Checks

• I agree to follow the MicroPython Code of Conduct to ensure a safe and respectful space for everyone.
• I've searched for existing issues matching this bug, and didn't find any.

Port, board and/or hardware

nrf port, tested with default PCA10040 board and MICROBIT board

MicroPython version

8762fe8b4c6a7608d48daa8458e6501fafd3eafc

Reproduction

git clone https://github.com/micropython/micropython.git
cd micropython/mpy-cross/
make
cd ../ports/nrf
make submodules
make USER_C_MODULES=../../examples/usercmodule

Expected behaviour

No build errors

Observed behaviour

The modules are correctly found:

Including User C Module from ../../examples/usercmodule/cexample
Including User C Module from ../../examples/usercmodule/cppexample
Including User C Module from ../../examples/usercmodule/subpackage

But it produces a build error on the cppexample/example.cpp file as it cannot find py/runtime.h:

In file included from ../../examples/usercmodule/cppexample/example.cpp:2:
../../examples/usercmodule/cppexample/examplemodule.h:2:10: fatal error: py/runtime.h: No such file or directory
    2 | #include "py/runtime.h"
      |          ^~~~~~~~~~~~~~
compilation terminated.
Command '['arm-none-eabi-gcc', '-E', '-I../../examples/usercmodule/cppexample', '-std=c++11', '-DNO_QSTR', '../../examples/usercmodule/cppexample/example.cpp']' returned non-zero exit status 1.
make: *** [build-PCA10040/genhdr/qstr.i.last] Error 1
make: *** Deleting file `build-PCA10040/genhdr/qstr.i.last'

Looking at the limited amount of flags used to compile the file something in the nrf port could be resetting CXXFLAGS? Or maybe they are not being set at all?

<details>
<summary>Full build output</summary>

<pre>

❯ git clone https://github.com/micropython/micropython.git
Cloning into 'micropython'...
remote: Enumerating objects: 120730, done.
remote: Counting objects: 100% (64/64), done.
remote: Compressing objects: 100% (33/33), done.
remote: Total 120730 (delta 31), reused 51 (delta 30), pack-reused 120666
Receiving objects: 100% (120730/120730), 61.44 MiB | 30.37 MiB/s, done.
Resolving deltas: 100% (90584/90584), done.

❯ cd micropython/mpy-cross/

❯ make
Use make V=1 or set BUILD_VERBOSE in your environment to increase build verbosity.
mkdir -p build/genhdr
GEN build/genhdr/mpversion.h
GEN build/genhdr/qstr.i.last
GEN build/genhdr/qstr.split
GEN build/genhdr/qstrdefs.collected.h
QSTR updated
GEN build/genhdr/qstrdefs.generated.h
GEN build/genhdr/moduledefs.split
GEN build/genhdr/moduledefs.collected
Module registrations updated
GEN build/genhdr/moduledefs.h
GEN build/genhdr/root_pointers.split
GEN build/genhdr/root_pointers.collected
Root pointer registrations updated
GEN build/genhdr/root_pointers.h
mkdir -p build/py
mkdir -p build/shared/runtime
CC ../py/mpstate.c
CC ../py/nlr.c
CC ../py/nlrx86.c
CC ../py/nlrx64.c
CC ../py/nlrthumb.c
CC ../py/nlraarch64.c
CC ../py/nlrmips.c
CC ../py/nlrpowerpc.c
CC ../py/nlrxtensa.c
CC ../py/nlrsetjmp.c
CC ../py/malloc.c
CC ../py/gc.c
CC ../py/pystack.c
CC ../py/qstr.c
CC ../py/vstr.c
CC ../py/mpprint.c
CC ../py/unicode.c
CC ../py/mpz.c
CC ../py/reader.c
CC ../py/lexer.c
CC ../py/parse.c
CC ../py/scope.c
CC ../py/compile.c
CC ../py/emitcommon.c
CC ../py/emitbc.c
CC ../py/asmbase.c
CC ../py/asmx64.c
CC ../py/emitnx64.c
CC ../py/asmx86.c
CC ../py/emitnx86.c
CC ../py/asmthumb.c
CC ../py/emitnthumb.c
CC ../py/emitinlinethumb.c
CC ../py/asmarm.c
CC ../py/emitnarm.c
CC ../py/asmxtensa.c
CC ../py/emitnxtensa.c
CC ../py/emitinlinextensa.c
CC ../py/emitnxtensawin.c
CC ../py/formatfloat.c
CC ../py/parsenumbase.c
CC ../py/parsenum.c
CC ../py/emitglue.c
CC ../py/persistentcode.c
CC ../py/runtime.c
CC ../py/runtime_utils.c
CC ../py/scheduler.c
CC ../py/nativeglue.c
CC ../py/pairheap.c
CC ../py/ringbuf.c
CC ../py/stackctrl.c
CC ../py/argcheck.c
CC ../py/warning.c
CC ../py/profile.c
CC ../py/map.c
CC ../py/obj.c
CC ../py/objarray.c
CC ../py/objattrtuple.c
CC ../py/objbool.c
CC ../py/objboundmeth.c
CC ../py/objcell.c
CC ../py/objclosure.c
CC ../py/objcomplex.c
CC ../py/objdeque.c
CC ../py/objdict.c
CC ../py/objenumerate.c
CC ../py/objexcept.c
CC ../py/objfilter.c
CC ../py/objfloat.c
CC ../py/objfun.c
CC ../py/objgenerator.c
CC ../py/objgetitemiter.c
CC ../py/objint.c
CC ../py/objint_longlong.c
CC ../py/objint_mpz.c
CC ../py/objlist.c
CC ../py/objmap.c
CC ../py/objmodule.c
CC ../py/objobject.c
CC ../py/objpolyiter.c
CC ../py/objproperty.c
CC ../py/objnone.c
CC ../py/objnamedtuple.c
CC ../py/objrange.c
CC ../py/objreversed.c
CC ../py/objset.c
CC ../py/objsingleton.c
CC ../py/objslice.c
CC ../py/objstr.c
CC ../py/objstrunicode.c
CC ../py/objstringio.c
CC ../py/objtuple.c
CC ../py/objtype.c
CC ../py/objzip.c
CC ../py/opmethods.c
CC ../py/sequence.c
CC ../py/stream.c
CC ../py/binary.c
CC ../py/builtinimport.c
CC ../py/builtinevex.c
CC ../py/builtinhelp.c
CC ../py/modarray.c
CC ../py/modbuiltins.c
CC ../py/modcollections.c
CC ../py/modgc.c
CC ../py/modio.c
CC ../py/modmath.c
CC ../py/modcmath.c
CC ../py/modmicropython.c
CC ../py/modstruct.c
CC ../py/modsys.c
CC ../py/moderrno.c
CC ../py/modthread.c
CC ../py/vm.c
CC ../py/bc.c
CC ../py/showbc.c
CC ../py/repl.c
CC ../py/smallint.c
CC ../py/frozenmod.c
CC main.c
CC gccollect.c
CC ../shared/runtime/gchelper_generic.c
LINK build/mpy-cross
__TEXT __DATA __OBJC others dec hex
327680 16384 0 4295000928 4295344992 10005c360

