Use a better technique for dealing with empty arrays when `set -u`.

https://news.ycombinator.com/item?id=11497636

2 files changed, 12 insertions, 7 deletions

diff --git a/HACKING/code-quality.md b/HACKING/code-quality.md
index a520ce5..8efd561 100644
--- a/HACKING/code-quality.md
+++ b/HACKING/code-quality.md
@@ -49,7 +49,8 @@ Use `set -u` if you can; it makes using an unset variable an error.
  - If a variable not being set is valid (perhaps a configuration
    option), use `${var:-}` when accessing it to suppress the error.
  - An empty array counts as unset, so if you have an array that may be
-   empty, use `set +u` before accessing it.
+   empty, use `${var+"${var[@]}"}` (don't put quotes around the outer
+   pair of braces) to only access it if it's non-empty.
    - The reason for this is that a normal string variable is basically
      an array with length=1; an unset variable looks like an array
      with length=0.  Weird stuff.
diff --git a/src/chroot-tools/librechroot b/src/chroot-tools/librechroot
index 5ff9c99..ba722c7 100755
--- a/src/chroot-tools/librechroot
+++ b/src/chroot-tools/librechroot
@@ -54,18 +54,22 @@ arch-nspawn() {
 	local copydir=$1; shift
 	local cmd=("$@")
 
-	set +u # if an array is empty, it counts as unbound
-	"$_arch_nspawn" "${arch_nspawn_flags[@]}" "$copydir" "${sysd_nspawn_flags[@]}" -- "${cmd[@]}"
-	set -u
+	"$_arch_nspawn" \
+	    ${arch_nspawn_flags+"${arch_nspawn_flags[@]}"} \
+	    "$copydir" \
+	    ${sysd_nspawn_flags+"${sysd_nspawn_flags[@]}"} \
+	    -- \
+	    "${cmd[@]}"
 }
 
 # Usage: mkarchroot $copydir $pkgs...
 mkarchroot() {
 	local copydir=$1; shift
 	local pkgs=("$@")
-	set +u # if an array is empty, it counts as unbound
-	"$_mkarchroot" "${arch_nspawn_flags[@]}" "$copydir" "${pkgs[@]}"
-	set -u
+	"$_mkarchroot" \
+	    ${arch_nspawn_flags+"${arch_nspawn_flags[@]}"} \
+	    "$copydir" \
+	    "${pkgs[@]}"
 }
 
 # Usage: _makechrootpkg $function $arguments...