modsys: Add sys.print_exception(exc, file=sys.stdout) function.

The function is modeled after traceback.print_exception(), but unbloated,
and put into existing module to save overhead on adding another module.
Compliant traceback.print_exception() is intended to be implemented in
micropython-lib in terms of sys.print_exception().

This change required refactoring mp_obj_print_exception() to take pfenv_t
interface arguments.

Addresses #751.

5 files changed, 40 insertions, 9 deletions

diff --git a/py/modsys.c b/py/modsys.c
index d9be7d1bc1..06bd4c80e1 100644
--- a/py/modsys.c
+++ b/py/modsys.c
@@ -38,6 +38,8 @@
 #include "objstr.h"
 #include "mpz.h"
 #include "objint.h"
+#include "pfenv.h"
+#include "stream.h"
 
 #if MICROPY_PY_SYS
 
@@ -78,6 +80,25 @@ STATIC mp_obj_t mp_sys_exit(mp_uint_t n_args, const mp_obj_t *args) {
 }
 MP_DEFINE_CONST_FUN_OBJ_VAR_BETWEEN(mp_sys_exit_obj, 0, 1, mp_sys_exit);
 
+STATIC mp_obj_t mp_sys_print_exception(mp_uint_t n_args, const mp_obj_t *args) {
+    #if MICROPY_PY_IO
+    mp_obj_t stream_obj = &mp_sys_stdout_obj;
+    if (n_args > 1) {
+        stream_obj = args[1];
+    }
+
+    pfenv_t pfenv;
+    pfenv.data = stream_obj;
+    pfenv.print_strn = (void (*)(void *, const char *, mp_uint_t))mp_stream_write;
+    mp_obj_print_exception((void (*)(void *env, const char *fmt, ...))pfenv_printf, &pfenv, args[0]);
+    #else
+    mp_obj_print_exception(printf_wrapper, NULL, args[0]);
+    #endif
+
+    return mp_const_none;
+}
+MP_DEFINE_CONST_FUN_OBJ_VAR_BETWEEN(mp_sys_print_exception_obj, 1, 2, mp_sys_print_exception);
+
 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) },
 
@@ -118,6 +139,12 @@ STATIC const mp_map_elem_t mp_module_sys_globals_table[] = {
     { MP_OBJ_NEW_QSTR(MP_QSTR_stdout), (mp_obj_t)&mp_sys_stdout_obj },
     { MP_OBJ_NEW_QSTR(MP_QSTR_stderr), (mp_obj_t)&mp_sys_stderr_obj },
 #endif
+
+    /*
+     * Extensions to CPython
+     */
+
+    { MP_OBJ_NEW_QSTR(MP_QSTR_print_exception), (mp_obj_t)&mp_sys_print_exception_obj },
 };
 
 STATIC MP_DEFINE_CONST_DICT(mp_module_sys_globals, mp_module_sys_globals_table);
diff --git a/py/obj.c b/py/obj.c
index c869a65465..d2801a3968 100644
--- a/py/obj.c
+++ b/py/obj.c
@@ -85,31 +85,31 @@ void mp_obj_print(mp_obj_t o_in, mp_print_kind_t kind) {
 }
 
 // helper function to print an exception with traceback
-void mp_obj_print_exception(mp_obj_t exc) {
+void mp_obj_print_exception(void (*print)(void *env, const char *fmt, ...), void *env, mp_obj_t exc) {
     if (mp_obj_is_exception_instance(exc)) {
         mp_uint_t n, *values;
         mp_obj_exception_get_traceback(exc, &n, &values);
         if (n > 0) {
             assert(n % 3 == 0);
-            printf("Traceback (most recent call last):\n");
+            print(env, "Traceback (most recent call last):\n");
             for (int i = n - 3; i >= 0; i -= 3) {
 #if MICROPY_ENABLE_SOURCE_LINE
-                printf("  File \"%s\", line %d", qstr_str(values[i]), (int)values[i + 1]);
+                print(env, "  File \"%s\", line %d", qstr_str(values[i]), (int)values[i + 1]);
 #else
-                printf("  File \"%s\"", qstr_str(values[i]));
+                print(env, "  File \"%s\"", qstr_str(values[i]));
 #endif
                 // the block name can be NULL if it's unknown
                 qstr block = values[i + 2];
                 if (block == MP_QSTR_NULL) {
-                    printf("\n");
+                    print(env, "\n");
                 } else {
-                    printf(", in %s\n", qstr_str(block));
+                    print(env, ", in %s\n", qstr_str(block));
                 }
             }
         }
     }
-    mp_obj_print(exc, PRINT_EXC);
-    printf("\n");
+    mp_obj_print_helper(print, env, exc, PRINT_EXC);
+    print(env, "\n");
 }
 
 bool mp_obj_is_true(mp_obj_t arg) {
diff --git a/py/obj.h b/py/obj.h
index 3721bea925..6db76405e9 100644
--- a/py/obj.h
+++ b/py/obj.h
@@ -418,7 +418,7 @@ mp_obj_t mp_instance_cast_to_native_base(mp_const_obj_t self_in, mp_const_obj_t
 
 void mp_obj_print_helper(void (*print)(void *env, const char *fmt, ...), void *env, mp_obj_t o_in, mp_print_kind_t kind);
 void mp_obj_print(mp_obj_t o, mp_print_kind_t kind);
-void mp_obj_print_exception(mp_obj_t exc);
+void mp_obj_print_exception(void (*print)(void *env, const char *fmt, ...), void *env, mp_obj_t exc);
 
 bool mp_obj_is_true(mp_obj_t arg);
 
diff --git a/py/pfenv.h b/py/pfenv.h
index fea2c883e9..98c1885f35 100644
--- a/py/pfenv.h
+++ b/py/pfenv.h
@@ -52,3 +52,6 @@ int pfenv_print_float(const pfenv_t *pfenv, mp_float_t f, char fmt, int flags, c
 
 //int pfenv_vprintf(const pfenv_t *pfenv, const char *fmt, va_list args);
 int pfenv_printf(const pfenv_t *pfenv, const char *fmt, ...);
+
+// Wrapper for system printf
+void printf_wrapper(void *env, const char *fmt, ...);
diff --git a/py/qstrdefs.h b/py/qstrdefs.h
index 449f44d3bc..f183c256fb 100644
--- a/py/qstrdefs.h
+++ b/py/qstrdefs.h
@@ -403,6 +403,7 @@ Q(version_info)
 #if MICROPY_PY_SYS_MAXSIZE
 Q(maxsize)
 #endif
+Q(print_exception)
 #endif
 
 #if MICROPY_PY_STRUCT