fix(flask): stop reading deprecated flask.__version__ (#4422)

* fix(flask): stop reading deprecated flask.__version__

Flask 3.1 deprecated the module-level __version__ attribute and emits a
DeprecationWarning on access; 3.2 will remove it. The Flask
instrumentor was hitting that warning at import time via

    _IS_FLASK_31_PLUS = hasattr(flask, "__version__") and
        package_version.parse(flask.__version__) >= package_version.parse("3.1.0")

even though it already computes the installed Flask version via
importlib.metadata.version("flask") a few lines below. Use that
flask_version for the 3.1+ check and drop the deprecated attribute
access entirely.

Fixes #4402

Signed-off-by: Ali <alliasgher123@gmail.com>

* style: apply ruff format

Signed-off-by: alliasgher <alliasgher123@gmail.com>

* fix(flask): also stop reading deprecated flask.__version__ in tests

Per @xrmx review — the test suite was the remaining caller of the
deprecated attribute. Switch to importlib.metadata.version("flask")
to match the production code change.

Signed-off-by: alliasgher <alliasgher123@gmail.com>

* Apply suggestions from code review

Co-authored-by: Riccardo Magliocchetti <riccardo.magliocchetti@gmail.com>

* Update CHANGELOG.md

---------

Signed-off-by: Ali <alliasgher123@gmail.com>
Signed-off-by: alliasgher <alliasgher123@gmail.com>
Co-authored-by: Riccardo Magliocchetti <riccardo.magliocchetti@gmail.com>

Author: alliasgher

CHANGELOG.md

@@ -26,6 +26,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
   ([#4427](https://github.com/open-telemetry/opentelemetry-python-contrib/pull/4427))
 - `opentelemetry-instrumentation-flask`: Clean up environ keys in `_teardown_request` to prevent duplicate execution
   ([#4341](https://github.com/open-telemetry/opentelemetry-python-contrib/pull/4341))
+- `opentelemetry-instrumentation-flask`: Stop reading the deprecated (from 3.1) `flask.__version__` attribute; resolve the Flask version via `importlib.metadata`
+  ([#4422](https://github.com/open-telemetry/opentelemetry-python-contrib/pull/4422))
 
 ### Breaking changes
 

instrumentation/opentelemetry-instrumentation-flask/src/opentelemetry/instrumentation/flask/__init__.py

@@ -301,10 +301,6 @@ def response_hook(span: Span, status: str, response_headers: List):
 )
 
 _logger = getLogger(__name__)
-# Global constants for Flask 3.1+ streaming context cleanup
-_IS_FLASK_31_PLUS = hasattr(flask, "__version__") and package_version.parse(
-    flask.__version__
-) >= package_version.parse("3.1.0")
 
 _ENVIRON_STARTTIME_KEY = "opentelemetry-flask.starttime_key"
 _ENVIRON_SPAN_KEY = "opentelemetry-flask.span_key"
@@ -316,6 +312,11 @@ def response_hook(span: Span, status: str, response_headers: List):
 
 flask_version = version("flask")
 
+# Global constant for Flask 3.1+ streaming context cleanup
+_IS_FLASK_31_PLUS = package_version.parse(
+    flask_version
+) >= package_version.parse("3.1.0")
+
 if package_version.parse(flask_version) >= package_version.parse("2.2.0"):
 
     def _request_ctx_ref() -> weakref.ReferenceType:

instrumentation/opentelemetry-instrumentation-flask/tests/test_flask_compatibility.py

@@ -20,6 +20,7 @@
 import io
 import threading
 import time
+from importlib.metadata import version
 from unittest import mock, skipIf
 
 import flask
@@ -37,7 +38,7 @@
 class TestFlaskCompatibility(WsgiTestBase):
     def setUp(self):
         super().setUp()
-        self.flask_version = flask.__version__
+        self.flask_version = version("flask")
 
     def test_streaming_response_context_cleanup(self):
         """Test that streaming responses properly clean up context"""