nix: add basic flake.nix

This just exposes the PostgREST package, not more.

The goal is to avoid duplication, so we're re-using only exports from
default.nix.

Resolves #3026
Supersedes #3105

.github/workflows/test.yaml

@@ -130,3 +130,27 @@ jobs:
         run: |
           postgrest-loadtest-against main ${{ steps.get-latest-tag.outputs.tag }}
           postgrest-loadtest-report >> "$GITHUB_STEP_SUMMARY"
+
+
+  flake:
+    strategy:
+      fail-fast: false
+      matrix:
+        runs-on:
+          - macos-13 # x86_64-darwin
+          - macos-14 # aarch64-darwin
+          - ubuntu-24.04 # x86_64-linux
+          - ubuntu-24.04-arm # aarch64-linux
+    name: Flake Check
+    runs-on: ${{ matrix.runs-on }}
+    steps:
+      - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
+        with:
+          fetch-depth: 0
+      - name: Setup Nix Environment
+        uses: ./.github/actions/setup-nix
+        with:
+          authToken: '${{ secrets.CACHIX_AUTH_TOKEN }}'
+      - name: Run flake check
+        run: |
+          nix flake check

docs/shared/installation.rst

@@ -28,7 +28,7 @@
 
           pacman -S postgrest
 
-      .. tab:: Nix
+      .. tab:: Nix via nixpkgs
 
         You can install PostgREST from nixpkgs.
 
@@ -36,6 +36,17 @@
 
           nix-env -i postgrest
 
+      .. tab:: Nix via flake
+
+        You can install PostgREST via flake.
+
+        .. code:: nix
+
+          {
+            inputs.postgrest.url = "github:postgrest/postgrest";
+            # ...
+          }
+
   .. group-tab:: Windows
 
     You can install PostgREST using `Chocolatey <https://community.chocolatey.org/packages/postgrest>`_ or `Scoop <https://github.com/ScoopInstaller/Scoop>`_.

flake.lock

@@ -0,0 +1,26 @@
+{
+  "nodes": {
+    "nixpkgs-lib": {
+      "locked": {
+        "lastModified": 1742692082,
+        "narHash": "sha256-s3XOULQj7BVO7myY5V4Sob0tRZ7nRpwEOIzXg/MkD/Q=",
+        "owner": "nix-community",
+        "repo": "nixpkgs.lib",
+        "rev": "a09310bc940f245e51b1ffea68731244ca38f2bd",
+        "type": "github"
+      },
+      "original": {
+        "owner": "nix-community",
+        "repo": "nixpkgs.lib",
+        "type": "github"
+      }
+    },
+    "root": {
+      "inputs": {
+        "nixpkgs-lib": "nixpkgs-lib"
+      }
+    }
+  },
+  "root": "root",
+  "version": 7
+}

flake.nix

@@ -0,0 +1,44 @@
+{
+  description = "REST API for any Postgres database";
+
+  inputs = {
+    nixpkgs-lib.url = "github:nix-community/nixpkgs.lib";
+  };
+
+  nixConfig = {
+    extra-substituters = "https://postgrest.cachix.org";
+    extra-trusted-public-keys = "postgrest.cachix.org-1:icgW4R15fz1+LqvhPjt4EnX/r19AaqxiVV+1olwlZtI=";
+  };
+
+  outputs = { nixpkgs-lib, ... }:
+    let
+      systems = [
+        "aarch64-darwin"
+        "aarch64-linux"
+        "x86_64-darwin"
+        "x86_64-linux"
+      ];
+
+      pgrstFor = system: import ./default.nix {
+        inherit system;
+      };
+
+      genSystems = f: nixpkgs-lib.lib.genAttrs systems (system: f (pgrstFor system));
+    in
+    {
+      packages = genSystems (attrs: {
+        default = attrs.postgrestPackage;
+        profiled = attrs.postgrestProfiled;
+      } // nixpkgs-lib.lib.optionalAttrs (attrs ? postgrestStatic) {
+        static = attrs.postgrestStatic;
+      });
+
+      apps = genSystems (attrs: {
+        default = {
+          type = "app";
+          program = "${attrs.postgrestStatic or attrs.postgrestPackage}/bin/postgrest";
+          meta.description = "REST API for any Postgres database";
+        };
+      });
+    };
+}