Support recursive nesting

[yanganto]

Or rather, recursive nesting does not work regardless of the flattening which I added, so that should be a separate issue probably

Originally posted by @faervan in #49 (comment)

[faervan]

This is not actually tied to flatten and it was a missing/not working feature even before #49

see this failing test:

    #[test]
    fn recursive_nesting() {
        #[derive(TomlExample, Default, Debug, Deserialize, PartialEq)]
        struct Outer {
            #[toml_example(nesting)]
            _middle: Middle,
        }
        #[derive(TomlExample, Default, Debug, Deserialize, PartialEq)]
        struct Middle {
            #[toml_example(nesting)]
            _inner: Inner,
        }
        #[derive(TomlExample, Default, Debug, Deserialize, PartialEq)]
        struct Inner {
            _value: usize,
        }
        let example = Outer::toml_example();
        assert_eq!(toml::from_str::<Outer>(&example).unwrap(), Outer::default());
        assert_eq!(
            example,
            r#"[_middle]
[_middle._inner]
_value = 0

"#
        );
    }

The [_middle._inner] part is actually just [_inner], so both assert_eq's fail

[yanganto]

Thanks for clarifying this. It seems we are not using recursive nesting at this moment, we can keep this issue here. Once anyone really use this, he will have a chance to design, implement and then join into this project. How do you think about this? 😄

[faervan]

I actually need this feature, else I wouldn't have even noticed it's absence. If I find the time for it I will definitely try my luck on implementing it.

[faervan]

So, looking into it, I think it is necessary to update the toml_example_with_prefix method with an additional argument...Which would be a breaking change I suppose, but no one should really use this method directly anyway, so it might be fine?

[faervan]

It could also be done without changing toml_example_with_prefix, but this would require to extract the previous label from its wrapping (e.g. get "foo" from [foo] or [[foo]] or # [foo] or # [[foo]])

[yanganto]

Add additional argument on toml_example_with_prefix is good from my end, if it is clear and straightforward for user to know how to upgrade the code, we have nothing to worry about this.

Currently, the using case for other user is only one layer deep nesting in #18, and I think toml_example_with_prefix is not directly used by user at this moment.

[yanganto]

By the way, if you don't mind, can you put your email in the authors field at the same time. When you breaking change something, that means the crate is use in a bigger scope. 😄