apache-airflow: remove from main pythonPackages

now exists solely as an application because its version demands
can't be met by the main pythonPackages. however, exposes its
modified python package set through passthru.pythonPackages which
can may be used by occasional external scripts etc. which need to
import airflow modules

pkgs/servers/apache-airflow/default.nix

@@ -12,6 +12,7 @@ let
       flask-appbuilder = pySuper.flask-appbuilder.overridePythonAttrs (o: {
         meta.broken = false;
       });
+      # a knock-on effect from overriding the sqlalchemy version
       flask-sqlalchemy = pySuper.flask-sqlalchemy.overridePythonAttrs (o: {
         src = fetchPypi {
           pname = "Flask-SQLAlchemy";
@@ -31,9 +32,19 @@ let
           hash = "sha256-qyD3uoxEnD2pdVvwpUlSqHB3drD4Zg/+ov4CzLFIlLs=";
         };
       });
+
+      apache-airflow = pySelf.callPackage ./python-package.nix { };
     };
   };
 in
-# See note in pkgs/development/python-modules/apache-airflow/default.nix for
+# See note in ./python-package.nix for
 # instructions on manually testing the web UI
-with python.pkgs; toPythonApplication apache-airflow
+with python.pkgs; (toPythonApplication apache-airflow).overrideAttrs (_:{
+  # Provide access to airflow's modified python package set
+  # for the cases where external scripts need to import
+  # airflow modules, though *caveat emptor* because many of
+  # these packages will not be built by hydra and many will
+  # not work at all due to the unexpected version overrides
+  # here.
+  passthru.pythonPackages = python.pkgs;
+})

pkgs/servers/apache-airflow/python-package.nix

@@ -300,7 +300,7 @@ buildPythonPackage rec {
   # Note on testing the web UI:
   # You can (manually) test the web UI as follows:
   #
-  #   nix shell .#python3Packages.apache-airflow
+  #   nix shell .#apache-airflow
   #   airflow db reset  # WARNING: this will wipe any existing db state you might have!
   #   airflow db init
   #   airflow standalone

pkgs/servers/apache-airflow/update-providers.py

@@ -13,7 +13,7 @@ from urllib.request import urlopen
 from urllib.error import HTTPError
 import yaml
 
-PKG_SET = "pkgs.python3Packages"
+PKG_SET = "apache-airflow.pythonPackages"
 
 # If some requirements are matched by multiple or no Python packages, the
 # following can be used to choose the correct one

pkgs/top-level/python-packages.nix

@@ -536,8 +536,6 @@ self: super: with self; {
 
   aocd = callPackage ../development/python-modules/aocd { };
 
-  apache-airflow = callPackage ../development/python-modules/apache-airflow { };
-
   apache-beam = callPackage ../development/python-modules/apache-beam { };
 
   apcaccess = callPackage ../development/python-modules/apcaccess { };