Port, board and/or hardware

N/A

MicroPython version

N/A, master

Reproduction

If you succeed in building a CMake port of MicroPython (ie: a dynamic library built with CMake from the embed port leveraging the existing cmake tooling) then setting no compiler definitions on ${MICROPY_TARGET} will result in this line of mkrules.cmake failing back to a "NOTFOUND" state:

get_target_property(MICROPY_CPP_DEF ${MICROPY_TARGET} COMPILE_DEFINITIONS)

This then pollutes the build and results in a stream of errors:

1 warning generated.
1 warning generated.
In file included from <built-in>:418:
<command line>:1:24: warning: ISO C99 requires whitespace after the macro name [-Wc99-extensions]
#define MICROPY_CPP_DEF-NOTFOUND 1

Setting any definitions fixes this, eg:

target_compile_definitions(${MICROPY_TARGET} PRIVATE DUMMY)

This is an extremely rare occurrence that involves monkeying around with MicroPython tooling while trying to bring up a CMake-ified embed port, but I'm raising it here for posterity.

It may be worthwhile adding a check for ${MICROPY_CPP_DEF} STREQUAL "MICROPY_CPP_DEF-NOTFOUND" and skipping the loop that appends MICROPY_CPP_FLAGS.

Code of Conduct

Yes, I agree