spec shaking v2: `export` flag is no longer applicable

[mootz12]

What version are you using?

main with experimental_spec_shaking_v2.

What did you do?

Enabled experimental_spec_shaking_v2 and used export = false on a spec-bearing type:

#[cfg(feature = "experimental_spec_shaking_v2")]
#[derive(Copy, Clone, Debug, Eq, PartialEq)]
#[contracttype(export = false)]
pub struct Hidden {
    pub x: u32,
}

The same problem can occur indirectly when a workspace enables soroban-sdk/experimental_spec_shaking_v2 and also builds helper crates such as soroban-token-spec or stellar-asset-spec that contain #[contractevent(..., export = false)].

What did you expect to see?

Spec shaking v2 should derive the final contract spec from reachable contract functions, events, errors, and referenced types. A type reachable from the contract boundary should either participate in shaking or produce a clear diagnostic if the annotation is unsupported.

What did you see instead?

export = false suppresses spec emission, so v2 marker generation is skipped for that type and reachable boundary types can fail trait-bound checks at compile time. export = true is also misleading under v2 because post-build shaking can still remove entries that are not reachable. Helper spec crates with export = false can fail to compile when the SDK macro dependency is unified with the v2 feature.

Alternatives

If we still see a need to allow developers to insert entries into the contractspecv0, we could add a flag or attribute that emits a keep-alive marker regardless of if the spec is reachable. Keeping export as the flag to use would mean we still need to error when export = false, or document that this is not recommended behavior and could result in incorrect specs.