Parse env-only vars

parse.go

@@ -54,6 +54,7 @@ type spec struct {
 	separate      bool                // if true, each slice and map entry will have its own --flag
 	help          string              // the help text for this option
 	env           string              // the name of the environment variable for this option, or empty for none
+	envOnly       bool
 	defaultValue  reflect.Value // default value for this option
 	defaultString string        // default value for this option, in string form to be displayed in help text
 	placeholder   string        // name of the data in help
@@ -343,7 +344,9 @@ func cmdFromStruct(name string, dest path, t reflect.Type) (*command, error) {
 
 		// Look at the tag
 		var isSubcommand bool // tracks whether this field is a subcommand
-		for _, key := range strings.Split(tag, ",") {
+		kvPairs := strings.Split(tag, ",")
+
+		for _, key := range kvPairs {
 			if key == "" {
 				continue
 			}
@@ -360,7 +363,7 @@ func cmdFromStruct(name string, dest path, t reflect.Type) (*command, error) {
 			case strings.HasPrefix(key, "--"):
 				spec.long = key[2:]
 			case strings.HasPrefix(key, "-"):
-				if len(key) != 2 {
+				if len(key) > 2 {
 					errs = append(errs, fmt.Sprintf("%s.%s: short arguments must be one character only",
 						t.Name(), field.Name))
 					return false
@@ -415,6 +418,12 @@ func cmdFromStruct(name string, dest path, t reflect.Type) (*command, error) {
 			spec.placeholder = strings.ToUpper(spec.field.Name)
 		}
 
+		if spec.env == "" && emptyLongAndShort(kvPairs) {
+			errs = append(errs, fmt.Sprintf("%s.%s: short arguments must be one character only",
+				t.Name(), field.Name))
+			return false
+		}
+
 		// if this is a subcommand then we've done everything we need to do
 		if isSubcommand {
 			return false
@@ -788,6 +797,22 @@ func isFlag(s string) bool {
 	return strings.HasPrefix(s, "-") && strings.TrimLeft(s, "-") != ""
 }
 
+func emptyLongAndShort(kv []string) bool {
+	var noShort, noLong bool
+	for _, key := range kv {
+		if key == "-" {
+			noShort = true
+		}
+
+		if key == "--" {
+			noLong = true
+		}
+	}
+
+	return noShort && noLong
+
+}
+
 // val returns a reflect.Value corresponding to the current value for the
 // given path
 func (p *Parser) val(dest path) reflect.Value {

usage_test.go

@@ -544,10 +544,10 @@ Options:
 }
 
 func TestUsageWithEnvOptions(t *testing.T) {
-	expectedUsage := "Usage: [CUSTOM=custom_value] [ENVONLY=envonly_value] example [-s SHORT]"
+	expectedUsage := "Usage: example [-s SHORT]"
 
 	expectedHelp := `
-Usage: [CUSTOM=custom_value] [ENVONLY=envonly_value] example [-s SHORT]
+Usage: example [-s SHORT]
 
 Options:
   -s SHORT [env: SHORT]
@@ -652,10 +652,10 @@ Options:
 }
 
 func TestFailEnvOnly(t *testing.T) {
-	expectedUsage := "Usage: [AUTH_KEY=auth_key_value] example [--arg ARG]"
+	expectedUsage := "Usage: example [--arg ARG]"
 
 	expectedHelp := `
-Usage: [AUTH_KEY=auth_key_value] example [--arg ARG]
+Usage: example [--arg ARG]
 
 Options:
   --arg ARG, -a ARG [env: MY_ARG]