Demonstrates the usage of an extra script and a special compilter invocation to get the active macros in a file.

E.g., if you have a file project_config.h

#ifndef _PROJECT_CONFIG_H_
#define _PROJECT_CONFIG_H_

// select driver here
#define DRIVER_ILI9341 1
//#define DRIVER_ST7789 1

#endif /* _PROJECT_CONFIG_H_ */

And you want to check in an extra script which macro was active or not, this repo shows a way to do that.

The script uses primarily env.Execute() to execute the C++ compiler (stored in env.["CXX"]) with the regular build flags given by the environment and saves the output to a file.

xtensa-esp32-elf-g++ -DPLATFORMIO=50202 [..more macros..] -w -dM -E -x c++ "C:\Users\Max\temp\check_flags\src\project_config.h" > flags.txt

The file then contains all compiler-builtin macros and explicitly enabled macros.

#define __DBL_MIN_EXP__ (-1021)
#define __UINT_LEAST16_MAX__ 0xffff
#define __ATOMIC_ACQUIRE 2
#define __FLT_MIN__ 1.1754943508222875e-38F
#define __GCC_IEC_559_COMPLEX 0
#define PLATFORMIO 50202
[..]
#define DRIVER_ILI9341 1
#define __DEC128_MIN__ 1E-6143DL
[...]

The file is then read out line-by-line and put into a Python dictionary, the key being the macro name and the value being the macro name

The resulting dictionary can then be checked for the existance of a certain key, in the standard if "KEY_NAME" in macros: way.

The built-up command does not include any -I flags to the e.g. Arduino core, so the target header file musn't #include <Arduino.h>. There is commented-out code in the script to fix that in a brute-force way, that is, adds all items from env["CPPPATH"] as -I flags. However, this probably misses out on library includes if additional libararies are used.

It's best to keep the configuration header file as simple as possible, only defining the configuration macros in the most minimal way.

With the unmodified source code, one should get

check_for_flags(["buildprog"], [".pio\build\esp32dev\firmware.bin"])
AFTER build!!
xtensa-esp32-elf-g++ -DPLATFORMIO=50202 -DARDUINO_ESP32_DEV -DESP32 -DESP_PLATFORM -DF_CPU=\""240000000L\"" -DHAVE_CONFIG_H -DMBEDTLS_CONFIG_FILE=\""mbedtls/esp_config.h\"" -DARDUINO=10805 -DARDUINO_ARCH_ESP32 -DARDUINO_VARIANT=\""esp32\"" -DARDUINO_BOARD=\""Espressif ESP32 Dev Module\"" -w -dM -E -x c++ "C:\Users\Max\temp\check_flags\src\project_config.h" > flags.txt
Parsed a total of 239 defines (explicit and implicitly set).
DRIVER_ILI9341 was defined!! With value: 1
echo Super special command here....
Super special command here....

At the end, showcasing that it was successfully detected that the DRIVER_ILI9341 macro was defined (and also to which value it was defined).

Copy the check_flags.py into the project and add it to the extra_scripts expression of your platformio.ini.

Adapt the logic in check_flags.py regarding the read-out file and the reaction to it accordingly.

extra_scripts =
   check_flags.py