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Make RawArray::from_ptr a simple cast #1587

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@workingjubilee workingjubilee commented Feb 26, 2024

I have been working on the DetoastDatum implementation, and because our ArrayType wrappers happen to exercise a lot of parts of pgrx while being something I understand very well, I am aiming to ship its MVP with Yet Another improvement on pgrx::datum::Array that will be a model for future safe abstractions of Datum-derived types. This will involve quite a lot of work with RawArray and the code that is currently living next to RawArray, so I decided to factor that out, modularize the ported code, and overall just spruce things up a bit.

As part of that, this ports pg_sys::ArrayGetNItems to simply live inside the implementation of RawArray::len. This allows us to perform the calculation entirely in Rust, so there is now no more FFI overhead for creating a RawArray, and we can delete the ARR_NELEMS port. This also means we can simply stop caching the total element count, as we aren't saving enough math to be worth it. Now casting to RawArray from a simple reference or other raw pointer is a zero-overhead pointer cast, allowing reusing its already-defined accessors without incurring needless math or calls to Postgres.

These are redundant with the public information documented on the fn,
and are "safety" comments within safe functions.
This allows us to perform the calculation entirely in Rust, so there is now
no more FFI overhead for creating a RawArray. This will become more useful
when it is being used more vigorously as part of the implementation of arrays.
@workingjubilee workingjubilee changed the title Stop caching RawArray::len Make RawArray::from_ptr a simple cast Feb 26, 2024
pgrx/src/array.rs Outdated Show resolved Hide resolved
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cc @NotGyro

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Looks good to me, this should be safe unless I'm missing something important.

pgrx/src/array/port.rs Show resolved Hide resolved
Comment on lines +190 to +192
///
/// # Panics
/// Panics if the Array's dimensions, multiplied together, exceed sizes Postgres can handle.
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This is really silly, but we're aiming to expose the ability to mutate an ArrayType eventually, which means that while I expect this to never happen for a Postgres-created array, they do assert on it for a reason! People would need to be able to check array invariants during constructing one, so...

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I may wind up adding RawArray::try_len but... later.

@workingjubilee workingjubilee merged commit 3e530b6 into pgcentralfoundation:develop Feb 27, 2024
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@workingjubilee workingjubilee deleted the cleanup-raw-array branch February 27, 2024 22:57
workingjubilee added a commit that referenced this pull request Mar 1, 2024
Welcome to pgrx 0.12.0-alpha.1!

Say the magic words with me!

```shell
cargo install cargo-pgrx --locked --version 0.12.0-alpha.1
```

# Breaking Changes

## No more dlopen!

Perhaps the most exciting change this round is @usamoi's contribution in
#1468 which means that
we no longer perform a `dlopen` in order to generate the schema. The
cost, such as it is, is that your pgrx extensions now require a
`src/bin/pgrx_embed.rs`, which will be used to generate the schema. This
has much less cross-platform issues and will enable supporting things
like `cargo binstall` down the line.

It may be a bit touchy on first-time setup for transitioning older
repos. If necessary, you may have to directly add a
`src/bin/pgrx_embed.rs` and add the following code (which should be the
only code in the file, though you can add comments if you like?):

```rust
::pgrx::pgrx_embed!();
```

Your Cargo.toml will also want to update its crate-type key for the
library:
```toml
[lib]
crate-type = ["cdylib", "lib"]
```

## Library Code

- pgrx-pg-sys will now use `ManuallyDropUnion` thanks to @NotGyro in
#1547
- VARHDRSZ `const`s are no longer `fn`, thanks to @workingjubilee in
#1584
- We no longer have `Interval::is_finite` since
#1594
- We translate more `*_tree_walker` functions to the same signature
their `*_impl` version in Postgres 16 has:
#1596
- Thanks to @eeeebbbbrrrr in
#1591 we no longer have
the `pg_sql_graph_magic!()` macro, which should help with more things in
the future!

# What's New

We have quite a lot of useful additions to our API:

- `SpiClient::prepare_mut` was added thanks to @XeniaLu in
#1275
- @usamoi also contributed bindings subscripting code in
#1562
- For `#[pg_test]`, you have been able to use `#[should_panic(expected =
"string")]` to anticipate a panic that contains that string in that
test. For various reasons, `#[pg_test(error = "string")]` is much the
same. Now, you can also use `#[pg_test(expected = "string")]`, in the
hopes that is easier to stumble across, as of
#1570

## `Result<composite_type!("..."), E>` support

- In #1560 @NotGyro
contributed support for using `Result<composite_type!("Name"), E>`, as a
case that had not been handled before.

## Significantly expanded docs
Thanks to @rjuju, @NotGyro, and @workingjubilee, we now have
significantly expanded docs for cargo-pgrx and pgrx in general. Some of
these are in the API docs on https://docs.rs or the READMEs, but there's
also a guide, now! It's not currently published, but is available as an
[mdbook](https://github.com/rust-lang/mdBook) in the repo.

Some diagnostic information that is also arguably documentation, like
comments and the suggestion to `cargo install`, have also been improved,
thanks to @workingjubilee in
- #1579
- #1573

## `#[pg_cast]`

An experimental macro for a `CREATE CAST` was contributed by @xwkuang5
in #1445!

## Legal Stuff

Thanks to @the-kenny in
#1490 and
@workingjubilee in
#1504, it was brought to
our attention that some dependencies had unusual legal requirements. So
we fixed this with CI! We now check our code included into pgrx-using
binaries is MIT/Apache 2.0 licensed, as is common across crates.io,
using `cargo deny`!. The build tools will have more flexible legal
requirements (partly due to the use of Mozilla Public License code in
rustls).

# Internal Changes
Many internal cleanups were done thanks to
- @workingjubilee in too many PRs to count!
- @thomcc found a needless condition in
#1501
- @nyurik in too many PRs to count!

In particular:
- we now actually `pfree` our `Array`s we detoasted as-of
#1571
- creating a `RawArray` is now low-overhead due to
#1587

## Soundness Fixes
We had a number of soundness issues uncovered or have added more tests
to catch them.
- Bounds-checking debug assertions for array access by @NotGyro in
#1514
- Fix unsound `&` and `&mut` in `fcinfo.rs` by @workingjubilee in
#1595

## Less Deps
Part of the cleanup by @workingjubilee was reducing the number of deps
we compile:
* cargo-pgrx: reduce trivial dep usages in
#1499
* Update 2 syn in #1557

Hopefully it will reduce compile time and disk usage!

## New Contributors
* @the-kenny made their first contribution in
#1490
* @xwkuang5 made their first contribution in
#1445
* @rjuju made their first contribution in
#1516
* @nyurik made their first contribution in
#1533
* @NotGyro made their first contribution in
#1514
* @XeniaLu made their first contribution in
#1275

**Full Changelog**:
v0.12.0-alpha.0...v0.12.0-alpha.1
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2 participants