Adapt to Tahoe-LAFS' new build system

flake.nix

@@ -201,7 +201,6 @@
                 in
                   writeScript "unit-tests"
                     ''
-                    ${python} setup.py update_version
                     export TAHOE_LAFS_HYPOTHESIS_PROFILE=ci
                     export PYTHONPATH=$PWD/src
                     ${python} -m twisted.trial "$@"

nix/tahoe-lafs.nix

@@ -9,6 +9,7 @@ in
 }:
 buildPythonPackage rec {
   inherit pname version;
+  pyproject = true;
   src = tahoe-lafs-src;
   propagatedBuildInputs = with pythonPackages; [
     attrs
@@ -22,6 +23,8 @@ buildPythonPackage rec {
     filelock
     foolscap
     future
+    hatchling
+    hatch-vcs
     klein
     magic-wormhole
     netifaces
@@ -70,24 +73,6 @@ buildPythonPackage rec {
     };
   };
 
-  postPatch =
-    let
-      versionFileContents = version: ''
-        # This _version.py is generated by tahoe-lafs.nix.
-        # TODO: We can have more metadata after we switch to flakes.
-        # Then the `self` input will have a `sourceInfo` attribute telling
-        __pkgname__ = "tahoe-lafs"
-        real_version = "${version}"
-        full_version = "${version}"
-        branch = ""
-        verstr = "${version}"
-        __version__ = verstr
-      '';
-    in
-      ''
-        cp ${builtins.toFile "_version.py" (versionFileContents version)} src/allmydata/_version.py
-      '';
-
   meta = with lib; {
     homepage = "https://tahoe-lafs.org/";
     description = "secure, decentralized, fault-tolerant file store";