Add new Nix packaging using mach-nix.buildPythonPackage

default.nix

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+let
+  sources = import nix/sources.nix;
+in
+{ pkgsVersion ? "nixpkgs-21.11"
+, pkgs ? import sources.${pkgsVersion} { }
+, pypiData ? sources.pypi-deps-db
+, pythonVersion ? "python37"
+, mach-nix ? import sources.mach-nix {
+    inherit pkgs pypiData;
+    python = pythonVersion;
+  }
+}:
+# The project name, version, and most other metadata are automatically
+# extracted from the source.  Some requirements are not properly extracted
+# and those cases are handled below.  The version can only be extracted if
+# `setup.py update_version` has been run (this is not at all ideal but it
+# seems difficult to fix) - so for now just be sure to run that first.
+mach-nix.buildPythonPackage {
+  # Define the location of the Tahoe-LAFS source to be packaged.  Clean up all
+  # as many of the non-source files (eg the `.git` directory, `~` backup
+  # files, nix's own `result` symlink, etc) as possible to avoid needing to
+  # re-build when files that make no difference to the package have changed.
+  src = pkgs.lib.cleanSource ./.;
+
+  # Define some extra requirements that mach-nix does not automatically detect
+  # from inspection of the source.  We typically don't need to put version
+  # constraints on any of these requirements.  The pypi-deps-db we're
+  # operating with makes dependency resolution deterministic so as long as it
+  # works once it will always work.  It could be that in the future we update
+  # pypi-deps-db and an incompatibility arises - in which case it would make
+  # sense to apply some version constraints here.
+  requirementsExtra = ''
+    # mach-nix does not yet support pyproject.toml which means it misses any
+    # build-time requirements of our dependencies which are declared in such a
+    # file.  Tell it about them here.
+    setuptools_rust
+
+    # mach-nix does not yet parse environment markers correctly.  It misses
+    # all of our requirements which have an environment marker.  Duplicate them
+    # here.
+    foolscap
+    eliot
+    pyrsistent
+  '';
+
+  providers = {
+    # Through zfec 1.5.5 the wheel has an incorrect runtime dependency
+    # declared on argparse, not available for recent versions of Python 3.
+    # Force mach-nix to use the sdist instead, side-stepping this issue.
+    zfec = "sdist";
+  };
+}

nix/sources.json

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+{
+    "mach-nix": {
+        "branch": "master",
+        "description": "Create highly reproducible python environments",
+        "homepage": "",
+        "owner": "davhau",
+        "repo": "mach-nix",
+        "rev": "bdc97ba6b2ecd045a467b008cff4ae337b6a7a6b",
+        "sha256": "12b3jc0g0ak6s93g3ifvdpwxbyqx276k1kl66bpwz8a67qjbcbwf",
+        "type": "tarball",
+        "url": "https://github.com/davhau/mach-nix/archive/bdc97ba6b2ecd045a467b008cff4ae337b6a7a6b.tar.gz",
+        "url_template": "https://github.com/<owner>/<repo>/archive/<rev>.tar.gz"
+    },
+    "niv": {
+        "branch": "master",
+        "description": "Easy dependency management for Nix projects",
+        "homepage": "https://github.com/nmattia/niv",
+        "owner": "nmattia",
+        "repo": "niv",
+        "rev": "5830a4dd348d77e39a0f3c4c762ff2663b602d4c",
+        "sha256": "1d3lsrqvci4qz2hwjrcnd8h5vfkg8aypq3sjd4g3izbc8frwz5sm",
+        "type": "tarball",
+        "url": "https://github.com/nmattia/niv/archive/5830a4dd348d77e39a0f3c4c762ff2663b602d4c.tar.gz",
+        "url_template": "https://github.com/<owner>/<repo>/archive/<rev>.tar.gz"
+    },
+    "nixpkgs": {
+        "branch": "release-20.03",
+        "description": "Nix Packages collection",
+        "homepage": "",
+        "owner": "NixOS",
+        "repo": "nixpkgs",
+        "rev": "eb73405ecceb1dc505b7cbbd234f8f94165e2696",
+        "sha256": "06k21wbyhhvq2f1xczszh3c2934p0m02by3l2ixvd6nkwrqklax7",
+        "type": "tarball",
+        "url": "https://github.com/NixOS/nixpkgs/archive/eb73405ecceb1dc505b7cbbd234f8f94165e2696.tar.gz",
+        "url_template": "https://github.com/<owner>/<repo>/archive/<rev>.tar.gz"
+    },
+    "nixpkgs-21.11": {
+        "branch": "nixos-21.11",
+        "description": "Nix Packages collection",
+        "homepage": "",
+        "owner": "nixos",
+        "repo": "nixpkgs",
+        "rev": "6c4b9f1a2fd761e2d384ef86cff0d208ca27fdca",
+        "sha256": "1yl5gj0mzczhl1j8sl8iqpwa1jzsgr12fdszw9rq13cdig2a2r5f",
+        "type": "tarball",
+        "url": "https://github.com/nixos/nixpkgs/archive/6c4b9f1a2fd761e2d384ef86cff0d208ca27fdca.tar.gz",
+        "url_template": "https://github.com/<owner>/<repo>/archive/<rev>.tar.gz"
+    },
+    "pypi-deps-db": {
+        "branch": "master",
+        "description": "Probably the most complete python dependency database",
+        "homepage": "",
+        "owner": "DavHau",
+        "repo": "pypi-deps-db",
+        "rev": "0f6de8bf1f186c275af862ec9667abb95aae8542",
+        "sha256": "1ygw9pywyl4p25hx761d1sbwl3qjhm630fa36gdf6b649im4mx8y",
+        "type": "tarball",
+        "url": "https://github.com/DavHau/pypi-deps-db/archive/0f6de8bf1f186c275af862ec9667abb95aae8542.tar.gz",
+        "url_template": "https://github.com/<owner>/<repo>/archive/<rev>.tar.gz"
+    }
+}