❯ cd ../ports/nrf

❯ make submodules
Use make V=1 or set BUILD_VERBOSE in your environment to increase build verbosity.
Updating submodules: lib/nrfx lib/tinyusb lib/micropython-lib
Submodule 'lib/micropython-lib' (https://github.com/micropython/micropython-lib.git) registered for path '../../lib/micropython-lib'
Submodule 'lib/nrfx' (https://github.com/NordicSemiconductor/nrfx.git) registered for path '../../lib/nrfx'
Submodule 'lib/tinyusb' (https://github.com/hathach/tinyusb) registered for path '../../lib/tinyusb'
Cloning into '/Users/microbit-carlos/workspace/mbef/micropython/rm/micropython/lib/micropython-lib'...
Cloning into '/Users/microbit-carlos/workspace/mbef/micropython/rm/micropython/lib/nrfx'...
Cloning into '/Users/microbit-carlos/workspace/mbef/micropython/rm/micropython/lib/tinyusb'...
Submodule path '../../lib/micropython-lib': checked out 'ddb1a279578bfff8c1b18aff3baa668620684f64'
Submodule path '../../lib/nrfx': checked out '7a4c9d946cf1801771fc180acdbf7b878f270093'
Submodule path '../../lib/tinyusb': checked out '1fdf29075d4e613eacfa881166015263797db0f6'

❯ make USER_C_MODULES=../../examples/usercmodule
Use make V=1 or set BUILD_VERBOSE in your environment to increase build verbosity.
Including User C Module from ../../examples/usercmodule/cexample
Including User C Module from ../../examples/usercmodule/cppexample
Including User C Module from ../../examples/usercmodule/subpackage
mkdir -p build-PCA10040/genhdr
Create build-PCA10040/genhdr/pins.h
GEN build-PCA10040/genhdr/mpversion.h
GEN build-PCA10040/genhdr/qstr.i.last
In file included from ../../examples/usercmodule/cppexample/example.cpp:2:
../../examples/usercmodule/cppexample/examplemodule.h:2:10: fatal error: py/runtime.h: No such file or directory
2 | #include "py/runtime.h"
| ^~~~~~~~~~~~~~
compilation terminated.
Command '['arm-none-eabi-gcc', '-E', '-I../../examples/usercmodule/cppexample', '-std=c++11', '-DNO_QSTR', '../../examples/usercmodule/cppexample/example.cpp']' returned non-zero exit status 1.
make: *** [build-PCA10040/genhdr/qstr.i.last] Error 1
make: *** Deleting file `build-PCA10040/genhdr/qstr.i.last'
</pre>

</details>

Additional Information

Also tested the MICROBIT board and produces the same error.

Building the c module examples in the Unix port or the PYBV11 board does build correctly.