py/modsys: Add sys.implementation._build entry.

For a given MicroPython firmware/executable it can be sometimes important
to know how it was built, which variant/board configuration it came from.

This commit adds a new field `sys.implementation._build` that can help
identify the configuration that MicroPython was built with.

For now it's either:
* <VARIANT> for unix, webassembly and windows ports
* <BOARD>-<VARIANT> for microcontroller ports (the variant is optional)

In the future additional elements may be added to this string, separated by
a hyphen.

Resolves issue #16498.

Signed-off-by: Damien George <damien@micropython.org>

5 files changed, 61 insertions, 4 deletions

diff --git a/docs/library/sys.rst b/docs/library/sys.rst
index c72214c13..baefd9270 100644
--- a/docs/library/sys.rst
+++ b/docs/library/sys.rst
@@ -75,6 +75,8 @@ Constants
    * *version* - tuple (major, minor, micro, releaselevel), e.g. (1, 22, 0, '')
    * *_machine* - string describing the underlying machine
    * *_mpy* - supported mpy file-format version (optional attribute)
+   * *_build* - string that can help identify the configuration that
+     MicroPython was built with
 
    This object is the recommended way to distinguish MicroPython from other
    Python implementations (note that it still may not exist in the very
@@ -83,6 +85,16 @@ Constants
    Starting with version 1.22.0-preview, the fourth node *releaselevel* in
    *implementation.version* is either an empty string or ``"preview"``.
 
+   The *_build* entry was added in version 1.25.0 and is a hyphen-separated
+   set of elements.  New elements may be appended in the future so it's best to
+   access this field using ``sys.implementation._build.split("-")``.  The
+   elements that are currently used are:
+
+   * On the unix, webassembly and windows ports the first element is the variant
+     name, for example ``'standard'``.
+   * On microcontroller targets, the first element is the board name and the second
+     element (if present) is the board variant, for example ``'RPI_PICO2-RISCV'``
+
    .. admonition:: Difference to CPython
       :class: attention
 
diff --git a/py/mkrules.cmake b/py/mkrules.cmake
index 907500dd6..cafcbce56 100644
--- a/py/mkrules.cmake
+++ b/py/mkrules.cmake
@@ -19,6 +19,19 @@ if(NOT MICROPY_PREVIEW_VERSION_2)
     set(MICROPY_PREVIEW_VERSION_2 0)
 endif()
 
+# Set the board name.
+if(MICROPY_BOARD)
+    if(MICROPY_BOARD_VARIANT)
+        set(MICROPY_BOARD_BUILD_NAME ${MICROPY_BOARD}-${MICROPY_BOARD_VARIANT})
+    else()
+        set(MICROPY_BOARD_BUILD_NAME ${MICROPY_BOARD})
+    endif()
+
+    target_compile_definitions(${MICROPY_TARGET} PRIVATE
+        MICROPY_BOARD_BUILD_NAME="${MICROPY_BOARD_BUILD_NAME}"
+    )
+endif()
+
 # Need to do this before extracting MICROPY_CPP_DEF below. Rest of frozen
 # manifest handling is at the end of this file.
 if(MICROPY_FROZEN_MANIFEST)
diff --git a/py/mkrules.mk b/py/mkrules.mk
index e9504ce39..ad855c0d7 100644
--- a/py/mkrules.mk
+++ b/py/mkrules.mk
@@ -27,6 +27,17 @@ OBJ_EXTRA_ORDER_DEPS += $(HEADER_BUILD)/compressed.data.h
 CFLAGS += -DMICROPY_ROM_TEXT_COMPRESSION=1
 endif
 
