Implement the chain= argument of traceback.print_exception

Author: jepler

shared-bindings/traceback/__init__.c

@@ -58,6 +58,7 @@ STATIC void traceback_exception_common(bool is_print_exception, mp_print_t *prin
     }
     mp_obj_t tb_obj = args[ARG_tb].u_obj;
     mp_obj_t limit_obj = args[ARG_limit].u_obj;
+    bool chain = args[ARG_chain].u_bool;
 
     if (args[ARG_file].u_obj != mp_const_none) {
         if (!is_print_exception) {
@@ -90,6 +91,15 @@ STATIC void traceback_exception_common(bool is_print_exception, mp_print_t *prin
 
     mp_obj_exception_t *exc = mp_obj_exception_get_native(value);
     mp_obj_traceback_t *trace_backup = exc->traceback;
+    #if MICROPY_CPYTHON_EXCEPTION_CHAIN
+    mp_obj_exception_t *context_backup = exc->context;
+    mp_obj_exception_t *cause_backup = exc->cause;
+
+    if (!chain) {
+        exc->context = NULL;
+        exc->cause = NULL;
+    }
+    #endif
 
     if (tb_obj == MP_OBJ_NULL) {
         /* Print the traceback's exception as is */
@@ -101,6 +111,10 @@ STATIC void traceback_exception_common(bool is_print_exception, mp_print_t *prin
 
     shared_module_traceback_print_exception(MP_OBJ_TO_PTR(value), print, limit);
     exc->traceback = trace_backup;
+    #if MICROPY_CPYTHON_EXCEPTION_CHAIN
+    exc->context = context_backup;
+    exc->cause = cause_backup;
+    #endif
 }
 
 //| def format_exception(
@@ -128,14 +142,12 @@ STATIC void traceback_exception_common(bool is_print_exception, mp_print_t *prin
 //|     these lines are concatenated and printed, exactly the same text is
 //|     printed as does print_exception().
 //|
-//|     .. note:: Setting ``chain`` will have no effect as chained exceptions are not yet implemented.
-//|
 //|     :param exc: The exception. Must be an instance of `BaseException`. Unused if value is specified.
 //|     :param value: If specified, is used in place of ``exc``.
 //|     :param TracebackType tb: When value is alsp specified, ``tb`` is used in place of the exception's own traceback. If `None`, the traceback will not be printed.
 //|     :param int limit: Print up to limit stack trace entries (starting from the caller’s frame) if limit is positive.
 //|                       Otherwise, print the last ``abs(limit)`` entries. If limit is omitted or None, all entries are printed.
-//|     :param bool chain: If `True` then chained exceptions will be printed (note: not yet implemented).
+//|     :param bool chain: If `True` then chained exceptions will be printed.
 //|     """
 //|
 STATIC mp_obj_t traceback_format_exception(size_t n_args, const mp_obj_t *pos_args, mp_map_t *kw_args) {
@@ -169,16 +181,14 @@ STATIC MP_DEFINE_CONST_FUN_OBJ_KW(traceback_format_exception_obj, 0, traceback_f
 //|     no traceback will be shown. This is compatible with CPython 3.5 and
 //|     newer.
 //|
-//|     .. note:: Setting ``chain`` will have no effect as chained exceptions are not yet implemented.
-//|
 //|     :param exc: The exception. Must be an instance of `BaseException`. Unused if value is specified.
 //|     :param value: If specified, is used in place of ``exc``.
 //|     :param tb: When value is alsp specified, ``tb`` is used in place of the exception's own traceback. If `None`, the traceback will not be printed.
 //|     :param int limit: Print up to limit stack trace entries (starting from the caller’s frame) if limit is positive.
 //|                       Otherwise, print the last ``abs(limit)`` entries. If limit is omitted or None, all entries are printed.
 //|     :param io.FileIO file: If file is omitted or `None`, the output goes to `sys.stderr`; otherwise it should be an open
 //|                            file or file-like object to receive the output.
-//|     :param bool chain: If `True` then chained exceptions will be printed (note: not yet implemented).
+//|     :param bool chain: If `True` then chained exceptions will be printed.
 //|
 //|     """
 //|     ...

tests/circuitpython/traceback_test_chained.py

@@ -11,9 +11,9 @@
     raise SystemExit
 
 
-def print_exc_info(e):
+def print_exc_info(e, chain=True):
     print("-" * 72)
-    traceback.print_exception(None, e, e.__traceback__)
+    traceback.print_exception(None, e, e.__traceback__, chain=chain)
     print("-" * 72)
     print()
 
@@ -24,6 +24,7 @@ def print_exc_info(e):
     except Exception as inner:
         raise RuntimeError() from inner
 except Exception as e:
+    print_exc_info(e, chain=False)
     print_exc_info(e)
 print()
 

tests/circuitpython/traceback_test_chained.py.exp

@@ -1,3 +1,9 @@
+------------------------------------------------------------------------
+Traceback (most recent call last):
+  File "circuitpython/traceback_test_chained.py", line 25, in <module>
+RuntimeError: 
+------------------------------------------------------------------------
+
 ------------------------------------------------------------------------
 Traceback (most recent call last):
   File "circuitpython/traceback_test_chained.py", line 23, in <module>
@@ -17,39 +23,39 @@ OSError:
 The above exception was the direct cause of the following exception:
 
 Traceback (most recent call last):
-  File "circuitpython/traceback_test_chained.py", line 34, in <module>
+  File "circuitpython/traceback_test_chained.py", line 35, in <module>
 RuntimeError: 
 ------------------------------------------------------------------------
 
 
 ------------------------------------------------------------------------
 Traceback (most recent call last):
-  File "circuitpython/traceback_test_chained.py", line 42, in <module>
+  File "circuitpython/traceback_test_chained.py", line 43, in <module>
 ZeroDivisionError: division by zero
 
 During handling of the above exception, another exception occurred:
 
 Traceback (most recent call last):
-  File "circuitpython/traceback_test_chained.py", line 44, in <module>
+  File "circuitpython/traceback_test_chained.py", line 45, in <module>
 RuntimeError: 
 ------------------------------------------------------------------------
 
 
 ------------------------------------------------------------------------
 Traceback (most recent call last):
-  File "circuitpython/traceback_test_chained.py", line 53, in <module>
+  File "circuitpython/traceback_test_chained.py", line 54, in <module>
 RuntimeError: 
 ------------------------------------------------------------------------
 
 ------------------------------------------------------------------------
 Traceback (most recent call last):
-  File "circuitpython/traceback_test_chained.py", line 59, in <module>
+  File "circuitpython/traceback_test_chained.py", line 60, in <module>
 RuntimeError: 
 
 During handling of the above exception, another exception occurred:
 
 Traceback (most recent call last):
-  File "circuitpython/traceback_test_chained.py", line 61, in <module>
+  File "circuitpython/traceback_test_chained.py", line 62, in <module>
 ZeroDivisionError: division by zero
 ------------------------------------------------------------------------