Use privacy barrier for all structs with invariants about rust-bitcoin

[apoelstra]

I guess we can certainly write a proc-macro which does nothing (except maybe when compiled with a specific flag, in which case it writes out some files) and then we definitely make up our own annotations.

[apoelstra]

I wonder if there's an easy way we can identify "types with invariants".

I guess, anything that's a newtype around a single type is probably one.

Can we tag stuff with like, #[rust_bitcoin::has_invariant] or will rustc/clippy/whatever complain?

[15IITian]

@apoelstra
I think we should create a privacy barrier -> as we have done so for the PushBytes related stuffs by introducing primitive module-> in order to have uniformity in our codebase.

rust-bitcoin/bitcoin/src/blockdata/script/push_bytes.rs

Line 16 in b3273cf

mod primitive {

Still if we decide to go with clippy or tag stuffs etc -> then IMO, we have to make changes for the PushBytes related stuffs as well.

[sanket1729]

Strong concept ACK. I have been doing it for me personal projects. Related #1327.

[Kixunil]

I wonder if there's an easy way we can identify "types with invariants".

Could be types that are Foo(X); with impl Foo { fn ...(...: X) -> Result<Self, ...> } or with TryFrom<X> for Foo.

I guess, anything that's a newtype around a single type is probably one.

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