Add -w/--write-config to bootstrap a fully-populated config file

Writes every supported config option explicitly -- the six
unshare-* bools defaulted via value_or(true), log-level captured
from the actually active spdlog level (so an explicit --log-level
passed alongside -w is persisted too) -- creating the file and its
parent directory if missing, and prints its full path. Existing
values (including volumes) are preserved untouched.

Also fixes a stale README row left over from unplugging the
namespace probe out of -t/--test.

CLAUDE.md

@@ -115,6 +115,22 @@ Source layout (all under `src/`):
   already gone) — see `config_file.{h,cpp}` below for what a "volume" means here (a
   distinct concept from `OciImageConfig::volumes`). `dispatch_command()`'s
   `Mode::volume`/`Mode::delete_volume`/`Mode::delete_volume_full` cases call these.
+  `write_config_command()` implements `-w/--write-config`: unlike
+  `create_volume_command()`/`delete_volume_command()`'s use of
+  `write_config_file()` (which only ever persists `AppConfig` fields that are
+  already set), this fills in *every* field before writing — the six
+  `unshare-*` bools via `.value_or(true)`, and `log_level` from the actually
+  active `spdlog::get_level()` (not merely a default for when unset — this
+  also captures an explicit `--log-level` passed alongside `-w` on the same
+  command line, overriding whatever an existing config file's own
+  `log-level` already was, since `main()`/`parse_args()` already applied it
+  in that precedence order by the time this runs) — so a bare `-w` bootstraps
+  a complete, fully-populated config file for hand-editing, and `-w` combined
+  with other flags captures their effective values into it. `volumes` is left
+  exactly as loaded — an open-ended list with no "default" entry to
+  materialize. Prints the config file's full path (`write_config_file()`
+  already creates the parent directory and the file itself if missing, so no
+  separate existence check is needed here).
   `run_container()` (the `Mode::run` dispatch case) resolves each `-v` spec
   (erroring out, `ok = false`, same as a failed `--user` resolution — `bwrap`
   is skipped but unmount/cleanup still runs) into a `ResolvedVolumeMount`,
@@ -814,8 +830,8 @@ Build directory is `buildDir/` (already configured).
   full flag list: `-m/--mount`, `-r/--run`, `-u/--umount`, `-c/--cleanup`,
   `-l/--list-images`, `-i/--inspect`, `-x/--exec`, `--kill`, `-n/--no-nsenter`, `-D/--daemonize`,
   `--user`, `--group`, `--hostname`, `--env`, `--env-file`, `-v/--volume`, `--list-volumes`, `--delete-volume`,
-  `--delete-volume-full`, `--list-processes`, `--clean-processes`, `-t/--test`, `--log-level`,
+  `--delete-volume-full`, `--list-processes`, `--clean-processes`, `-w/--write-config`,
-  `-h/--help`, `-V/--version`)
+  `-t/--test`, `--log-level`, `-h/--help`, `-V/--version`)
 - Run tests: `meson test -C buildDir`
 
 ## Code style

README.md

@@ -94,7 +94,8 @@ slocker-lite -V|--version
 | `--delete-volume-full <name>` | Like `--delete-volume`, but also recursively deletes the volume's host directory. |
 | `--list-processes` | List running `--run` sessions found by their pid files under `$XDG_STATE_HOME/slocker-lite/run/`, with their pid, container name, and status (`running` or `exited`). |
 | `--clean-processes` | Remove stale pid files (see `--list-processes`) left behind by sessions that are no longer running. |
-| `-t, --test` | Print which `bwrap --unshare-xxx` namespaces the running kernel supports. |
+| `-w, --write-config` | Write a complete config file (creating it, and its parent directory, if missing), filling in every option's current or default value. Useful to bootstrap one for hand-editing. Prints the config file's full path. |
+| `-t, --test` | Run the (currently empty) self-test placeholder. |
 | `--log-level <level>` | Set log verbosity (`trace`, `debug`, `info`, `warn`, `error`, `critical`, `off`). |
 | `-h, --help` | Print usage and exit. |
 | `-V, --version` | Print version information and exit. |
@@ -194,6 +195,14 @@ managed by `-v/--volume` (see above) rather than hand-edited — it's what
 is fine either way (nothing is overridden, and one gets created the first
 time `-v/--volume` is used).
 
+Run `-w/--write-config` to bootstrap a config file: it writes out every
+supported option explicitly (filling in the current or default value for
+anything not already set — so the block above is exactly what a fresh `-w`
+produces), creating the file and its parent directory if they don't exist
+yet, and prints the file's full path. Combine it with other flags to seed
+specific values, e.g. `slocker-lite --log-level debug -w` writes
+`log-level: debug`.
+
 ## How it works
 
 Image layers are imported into `containers-storage` (parent-chained) and the

src/cli_args.cpp

@@ -50,7 +50,7 @@ constexpr int env_file = 266;
 constexpr int kill = 267;
 }  // namespace options
 
-constexpr std::array<struct option, 26> long_options = {{
+constexpr std::array<struct option, 27> long_options = {{
     {"help", no_argument, nullptr, 'h'},
     {"version", no_argument, nullptr, 'V'},
     {"test", no_argument, nullptr, 't'},
@@ -76,6 +76,7 @@ constexpr std::array<struct option, 26> long_options = {{
     {"clean-processes", no_argument, nullptr, options::clean_processes},
     {"env", required_argument, nullptr, options::env},
     {"env-file", required_argument, nullptr, options::env_file},
+    {"write-config", no_argument, nullptr, 'w'},
     {nullptr, 0, nullptr, 0},
 }};
 
