mautrix-telegram: patch away alembic dependency

`alembic`[1] is a database migration tool which is invoked from the CLI
when installing the telegram bridge, but never needed during the
runtime.

The reason why `alembic` is required here is to ensure that it
exists in the Python environment when deploying the bridge. However
`alembic` requires `mautrix-telegram` in its environment to create a
database schema from the Python models.

Such a dependency relation may be possible with tools like virtualenv,
however it'll result in an infinite recursion at evaluation time in Nix.

With this patch, `mautrix-telegram` doesn't depend on `alembic` anymore
and provides a patched alembic (`pkgs.mautrix-telegram.alembic`) which
has `mautrix-telegram` in its path.

[1] https://alembic.sqlalchemy.org/en/latest/

pkgs/servers/mautrix-telegram/default.nix

@@ -1,4 +1,4 @@
-{ lib, python3 }:
+{ lib, python3, mautrix-telegram }:
 
 with python3.pkgs;
 
@@ -11,11 +11,15 @@ buildPythonPackage rec {
     sha256 = "51951845e52c4ca5410e0f4a51d99014dd6df2fcedfca8b7241e045359cbf112";
   };
 
+  postPatch = ''
+    sed -i -e '/alembic>/d' setup.py
+  '';
+
   propagatedBuildInputs = [
+    Mako
     aiohttp
     mautrix-appservice
     sqlalchemy
-    alembic
     CommonMark
     ruamel_yaml
     future-fstrings
@@ -26,6 +30,18 @@ buildPythonPackage rec {
     lxml
   ];
 
+  # `alembic` (a database migration tool) is only needed for the initial setup,
+  # and not needed during the actual runtime. However `alembic` requires `mautrix-telegram`
+  # in its environment to create a database schema from all models.
+  #
+  # Hence we need to patch away `alembic` from `mautrix-telegram` and create an `alembic`
+  # which has `mautrix-telegram` in its environment.
+  passthru.alembic = alembic.overrideAttrs (old: {
+    propagatedBuildInputs = old.propagatedBuildInputs ++ [
+      mautrix-telegram
+    ];
+  });
+
   checkInputs = [
     pytest
     pytestrunner
@@ -37,6 +53,6 @@ buildPythonPackage rec {
     homepage = https://github.com/tulir/mautrix-telegram;
     description = "A Matrix-Telegram hybrid puppeting/relaybot bridge";
     license = licenses.agpl3Plus;
-    maintainers = with maintainers; [ nyanloutre ];
+    maintainers = with maintainers; [ nyanloutre ma27 ];
   };
 }

pkgs/top-level/all-packages.nix

@@ -3908,7 +3908,7 @@ in
 
   matrix-synapse = callPackage ../servers/matrix-synapse { };
 
-  mautrix-telegram = callPackage ../servers/mautrix-telegram { };
+  mautrix-telegram = recurseIntoAttrs (callPackage ../servers/mautrix-telegram { });
 
   mautrix-whatsapp = callPackage ../servers/mautrix-whatsapp { };