Improve canonicalize_exception_traceback for RecursionError (#1455)

Author: alexmojaki

logfire/_internal/utils.py

@@ -449,14 +449,25 @@ def canonicalize_exception_traceback(exc: BaseException, seen: set[int] | None =
     try:
         exc_type = type(exc)
         parts = [f'\n{exc_type.__module__}.{exc_type.__qualname__}\n----']
+        num_repeats = 0
         if exc.__traceback__:
             visited: set[str] = set()
             for frame, lineno in traceback.walk_tb(exc.__traceback__):
                 filename = frame.f_code.co_filename
                 source_line = linecache.getline(filename, lineno, frame.f_globals).strip()
                 module = frame.f_globals.get('__name__', filename)
                 frame_summary = f'{module}.{frame.f_code.co_name}\n   {source_line}'
-                if frame_summary not in visited:  # ignore repeated frames
+                if frame_summary in visited:
+                    num_repeats += 1
+                    if num_repeats >= 100 and isinstance(exc, RecursionError):
+                        # The last few frames of a RecursionError traceback are often *not* the recursive function(s)
+                        # being called repeatedly (which are already deduped here) but instead some other function(s)
+                        # called normally which happen to use up the last bit of the recursion limit.
+                        # These can easily vary between runs and we don't want to pay attention to them,
+                        # the real problem is the recursion itself.
+                        parts.append('\n<recursion detected>')
+                        break
+                else:  # skip repeated frames
                     visited.add(frame_summary)
                     parts.append(frame_summary)
         seen = seen or set()

tests/test_canonicalize_exception.py

@@ -1,4 +1,5 @@
 import sys
+from typing import Callable
 
 import pytest
 from inline_snapshot import snapshot
@@ -255,3 +256,65 @@ def test_canonicalize_no_traceback():
 builtins.ValueError
 ----\
 """)
+
+
+def test_recursion():
+    def foo(b: Callable[[], None]):
+        b()
+        foo(b)
+
+    def foo2():
+        foo(foo2)
+
+    def bar():
+        baz()
+
+    def baz():
+        pass
+
+    try:
+        foo(bar)
+    except Exception as e:
+        assert canonicalize_exception_traceback(e).replace(__file__, '__file__') == snapshot("""\
+
+builtins.RecursionError
+----
+tests.test_canonicalize_exception.test_recursion
+   foo(bar)
+tests.test_canonicalize_exception.foo
+   foo(b)
+
+<recursion detected>\
+""")
+
+    try:
+        foo(baz)
+    except Exception as e:
+        assert canonicalize_exception_traceback(e).replace(__file__, '__file__') == snapshot("""\
+
+builtins.RecursionError
+----
+tests.test_canonicalize_exception.test_recursion
+   foo(baz)
+tests.test_canonicalize_exception.foo
+   foo(b)
+
+<recursion detected>\
+""")
+
+    try:
+        foo2()
+    except Exception as e:
+        assert canonicalize_exception_traceback(e).replace(__file__, '__file__') == snapshot("""\
+
+builtins.RecursionError
+----
+tests.test_canonicalize_exception.test_recursion
+   foo2()
+tests.test_canonicalize_exception.foo2
+   foo(foo2)
+tests.test_canonicalize_exception.foo
+   b()
+
+<recursion detected>\
+""")