nix/sources.nix

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+# This file has been generated by Niv.
+
+let
+
+  #
+  # The fetchers. fetch_<type> fetches specs of type <type>.
+  #
+
+  fetch_file = pkgs: name: spec:
+    let
+      name' = sanitizeName name + "-src";
+    in
+      if spec.builtin or true then
+        builtins_fetchurl { inherit (spec) url sha256; name = name'; }
+      else
+        pkgs.fetchurl { inherit (spec) url sha256; name = name'; };
+
+  fetch_tarball = pkgs: name: spec:
+    let
+      name' = sanitizeName name + "-src";
+    in
+      if spec.builtin or true then
+        builtins_fetchTarball { name = name'; inherit (spec) url sha256; }
+      else
+        pkgs.fetchzip { name = name'; inherit (spec) url sha256; };
+
+  fetch_git = name: spec:
+    let
+      ref =
+        if spec ? ref then spec.ref else
+          if spec ? branch then "refs/heads/${spec.branch}" else
+            if spec ? tag then "refs/tags/${spec.tag}" else
+              abort "In git source '${name}': Please specify `ref`, `tag` or `branch`!";
+    in
+      builtins.fetchGit { url = spec.repo; inherit (spec) rev; inherit ref; };
+
+  fetch_local = spec: spec.path;
+
+  fetch_builtin-tarball = name: throw
+    ''[${name}] The niv type "builtin-tarball" is deprecated. You should instead use `builtin = true`.
+        $ niv modify ${name} -a type=tarball -a builtin=true'';
+
+  fetch_builtin-url = name: throw
+    ''[${name}] The niv type "builtin-url" will soon be deprecated. You should instead use `builtin = true`.
+        $ niv modify ${name} -a type=file -a builtin=true'';
+
+  #
+  # Various helpers
+  #
+
+  # https://github.com/NixOS/nixpkgs/pull/83241/files#diff-c6f540a4f3bfa4b0e8b6bafd4cd54e8bR695
+  sanitizeName = name:
+    (
+      concatMapStrings (s: if builtins.isList s then "-" else s)
+        (
+          builtins.split "[^[:alnum:]+._?=-]+"
+            ((x: builtins.elemAt (builtins.match "\\.*(.*)" x) 0) name)
+        )
+    );
+
+  # The set of packages used when specs are fetched using non-builtins.
+  mkPkgs = sources: system:
+    let
+      sourcesNixpkgs =
+        import (builtins_fetchTarball { inherit (sources.nixpkgs) url sha256; }) { inherit system; };
+      hasNixpkgsPath = builtins.any (x: x.prefix == "nixpkgs") builtins.nixPath;
+      hasThisAsNixpkgsPath = <nixpkgs> == ./.;
+    in
+      if builtins.hasAttr "nixpkgs" sources
+      then sourcesNixpkgs
+      else if hasNixpkgsPath && ! hasThisAsNixpkgsPath then
+        import <nixpkgs> {}
+      else
+        abort
+          ''
+            Please specify either <nixpkgs> (through -I or NIX_PATH=nixpkgs=...) or
+            add a package called "nixpkgs" to your sources.json.
+          '';
+
+  # The actual fetching function.
+  fetch = pkgs: name: spec:
+
+    if ! builtins.hasAttr "type" spec then
+      abort "ERROR: niv spec ${name} does not have a 'type' attribute"
+    else if spec.type == "file" then fetch_file pkgs name spec
+    else if spec.type == "tarball" then fetch_tarball pkgs name spec
+    else if spec.type == "git" then fetch_git name spec
+    else if spec.type == "local" then fetch_local spec
+    else if spec.type == "builtin-tarball" then fetch_builtin-tarball name
+    else if spec.type == "builtin-url" then fetch_builtin-url name
+    else
+      abort "ERROR: niv spec ${name} has unknown type ${builtins.toJSON spec.type}";
+
