Compile error under 2.0.8 if library function explicitly returns const __FlashStringHelper * from F() macro

[avillacis]

Board

ESP32

Device Description

YUBOX-Node

Hardware Configuration

No special hardware configuration needed.

Version

v2.0.8

IDE Name

Arduino IDE 2.1.0

Operating System

Fedora Linux 38 x86_64

Flash frequency

80MHz

PSRAM enabled

no

Upload speed

115200

Description

After updating to Arduino-ESP32 2.0.8, the attached sketch will no longer compile, and displays the following error messages:

In file included from /home/alex/.arduino15/packages/esp32-alternatives/2.0.8/hardware/esp32/2.0.8/cores/esp32/Arduino.h:176,
                 from /home/alex/programa/practica/arduino/esp32/test-bug-compile-fail-flashstringhelper/test-bug-compile-fail-flashstringhelper.ino:1:
/home/alex/programa/practica/arduino/esp32/test-bug-compile-fail-flashstringhelper/test-bug-compile-fail-flashstringhelper.ino: In function 'const __FlashStringHelper* testfunc()':
/home/alex/.arduino15/packages/esp32-alternatives/2.0.8/hardware/esp32/2.0.8/cores/esp32/WString.h:38:42: error: cannot convert 'const char*' to 'const __FlashStringHelper*' in return
 #define F(string_literal) (string_literal)
                                          ^
/home/alex/programa/practica/arduino/esp32/test-bug-compile-fail-flashstringhelper/test-bug-compile-fail-flashstringhelper.ino:5:10: note: in expansion of macro 'F'
   return F("test");
          ^

exit status 1

Compilation error: exit status 1

The same sketch compiles correctly under previous 2.0.7.

Sketch

#include <Arduino.h>

const __FlashStringHelper * testfunc(void)
{
  return F("test");
}

void setup() {
  // put your setup code here, to run once:

}

void loop() {
  // put your main code here, to run repeatedly:
  delay(1000);
}

Debug Message

In file included from /home/alex/.arduino15/packages/esp32-alternatives/2.0.8/hardware/esp32/2.0.8/cores/esp32/Arduino.h:176,
                 from /home/alex/programa/practica/arduino/esp32/test-bug-compile-fail-flashstringhelper/test-bug-compile-fail-flashstringhelper.ino:1:
/home/alex/programa/practica/arduino/esp32/test-bug-compile-fail-flashstringhelper/test-bug-compile-fail-flashstringhelper.ino: In function 'const __FlashStringHelper* testfunc()':
/home/alex/.arduino15/packages/esp32-alternatives/2.0.8/hardware/esp32/2.0.8/cores/esp32/WString.h:38:42: error: cannot convert 'const char*' to 'const __FlashStringHelper*' in return
 #define F(string_literal) (string_literal)
                                          ^
/home/alex/programa/practica/arduino/esp32/test-bug-compile-fail-flashstringhelper/test-bug-compile-fail-flashstringhelper.ino:5:10: note: in expansion of macro 'F'
   return F("test");
          ^

exit status 1

Compilation error: exit status 1

Other Steps to Reproduce

No response

I have checked existing issues, online documentation and the Troubleshooting Guide

• I confirm I have checked existing issues, online documentation and Troubleshooting guide.

[avillacis]

Forgot to mention: although the sketch shown above does not explicitly need the F() macro, several libraries available through the Arduino IDE library manager do use this pattern internally. I was bitten by this issue when trying to compile a project using the ESPAsyncWebServer library.

[avillacis]

Apparently the breaking change was introduced in b98255d .

[me-no-dev]

@dok-net any comments? Please take some action or we will need to revert your PR

[dok-net]

@me-no-dev Now people start calling the fix a bug... #7940 details how there is an inconsistency in this core's libraries, on the other hand. Do we want to add __FlashStringHelper wrappers to all ESP32 libs that don't use it now, because it is redundant on ESP32, then? It seems like a lot of work for nothing. This has just been left to rot for far too long, it seems?

[dok-net]

Anyway, here's a PR #8111 to fix what originally got in my way.

[tueddy]

Same problem compiling this popular RFID lib with 2.0.8:
https://github.com/miguelbalboa/rfid

[dok-net]

@tueddy RFID lib (I used the example ReadUidMultiReader.ino) also fixed by #8111.

[ryancasler]

Same problem here with the WS2812FX Library too.

In file included from C:\Users\ryanc\AppData\Local\Arduino15\packages\esp32\hardware\esp32\2.0.8\cores\esp32/Arduino.h:176,
                 from c:\Users\ryanc\Documents\Arduino\libraries\Adafruit_NeoPixel/Adafruit_NeoPixel.h:41,
                 from c:\Users\ryanc\Documents\Arduino\libraries\WS2812FX\src\WS2812FX.h:43,
                 from c:\Users\ryanc\Documents\Arduino\libraries\WS2812FX\src\WS2812FX.cpp:55:
c:\Users\ryanc\Documents\Arduino\libraries\WS2812FX\src\WS2812FX.cpp: In member function 'const __FlashStringHelper* WS2812FX::getModeName(uint8_t)':
C:\Users\ryanc\AppData\Local\Arduino15\packages\esp32\hardware\esp32\2.0.8\cores\esp32/WString.h:38:42: error: cannot convert 'const char*' to 'const __FlashStringHelper*' in return
 #define F(string_literal) (string_literal)
                                          ^
c:\Users\ryanc\Documents\Arduino\libraries\WS2812FX\src\WS2812FX.cpp:404:12: note: in expansion of macro 'F'
     return F("");
            ^
Multiple libraries were found for "WiFi.h"
  Used: C:\Users\ryanc\AppData\Local\Arduino15\packages\esp32\hardware\esp32\2.0.8\libraries\WiFi
  Not used: C:\Users\ryanc\Documents\Arduino\libraries\WiFiEspAT
  Not used: C:\Users\ryanc\Documents\Arduino\libraries\WiFiNINA
exit status 1

Compilation error: exit status 1

[me-no-dev]

@P-R-O-C-H-Y can you please add those libs and examples to the CI? Let's see what will fix it for them

[zekageri]

So how to fix it while we are waiting for the release?

[P-R-O-C-H-Y]

@zekageri You have to apply fix from PR #8147 manually until we release 2.0.9

[zekageri]

Thanks, i did copy these two lines

#define FPSTR(pstr_pointer) (reinterpret_cast<const __FlashStringHelper *>(pstr_pointer))
#define F(string_literal) (FPSTR(PSTR(string_literal)))

to my project and it fixed it. ( with a lot of prev def warning ) Thanks!