devshells: improve select-shell

devShell.nix

@@ -38,7 +38,7 @@
         ];
         shellHook = ''
           echo -e "${ansiEscapes.green}switch to another dev-shell using: select-shell${ansiEscapes.reset}"
-          export PROJECT_ROOT=$(git rev-parse --show-toplevel)
+          export PRJ_ROOT=$(git rev-parse --show-toplevel)
         '';
       };
     };

pkgs/scripts/select-shell.py

@@ -1,39 +1,79 @@
 import argparse
 import json
+import os
 import pathlib
 import subprocess
 import sys
 
+selected_shell_file = pathlib.Path(".direnv/selected-shell")
+
+
+def parse_args() -> argparse.Namespace:
     parser = argparse.ArgumentParser(description="Select a devshell")
     parser.add_argument("shell", help="the name of the devshell to select", nargs="?")
     parser.add_argument("--list", action="store_true", help="list available devshells")
-args = parser.parse_args()
+    parser.add_argument(
-
+        "--show", action="store_true", help="show the currently selected devshell"
-selected_shell_file = pathlib.Path(".direnv/selected-shell")
-
-if not args.list and not args.shell:
-    parser.print_help()
-    exit(0)
-if args.list:
-    flake_show = subprocess.run(
-        ["nix", "flake", "show", "--json", "--no-write-lock-file"],
-        stdout=subprocess.PIPE,
     )
-    data = json.loads(flake_show.stdout.decode())
+    return parser.parse_args()
-    print("Available devshells:")
+
-    print("\n".join(data["devShells"]["x86_64-linux"].keys()))
+
-    exit(0)
+def get_current_shell() -> str | None:
     if selected_shell_file.exists():
         with open(selected_shell_file) as f:
-        current_shell = f.read().strip()
+            return f.read().strip()
+    return None
+
+
+def print_current_shell() -> None:
+    current_shell = get_current_shell()
+    if current_shell:
+        print(f"Currently selected devshell: {current_shell}")
     else:
-    current_shell = ""
+        print("No devshell selected")
 
-if current_shell == args.shell:
+
-    print(f"{args.shell} devshell already selected. No changes made.")
+def print_devshells() -> None:
+    project_root = os.environ.get("PRJ_ROOT")
+    flake_show = subprocess.run(
+        [
+            "nix",
+            "eval",
+            "--json",
+            "--no-write-lock-file",
+            "--apply",
+            "shells: builtins.mapAttrs (name: _shell: name) shells",
+            f"{project_root}#devShells.x86_64-linux",
+        ],
+        stdout=subprocess.PIPE,
+    )
+    names = json.loads(flake_show.stdout.decode())
+    print("Available devshells:\n")
+    print("\n".join(names))
+
+
+def select_shell(shell: str) -> None:
+    if shell == get_current_shell():
+        print(f"{shell} devshell already selected. No changes made.")
         sys.exit(0)
-
+    else:
         with open(selected_shell_file, "w") as f:
-    f.write(args.shell)
+            f.write(shell)
+        print(f"{shell} devshell selected")
 
-print(f"{args.shell} devshell selected")
+
+def main() -> None:
+    args = parse_args()
+    if args.show:
+        print_current_shell()
+    elif args.list:
+        print_devshells()
+    elif args.shell:
+        select_shell(args.shell)
+    else:
+        print_current_shell()
+        print("Use --help for more information")
+
+
+if __name__ == "__main__":
+    main()