fix(debugger): max match in probe file resolution (#15143)

## Description

We change the probe source file path matching logic to return the
longest matching path instead of the first result. This deals with cases
where sources with the same name can be found on different entries of
the Python path.

## Testing

<!-- Describe your testing strategy or note what tests are included -->

Author: P403n1x87

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