Support method injection with `@ParentCommand` (and others).

[garretwilson]

The general consensus in the dependency injection community over the past couple of decades has been to move away from field injection, to prefer constructor injection, and to use method injection as a last resort. Having classes that allow other tools to come and muck around with their fields is no longer best practice. A quick search yielded the following:

• Why Field Injection is Fading Away with Spring 5.0
• Why Is Field Injection Not Recommended?
• What exactly is Field Injection and how to avoid it?
• (dozens or hundreds more)

In general picocli supports this: e.g. I can annotate a setMyOption(…) method with @Option, or setSpec(…) with @Spec. But for some reason @ParentCommand (and probably a few others; I didn't do a comprehensive search, as this was the one I ran into) only supports field injection.

Was this an oversight?

All annotations that support field injection need to support method injection as well; even if the library doesn't promote this practice, it should at least support it. Thanks.

[remkop]

It took me a while to figure out what the issue was, but what you mean is that @Target(ElementType.METHOD) is missing from public @interface ParentCommand. It only has @Target(ElementType.FIELD).

The actual injection logic already supports both method injection and field injection for the following annotations:
Mixin, ArgGroup, Unmatched, Option, Parameters, Spec, and ParentCommand. (Hence my confusion.)

So, all that is missing is the @Target(ElementType.METHOD) annotation and a JUnit test to verify.
I have no objection to doing this.

[remkop]

The other annotation that only is allowed on fields is @Unmatched.
This one has a different implementation; if it is too much effort, I may decide not to support method injection for @Unmatched.

[garretwilson]

The actual injection logic already supports both method injection and field injection for the following annotations:
Mixin, ArgGroup, Unmatched, Option, Parameters, Spec, and ParentCommand. (Hence my confusion.)

I see. I didn't look at the implementations; I just saw my IDE wasn't allowing me to add @ParentCommand to a setter method, and looked and realized @Target(ElementType.METHOD) wasn't present. It's great that this will be an easy fix.

… if it is too much effort, I may decide not to support method injection for @Unmatched.

That won't affect me personally at the moment; I'm not using @Unmatched and have no plans to do so at this time.

Thank you.