fix(logging): configuration debug call [backport 1.20] (#7566)

Backport 0800d81 from #6252 to 1.20.

Trying to run with DD_TRACE_DEBUG set and the agent writer fails with
`TypeError: Object of type AgentWriter is not JSON serializable`. This
fixes it.

## Checklist

- [x] Change(s) are motivated and described in the PR description.
- [x] Testing strategy is described if automated tests are not included
in the PR.
- [x] Risk is outlined (performance impact, potential for breakage,
maintainability, etc).
- [x] Change is maintainable (easy to change, telemetry, documentation).
- [x] [Library release note
guidelines](https://ddtrace.readthedocs.io/en/stable/releasenotes.html)
are followed. If no release note is required, add label
`changelog/no-changelog`.
- [x] Documentation is included (in-code, generated user docs, [public
corp docs](https://github.com/DataDog/documentation/)).
- [x] Backport labels are set (if
[applicable](https://ddtrace.readthedocs.io/en/latest/contributing.html#backporting))

## Reviewer Checklist

- [x] Title is accurate.
- [x] No unnecessary changes are introduced.
- [x] Description motivates each change.
- [x] Avoids breaking
[API](https://ddtrace.readthedocs.io/en/stable/versioning.html#interfaces)
changes unless absolutely necessary.
- [x] Testing strategy adequately addresses listed risk(s).
- [x] Change is maintainable (easy to change, telemetry, documentation).
- [x] Release note makes sense to a user of the library.
- [x] Reviewer has explicitly acknowledged and discussed the performance
implications of this PR as reported in the benchmarks PR comment.
- [x] Backport labels are set in a manner that is consistent with the
[release branch maintenance
policy](https://ddtrace.readthedocs.io/en/latest/contributing.html#backporting)

Co-authored-by: Thomas Hervé <[email protected]>

Author: github-actions[bot]

ddtrace/tracer.py

@@ -1,6 +1,5 @@
 import functools
 from itertools import chain
-import json
 import logging
 import os
 from os import environ
@@ -540,7 +539,7 @@ def _generate_diagnostic_logs(self):
                 self._log_compat(logging.WARNING, "- DATADOG TRACER DIAGNOSTIC - %s" % msg)
             else:
                 if log.isEnabledFor(logging.INFO):
-                    msg = "- DATADOG TRACER CONFIGURATION - %s" % json.dumps(info)
+                    msg = "- DATADOG TRACER CONFIGURATION - %s" % info
                     self._log_compat(logging.INFO, msg)
 
                 # Always log errors since we're either in debug_mode or start up logs

docs/spelling_wordlist.txt

@@ -235,6 +235,7 @@ unpatch
 unpatched
 unobfuscated
 unregister
+unserializable
 unshallow
 unvendored
 uri

releasenotes/notes/json-debug-4e2db6b36edfb3ac.yaml

@@ -0,0 +1,5 @@
+---
+fixes:
+  - |
+    tracing: This fix resolves an issue where unserializable tracer attributes caused crashes when
+    ``DD_TRACE_DEBUG`` was set.

tests/integration/test_debug.py

@@ -16,6 +16,7 @@
 from ddtrace.internal import debug
 from ddtrace.internal.compat import PY2
 from ddtrace.internal.compat import PY3
+from ddtrace.internal.writer import AgentWriter
 from ddtrace.internal.writer import TraceWriter
 import ddtrace.sampler
 from tests.subprocesstest import SubprocessTestCase
@@ -197,6 +198,9 @@ def test_tracer_loglevel_info_connection(self):
         tracer = ddtrace.Tracer()
         logging.basicConfig(level=logging.INFO)
         with mock.patch.object(logging.Logger, "log") as mock_logger:
+            # shove an unserializable object into the config log output
+            # regression: this used to cause an exception to be raised
+            ddtrace.config.version = AgentWriter(agent_url="foobar")
             tracer.configure()
         assert mock.call(logging.INFO, re_matcher("- DATADOG TRACER CONFIGURATION - ")) in mock_logger.mock_calls