+# Set the variant or board name.
+ifneq ($(VARIANT),)
+CFLAGS += -DMICROPY_BOARD_BUILD_NAME=\"$(VARIANT)\"
+else ifneq ($(BOARD),)
+ifeq ($(BOARD_VARIANT),)
+CFLAGS += -DMICROPY_BOARD_BUILD_NAME=\"$(BOARD)\"
+else
+CFLAGS += -DMICROPY_BOARD_BUILD_NAME=\"$(BOARD)-$(BOARD_VARIANT)\"
+endif
+endif
+
 # QSTR generation uses the same CFLAGS, with these modifications.
 QSTR_GEN_FLAGS = -DNO_QSTR
 # Note: := to force evaluation immediately.
diff --git a/py/modsys.c b/py/modsys.c
index e90ea2233..9ab02293b 100644
--- a/py/modsys.c
+++ b/py/modsys.c
@@ -92,6 +92,17 @@ static const MP_DEFINE_STR_OBJ(mp_sys_implementation_machine_obj, MICROPY_BANNER
 #endif
 
 #if MICROPY_PY_ATTRTUPLE
+
+#if defined(MICROPY_BOARD_BUILD_NAME)
+static const MP_DEFINE_STR_OBJ(mp_sys_implementation__build_obj, MICROPY_BOARD_BUILD_NAME);
+#define MICROPY_BOARD_BUILD (1)
+#define SYS_IMPLEMENTATION_ELEMS__BUILD \
+    , MP_ROM_PTR(&mp_sys_implementation__build_obj)
+#else
+#define MICROPY_BOARD_BUILD (0)
+#define SYS_IMPLEMENTATION_ELEMS__BUILD
+#endif
+
 #if MICROPY_PREVIEW_VERSION_2
 #define SYS_IMPLEMENTATION_ELEMS__V2 \
     , MP_ROM_TRUE
@@ -106,6 +117,9 @@ static const qstr impl_fields[] = {
     #if MICROPY_PERSISTENT_CODE_LOAD
     MP_QSTR__mpy,
     #endif
+    #if defined(MICROPY_BOARD_BUILD_NAME)
+    MP_QSTR__build,
+    #endif
     #if MICROPY_PREVIEW_VERSION_2
     MP_QSTR__v2,
     #endif
@@ -113,19 +127,20 @@ static const qstr impl_fields[] = {
 static MP_DEFINE_ATTRTUPLE(
     mp_sys_implementation_obj,
     impl_fields,
-    3 + MICROPY_PERSISTENT_CODE_LOAD + MICROPY_PREVIEW_VERSION_2,
+    3 + MICROPY_PERSISTENT_CODE_LOAD + MICROPY_BOARD_BUILD + MICROPY_PREVIEW_VERSION_2,
     SYS_IMPLEMENTATION_ELEMS_BASE
     SYS_IMPLEMENTATION_ELEMS__MPY
+    SYS_IMPLEMENTATION_ELEMS__BUILD
     SYS_IMPLEMENTATION_ELEMS__V2
     );
 #else
 static const mp_rom_obj_tuple_t mp_sys_implementation_obj = {
     {&mp_type_tuple},
     3 + MICROPY_PERSISTENT_CODE_LOAD,
-    // Do not include SYS_IMPLEMENTATION_ELEMS__V2 because
-    // SYS_IMPLEMENTATION_ELEMS__MPY may be empty if
+    // Do not include SYS_IMPLEMENTATION_ELEMS__BUILD or SYS_IMPLEMENTATION_ELEMS__V2
+    // because SYS_IMPLEMENTATION_ELEMS__MPY may be empty if
     // MICROPY_PERSISTENT_CODE_LOAD is disabled, which means they'll share
-    // the same index. Cannot query _v2 if MICROPY_PY_ATTRTUPLE is
+    // the same index. Cannot query _build or _v2 if MICROPY_PY_ATTRTUPLE is
     // disabled.
     {
         SYS_IMPLEMENTATION_ELEMS_BASE
diff --git a/tests/basics/sys1.py b/tests/basics/sys1.py
index 95d8905d1..94220fe4a 100644
--- a/tests/basics/sys1.py
+++ b/tests/basics/sys1.py
@@ -24,6 +24,12 @@ else:
     # Effectively skip subtests
     print(int)
 
+if hasattr(sys.implementation, '_build'):
+    print(type(sys.implementation._build))
+else:
+    # Effectively skip subtests
+    print(str)
+
 try:
     print(sys.intern('micropython') == 'micropython')
     has_intern = True