cli: help command now also prints usage

The help command now adds command usage to its output by calling each
command handler in CMD_USAGE mode.

Instead of seeing, for example:

	decodepay
	    Decode {bolt11}, using {description} if necessary

we see:

	decodepay bolt11 [description]
	    Decode {bolt11}, using {description} if necessary

Signed-off-by: Mark Beckwith <wythe@intrig.com>

lightningd/jsonrpc.c

@@ -62,7 +62,7 @@ static void json_help(struct command *cmd,
 static const struct json_command help_command = {
 	"help",
 	json_help,
-	"List available commands, or give verbose help on one command.",
+	"List available commands, or give verbose help on one {command}.",
 
 	.verbose = "help [command]\n"
 	"Without [command]:\n"
@@ -196,7 +196,10 @@ static void json_help(struct command *cmd,
 	struct json_result *response = new_json_result(cmd);
 	struct json_command **cmdlist = get_cmdlist();
 	const jsmntok_t *cmdtok;
+	char *usage;
 
+	/* FIXME: This is never called with a command parameter because lightning-cli
+	 * attempts to launch the man page and then exits. */
 	if (!param(cmd, buffer, params,
 		   p_opt("command", json_tok_tok, &cmdtok),
 		   NULL))
@@ -231,11 +234,15 @@ static void json_help(struct command *cmd,
 		return;
 	}
 
+	cmd->mode = CMD_USAGE;
 	json_array_start(response, "help");
 	for (i = 0; i < num_cmdlist; i++) {
+		cmdlist[i]->dispatch(cmd, NULL, NULL);
+		usage = tal_fmt(cmd, "%s %s", cmdlist[i]->name,
+			cmd->usage);
 		json_add_object(response,
 				"command", JSMN_STRING,
-				cmdlist[i]->name,
+				usage,
 				"description", JSMN_STRING,
 				cmdlist[i]->description,
 				NULL);

lightningd/param.c

@@ -244,7 +244,7 @@ static bool param_arr(struct command *cmd, const char *buffer,
 {
 #if DEVELOPER
 	if (!check_params(params)) {
-		command_fail(cmd, PARAM_DEV_ERROR, "developer error");
+		command_fail(cmd, PARAM_DEV_ERROR, "developer error: check_params");
 		return false;
 	}
 #endif
@@ -271,7 +271,8 @@ bool param(struct command *cmd, const char *buffer,
 		param_cbx cbx = va_arg(ap, param_cbx);
 		void *arg = va_arg(ap, void *);
 		if  (!param_add(&params, name, required, cbx, arg)) {
-			command_fail(cmd, PARAM_DEV_ERROR, "developer error");
+			command_fail(cmd, PARAM_DEV_ERROR,
+				     "developer error: param_add %s", name);
 			va_end(ap);
 			return false;
 		}

tests/test_misc.py

@@ -622,7 +622,7 @@ def test_cli(node_factory):
                                    .format(l1.daemon.lightning_dir),
                                    'help']).decode('utf-8')
     # Test some known output.
-    assert 'help\n    List available commands, or give verbose help on one command' in out
+    assert 'help [command]\n    List available commands, or give verbose help on one {command}' in out
 
     # Test JSON output.
     out = subprocess.check_output(['cli/lightning-cli',