v: show help for -h, -help, and --help, in addition to v help

cmd/v/help/help.v

@@ -5,7 +5,7 @@ import os
 import v.pref
 
 const (
-	unknown_topic = 'V Error: Unknown help topic provided. Use `v help` for usage information.'
+	unknown_topic = '`v help`: unknown help topic provided. Use `v help` for usage information.'
 )
 
 pub fn print_and_exit(topic string) {
@@ -15,12 +15,12 @@ pub fn print_and_exit(topic string) {
 		if (b >= `a` && b <= `z`) || b == `-` || (b >= `0` && b <= `9`) {
 			continue
 		}
-		eprintln(unknown_topic)
+		eprintln(help.unknown_topic)
 		exit(1)
 	}
 	target_topic := os.join_path(vroot, 'cmd', 'v', 'help', '${topic}.txt')
 	content := os.read_file(target_topic) or {
-		eprintln(unknown_topic)
+		eprintln(help.unknown_topic)
 		exit(1)
 	}
 	println(content)

cmd/v/help/help_test.v

@@ -0,0 +1,22 @@
+import os
+
+fn test_help() {
+	vexe := os.getenv('VEXE')
+	res := os.exec('"$vexe" help') or { panic(err) }
+	assert res.exit_code == 0
+	assert res.output.starts_with('V is a tool for managing V source code.')
+}
+
+fn test_help_as_short_option() {
+	vexe := os.getenv('VEXE')
+	res := os.exec('"$vexe" -h') or { panic(err) }
+	assert res.exit_code == 0
+	assert res.output.starts_with('V is a tool for managing V source code.')
+}
+
+fn test_help_as_long_option() {
+	vexe := os.getenv('VEXE')
+	res := os.exec('"$vexe" --help') or { panic(err) }
+	assert res.exit_code == 0
+	assert res.output.starts_with('V is a tool for managing V source code.')
+}

cmd/v/v.v

@@ -71,6 +71,9 @@ fn main() {
 	}
 	args_and_flags := util.join_env_vflags_and_os_args()[1..]
 	prefs, command := pref.parse_args(external_tools, args_and_flags)
+	if prefs.is_help {
+		invoke_help_and_exit(args)
+	}
 	if prefs.is_verbose {
 		// println('args= ')
 		// println(args) // QTODO
@@ -145,7 +148,7 @@ fn invoke_help_and_exit(remaining []string) {
 		2 { help.print_and_exit(remaining[1]) }
 		else {}
 	}
-	println('V Error: Expected only one help topic to be provided.')
+	println('`v help`: provide only one help topic.')
 	println('For usage information, use `v help`.')
 	exit(1)
 }