@@ -95,6 +96,7 @@ void print_usage(const char* prog) {
         "       {0} --delete-volume-full <name>\n"
         "       {0} --list-processes\n"
         "       {0} --clean-processes\n"
+        "       {0} -w|--write-config\n"
         "       {0} -t|--test\n"
         "       {0} -h|--help\n"
         "       {0} -V|--version\n"
@@ -194,6 +196,11 @@ void print_usage(const char* prog) {
         "      --clean-processes     remove stale pid files (see --list-processes)\n"
         "                            left behind by sessions that are no longer\n"
         "                            running\n"
+        "  -w, --write-config        write a complete config file (creating it, and\n"
+        "                            its parent directory, if missing), filling in\n"
+        "                            every option's current or default value --\n"
+        "                            useful to bootstrap one for hand-editing.\n"
+        "                            Prints the config file's full path\n"
         "  -t, --test                run the test suite\n"
         "      --log-level <level>   set log verbosity (trace, debug, info, warn,\n"
         "                            error, critical, off)\n"
@@ -240,7 +247,7 @@ bool apply_log_level(std::string_view name) {
 std::optional<int> parse_args(int argc, char* argv[], ParsedArgs& out) {
     opterr = 0;
     int opt;
-    while ((opt = getopt_long(argc, argv, ":hVtm:u:r:c:nl:v:i:x:D", long_options.data(), nullptr)) != -1) {
+    while ((opt = getopt_long(argc, argv, ":hVtm:u:r:c:nl:v:i:x:Dw", long_options.data(), nullptr)) != -1) {
         switch (opt) {
             case 'h':
                 print_usage(argv[0]);
@@ -256,6 +263,7 @@ std::optional<int> parse_args(int argc, char* argv[], ParsedArgs& out) {
             case 'l':
             case 'i':
             case 'x':
+            case 'w':
             case options::list_volumes:
             case options::delete_volume:
             case options::delete_volume_full:
@@ -267,6 +275,9 @@ std::optional<int> parse_args(int argc, char* argv[], ParsedArgs& out) {
                     case 't':
                         requested = Mode::test;
                         break;
+                    case 'w':
+                        requested = Mode::write_config;
+                        break;
                     case 'm':
                         requested = Mode::mount;
                         break;

src/cli_args.h

@@ -42,7 +42,8 @@ enum class Mode {
     list_processes,
     clean_processes,
     exec,
-    kill
+    kill,
+    write_config
 };
 
 // Everything parse_args() extracts from argv, ready to hand to

src/commands.cpp

@@ -366,6 +366,42 @@ int delete_volume_command(const std::string& name, const std::filesystem::path&
     return 0;
 }
 
+// Writes out every supported config option explicitly, defaulting anything
+// currently unset to its effective value, creating the file (and its parent
+// directory) if it doesn't exist yet -- unlike create_volume_command()/
+// delete_volume_command()'s use of write_config_file(), which only ever
+// persists fields the user actually set. Meant to bootstrap a complete config
+// file for hand-editing.
+int write_config_command(const std::filesystem::path& config_path, const AppConfig& config) {
+    AppConfig full = config;
+    // Always the actually active spdlog level -- not merely a default for when
+    // full.log_level is unset -- so that an explicit --log-level passed
+    // alongside -w on this same command line is captured too, not shadowed by
+    // whatever an existing config file's own log-level already was (SPDLOG_LEVEL
+    // env var, an existing config's log-level, and --log-level are applied in
+    // that order, earlier, by main()/parse_args(); spdlog::get_level() reflects
+    // whichever of them won). spdlog::level::to_string_view() returns its own
+    // string_view_t (fmt::basic_string_view), not std::string_view --
+    // constructed explicitly from its data()/size() rather than relying on an
+    // implicit conversion that this fmt/spdlog version doesn't offer.
+    auto level_name = spdlog::level::to_string_view(spdlog::get_level());
+    full.log_level = std::string(level_name.data(), level_name.size());
+    full.unshare_user = full.unshare_user.value_or(true);
+    full.unshare_ipc = full.unshare_ipc.value_or(true);
+    full.unshare_pid = full.unshare_pid.value_or(true);
+    full.unshare_net = full.unshare_net.value_or(true);
+    full.unshare_uts = full.unshare_uts.value_or(true);
+    full.unshare_cgroup = full.unshare_cgroup.value_or(true);
+    // `volumes` is left exactly as loaded -- an open-ended list with no
+    // "default" entry to materialize, unlike the six fixed unshare-* flags.
+
+    if (!write_config_file(config_path, full)) {
+        return 1;
+    }
+    fmt::print("{}\n", config_path.string());
+    return 0;
+}
+
 int run_container(const std::filesystem::path& image_tar,
                    const std::vector<std::string>& requested_command, bool use_nsenter,
                    const std::optional<std::string>& user, const std::optional<std::string>& group,
@@ -535,6 +571,8 @@ int dispatch_command(const ParsedArgs& args, const std::filesystem::path& config
             return exec_in_session(*args.exec_pid, args.command, args.user_flag, args.group_flag);
         case Mode::kill:
             return kill_session(*args.kill_pid);
+        case Mode::write_config:
+            return write_config_command(config_path, config);
         case Mode::run: {
             // As root, containers-storage mount doesn't need to reexec into a private
             // user namespace to gain privilege, so the mount is already directly