+  # If the environment variable NIV_OVERRIDE_${name} is set, then use
+  # the path directly as opposed to the fetched source.
+  replace = name: drv:
+    let
+      saneName = stringAsChars (c: if isNull (builtins.match "[a-zA-Z0-9]" c) then "_" else c) name;
+      ersatz = builtins.getEnv "NIV_OVERRIDE_${saneName}";
+    in
+      if ersatz == "" then drv else
+        # this turns the string into an actual Nix path (for both absolute and
+        # relative paths)
+        if builtins.substring 0 1 ersatz == "/" then /. + ersatz else /. + builtins.getEnv "PWD" + "/${ersatz}";
+
+  # Ports of functions for older nix versions
+
+  # a Nix version of mapAttrs if the built-in doesn't exist
+  mapAttrs = builtins.mapAttrs or (
+    f: set: with builtins;
+    listToAttrs (map (attr: { name = attr; value = f attr set.${attr}; }) (attrNames set))
+  );
+
+  # https://github.com/NixOS/nixpkgs/blob/0258808f5744ca980b9a1f24fe0b1e6f0fecee9c/lib/lists.nix#L295
+  range = first: last: if first > last then [] else builtins.genList (n: first + n) (last - first + 1);
+
+  # https://github.com/NixOS/nixpkgs/blob/0258808f5744ca980b9a1f24fe0b1e6f0fecee9c/lib/strings.nix#L257
+  stringToCharacters = s: map (p: builtins.substring p 1 s) (range 0 (builtins.stringLength s - 1));
+
+  # https://github.com/NixOS/nixpkgs/blob/0258808f5744ca980b9a1f24fe0b1e6f0fecee9c/lib/strings.nix#L269
+  stringAsChars = f: s: concatStrings (map f (stringToCharacters s));
+  concatMapStrings = f: list: concatStrings (map f list);
+  concatStrings = builtins.concatStringsSep "";
+
+  # https://github.com/NixOS/nixpkgs/blob/8a9f58a375c401b96da862d969f66429def1d118/lib/attrsets.nix#L331
+  optionalAttrs = cond: as: if cond then as else {};
+
+  # fetchTarball version that is compatible between all the versions of Nix
+  builtins_fetchTarball = { url, name ? null, sha256 }@attrs:
+    let
+      inherit (builtins) lessThan nixVersion fetchTarball;
+    in
+      if lessThan nixVersion "1.12" then
+        fetchTarball ({ inherit url; } // (optionalAttrs (!isNull name) { inherit name; }))
+      else
+        fetchTarball attrs;
+
+  # fetchurl version that is compatible between all the versions of Nix
+  builtins_fetchurl = { url, name ? null, sha256 }@attrs:
+    let
+      inherit (builtins) lessThan nixVersion fetchurl;
+    in
+      if lessThan nixVersion "1.12" then
+        fetchurl ({ inherit url; } // (optionalAttrs (!isNull name) { inherit name; }))
+      else
+        fetchurl attrs;
+
+  # Create the final "sources" from the config
+  mkSources = config:
+    mapAttrs (
+      name: spec:
+        if builtins.hasAttr "outPath" spec
+        then abort
+          "The values in sources.json should not have an 'outPath' attribute"
+        else
+          spec // { outPath = replace name (fetch config.pkgs name spec); }
+    ) config.sources;
+
+  # The "config" used by the fetchers
+  mkConfig =
+    { sourcesFile ? if builtins.pathExists ./sources.json then ./sources.json else null
+    , sources ? if isNull sourcesFile then {} else builtins.fromJSON (builtins.readFile sourcesFile)
+    , system ? builtins.currentSystem
+    , pkgs ? mkPkgs sources system
+    }: rec {
+      # The sources, i.e. the attribute set of spec name to spec
+      inherit sources;
+
+      # The "pkgs" (evaluated nixpkgs) to use for e.g. non-builtin fetchers
+      inherit pkgs;
+    };
+
+in
+mkSources (mkConfig {}) // { __functor = _: settings: mkSources (mkConfig settings); }