Merge #3: Print help if run without a subcommand

a79d139 cli: print help if no subcommand given (Andrew Cann)

Pull request description:

  Builds on #1
  
  Print help/usage info if run without a subcommand instead of printing `Execution failed: Subcommand not found:`


ACKs for top commit:
  apoelstra:
    ACK a79d139; successfully ran local tests; nice!


Tree-SHA512: a3b1d9f30cdedfa51f09782572f0513078d958807bd41b65b147676ca12df0d07113f1b1ffd18c7564af2beb979c6cb8dbd746c3145b58bcb2245569eeaf62b9

Author: apoelstra

src/bin/hal-simplicity/main.rs

@@ -32,6 +32,7 @@ fn init_app<'a, 'b>() -> clap::App<'a, 'b> {
 				.setting(clap::AppSettings::AllArgsOverrideSelf)
 				.subcommands(cmd::subcommands()),
 		)
+		.setting(clap::AppSettings::SubcommandRequiredElseHelp)
 		.arg(
 			cmd::opt("verbose", "print verbose logging output to stderr")
 				.short("v")
@@ -84,6 +85,6 @@ fn main() {
 				panic!("Subcommand not found: {}", m.subcommand().0);
 			}
 		}
-		(cmd, _) => panic!("Subcommand not found: {}", cmd),
+		(cmd, _) => panic!("Subcommand not found: {:?}", cmd),
 	}
 }

tests/cli.rs

@@ -47,13 +47,24 @@ fn assert_cmd(args: &[&str], expected_stdout: impl AsRef<str>, expected_stderr:
 
 #[test]
 fn cli_empty() {
-	// FIXME this is definitely not what we want to show the user
 	assert_cmd(
 		&[],
+		"",
 		"\
-Execution failed: Subcommand not found: 
+hal-simplicity 0.2.1
+
+USAGE:
+    hal [FLAGS] <SUBCOMMAND>
+
+FLAGS:
+    -h, --help       Prints help information
+    -V, --version    Prints version information
+    -v, --verbose    print verbose logging output to stderr
+
+SUBCOMMANDS:
+    elements    hal-simplicity -- a Simplicity extension of hal
+    help        Prints this message or the help of the given subcommand(s)
 ",
-		"",
 	);
 }
 
@@ -63,7 +74,7 @@ fn cli_help() {
 hal-simplicity 0.2.1
 
 USAGE:
-    hal [FLAGS] [SUBCOMMAND]
+    hal [FLAGS] <SUBCOMMAND>
 
 FLAGS:
     -h, --help       Prints help information
@@ -88,7 +99,7 @@ fn cli_bad_flag() {
 error: Found argument '-?' which wasn't expected, or isn't valid in this context
 
 USAGE:
-    hal [FLAGS] [SUBCOMMAND]
+    hal [FLAGS] <SUBCOMMAND>
 
 For more information try --help
 ",