Fix inspect.getsourcelines() indexing bug in --spew trace hook

gunicorn/debug.py

@@ -34,9 +34,9 @@ def __call__(self, frame, event, arg):
             else:
                 name = '[unknown]'
                 try:
-                    src = inspect.getsourcelines(frame)
-                    line = src[lineno]
-                except OSError:
+                    src_lines, src_start = inspect.getsourcelines(frame)
+                    line = src_lines[lineno - src_start]
+                except (OSError, IndexError):
                     line = 'Unknown code named [%s].  VM instruction #%d' % (
                         frame.f_code.co_name, frame.f_lasti)
             if self.trace_names is None or name in self.trace_names:

tests/test_debug.py

@@ -0,0 +1,61 @@
+# -*- coding: utf-8 -*-
+#
+# This file is part of gunicorn released under the MIT license.
+# See the NOTICE for more information.
+
+"""Tests for the debug module (--spew functionality)."""
+
+import io
+import linecache
+import sys
+
+from gunicorn.debug import Spew
+
+
+class TestSpew:
+    """Tests for the Spew trace hook used by --spew."""
+
+    def test_getsourcelines_indexing(self):
+        """Verify that Spew correctly indexes inspect.getsourcelines() result.
+
+        Regression test for https://github.com/benoitc/gunicorn/issues/3344
+
+        inspect.getsourcelines() returns (lines_list, start_lineno), a tuple
+        of length 2. The old code did ``src[lineno]`` which indexed the tuple
+        by the frame's line number instead of indexing the list of source
+        lines. When the line number was 1, ``src[1]`` returned the integer
+        start_lineno, causing ``AttributeError: 'int' object has no attribute
+        'rstrip'``. For any line number >= 2, it raised an IndexError.
+        """
+        spew = Spew(show_values=False)
+
+        # Register source in linecache for a dynamically compiled function
+        # so that inspect.getsourcelines() succeeds even though __file__ is
+        # absent from f_globals -- this is exactly the pattern that triggers
+        # the bug (e.g. code dynamically generated by the attrs library).
+        filename = "<spew-test-generated>"
+        source = "def _test_fn():\n    x = 1\n    return x\n"
+        lines = source.splitlines(True)
+        linecache.cache[filename] = (len(source), None, lines, filename)
+
+        code = compile(source, filename, "exec")
+        # Execute without __file__ in globals to trigger the fallback path
+        ns = {"__name__": "__spew_test__"}
+        exec(code, ns)
+        fn = ns["_test_fn"]
+
+        old_stdout = sys.stdout
+        sys.stdout = captured = io.StringIO()
+        try:
+            sys.settrace(spew)
+            fn()
+        finally:
+            sys.settrace(None)
+            sys.stdout = old_stdout
+
+        output = captured.getvalue()
+        # The trace hook should have printed source lines without crashing.
+        # Before the fix, this would crash with:
+        #   AttributeError: 'int' object has no attribute 'rstrip'
+        assert output, "Expected trace output but got nothing"
+        assert "x = 1" in output or "return x" in output