fix(debugger): max match in probe file resolution

ddtrace/debugging/_probe/model.py

@@ -41,9 +41,8 @@ def _resolve_source_file(_path: str) -> Optional[Path]:
     if path.is_file():
         return path.resolve()
 
-    for relpath in (path.relative_to(_) for _ in path.parents):
-        resolved_path = _resolve(relpath)
-        if resolved_path is not None:
+    for relpath in (path.relative_to(_) for _ in reversed(path.parents)):
+        if (resolved_path := _resolve(relpath)) is not None:
             return resolved_path
 
     return None

releasenotes/notes/debugging-probe-source-file-resolution-bd73a5fd172c3711.yaml

@@ -0,0 +1,6 @@
+---
+fixes:
+  - |
+    dynamic instrumentation: fix issue with line probes matching the wrong
+    source file when multiple source files from different Python path entries
+    share the same name.

tests/debugging/probe/test_model.py

@@ -1,4 +1,5 @@
 from pathlib import Path
+import sys
 
 from ddtrace.debugging._expressions import DDExpression
 from ddtrace.debugging._expressions import dd_compile
@@ -57,3 +58,26 @@ def test_probe_hash():
     )
 
     assert hash(probe)
+
+
+def test_resolve_source_file_same_filename_on_different_paths(tmp_path: Path):
+    """
+    Test that if we have sources with the same name along different Python
+    paths, we resolve to the longest matching path.
+    """
+    # Setup the file system for the test
+    (p := tmp_path / "a" / "b").mkdir(parents=True)
+    (q := tmp_path / "c" / "b").mkdir(parents=True)
+
+    (fp := p / "test_model.py").touch()
+    (fq := q / "test_model.py").touch()
+
+    # Patch the python path
+    original_pythonpath = sys.path
+
+    try:
+        sys.path = [str(tmp_path / "c"), str(tmp_path)]
+        assert (r := _resolve_source_file("a/b/test_model.py")) is not None and r.resolve() == fp.resolve(), r
+        assert (r := _resolve_source_file("c/b/test_model.py")) is not None and r.resolve() == fq.resolve(), r
+    finally:
+        sys.path = original_pythonpath