modsys: Add basic sys.exc_info() implementation.

The implementation is very basic and non-compliant and provided solely for
CPython compatibility. The function itself is bad Python2 heritage, its
usage is discouraged.

py/modsys.c

@@ -121,6 +121,26 @@ STATIC mp_obj_t mp_sys_print_exception(mp_uint_t n_args, const mp_obj_t *args) {
 }
 MP_DEFINE_CONST_FUN_OBJ_VAR_BETWEEN(mp_sys_print_exception_obj, 1, 2, mp_sys_print_exception);
 
+#if MICROPY_PY_SYS_EXC_INFO
+STATIC mp_obj_t mp_sys_exc_info(void) {
+    mp_obj_t cur_exc = MP_STATE_VM(cur_exception);
+    mp_obj_tuple_t *t = mp_obj_new_tuple(3, NULL);
+
+    if (cur_exc == MP_OBJ_NULL) {
+        t->items[0] = mp_const_none;
+        t->items[1] = mp_const_none;
+        t->items[2] = mp_const_none;
+        return t;
+    }
+
+    t->items[0] = mp_obj_get_type(cur_exc);
+    t->items[1] = cur_exc;
+    t->items[2] = mp_const_none;
+    return t;
+}
+MP_DEFINE_CONST_FUN_OBJ_0(mp_sys_exc_info_obj, mp_sys_exc_info);
+#endif
+
 STATIC const mp_map_elem_t mp_module_sys_globals_table[] = {
     { MP_OBJ_NEW_QSTR(MP_QSTR___name__), MP_OBJ_NEW_QSTR(MP_QSTR_sys) },
 
@@ -163,6 +183,10 @@ STATIC const mp_map_elem_t mp_module_sys_globals_table[] = {
     { MP_OBJ_NEW_QSTR(MP_QSTR_stderr), (mp_obj_t)&mp_sys_stderr_obj },
 #endif
 
+    #if MICROPY_PY_SYS_EXC_INFO
+    { MP_OBJ_NEW_QSTR(MP_QSTR_exc_info), (mp_obj_t)&mp_sys_exc_info_obj },
+    #endif
+
     /*
      * Extensions to CPython
      */

py/mpconfig.h

@@ -573,6 +573,12 @@ typedef double mp_float_t;
 #define MICROPY_PY_SYS_MAXSIZE (0)
 #endif
 
+// Whether to provide "sys.exc_info" function
+// Avoid enabling this, this function is Python2 heritage
+#ifndef MICROPY_PY_SYS_EXC_INFO
+#define MICROPY_PY_SYS_EXC_INFO (0)
+#endif
+
 // Whether to provide "sys.exit" function
 #ifndef MICROPY_PY_SYS_EXIT
 #define MICROPY_PY_SYS_EXIT (0)

py/mpstate.h

@@ -107,6 +107,11 @@ typedef struct _mp_state_vm_t {
     // pending exception object (MP_OBJ_NULL if not pending)
     mp_obj_t mp_pending_exception;
 
+    // current exception being handled, for sys.exc_info()
+    #if MICROPY_PY_SYS_EXC_INFO
+    mp_obj_t cur_exception;
+    #endif
+
     // dictionary for the __main__ module
     mp_obj_dict_t dict_main;
 

py/qstrdefs.h

@@ -457,6 +457,9 @@ Q(implementation)
 #if MICROPY_PY_SYS_MAXSIZE
 Q(maxsize)
 #endif
+#if MICROPY_PY_SYS_EXC_INFO
+Q(exc_info)
+#endif
 Q(print_exception)
 #endif
 

py/vm.c

@@ -1228,6 +1228,10 @@ pending_exception_check:
 exception_handler:
             // exception occurred
 
+            #if MICROPY_PY_SYS_EXC_INFO
+            MP_STATE_VM(cur_exception) = nlr.ret_val;
+            #endif
+
             #if SELECTIVE_EXC_IP
             // with selective ip, we store the ip 1 byte past the opcode, so move ptr back
             code_state->ip -= 1;

tests/misc/sys_exc_info.py

@@ -0,0 +1,22 @@
+import sys
+try:
+    sys.exc_info
+except:
+    print("SKIP")
+    sys.exit()
+
+def f():
+    print(sys.exc_info()[0:2])
+
+try:
+    1/0
+except:
+    print(sys.exc_info()[0:2])
+    f()
+
+# MicroPython currently doesn't reset sys.exc_info() value
+# on exit from "except" block.
+#f()
+
+# Recursive except blocks are not handled either - just don't
+# use exc_info() at all!

tests/run-tests

@@ -171,6 +171,7 @@ def run_tests(pyb, tests, args):
         skip_tests.add('misc/features.py') # requires raise_varargs
         skip_tests.add('misc/rge_sm.py') # requires yield
         skip_tests.add('misc/print_exception.py') # because native doesn't have proper traceback info
+        skip_tests.add('misc/sys_exc_info.py') # sys.exc_info() is not supported for native
 
     for test_file in tests:
         test_basename = os.path.basename(test_file)

unix/mpconfigport.h

@@ -71,6 +71,7 @@
 #define MICROPY_PY_SYS_PLATFORM     "linux"
 #define MICROPY_PY_SYS_MAXSIZE      (1)
 #define MICROPY_PY_SYS_STDFILES     (1)
+#define MICROPY_PY_SYS_EXC_INFO     (1)
 #define MICROPY_PY_COLLECTIONS_ORDEREDDICT (1)
 #define MICROPY_PY_MATH_SPECIAL_FUNCTIONS (1)
 #define MICROPY_PY_CMATH            (1)