cbindgen shouldn't emit errors for declarations that won't be printed anyway

[jrose-signal]

At https://github.com/signalapp/libsignal-client/commit/7be34d74461578b326b68007be7ee0c9374c0c7e, running cbindgen in rust/bridge/ffi produces the following errors:

ERROR: Conflicting name for constant signal-crypto::Aes256GcmEncryption::NONCE_SIZE.
ERROR: Conflicting name for constant signal-crypto::Aes256GcmDecryption::TAG_SIZE.
ERROR: Conflicting name for constant signal-crypto::Aes256GcmDecryption::NONCE_SIZE.

However, the cbindgen.toml in that directory has constants disabled:

[export]
item_types = ["enums", "functions", "opaque", "structs", "typedefs"]

So there's no problem with conflicting names, and indeed the resulting header is correct.

[emilio]

Yeah, we filter out stuff later after parsing, so we still get the parsing warnings. My guess is that this shouldn't be hard to fix.

[samuelscheit]

@jrose-signal were you able to resolve this issue with signal? (I'm trying to generate signal_ffi)

[jrose-signal]

No, we just ignore the errors, assuming that we'll see any problems when we actually try to use the header from Swift. :-(