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Adding a new extension package

Pre-packaging steps

Make sure you have nix installed Nix installer
Create a branch off of develop

C/C++ postgres extensions

If you are creating a C/C++ extension, the pattern found in https://github.com/supabase/postgres/blob/develop/nix/ext/pgvector.nix will work well.

{ lib, stdenv, fetchFromGitHub, postgresql }:

stdenv.mkDerivation rec {
  pname = "pgvector";
  version = "0.7.4";

  buildInputs = [ postgresql ];

  src = fetchFromGitHub {
    owner = "pgvector";
    repo = pname;
    rev = "refs/tags/v${version}";
    hash = "sha256-qwPaguQUdDHV8q6GDneLq5MuhVroPizpbqt7f08gKJI=";
  };

  installPhase = ''
    mkdir -p $out/{lib,share/postgresql/extension}

    cp *.so      $out/lib
    cp sql/*.sql $out/share/postgresql/extension
    cp *.control $out/share/postgresql/extension
  '';

  meta = with lib; {
    description = "Open-source vector similarity search for Postgres";
    homepage = "https://github.com/${src.owner}/${src.repo}";
    maintainers = with maintainers; [ olirice ];
    platforms = postgresql.meta.platforms;
    license = licenses.postgresql;
  };
}

This uses stdenv.mkDerivation which is a general nix builder for C and C++ projects (and others). It can auto detect the Makefile, and attempt to use it. It's a good practice to not have steps in the Makefile of your project that try to deal with OS specific system paths, or make calls out to the internet, as Nix cannot use these steps to build your project.

Your build should produce all of the sql and control files needed for the install phase.

Once you have created this file, you can add it to nix/ext/<yourname>.nix and edit flake.nix and add it to the ourExtensions list.
git add . as nix uses git to track changes
In your package file, temporarily empty the hash = "sha256<...>="; to hash = ""; and save and git add .
Run nix build .#psql_15/exts/<yourname> to try to trigger a build, nix will print the calculated sha256 value that you can add back the the hash variable, save the file again, and re-run nix build .#psql_15/exts/<yourname>.
Add any needed migrations into the supabase/postgres migrations directory.
You can then run tests locally to verify that the update of the package succeeded.
Now it's ready for PR review!

Extensions written in Rust that use `buildPgrxExtension` builder

Extensions like:

Are written in Rust, built with cargo, and need to use https://github.com/pgcentralfoundation/pgrx to build the extension.

We in turn have a special nix package builder which is sourced from nixpkgs and called buildPgrxExtension

A simple example is found in pg_jsonschema

{ lib, stdenv, fetchFromGitHub, postgresql, buildPgrxExtension_0_11_3, cargo }:

buildPgrxExtension_0_11_3 rec {
  pname = "pg_jsonschema";
  version = "0.3.1";
  inherit postgresql;

  src = fetchFromGitHub {
    owner = "supabase";
    repo = pname;
    rev = "v${version}";
    hash = "sha256-YdKpOEiDIz60xE7C+EzpYjBcH0HabnDbtZl23CYls6g=";
  };

  nativeBuildInputs = [ cargo ];
  buildInputs = [ postgresql ];
  # update the following array when the pg_jsonschema version is updated
  # required to ensure that extensions update scripts from previous versions are generated

  previousVersions = ["0.3.0" "0.2.0" "0.1.4" "0.1.4" "0.1.2" "0.1.1" "0.1.0"];
  CARGO="${cargo}/bin/cargo";
  env = lib.optionalAttrs stdenv.isDarwin {
    POSTGRES_LIB = "${postgresql}/lib";
    RUSTFLAGS = "-C link-arg=-undefined -C link-arg=dynamic_lookup";
  };
  cargoHash = "sha256-VcS+efMDppofuFW2zNrhhsbC28By3lYekDFquHPta2g=";

  # FIXME (aseipp): testsuite tries to write files into /nix/store; we'll have
  # to fix this a bit later.
  doCheck = false;

  preBuild = ''
    echo "Processing git tags..."
    echo '${builtins.concatStringsSep "," previousVersions}' | sed 's/,/\n/g' > git_tags.txt
  '';

  postInstall = ''
    echo "Creating SQL files for previous versions..."
    current_version="${version}"
    sql_file="$out/share/postgresql/extension/pg_jsonschema--$current_version.sql"
    
    if [ -f "$sql_file" ]; then
      while read -r previous_version; do
        if [ "$(printf '%s\n' "$previous_version" "$current_version" | sort -V | head -n1)" = "$previous_version" ] && [ "$previous_version" != "$current_version" ]; then
          new_file="$out/share/postgresql/extension/pg_jsonschema--$previous_version--$current_version.sql"
          echo "Creating $new_file"
          cp "$sql_file" "$new_file"
        fi
      done < git_tags.txt
    else
      echo "Warning: $sql_file not found"
    fi
    rm git_tags.txt
  '';


  meta = with lib; {
    description = "JSON Schema Validation for PostgreSQL";
    homepage = "https://github.com/supabase/${pname}";
    maintainers = with maintainers; [ samrose ];
    platforms = postgresql.meta.platforms;
    license = licenses.postgresql;
  };
}

Here we have built support in our overlay to specify and pin the version of buildPgrxExtension to a specific version (in this case buildPgrxExtension_0_11_3). This is currently the only version we can support, but this can be extended in our overlay https://github.com/supabase/postgres/blob/develop/nix/overlays/cargo-pgrx-0-11-3.nix to support other versions.

A few things about buildPgrxExtension_x:

It doesn't support buildPhase, installPhase and those are implemented directly in the builder already
It mostly just allows cargo build to do it's thing, but you may need to set env vars for the build process as seen above
It caclulates a special cargoHash that will be generated after the first in src is generated, when running nix build .#psql_15/exts/<yourname> to build the extension

Post Nix derivation release steps

You can add and run tests as described in https://github.com/supabase/postgres/blob/develop/nix/docs/adding-tests.md
You may need to add tests to our test.yml gh action workflow as well.
You can add the package and name and version to ansible/vars.yml it is not necessary to add the sha256 hash here, as the package is already built and cached in our release process before these vars are ever run.
to check that all your files will land in the overall build correctly, you can run nix profile install .#psql_15/bin on your machine, and check in ~/.nix-profile/bin, ~/.nix-profile/lib, ~/.nix-profile/share/postgresql/* and you should see your lib, .control and sql files there.
You can also run nix run .#start-server 15 and in a new terminal window run nix run .#star-client-and-migrate 15 and try to CREATE EXTENSION <yourname> and work with it there
Check that your extension works with the pg_upgrade process (TODO documentation forthcoming)
Now you are ready to PR the extension
From here, the release process should typically take care of the rest.

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