home: direnv: add 'nix' library file

home/direnv/lib/nix.sh

@@ -0,0 +1,31 @@
+#shellcheck shell=bash
+
+use_pkgs() {
+    if ! has nix; then
+        # shellcheck disable=2016
+        log_error 'use_pkgs: `nix` is not in PATH'
+        return 1
+    fi
+
+    local DEFAULT_FLAKE="pkgs"
+
+    # Allow changing the default flake through a command line switch
+    if [ "$1" = "-f" ] || [ "$1" = "--flake" ]; then
+        DEFAULT_FLAKE="$2"
+        shift 2
+    fi
+
+
+    # Allow specifying a full installable, or just a package name and use the default flake
+    local packages=()
+    for pkg; do
+        if [[ $pkg =~ .*#.* ]]; then
+            packages+=("$pkg")
+        else
+            packages+=("$DEFAULT_FLAKE#$pkg")
+        fi
+    done
+
+    # shellcheck disable=2154
+    direnv_load nix shell "${packages[@]}" --command "$direnv" dump
+}