home: create 'modules/home' folder

Consolidating all modules under the same path, to clear out the
top-level directory.

modules/home/direnv/lib/nix.sh

@@ -0,0 +1,69 @@
+#shellcheck shell=bash
+
+use_pkgs() {
+    if ! has nix; then
+        # shellcheck disable=2016
+        log_error 'use_pkgs: `nix` is not in PATH'
+        return 1
+    fi
+
+    # Use user-provided default value, or fallback to nixpkgs
+    local DEFAULT_FLAKE="${DIRENV_DEFAULT_FLAKE:-nixpkgs}"
+    # Additional args that should be forwarded to `nix`
+    local args=()
+
+    # Allow changing the default flake through a command line switch
+    while true; do
+        case "$1" in
+            -b|--broken)
+                args+=(--impure)
+                export NIXPKGS_ALLOW_BROKEN=1
+                shift
+                ;;
+            -f|--flake)
+                DEFAULT_FLAKE="$2"
+                shift 2
+                ;;
+            -i|--impure)
+                args+=(--impure)
+                shift
+                ;;
+            -s|--insecure)
+                args+=(--impure)
+                export NIXPKGS_ALLOW_INSECURE=1
+                shift
+                ;;
+            -u|--unfree)
+                args+=(--impure)
+                export NIXPKGS_ALLOW_UNFREE=1
+                shift
+                ;;
+            --)
+                shift
+                break
+                ;;
+            *)
+                break
+                ;;
+        esac
+    done
+
+
+    # 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 "${args[@]}" "${packages[@]}" --command "$direnv" dump
+
+    # Clean-up after ourselves (assumes the user does not set them before us)
+    unset NIXPKGS_ALLOW_BROKEN
+    unset NIXPKGS_ALLOW_INSECURE
+    unset NIXPKGS_ALLOW_UNFREE
+}