Support explicit arity min max with @Option

- @Option now has arityMin/arityMax which if defined,
  non-negative, are used instead of arity.
- Fixes #731

spring-shell-core/src/main/java/org/springframework/shell/command/annotation/Option.java

@@ -74,6 +74,28 @@ public @interface Option {
 	 * Define option arity.
 	 *
 	 * @return option arity
+	 * @see #arityMin()
+	 * @see #arityMax()
 	 */
 	OptionArity arity() default OptionArity.NONE;
+
+	/**
+	 * Define option arity min. If Defined non-negative will be used instead of
+	 * {@link #arity()}. If {@code arityMax} is not set non-negative it is set to
+	 * same as this.
+	 *
+	 * @return option arity min
+	 * @see #arity()
+	 */
+	int arityMin() default -1;
+
+	/**
+	 * Define option arity max. If Defined non-negative will be used instead of
+	 * {@link #arity()}. If {@code arityMin} is not set non-negative it is set to
+	 * zero.
+	 *
+	 * @return option arity max
+	 * @see #arity()
+	 */
+	int arityMax() default -1;
 }

spring-shell-core/src/main/java/org/springframework/shell/command/annotation/support/CommandRegistrationFactoryBean.java

@@ -251,7 +251,22 @@ class CommandRegistrationFactoryBean implements FactoryBean<CommandRegistration>
 				optionSpec.shortNames(shortNames.toArray(new Character[0]));
 				optionSpec.position(mp.getParameterIndex());
 				optionSpec.description(so.description());
-				if (so.arity() != OptionArity.NONE) {
+				int arityMin = so.arityMin();
+				int arityMax = so.arityMax();
+				if (arityMin > -1) {
+					if (arityMax < arityMin) {
+						arityMax = arityMin;
+					}
+				}
+				else if (arityMax > -1) {
+					if (arityMin < 0) {
+						arityMin = 0;
+					}
+				}
+				if (arityMin > -1 && arityMax > -1) {
+					optionSpec.arity(arityMin, arityMax);
+				}
+				else if (so.arity() != OptionArity.NONE) {
 					optionSpec.arity(so.arity());
 				}
 				else {