Installing ArduinoJson made the project stop compiling, with an error that
never mentioned ArduinoJson:
CMake Error at user_libs/user_libs_all/CMakeLists.txt:15
(target_compile_definitions):
target_compile_definitions may only set INTERFACE properties on
INTERFACE targets
-- Configuring incomplete, errors occurred!
ArduinoJson ships headers only. With no sources, idf_component_register()
builds the merged user-libs component as an INTERFACE library, and PRIVATE
scope on an INTERFACE target is a hard CMake error - so the configure step
died before a single file was compiled. The user saw only a failing build
and reported it as "ArduinoJson can't be found even after it has been
installed" (#124).
Those definitions map alloca/memcpy_P/memcmp_P for library C sources that
use them undeclared; with no sources there is nothing to define, so they are
emitted only when the component actually compiles something. A library that
carries its own .cpp is unchanged - which is why LiquidCrystal_I2C (#257)
worked and hid this.
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