Re: determine what column(s) form the primary key, in C extention

>
> (2)
>
> I'll use this C code as an example to build an extention in Rust. The
> Postgresql bindings for Rust I have don't contain a definition of
> `FirstLowInvalidHeapAttributeNumber` for some reason. I can define it
> since it's simply single digit constant.
>

Not an answer to your question - but use better bindings!
https://github.com/zombodb/pgx <https://github.com/zombodb/pgx>

[nix-shell:~/rust/pgx_master]$ grep -R FirstLowInvalidHeapAttributeNumber
pgx-pg-sys/
pgx-pg-sys/generated-bindings/pg12_specific.rs:pub const
FirstLowInvalidHeapAttributeNumber: i32 = -7;

Which is obviously not quite right still, so I pushed a version with some
extra includes. Now you will get:

[nix-shell:~/rust/pgx_master]$ grep -R FirstLowInvalidHeapAttributeNumber
./pgx-pg-sys/
./pgx-pg-sys/generated-bindings/pg10_specific.rs:pub const
FirstLowInvalidHeapAttributeNumber: i32 = -8;
./pgx-pg-sys/generated-bindings/pg12_specific.rs:pub const
FirstLowInvalidHeapAttributeNumber: i32 = -7;
./pgx-pg-sys/generated-bindings/pg11_specific.rs:pub const
FirstLowInvalidHeapAttributeNumber: i32 = -8;

You'll need to use the Github version not the crates.io until the next
release if you want all the versions.