With Nix it's possible to quickly and reliably recreate the full environments for developing, testing and building PostgREST.

You'll need to get Nix. Follow the recommended installation for your operating system from the official download website.

To build PostgREST from your local checkout of the repository, run:

$ nix-build --attr postgrestPackage

This will create a result directory that contains the PostgREST binary at result/bin/postgrest. The --attr parameter (or short: -A) tells Nix to build the postgrestPackage attribute from the Nix expression it finds in our default.nix (see below for details). Nix will take care of getting the right GHC version and all the build dependencies.

You can also build a statically linked binary with:

$ nix-build --attr postgrestStatic

$ ldd result/bin/postgrest
$       not a dynamic executable

We recommend that you use the PostgREST binary cache on cachix:

# Install cachix:
$ nix-env -iA cachix -f https://cachix.org/api/v1/install

# Set cachix up to use the PostgREST binary cache:
$ cachix use postgrest

Without cachix, your machine will have to rebuild all the dependencies that are derived on top of Musl for the static builds, which can take a very long time.

A development environment for PostgREST is available with nix-shell. The following command will put you into a new shell that has GHC and Cabal on the PATH:

$ nix-shell

Within nix-shell, you can run Cabal commands as usual. You can also run stack with the --nix option, which causes stack to pick up the non-Haskell dependencies from the same pinned Nixpkgs version that the Nix builds use.

The PostgREST utilities available in nix-shell all have names that begin with postgrest-, so you can use tab completion (typing postgrest- and pressing <tab>) in nix-shell to see all that are available:

# Note: The utilities listed here might not be up to date.
[nix-shell]$ postgrest-<tab>
postgrest-build                   postgrest-test-spec
postgrest-check                   postgrest-watch
postgrest-clean                   postgrest-with-all
postgrest-coverage                postgrest-with-postgresql-12
postgrest-lint                    postgrest-with-postgresql-13
postgrest-run                     postgrest-with-postgresql-14
postgrest-style                   postgrest-with-postgresql-15
postgrest-style-check             postgrest-with-postgresql-16
postgrest-test-io                 postgrest-with-postgresql-17
...

[nix-shell]$

Some additional modules like memory, docker and release have large dependencies that would need to be built before the shell becomes available, which could take an especially long time if the cachix binary cache is not used. You can activate those by passing a flag to nix-shell with nix-shell --arg <module> true. This will make the respective utilities available:

$ nix-shell --arg memory true
[nix-shell]$ postgrest-<tab>
postgrest-build                   postgrest-test-spec
postgrest-check                   postgrest-watch
postgrest-clean                   postgrest-with-all
postgrest-coverage                postgrest-with-postgresql-12
postgrest-lint                    postgrest-with-postgresql-13
postgrest-run                     postgrest-with-postgresql-14
postgrest-style                   postgrest-with-postgresql-15
postgrest-style-check             postgrest-with-postgresql-16
postgrest-test-io                 postgrest-with-postgresql-17
postgrest-test-memory
...

Note that postgrest-test-memory is now also available.

To run one-off commands, you can also use nix-shell --run <command>, which will launch the Nix shell, run that one command and exit. Note that the tab completion will not work with nix-shell --run, as Nix has yet to evaluate our Nix expressions to see which utilities are available.

$ nix-shell --run postgrest-style

# Note that you need to quote any arguments that you would like to pass to
# the command to be run in nix-shell:
$ nix-shell --run "postgrest-foo --bar"

A third option is to install utilities that you use very often locally:

$ nix-env -f default.nix -iA devTools

# `postgrest-style` can now be run directly:
$ postgrest-style

If you use nix-shell very often, you might like to use https://github.com/xzfc/cached-nix-shell, which skips evaluating all our Nix expressions if nothing changed, reducing startup time for the shell considerably.

Note: Once inside nix-shell, the utilities work from any directory inside the PostgREST repo. Paths are resolved relative to the repo root:

[nix-shell]$ cd src
# Even though the current directory is ./src, the config path must still start
# from the repo root:
[nix-shell]$ postgrest-run test/io/configs/simple.conf

In nix-shell, you'll find utility scripts that make it very easy to run our test suite, including setting up all required dependencies and temporary test databases:

# Run the tests against the most recent version of PostgreSQL:
$ nix-shell --run postgrest-test-spec

# Run the tests against all supported versions of PostgreSQL:
$ nix-shell --run "postgrest-with-all postgrest-test-spec"

# Run the tests against a specific version of PostgreSQL (use tab-completion in
# nix-shell to see all available versions):
$ nix-shell --run "postgrest-with-postgresql-13 postgrest-test-spec"

The io-test that test PostgREST as a black box with inputs and outputs can be run with postgrest-test-io. The test runner under the hood is pytest and you can pass it the usual options:

# Filter the tests to run by name, including all that contain 'config':
[nix-shell]$ postgrest-test-io -k config

# Run tests in parallel using xdist, specifying the number of processes:
[nix-shell]$ postgrest-test-io -n auto
[nix-shell]$ postgrest-test-io -n 8

The memory tests check that we don't surpass a memory threshold for big request bodies.

# Build the dependencies needed for the memory test
$ nix-shell --arg memory true

# Run the memory test
[nix-shell]$ postgrest-test-memory

The loadtests ensure that performance doesn't drop on a change. Underlyingly they use vegeta.

