Handle exception chaining and groups in Dev's traceback handling (#6178)

redbot/core/dev_commands.py

@@ -337,11 +337,36 @@ class DevOutput:
                         pass
                     else:
                         exc.lineno -= line_offset
+                        if sys.version_info >= (3, 10) and exc.end_lineno is not None:
+                            exc.end_lineno -= line_offset
                 else:
                     exc.lineno -= line_offset
+                    if sys.version_info >= (3, 10) and exc.end_lineno is not None:
+                        exc.end_lineno -= line_offset
 
-        traceback_exc = traceback.TracebackException(exc_type, exc, tb)
+        top_traceback_exc = traceback.TracebackException(exc_type, exc, tb)
         py311_or_above = sys.version_info >= (3, 11)
+        queue = [  # actually a stack but 'stack' is easy to confuse with actual traceback stack
+            top_traceback_exc,
+        ]
+        seen = {id(top_traceback_exc)}
+        while queue:
+            traceback_exc = queue.pop()
+
+            # handle exception groups; this uses getattr() to support `exceptiongroup` backport lib
+            exceptions: List[traceback.TracebackException] = (
+                getattr(traceback_exc, "exceptions", None) or []
+            )
+            # handle exception chaining
+            if traceback_exc.__cause__ is not None:
+                exceptions.append(traceback_exc.__cause__)
+            if traceback_exc.__context__ is not None:
+                exceptions.append(traceback_exc.__context__)
+            for te in exceptions:
+                if id(te) not in seen:
+                    queue.append(te)
+                    seen.add(id(te))
+
             stack_summary = traceback_exc.stack
             for idx, frame_summary in enumerate(stack_summary):
                 try:
@@ -379,7 +404,7 @@ class DevOutput:
                     )
                 stack_summary[idx] = frame_summary
 
-        return "".join(traceback_exc.format())
+        return "".join(top_traceback_exc.format())
 
 
 @cog_i18n(_)

tests/core/test_dev_commands.py

@@ -330,6 +330,132 @@ STATEMENT_TESTS = {
             """,
         ),
     ),
+    # exception chaining
+    """\
+    try:
+        1 / 0
+    except ZeroDivisionError as exc:
+        try:
+            raise RuntimeError("direct cause") from exc
+        except RuntimeError:
+            raise ValueError("indirect cause")
+    """: (
+        (
+            lambda v: v < (3, 11),
+            """\
+            Traceback (most recent call last):
+              File "<test run - snippet #0>", line 2, in <module>
+                1 / 0
+            ZeroDivisionError: division by zero
+
+            The above exception was the direct cause of the following exception:
+
+            Traceback (most recent call last):
+              File "<test run - snippet #0>", line 5, in <module>
+                raise RuntimeError("direct cause") from exc
+            RuntimeError: direct cause
+
+            During handling of the above exception, another exception occurred:
+
+            Traceback (most recent call last):
+              File "<test run - snippet #0>", line 7, in <module>
+                raise ValueError("indirect cause")
+            ValueError: indirect cause
+            """,
+        ),
+        (
+            lambda v: v >= (3, 11),
+            """\
+            Traceback (most recent call last):
+              File "<test run - snippet #0>", line 2, in <module>
+                1 / 0
+                ~~^~~
+            ZeroDivisionError: division by zero
+
+            The above exception was the direct cause of the following exception:
+
+            Traceback (most recent call last):
+              File "<test run - snippet #0>", line 5, in <module>
+                raise RuntimeError("direct cause") from exc
+            RuntimeError: direct cause
+
+            During handling of the above exception, another exception occurred:
+
+            Traceback (most recent call last):
+              File "<test run - snippet #0>", line 7, in <module>
+                raise ValueError("indirect cause")
+            ValueError: indirect cause
+            """,
+        ),
+    ),
+    # exception groups
+    """\
+    def f(v):
+        try:
+            1 / 0
+        except ZeroDivisionError:
+            try:
+                raise ValueError(v)
+            except ValueError as e:
+                return e
+    try:
+        raise ExceptionGroup("one", [f(1)])
+    except ExceptionGroup as e:
+        eg = e
+    try:
+        raise ExceptionGroup("two", [f(2), eg])
+    except ExceptionGroup as e:
+        raise RuntimeError("wrapping") from e
+    """: (
+        (
+            lambda v: v >= (3, 11),
+            """\
+              + Exception Group Traceback (most recent call last):
+              |   File "<test run - snippet #0>", line 14, in <module>
+              |     raise ExceptionGroup("two", [f(2), eg])
+              | ExceptionGroup: two (2 sub-exceptions)
+              +-+---------------- 1 ----------------
+                | Traceback (most recent call last):
+                |   File "<test run - snippet #0>", line 3, in f
+                |     1 / 0
+                |     ~~^~~
+                | ZeroDivisionError: division by zero
+                | 
+                | During handling of the above exception, another exception occurred:
+                | 
+                | Traceback (most recent call last):
+                |   File "<test run - snippet #0>", line 6, in f
+                |     raise ValueError(v)
+                | ValueError: 2
+                +---------------- 2 ----------------
+                | Exception Group Traceback (most recent call last):
+                |   File "<test run - snippet #0>", line 10, in <module>
+                |     raise ExceptionGroup("one", [f(1)])
+                | ExceptionGroup: one (1 sub-exception)
+                +-+---------------- 1 ----------------
+                  | Traceback (most recent call last):
+                  |   File "<test run - snippet #0>", line 3, in f
+                  |     1 / 0
+                  |     ~~^~~
+                  | ZeroDivisionError: division by zero
+                  | 
+                  | During handling of the above exception, another exception occurred:
+                  | 
+                  | Traceback (most recent call last):
+                  |   File "<test run - snippet #0>", line 6, in f
+                  |     raise ValueError(v)
+                  | ValueError: 1
+                  +------------------------------------
+
+            The above exception was the direct cause of the following exception:
+
+            Traceback (most recent call last):
+              File "<test run - snippet #0>", line 16, in <module>
+                raise RuntimeError("wrapping") from e
+            RuntimeError: wrapping
+            """,
+        ),
+    ),
 }