This is useful because currently, when using `rusqlite` in a Cargo
workspace with one crate that uses `sqlcipher` and another that uses
`bundled`, a build error will be triggered by an unqualified `cargo
build` (as cargo will use the union of all features enabled by crates in
the workspace).
Instead of panicing, this just emits a warning, before (mostly) ignoring
that the `bundled` feature was specified. Note: in this configuration,
we still use our bundled bindings, to avoid changing `rusqlite` to
handle this edge case (hence 'mostly').
This is behind the `i128_blob` feature.
Blobs are stored as 16 byte big-endian values, with their most significant bit
flipped. This is so that sorting, comparison, etc all work properly, even with
negative numbers. This also allows the representation to be stable across
different computers.
It's possible that the `FromSql` implementation should handle the case that the
real value is stored in an integer. I didn't do this, but would be willing to
make the change. I don't think we should store them this way though, since I
don't think users would be able to sort/compare them sanely.
Support for `u128` is not implemented, as comparison with i128 values would work
strangely. This also is consistent with `u64` not being allowed, not that I
think that would be reason enough on it's own.
The `byteorder` crate is used if this feature is flipped, as it's quite small
and implements things more or less optimally. If/when `i128::{to,from}_be_bytes`
gets stabilized (https://github.com/rust-lang/rust/issues/52963), we should
probably use that instead.
See comment in libsqlite3-sys/build.rs for details - adding this flag is
harmless if it's not present in the header, and not having it can break
builds against older SQLite versions.