# Run the loadtests on the latest commit(HEAD)
[nix-shell]$ postgrest-loadtest

# You can loadtest comparing to a different branch
[nix-shell]$ postgrest-loadtest-against master

# You can simulate latency client/postgrest and postgrest/database
[nix-shell]$ PGRST_DELAY=5ms PGDELAY=5ms postgrest-loadtest

# You can build postgrest directly with cabal for faster iteration
[nix-shell]$ PGRST_BUILD_CABAL=1 postgrest-loadtest

# Produce a markdown report to be used on CI
[nix-shell]$ postgrest-loadtest-report

doctests for some of our modules are also available:

[nix-shell]$ postgrest-test-doctest

Code coverage is available under the postgrest-coverage command. This will produce a ./coverage directory that can be visualized on a browser.

# Will run all the tests and produce a coverage dir
[nix-shell]$ postgrest-coverage
...

postgrest-coverage: To see the results, visit file://$(pwd)/coverage/check/hpc_index.html

The nix-shell also contains scripts for linting and styling the PostgREST source code:

# Linting
$ nix-shell --run postgrest-lint

# Styling / auto-formatting code
$ nix-shell --run postgrest-style

There is also postgrest-style-check that exits with a non-zero exit code if the check resulted in any uncommitted changes. It's mostly useful for CI.

The following commands can help you when working on the PostgREST docs:

# Build the docs
[nix-shell]$ postgrest-docs-build

# Build the docs and start a livereload server on `http://localhost:5500`
[nix-shell]$ postgrest-docs-serve

# Run aspell, to verify spelling mistakes
[nix-shell]$ postgrest-docs-spellcheck

# Detect obsolete entries in postgrest.dict
[nix-shell]$ postgrest-docs-dictcheck

# Build and run all the validation scripts
[nix-shell]$ postgrest-docs-check

Tools like postgrest-build, postgrest-run, postgrest-repl etc. are simple wrappers around cabal and should do what you expect. postgrest-check runs most checks that will also run in CI, with the exception of the IO and Memory checks that need to be run separately.

postgrest-with-postgresql-* take a command as an argument and will run it with a temporary database. postgrest-with-all will run the command against all supported PostgreSQL versions. Tests run without postgrest-with-* are run against the latest PostgreSQL version by default.

postgrest-watch takes a command as an argument that it will re-run if any source file is changed. For example, postgrest-watch postgrest-with-all postgrest-test-spec will re-run the full spec test suite against all PostgreSQL versions on every change.

You can use postgrest-repl to manually inspect the PostgREST modules.

$ postgrest-repl

ghci> import PostgREST.<tab>
PostgREST.Admin                        PostgREST.Config.Database              PostgREST.Plan.MutatePlan              PostgREST.Response.OpenAPI
PostgREST.ApiRequest                   PostgREST.Config.JSPath                PostgREST.Plan.ReadPlan                PostgREST.SchemaCache
...

ghci> import PostgREST.MediaType
ghci> decodeMediaType "application/json"
MTApplicationJSON

Sometimes, we need to modify Haskell libraries in order to debug them or enhance them. For example, if you want to debug the hasql-pool library:

First, copy the package to the repo root. We'll use GitHub in this example.

$ git clone --depth=1 --branch=0.10.1 https://github.com/nikita-volkov/hasql-pool.git
$ rm -rf ./hasql-pool/.git

Then, pin the local package to the haskell-packages.nix file.

  overrides =
    # ...
    rec {

      # Different subpath may be needed if the cabal file is not in the library's base directory
      hasql-pool = lib.dontCheck
        (prev.callCabal2nixWithOptions "hasql-pool" ../../hasql-pool "--subpath=." {} );

    };

Next, both cabal.project and stack.yaml need to be updated with the local library:

-- cabal.project
packages:
  ./hasql-pool/hasql-pool.cabal

# stack.yaml
extra-deps:
  - ./hasql-pool/hasql-pool.cabal

Lastly, run nix-shell to build the local package. You don't need to exit and enter the Nix shell every time you modify the library's code, re-executing postgrest-run should be enough.

This is done for development purposes only. Local libraries must not be left in production ready code.

The following is not required for working on PostgREST with Nix, but it will give you some more background and details on how it works.

default.nix is our 'repository expression' that pulls all the pieces that we define with Nix together. It returns a set (like a dict in other programming languages), where each attribute is a derivation that Nix knows how to build, like the postgrest attribute from earlier.

Internally, our default.nix uses the pkgs.callPackage function to import the modules that we defined in the nix directory. It automatically passes the arguments those modules require if they are available in pkgs (this means that pkgs is defined in terms of itself, better not to think too much about that).

We also use default.nix to load our pinned version of the nixpkgs repository. This set of packages will always be the same, independently from where or when you use it. The pinned version can be upgraded with the small nixpkgs-upgrade utility. Running nixpkgs-upgrade > nix/nixpkgs-version.nix in nix-shell will upgrade the pinned version to the latest nixpkgs-unstable version.

shell.nix defines an environment in which PostgREST can be built and developed. It extends the build environment from our postgrest attribute with useful utilities that will be put on the PATH in nix-shell.

Our overlays to the Nix package set are defined here. They allow us to tweak our pkgs in default.nix by adding new packages or overriding existing ones.

See the upgrading checklist for how to upgrade the PostgREST dependencies.