Register option without prefix

- While option should be defined i.e. using "--arg", discover
  prefix from ShellMethod#prefix and use that if just "arg"
  is defined.
- Backport #575
- Fixes #577

spring-shell-docs/src/main/asciidoc/using-shell-options-definition.adoc

@@ -25,6 +25,16 @@ include::{snippets}/OptionSnippets.java[tag=option-with-annotation]
 ----
 ====
 
+If option name is defined without prefix, either `-` or `--`, it is discovered
+from _ShellMethod#prefix_.
+
+====
+[source, java, indent=0]
+----
+include::{snippets}/OptionSnippets.java[tag=option-with-annotation-without-prefix]
+----
+====
+
 Programmatic way with `CommandRegistration` is to use method adding a long name.
 
 ====

spring-shell-docs/src/test/java/org/springframework/shell/docs/OptionSnippets.java

@@ -23,12 +23,20 @@ public class OptionSnippets {
 
 	class Dump1 {
 		// tag::option-with-annotation[]
-		public String example(@ShellOption(value = { "argx" }) String arg1) {
+		public String example(@ShellOption(value = { "--argx" }) String arg1) {
 			return "Hello " + arg1;
 		}
 		// end::option-with-annotation[]
 	}
 
+	class Dump7 {
+		// tag::option-with-annotation-without-prefix[]
+		public String example(@ShellOption(value = { "argx" }) String arg1) {
+			return "Hello " + arg1;
+		}
+		// end::option-with-annotation-without-prefix[]
+	}
+
 	class Dump2 {
 		// tag::option-without-annotation[]
 		public String example(String arg1) {

spring-shell-standard/src/main/java/org/springframework/shell/standard/StandardMethodTargetRegistrar.java

@@ -118,6 +118,14 @@ public class StandardMethodTargetRegistrar implements MethodTargetRegistrar, App
 								else if (o.length() == stripped.length() + 1 && stripped.length() == 1) {
 									shortNames.add(stripped.charAt(0));
 								}
+								else if (o.length() == stripped.length()) {
+									if ("--".equals(shellMapping.prefix())) {
+										longNames.add(stripped);
+									}
+									else if ("-".equals(shellMapping.prefix()) && stripped.length() == 1) {
+										shortNames.add(stripped.charAt(0));
+									}
+								}
 							});
 						}
 						else {

spring-shell-standard/src/test/java/org/springframework/shell/standard/StandardMethodTargetRegistrarTests.java

@@ -443,4 +443,44 @@ public class StandardMethodTargetRegistrarTests {
 		public void foo3(@ShellOption boolean arg1) {
 		}
 	}
+
+	@Test
+	public void testOptionWithoutHyphenRegisterFromDefaultPrefix() {
+		applicationContext = new AnnotationConfigApplicationContext(OptionWithoutHyphenRegisterFromDefaultPrefix.class);
+		registrar.setApplicationContext(applicationContext);
+		registrar.register(catalog);
+
+		assertThat(catalog.getRegistrations().get("foo1")).isNotNull();
+		assertThat(catalog.getRegistrations().get("foo1").getOptions()).hasSize(1);
+		assertThat(catalog.getRegistrations().get("foo1").getOptions().get(0).getLongNames()).hasSize(1);
+		assertThat(catalog.getRegistrations().get("foo1").getOptions().get(0).getShortNames()).hasSize(0);
+	}
+
+	@ShellComponent
+	public static class OptionWithoutHyphenRegisterFromDefaultPrefix {
+
+		@ShellMethod(value = "foo1")
+		public void foo1(@ShellOption("xxx") boolean arg1) {
+		}
+	}
+
+	@Test
+	public void testOptionWithoutHyphenRegisterFromChangedPrefix() {
+		applicationContext = new AnnotationConfigApplicationContext(OptionWithoutHyphenRegisterFromChangedPrefix.class);
+		registrar.setApplicationContext(applicationContext);
+		registrar.register(catalog);
+
+		assertThat(catalog.getRegistrations().get("foo1")).isNotNull();
+		assertThat(catalog.getRegistrations().get("foo1").getOptions()).hasSize(1);
+		assertThat(catalog.getRegistrations().get("foo1").getOptions().get(0).getLongNames()).hasSize(0);
+		assertThat(catalog.getRegistrations().get("foo1").getOptions().get(0).getShortNames()).hasSize(1);
+	}
+
+	@ShellComponent
+	public static class OptionWithoutHyphenRegisterFromChangedPrefix {
+
+		@ShellMethod(value = "foo1", prefix = "-")
+		public void foo1(@ShellOption("x") boolean arg1) {
+		}
+	}
 }