Enable back iterative development of latest providers with old airflo…

…ws (apache#43617)

* Enable back iterative development of latest providers with old airflows

The compatibility tests in CI are using providers built as packages
from sources, so the compatibility tests run there using
"providers/tests" work just fine, because all providers are installed
in the airflow.providers site library. However when we are iterating
and debugging backwards compatiblity provider tests, we should be
able to use local provider sources, rather than installed packages
and we have the possibility of mounting both - providers sources
and tests to the image.

See `contributing-docs/testing/unit_tests.rst` on how to do it
by using ``--mount-sources providers-and-tests`` flag connected
with `--use-airflow-version`.

However as of apache#42505 this has been broken, because currently in
main we  rely on airflow having "pkgutil" namespace package for
both - airflow, and airflow.providers packages (previous airflow
versions had implicit package for airflow.providers package) - so
providers installed locally cannot be used as "another" source of
providers.  Previously it was working because both "installed" and
"sources" `airflow.providers` package were implicit namespace packages.

As explained in https://packaging.python.org/en/latest/guides/packaging-namespace-packages/#native-namespace-packages

> Every distribution that uses the namespace package must include such
> an `__init__.py`. If any distribution does not, it will cause the
> namespace logic to fail and the other sub-packages will not be
> importable. Any additional code in __init__.py will be inaccessible.

So because old airflow uses implicit provider's packages and
main airflow from source uses "explicit" provider's package,
the only way we can make the "source" providers is to mount
them or symbolically link them to inside installed distribution
of airflow package (in site directory) (or dynamically remove
the __init__.py from provider's source directory.

We cannot mount the provider package sources ot inside the
installed airflow - because when --use-airflow-version is used,
airflow is installed dynamically inside the container - after
the container is started.

This PR solves the problem by adding an env variable that
will make the initialization script to remove the installed
airflow.providers folder after installing airflow and linking the
"providers/src/airflow/providers" folder there. This has the
added benefit that all providers (including the preinstalled ones)
are used from "main" sources rather than from installed packages -
which was problematic for the past way of using providers from
sources - which used the fact that both "airflow.providers" in
the site-library and the one in sources were implicit namespace
packages.

* Update Dockerfile.ci

Co-authored-by: GPK <gopidesupavan@gmail.com>

* Update scripts/docker/entrypoint_ci.sh

Co-authored-by: GPK <gopidesupavan@gmail.com>

---------

Co-authored-by: GPK <gopidesupavan@gmail.com>

Dockerfile.ci

@@ -1017,6 +1017,13 @@ function determine_airflow_to_use() {
            --constraint https://raw.githubusercontent.com/apache/airflow/constraints-main/constraints-${PYTHON_MAJOR_MINOR_VERSION}.txt
         # Some packages might leave legacy typing module which causes test issues
         pip uninstall -y typing || true
+        if [[ ${LINK_PROVIDERS_TO_AIRFLOW_PACKAGE=} == "true" ]]; then
+            echo
+            echo "${COLOR_BLUE}Linking providers to airflow package as we are using them from mounted sources.${COLOR_RESET}"
+            echo
+            rm -rf /usr/local/lib/python${PYTHON_MAJOR_MINOR_VERSION}/site-packages/airflow/providers
+            ln -s "${AIRFLOW_SOURCES}/providers/src/airflow/providers" "/usr/local/lib/python${PYTHON_MAJOR_MINOR_VERSION}/site-packages/airflow/providers"
+        fi
     fi
 
     if [[ "${USE_AIRFLOW_VERSION}" =~ ^2\.2\..*|^2\.1\..*|^2\.0\..* && "${AIRFLOW__DATABASE__SQL_ALCHEMY_CONN=}" != "" ]]; then

scripts/ci/docker-compose/providers-and-tests-sources.yml

@@ -21,6 +21,7 @@ services:
     tty: true  # docker run -t
     environment:
       - AIRFLOW__CORE__PLUGINS_FOLDER=/files/plugins
+      - LINK_PROVIDERS_TO_AIRFLOW_PACKAGE=true
     # We only mount tests folder
     volumes:
       - ../../../.bash_aliases:/root/.bash_aliases:cached
@@ -30,8 +31,8 @@ services:
       - ../../../empty:/opt/airflow/airflow
       # but keep tests
       - ../../../tests/:/opt/airflow/tests:cached
-      # and providers
-      - ../../../providers/src/airflow/providers:/opt/airflow/airflow/providers:cached
+      # Mount providers to make sure that we have the latest providers - both tests and sources
+      - ../../../providers/:/opt/airflow/providers:cached
       # and entrypoint and in_container scripts for testing
       - ../../../scripts/docker/entrypoint_ci.sh:/entrypoint
       - ../../../scripts/in_container/:/opt/airflow/scripts/in_container

scripts/docker/entrypoint_ci.sh

@@ -236,6 +236,13 @@ function determine_airflow_to_use() {
            --constraint https://raw.githubusercontent.com/apache/airflow/constraints-main/constraints-${PYTHON_MAJOR_MINOR_VERSION}.txt
         # Some packages might leave legacy typing module which causes test issues
         pip uninstall -y typing || true
+        if [[ ${LINK_PROVIDERS_TO_AIRFLOW_PACKAGE=} == "true" ]]; then
+            echo
+            echo "${COLOR_BLUE}Linking providers to airflow package as we are using them from mounted sources.${COLOR_RESET}"
+            echo
+            rm -rf /usr/local/lib/python${PYTHON_MAJOR_MINOR_VERSION}/site-packages/airflow/providers
+            ln -s "${AIRFLOW_SOURCES}/providers/src/airflow/providers" "/usr/local/lib/python${PYTHON_MAJOR_MINOR_VERSION}/site-packages/airflow/providers"
+        fi
     fi
 
     if [[ "${USE_AIRFLOW_VERSION}" =~ ^2\.2\..*|^2\.1\..*|^2\.0\..* && "${AIRFLOW__DATABASE__SQL_ALCHEMY_CONN=}" != "" ]]; then