}