From fb2e18ef018aaadc7e2a526124b673cade87f0a6 Mon Sep 17 00:00:00 2001
From: Zachary Groves <32471391+ZStriker19@users.noreply.github.com>
Date: Fri, 25 Apr 2025 14:09:48 -0400
Subject: [PATCH] fix(tracing): do not incorrectly match on None with ?*
 (#13100)

Fixes https://github.com/DataDog/dd-trace-py/issues/12775

## Checklist
- [x] PR author has checked that all the criteria below are met
- The PR description includes an overview of the change
- The PR description articulates the motivation for the change
- The change includes tests OR the PR description describes a testing
strategy
- The PR description notes risks associated with the change, if any
- Newly-added code is easy to change
- The change follows the [library release note
guidelines](https://ddtrace.readthedocs.io/en/stable/releasenotes.html)
- The change includes or references documentation updates if necessary
- Backport labels are set (if
[applicable](https://ddtrace.readthedocs.io/en/latest/contributing.html#backporting))

## Reviewer Checklist
- [x] Reviewer has checked that all the criteria below are met
- Title is accurate
- All changes are related to the pull request's stated goal
- Avoids breaking
[API](https://ddtrace.readthedocs.io/en/stable/versioning.html#interfaces)
changes
- Testing strategy adequately addresses listed risks
- Newly-added code is easy to change
- Release note makes sense to a user of the library
- If necessary, author has acknowledged and discussed the performance
implications of this PR as reported in the benchmarks PR comment
- 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)

(cherry picked from commit ea64efc698bb158da34e6ed1aaad670485987eca)
---
 ddtrace/_trace/sampling_rule.py                   | 15 +++++++--------
 ...ct_sampler_match_on_none-c6e04cc4dfdf9007.yaml |  5 +++++
 tests/tracer/test_sampler.py                      | 10 ++++++++++
 3 files changed, 22 insertions(+), 8 deletions(-)
 create mode 100644 releasenotes/notes/fix_incorrect_sampler_match_on_none-c6e04cc4dfdf9007.yaml

diff --git a/ddtrace/_trace/sampling_rule.py b/ddtrace/_trace/sampling_rule.py
index 532a0b71f51..cc8667b6bad 100644
--- a/ddtrace/_trace/sampling_rule.py
+++ b/ddtrace/_trace/sampling_rule.py
@@ -154,26 +154,25 @@ def check_tags(self, meta, metrics):
         tag_match = False
         for tag_key in self._tag_value_matchers.keys():
             value = meta.get(tag_key)
-            tag_match = self._tag_value_matchers[tag_key].match(str(value))
-            # If the value doesn't match in meta, check the metrics
-            if tag_match is False:
+            # it's because we're not checking metrics first before continuing
+            if value is None:
                 value = metrics.get(tag_key)
+                if value is None:
+                    continue
                 # Floats: Matching floating point values with a non-zero decimal part is not supported.
                 # For floating point values with a non-zero decimal part, any all * pattern always returns true.
                 # Other patterns always return false.
                 if isinstance(value, float):
                     if not value.is_integer():
-                        if self._tag_value_matchers[tag_key].pattern == "*":
+                        if all(c == "*" for c in self._tag_value_matchers[tag_key].pattern):
                             tag_match = True
+                            continue
                         else:
                             return False
-                        continue
                     else:
                         value = int(value)
 
-                tag_match = self._tag_value_matchers[tag_key].match(str(value))
-            else:
-                continue
+            tag_match = self._tag_value_matchers[tag_key].match(str(value))
             # if we don't match with all specified tags for a rule, it's not a match
             if tag_match is False:
                 return False
diff --git a/releasenotes/notes/fix_incorrect_sampler_match_on_none-c6e04cc4dfdf9007.yaml b/releasenotes/notes/fix_incorrect_sampler_match_on_none-c6e04cc4dfdf9007.yaml
new file mode 100644
index 00000000000..65e5687d6e1
--- /dev/null
+++ b/releasenotes/notes/fix_incorrect_sampler_match_on_none-c6e04cc4dfdf9007.yaml
@@ -0,0 +1,5 @@
+---
+fixes:
+  - |
+    fix(tracer):Fixed a bug in the sampling rule matcher where the pattern ``?*`` was not being matched correctly 
+    for ``DD_TRACE_SAMPLING_RULES`` tags, due to it matching on spans with no tag matching the specified key.
\ No newline at end of file
diff --git a/tests/tracer/test_sampler.py b/tests/tracer/test_sampler.py
index 813dc1be439..64beed7ecda 100644
--- a/tests/tracer/test_sampler.py
+++ b/tests/tracer/test_sampler.py
@@ -932,6 +932,16 @@ def sample(self, span):
             0,
             None,
         ),
+        (  # Regression test for https://github.com/DataDog/dd-trace-py/issues/12775
+            # We should not match None values with ?* patterns.
+            DatadogSampler(
+                rules=[SamplingRule(sample_rate=0, name="?*", resource="?*", service="?*", tags={"key": "?*"})],
+            ),
+            AUTO_KEEP,
+            SamplingMechanism.DEFAULT,
+            0,
+            None,
+        ),
     ],
 )
 def test_datadog_sampler_sample_rules(sampler, sampling_priority, sampling_mechanism, rule, limit, dummy_tracer):