Fix CLI token set command

internal/config/flags.go

@@ -42,7 +42,6 @@ func NewSet(name, envPrefix string) *Set {
 	return s
 }
 
-func (s *Set) Args() []string        { return s.fs.Args() }
 func (s *Set) SetOutput(w io.Writer) { s.fs.SetOutput(w) }
 func (s *Set) register(sp *spec)     { s.specs = append(s.specs, sp) }
 func (s *Set) note(long, short string) {
@@ -208,7 +207,19 @@ func (s *Set) Parse(args []string) error {
 	if err := s.checkConvention(args); err != nil {
 		return err
 	}
-	return s.fs.Parse(args)
+	if err := s.fs.Parse(args); err != nil {
+		return err
+	}
+	// A stray word is never harmless: the flag package stops parsing at the
+	// first non-flag argument, so every option after it is dropped in silence.
+	// Writing a boolean as "--vanity false" is the way this bites - it sets
+	// the flag to true and then discards the --data that says which file to
+	// write, leaving a cheerful message about the opposite of what was meant.
+	if extra := s.fs.Args(); len(extra) > 0 {
+		return fmt.Errorf("unexpected argument %q: an option's value attaches with %q, as in --name=value, and any positional argument comes first",
+			extra[0], "=")
+	}
+	return nil
 }
 
 // Changed reports whether an option was given on the command line.