cli: don't crash when there's no argument

cli/lightning-cli.c

@@ -650,7 +650,7 @@ int main(int argc, char *argv[])
 	jsmntok_t *toks;
 	const jsmntok_t *result, *error, *id;
 	const tal_t *ctx = tal(NULL, char);
-	char *net_dir, *rpc_filename;
+	char *config_filename, *base_dir, *net_dir, *rpc_filename;
 	jsmn_parser parser;
 	int parserr;
 	enum format format = DEFAULT_FORMAT;
@@ -668,7 +668,8 @@ int main(int argc, char *argv[])
 	setup_option_allocators();
 
 	opt_exitcode = ERROR_USAGE;
-	minimal_config_opts(ctx, argc, argv, &net_dir, &rpc_filename);
+	minimal_config_opts(ctx, argc, argv, &config_filename, &base_dir,
+			    &net_dir, &rpc_filename);
 
 	opt_register_noarg("--help|-h", opt_usage_and_exit,
 			   "<command> [<params>...]", "Show this message. Use the command help (without hyphens -- \"lightning-cli help\") to get a list of all RPC commands");

common/configdir.c

@@ -281,16 +281,18 @@ static struct configvar **gather_cmdline_args(const tal_t *ctx,
 
 void minimal_config_opts(const tal_t *ctx,
 			 int argc, char *argv[],
+			 char **config_filename,
+			 char **basedir,
 			 char **config_netdir,
 			 char **rpc_filename)
 {
-	char *unused_filename, *unused_basedir;
-
 	initial_config_opts(tmpctx, &argc, argv, false,
-			    &unused_filename,
-			    &unused_basedir,
+			    config_filename,
+			    basedir,
 			    config_netdir,
 			    rpc_filename);
+	tal_steal(ctx, *config_filename);
+	tal_steal(ctx, *basedir);
 	tal_steal(ctx, *config_netdir);
 	tal_steal(ctx, *rpc_filename);
 }

common/configdir.h

@@ -15,6 +15,8 @@ void setup_option_allocators(void);
 /* Minimal config parsing for tools: use opt_early_parse/opt_parse after */
 void minimal_config_opts(const tal_t *ctx,
 			 int argc, char *argv[],
+			 char **config_filename,
+			 char **basedir,
 			 char **config_netdir,
 			 char **rpc_filename);
 

devtools/checkchannels.c

@@ -109,6 +109,7 @@ static void copy_column(void *dst, size_t size,
 
 int main(int argc, char *argv[])
 {
+	char *config_filename, *base_dir;
 	char *net_dir, *rpc_filename, *hsmfile, *dbfile;
 	sqlite3 *sql;
 	sqlite3_stmt *stmt;
@@ -124,7 +125,8 @@ int main(int argc, char *argv[])
 
 	setup_option_allocators();
 
-	minimal_config_opts(top_ctx, argc, argv, &net_dir, &rpc_filename);
+	minimal_config_opts(top_ctx, argc, argv, &config_filename, &base_dir,
+			    &net_dir, &rpc_filename);
 
 	opt_register_noarg("-v|--verbose", opt_set_bool, &verbose,
 			 "Print everything");

tests/test_misc.py

@@ -1195,6 +1195,13 @@ def test_daemon_option(node_factory):
         assert 'No child process' not in f.read()
 
 
+def test_cli_no_argument():
+    """If no arguments are provided, should display help and exit."""
+    out = subprocess.run(['cli/lightning-cli'], stdout=subprocess.PIPE)
+    assert out.returncode in [0, 2]  # returns 2 if lightning-rpc not available
+    assert "Usage: cli/lightning-cli <command> [<params>...]" in out.stdout.decode()
+
+
 @pytest.mark.developer("needs DEVELOPER=1")
 def test_blockchaintrack(node_factory, bitcoind):
     """Check that we track the blockchain correctly across reorgs