Improve error reporting when non mandatory options are misconfigured or not incorrectly specified at runtime

[czpilar]

This seems like regression from some of the latests commits.

Consider this configuration:

@SpringBootApplication
public class SpringShellApplication {

    public static void main(String[] args) {
        SpringApplication.run(SpringShellApplication.class, args);
    }

    @Command(name = "hello", completionProvider = "helloNameCompletionProvider")
    public void sayHello(@Option(longName = "name", shortName = 'n') String name) {
        System.out.println("Hello " + name + "!");
    }

    @Bean
    public CompletionProvider helloNameCompletionProvider() {
        return completionContext -> Stream.of("Peter", "Paul", "Mary").map(CompletionProposal::new).toList();
    }

}

There are some issues:

1. If a command is invoked without any option, the warning is logged. Which is not consistent if command is invoked with and option without value (there is no warning message).

   shell:>hello
   11:32:19.249 [main] WARN  o.s.s.c.c.a.MethodInvokerCommandAdapter - No value provided for optional option '--name' and no default value specified.
   Hello !
   
   shell:>hello --name
   Hello !
   
   shell:>hello -n
   Hello !
   

2. If option is specified with a short or long name with space before the value, it's not recognized.

   shell:>hello --name Paul
   Hello !
   
   shell:>hello -n Paul
   Hello !
   

3. The value is recognized only if specified with equal sign.

   shell:>hello --name=Paul
   Hello Paul!
   
   shell:>hello -n=Paul
   Hello Paul!
   

[fmbenhassine]

1. If a command is invoked without any option, the warning is logged. Which is not consistent if command is invoked with and option without value (there is no warning message).

I think those are different things: 1) not providing an optional option not having a default value vs 2) providing an option with incorrect syntax (missing value)

1. is a command configuration problem and should fail fast at command configuration time (introspection time, ie in CommandFactoryBean)
2. is a command usage problem which is can happen at runtime (command invoking time, ie in MethodInvokerCommandAdapter).

I think there is a room for improvement here, but this is not blocking for 4.0 GA.

2. If option is specified with a short or long name with space before the value, it's not recognized.
3. The value is recognized only if specified with equal sign.

The default parser only supports key=value pairs. This is mentioned in the docs here: https://docs.spring.io/spring-shell/reference/4.0-SNAPSHOT/commands/syntax.html

---

EDIT:

Option values without an equal sign are not recognized

Since this is not supported in the default parser as explained, I am changing the title of this issue to focus on issue 1): improve error reporting when non mandatory options are not specified or incorrectly specified.

[fmbenhassine]

The default parser only supports key=value pairs. This is mentioned in the docs here

@czpilar While thinking about this, I improved the default parser to support the --key value / -k value syntax in addition to the --key=value / -k=valule form, see #1248.

This works way better with command completion now! I think the updated DefaultCommandParserTests suite is fairly complete, but I might have missed a corner case or two at this time of the day 😅. I will retest this with a fresh head again before GA. Any feedback is welcome!