I don't think that is a good idea I overcame that by simply declaring all the string in progmem.h and then just reused them across the firmware there is no need to make constants per each file by wrapping in a modified F() with a counter when you can have them all in one place and just reuse across

Uniqueness is not a problem for debug messages though, which is what this solves:
dev...mcspr:travis-progmem-test
https://travis-ci.org/mcspr/espurna/jobs/460520688#L526 changes DEBUG_MSG -> DEBUG_MSG_P when SENSOR_DEBUG is enabled and builds ok
https://travis-ci.org/mcspr/espurna/jobs/460524020#L546 same as above, but without the unique section attr

edit: links

@mcspr for the first link the warnings are telling you that comparing a const == a & b is not safe and you should use const == (a & b) if that was what caught you attention
for the second it's a legit thing when you are using F() in classes and that is solved the way I've described above

@Valcob your suggestion is to move all progmem strings in the code to a separate file? It makes sense to save size for those strings used multiple times and there are some of those. But it also requires some major refactoring.

In the meantime @mcspr changes go in the line of the Arduino Core for ESP8266 project. I would add a check to only apply them if < 2.5.0

Just for reference:
Change included here: esp8266/Arduino#5048
Current code here: https://github.com/esp8266/Arduino/blob/master/tools/sdk/libc/xtensa-lx106-elf/include/sys/pgmspace.h

Added comments + defguards.

Have been wondering about PSTR comment from the link above. Testing size, can be removed if it is noticeable.

@mcspr is there any alternative for debugging inside sensor classes while this isn't merged?

DEBUG_MSG should work ok (as all SENSOR_DEBUG parts are using it)
Does this patch work ok though?