Can still be enabled by passing --cmake-warn-uninitialized on the command line
Prevents CMake warnings printed by default if IDF_PATH is underneath the CMake
project directory.
The reason for this is that CMake --warn-uninitialized only enables checks
inside the project directory (ie top-level CMakeLists.txt directory and
subdirectories), it doesn't enable for files included from other directories.
(The only way to enable warnings in other directories is to pass
--check-system-dirs and this looks like it's only useful for CMake's own
developers as it prints a lot of warnings from inside CMake otherwise - see
https://gitlab.kitware.com/cmake/cmake/-/issues/19645 )
Plan to follow up with a later commit to clean up most of the warnings (which
aren't problems for CMake execution), but we'll also disable this option by
default to avoid this unexpected triggering of IDF warnings.
This solves the issue that target is changed to the default one after
idf.py fullclean.
Also allow setting the default target using sdkconfig.defaults, e.g.
CONFIG_IDF_TARGET="esp32s2"
Closes IDF-1040
Python 2 expect the environ variables are all of type 'str', but
sometimes wrong 'unicode' type is given.
Here we force all variables that are not str to become str.
