chore!: split ValidationError from MaxSizeError; validate and max_serialized_size made BorshSchemaContainer's methods

[dj8yfo]

• summary of changes:
  • most of max_serialized_size code moved from borsh/src/schema_helpers.rs to borsh/src/schema/container_ext/max_size.rs
  • max_serialized_size made a method of BorshSchemaContainer
  • borsh::MaxSizeError moved to borsh::schema::SchemaMaxSerializedSizeError
  • SchemaMaxSerializedSizeError::MissingDefinition -> SchemaMaxSerializedSizeError::MissingDefinition(Declaration)
  • is_zero_size private function tries to detect recursion too, its return type changed to Result<bool, ()> (Err on recursive call)
  • MaxSizeError::ZSTSequenceNotArray check and enum variant split into separate types and module borsh/src/schema/container_ext/validate.rs
    • validate method of BorshSchemaContainer

---

split

pub enum MaxSizeError {
    Overflow,
    Recursive,
    MissingDefinition,
    ZSTSequenceNotArray,
}

into

pub enum MaxSizeError {
    Overflow,
    Recursive,
    MissingDefinition,
}

and

pub enum ValidateError {
    /// sequences of zero sized types of dynamic length are forbidden by definition
    /// see <https://github.com/near/borsh-rs/pull/202> and related ones
    ZSTSequence,
}

[dj8yfo]

a valid alternative might be to remove second commit and newly added module borsh/src/schema/container_ext/validate.rs,
and just remove MaxSizeError::ZSTSequenceNotArray variant and corresponding check

[dj8yfo]

a similar test in current master was causing stack overflow

    #[test]
    fn test_is_zero_size_recursive_check_err() {
        use crate as borsh;

        #[derive(::borsh_derive::BorshSchema)]
        struct RecursiveNoExitStructUnnamed(Box<RecursiveNoExitStructUnnamed>);

        let schema = BorshSchemaContainer::for_type::<RecursiveNoExitStructUnnamed>();
        assert_eq!(false, is_zero_size(schema.declaration(), &schema));
    }

thread 'schema_helpers::tests::test_is_zero_size_recursive_check_err' has overflowed its stack
fatal runtime error: stack overflow

Though rustc prevents from constructing a type, which would hit a branch with recursing indefinetely into is_zero_size inside of max_serialized_size_impl:

error: values of the type `[[[RecursiveNoExitStructUnnamed2; 4294967295]; 2]; 4294967295]` are too big for the current architecture

// can be defined without error
// cannot be used as the value of type parameter in a function
struct RecursiveNoExitStructUnnamed2(Box<[[[RecursiveNoExitStructUnnamed2; u32::MAX as usize]; 2]; u32::MAX as usize]>);

[frol]

Looks good to me 👍