fix(tracing): fix traceback max size for exceptions [backport 2.9] (#…

…9391)

Backport 1b954de from #9112 to 2.9.

#7558 made the traceback size
configurable via `DD_TRACE_SPAN_TRACEBACK_MAX_SIZE`, but tracebacks for
exceptions were still hardcoded with a limit of 30.

The fix is modeled after `Span#set_traceback`'s existing logic, and
tests were modeled after both `test_traceback_with_error` and
`test_custom_traceback_size`. Not much new logic, just an edge case.

## 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] Risks are described (performance impact, potential for breakage,
maintainability)
- [x] Change is maintainable (easy to change, telemetry, documentation)
- [x] [Library release note
guidelines](https://ddtrace.readthedocs.io/en/stable/releasenotes.html)
are followed or label `changelog/no-changelog` is set
- [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))
- [x] If this PR changes the public interface, I've notified
`@DataDog/apm-tees`.

## Reviewer Checklist

- [x] Title is accurate
- [x] All changes are related to the pull request's stated goal
- [x] Description motivates each change
- [x] Avoids breaking
[API](https://ddtrace.readthedocs.io/en/stable/versioning.html#interfaces)
changes
- [x] Testing strategy adequately addresses listed risks
- [x] Change is maintainable (easy to change, telemetry, documentation)
- [x] Release note makes sense to a user of the library
- [x] Author has 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: Matt Alexander <1710128+quiqueg@users.noreply.github.com>

ddtrace/_trace/span.py

@@ -552,9 +552,13 @@ def set_exc_info(self, exc_type, exc_val, exc_tb):
         self._set_exc_tags(exc_type, exc_val, exc_tb)
 
     def _set_exc_tags(self, exc_type, exc_val, exc_tb):
+        limit = config._span_traceback_max_size
+        if limit is None:
+            limit = 30
+
         # get the traceback
         buff = StringIO()
-        traceback.print_exception(exc_type, exc_val, exc_tb, file=buff, limit=30)
+        traceback.print_exception(exc_type, exc_val, exc_tb, file=buff, limit=limit)
         tb = buff.getvalue()
 
         # readable version of type (e.g. exceptions.ZeroDivisionError)

releasenotes/notes/fix-tracing-traceback-size-for-exceptions-3739fa96d09290fd.yaml

@@ -0,0 +1,4 @@
+---
+fixes:
+  - |
+    tracing: Fixes an issue where ``DD_TRACE_SPAN_TRACEBACK_MAX_SIZE`` was not applied to exception tracebacks.

tests/tracer/test_span.py

@@ -235,6 +235,32 @@ def test_custom_traceback_size(self):
             stack = s.get_tag(ERROR_STACK)
             assert len(stack.splitlines()) == tb_length_limit * 2, "stacktrace should contain two lines per entry"
 
+    def test_custom_traceback_size_with_error(self):
+        tb_length_limit = 2
+        with override_global_config(dict(_span_traceback_max_size=tb_length_limit)):
+            s = Span("test.span")
+
+            def divide_by_zero():
+                1 / 0
+
+            # Wrapper function to generate a larger traceback
+            def wrapper():
+                divide_by_zero()
+
+            try:
+                wrapper()
+            except ZeroDivisionError:
+                s.set_traceback()
+            else:
+                assert 0, "should have failed"
+
+            stack = s.get_tag(ERROR_STACK)
+            # one header "Traceback (most recent call last):" and one footer "ZeroDivisionError: division by zero"
+            header_and_footer_lines = 2
+            assert (
+                len(stack.splitlines()) == tb_length_limit * 2 + header_and_footer_lines
+            ), "stacktrace should contain two lines per entry"
+
     def test_ctx_mgr(self):
         s = Span("bar")
         assert not s.duration