Optionally emit versioned .so

[JamesGuthrie]

pgx now experimentally supports the option to produce a versioned
shared library. This option is activated by removing the
module_pathname parameter in the extension's .control file.

When activated, it does the following:

• appends current package version to shared library name
• points generated function SQL to the versioned shared library (instead
  of MODULE_PATHNAME)
• replaces @MODULE_PATHNAME@ placeholder with the path to the versioned
  shared library

Background:

There is an implicit requirement that C extensions maintain ABI
compatibility between versions. Emitting a versioned .so allows for ABI
breaks between versions.

This functionality is experimental and that care must be taken in the
following scenarios:

• when using shared memory
• when using query planner hooks
• when producing SQL schema migrations

[eeeebbbbrrrr]

I think overall this is pretty close.

Before merging, I'd like to see the cargo-pgx/README.md updated to reflect this new argument and detail what it does any why it might be necessary.

[JamesGuthrie]

I think overall this is pretty close.

Before merging, I'd like to see the cargo-pgx/README.md updated to reflect this new argument and detail what it does any why it might be necessary.

I've updated the docs. I'm having difficulty seeing where somebody who is unfamiliar with these concepts will have difficulty, so if there's anything that you find unclear please let me know and I'll take another pass.

[eeeebbbbrrrr]

@JamesGuthrie this is super nice now. Great work and thanks for sticking through the process. When you address those three minor comments above this will be ready to merge.

Oh, please retarget the PR to the develop branch as well. We're weird and don't merge directly into master, unless you're me and are prepared to be chastised by @Hoverbear for doing it. ;)

[JamesGuthrie]

@JamesGuthrie this is super nice now. Great work and thanks for sticking through the process. When you address those three minor comments above this will be ready to merge.

Oh, please retarget the PR to the develop branch as well. We're weird and don't merge directly into master, unless you're me and are prepared to be chastised by @Hoverbear for doing it. ;)

No problem, thanks for the quick review! I've fixed the three things above and retargeted against develop.

[eeeebbbbrrrr]

Approved. Lets see what CI says and then I'll merge it.

And as promised, I'm happy to put out a v0.4.4 this week so y'all can get back to your real work.

[eeeebbbbrrrr]

hmm, the new versioned_so example test failed: https://github.com/tcdi/pgx/runs/6161094219?check_suite_focus=true

Error message sucks. Did it work for you locally?

[Hoverbear]

Some minor readme expansions requested, but otherwise I'm happy with how this turned out!

[JamesGuthrie]

Okay, managed to get the build to work locally. Let's hope that CI accepts it.

[Hoverbear]

This is great James. :)

[eeeebbbbrrrr]

Thanks a bunch, @JamesGuthrie! Merged. We'll get it out in a new release in the next few days.

[Hoverbear]

We didn't catch this during review, but this should have been removed as it causes some conflicts with the workspace override. @eeeebbbbrrrr is fixing this up before release.

[eeeebbbbrrrr]

yah. totally our bad.

In a workspace crate environment like pgx is, you only need the .cargo/config at the root workspace crate. If it's in any "child" crates, the compiler goes stupid and you spend all day trying to figure it out and then you're thankful @Hoverbear is on your team!