Future proof schema API

[matklad]

Currently this is a public type:

#[derive(PartialEq, Debug, BorshSerialize, BorshDeserialize, BorshSchemaMacro)]
pub struct BorshSchemaContainer {
    /// Declaration of the type.
    pub declaration: Declaration,
    /// All definitions needed to deserialize the given type.
    pub definitions: HashMap<Declaration, Definition>,
}

This is ungreat -- all public fields make it impossible to make any kind of change to this structure. See #45 for example of the change we might want to do here (replacing HashMap with a BTreeMap to avoid hashbrown).

We should make it possible to change the internal representation without breaking public API, but that itself would necessitate a semver break.

[dj8yfo]

current issue is great detail on #51 's sub-issue

[dj8yfo]

@frol
Taking into account container ser/de guarantee https://github.com/dj8yfo/borsh-rs/blob/tmp_link_container_guarantee/borsh/tests/test_schema_enums.rs#L164,
the below link is a straightforward approach, which compiles, how this could be done, taking the above into account.

https://gist.github.com/dj8yfo/da468206a03feca6d08698cbfc868ea0

[frol]

@dj8yfo Do you mean canonicity enforcement (#160) when say "container ser/de guarantee"? Can you shed some light on why it matters here?

https://gist.github.com/dj8yfo/da468206a03feca6d08698cbfc868ea0#file-f_p_schema_api-rs-L139-L174 - This interface looks good to me (I would only ask not to shorten the names to "*_def", instead, use a full word get_definition)

[dj8yfo]

@frol No, i mean, that the container BorshSchemaContainer has some format of ser/de, which has been committed to in insta test.
It also has some BorshSchema implementation which is supposed to describe the format.

In gist i've removed derived implementations of BorshSerialize, BorshDeserialize for BorshSchemaContainer, as they depend on internal BorshSchemaContainer struct representation and replaced them with versions, that depend on declared public methods declaration() and definitions(), which are supposed to allow not changing the ser/de format, which has been committed to.

I missed to do the same for impl BorshSchema for BorshSchemaContainer in the gist at first, updated it now.

[dj8yfo]

taking this issue