v0.5.0-beta.0

This is an experimental version for the upcoming 0.5.0 release.
Make sure to run cargo install --locked cargo-pgx --version 0.5.0-beta.0.

Handling Datums

pg_sys::Datum is no longer type Datum = usize;, but a "newtype": a struct wrapping a pointer that indicates it is an opaque type. This is for correctness and to better represent the unique nature of the type with respect to Postgres. A fair amount of your code may have relied on T as pg_sys::Datum or datum as T working. Certainly some in pgx did, resulting in patterns like:

// generating fresh arrays for data
let mut datums: Vec<pg_sys::Datum> = vec![0; N];
let mut nulls = vec![false; N];

// treating a datum as a pass-by-value type
let index = datum as i32;

// treating a datum as a pointer type
let varlena = datum as *mut pg_sys::varlena;

Now it doesn't! To make the transition easy, From<T> for pg_sys::Datum is implemented for everything it is reasonable to convert directly into it in a "by-value" fashion. Use IntoDatum for anything more complex. To get the usize hiding inside Datum out, use Datum::value(self) -> usize, to cast it as a pointer, Datum::ptr_cast::<T>(self) -> *mut T is available.

// (getting|putting) data (from|into) Postgres as a datum array
let mut datums = vec![pg_sys::Datum::from(0); N];
let mut nulls = vec![false; N];

// treating a datum as a pass-by-value type
let index = datum.value() as i32;

// treating a datum as a pointer type
let varlena = datum.ptr_cast::<pg_sys::varlena>();

Because a pg_sys::Datum is a union of types, only certain traits that are implemented on usize are also implemented on Datum, as it was deemed safest to limit implementations to those that are also valid if Datum is a pointer or float. This can induce code to reveal any assumptions it was making.

Enhancements

Considerable enhancements have been made to heap tuple and trigger support, introducing pg_trigger and a new PgHeapTuple type! Try them out!

• Improved "HeapTuple" support by @eeeebbbbrrrr in #532
• Trigger support improvements by @Hoverbear in #558

Fixes

• Hang onto libraries by @Hoverbear in #573
  A cargo pgx bug that could cause segfaults on old versions of glibc was fixed by no longer using dlclose on the libraries we dynamically load until the process ends.

Experimental features

You may have noticed the "postgrestd" feature. This is a highly experimental feature for using PGX to back a very special configuration of Rust as a trusted procedural language: PL/Rust. It's best to assume this feature can induce unsound changes if they aren't combined with the rest of the configuration for the trusted language handler's building and running of functions.

Full Changelog: v0.4.5...v0.5.0-beta.0