docs/tests: document --show-keys usage; add smoke-test script

Signed-off-by: SupananWC <[email protected]>

Author: SupananWC

external-tests/show_flag_test.sh

@@ -0,0 +1,20 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+# Simple smoke test: build the `wg` binary and verify `--show-keys` appears
+# in the `wg show --help` output. This runs locally and is intentionally
+# lightweight (does not require creating kernel devices).
+
+cd src
+echo "Building src/... (this may take a moment)"
+make V=1
+
+echo "Checking help for --show-keys"
+if ./wg show --help 2>&1 | grep -q -- '--show-keys'; then
+    echo "OK: --show-keys present in help"
+    exit 0
+else
+    echo "FAIL: --show-keys not found in help output"
+    ./wg show --help 2>&1 | sed -n '1,200p'
+    exit 2
+fi

src/show.c

@@ -209,7 +209,8 @@ static void show_usage(void)
 	fprintf(stderr, "Usage: %s %s { <interface> | all | interfaces } [public-key | private-key | listen-port | fwmark | peers | preshared-keys | endpoints | allowed-ips | latest-handshakes | transfer | persistent-keepalive | dump]\n", PROG_NAME, COMMAND_NAME);
 	fprintf(stderr, "Optional flags: --show-keys\n");
 }
-
+	fprintf(stderr, "Usage: %s %s [--show-keys] { <interface> | all | interfaces } [public-key | private-key | listen-port | fwmark | peers | preshared-keys | endpoints | allowed-ips | latest-handshakes | transfer | persistent-keepalive | dump]\n", PROG_NAME, COMMAND_NAME);
+	fprintf(stderr, "Options:\n  --show-keys    Reveal keys temporarily for debugging (respects WG_HIDE_KEYS=never)\n");
 static void pretty_print(struct wgdevice *device)
 {
 	struct wgpeer *peer;