error: a15 cannot be used in asm here

[Tony763]

Hello, I have a problem compiling deserializeJson example in PlatformIO and Espressif 8266 (2.6.2).

Code is placed in function called from class function:

StaticJsonDocument<200> doc_in;
DeserializationError error = deserializeJson(doc_in, msgch);

if (error) {
    Serial.print(F("deserializeJson() failed: "));
    Serial.println(error.f_str());
    return;
}

Above code gives me error error: a15 cannot be used in asm here.

Problem is with use of error.f_str() as error.c_str()) works.

As discussed in ArduinoJson Issue Tracker it seems to be related to arduino core. At first I think that PlatformIO do not use latest version of Arduino Core but I just found that version is same as latest 3.20704.0 (2.7.4) so there must be other other issue as in ArduinoIDE it works.

Maybe related to #242, but I can't tell.