From 80df377e9512ac839ab19192ff1897ba30be098b Mon Sep 17 00:00:00 2001
From: Damien George <damien.p.george@gmail.com>
Date: Wed, 30 Oct 2019 16:26:11 +1100
Subject: [PATCH] py/modsys: Report .mpy version in sys.implementation.

This commit adds a sys.implementation.mpy entry when the system supports
importing .mpy files.  This entry is a 16-bit integer which encodes two
bytes of information from the header of .mpy files that are supported by
the system being run: the second and third bytes, .mpy version, and flags
and native architecture.  This allows determining the supported .mpy file
dynamically by code, and also for the user to find it out by inspecting
this value.  It's further possible to dynamically detect if the system
supports importing .mpy files by `hasattr(sys.implementation, 'mpy')`.
---
 py/modsys.c          | 29 ++++++++++++++++++++++-------
 py/persistentcode.h  |  4 ++++
 tests/basics/sys1.py |  6 ++++++
 3 files changed, 32 insertions(+), 7 deletions(-)

diff --git a/py/modsys.c b/py/modsys.c
index 4886419d0..29fac7c31 100644
--- a/py/modsys.c
+++ b/py/modsys.c
@@ -34,6 +34,7 @@
 #include "py/stream.h"
 #include "py/smallint.h"
 #include "py/runtime.h"
+#include "py/persistentcode.h"
 
 #if MICROPY_PY_SYS_SETTRACE
 #include "py/objmodule.h"
@@ -66,22 +67,36 @@ STATIC const mp_obj_tuple_t mp_sys_implementation_version_info_obj = {
     3,
     { I(MICROPY_VERSION_MAJOR), I(MICROPY_VERSION_MINOR), I(MICROPY_VERSION_MICRO) }
 };
+#if MICROPY_PERSISTENT_CODE_LOAD
+#define SYS_IMPLEMENTATION_ELEMS \
+    MP_ROM_QSTR(MP_QSTR_micropython), \
+    MP_ROM_PTR(&mp_sys_implementation_version_info_obj), \
+    MP_ROM_INT(MPY_FILE_HEADER_INT)
+#else
+#define SYS_IMPLEMENTATION_ELEMS \
+    MP_ROM_QSTR(MP_QSTR_micropython), \
+    MP_ROM_PTR(&mp_sys_implementation_version_info_obj)
+#endif
 #if MICROPY_PY_ATTRTUPLE
-STATIC const qstr impl_fields[] = { MP_QSTR_name, MP_QSTR_version };
+STATIC const qstr impl_fields[] = {
+    MP_QSTR_name,
+    MP_QSTR_version,
+    #if MICROPY_PERSISTENT_CODE_LOAD
+    MP_QSTR_mpy,
+    #endif
+};
 STATIC MP_DEFINE_ATTRTUPLE(
     mp_sys_implementation_obj,
     impl_fields,
-    2,
-        MP_ROM_QSTR(MP_QSTR_micropython),
-        MP_ROM_PTR(&mp_sys_implementation_version_info_obj)
+    2 + MICROPY_PERSISTENT_CODE_LOAD,
+        SYS_IMPLEMENTATION_ELEMS
 );
 #else
 STATIC const mp_rom_obj_tuple_t mp_sys_implementation_obj = {
     {&mp_type_tuple},
-    2,
+    2 + MICROPY_PERSISTENT_CODE_LOAD,
     {
-        MP_ROM_QSTR(MP_QSTR_micropython),
-        MP_ROM_PTR(&mp_sys_implementation_version_info_obj),
+        SYS_IMPLEMENTATION_ELEMS
     }
 };
 #endif
diff --git a/py/persistentcode.h b/py/persistentcode.h
index a6978c2a3..07e018f8a 100644
--- a/py/persistentcode.h
+++ b/py/persistentcode.h
@@ -70,6 +70,10 @@
 #define MPY_FEATURE_ARCH (MP_NATIVE_ARCH_NONE)
 #endif
 
+// 16-bit little-endian integer with the second and third bytes of supported .mpy files
+#define MPY_FILE_HEADER_INT (MPY_VERSION \
+    | (MPY_FEATURE_ENCODE_FLAGS(MPY_FEATURE_FLAGS) | MPY_FEATURE_ENCODE_ARCH(MPY_FEATURE_ARCH)) << 8)
+
 enum {
     MP_NATIVE_ARCH_NONE = 0,
     MP_NATIVE_ARCH_X86,
diff --git a/tests/basics/sys1.py b/tests/basics/sys1.py
index ab9138024..095824afa 100644
--- a/tests/basics/sys1.py
+++ b/tests/basics/sys1.py
@@ -18,3 +18,9 @@ try:
 except AttributeError:
     # Effectively skip subtests
     print(True)
+
+if hasattr(sys.implementation, 'mpy'):
+    print(type(sys.implementation.mpy))
+else:
+    # Effectively skip subtests
+    print(int)