Compilation error for ESP8266 using PlatformIO ESP8266 platform 4.1.0 (latest)

[Blaž Kristan]

Describe the bug
When compiling for ESP8266 using PlatformIO (with latest platform v4.1.0) errors are displayed and compile fails.

.pio/libdeps/d1_mini_custom_debug/NeoPixelBus/src/internal/NeoEsp8266DmaMethod.h:214:29: error: expected unqualified-id before '[' token
     NeoEsp8266DmaMethodBase([[maybe_unused]] uint8_t pin, uint16_t pixelCount, size_t elementSize, size_t settingsSize) : 
                             ^
.pio/libdeps/d1_mini_custom_debug/NeoPixelBus/src/internal/NeoEsp8266DmaMethod.h:214:29: error: expected ')' before '[' token

.pio/libdeps/d1_mini_custom_debug/NeoPixelBus/src/internal/NeoEsp8266I2sDmx512Method.h:161:35: error: expected unqualified-id before '[' token
     NeoEsp8266I2sDmx512MethodBase([[maybe_unused]] uint8_t pin, uint16_t pixelCount, size_t elementSize, size_t settingsSize) : 
                                   ^
.pio/libdeps/d1_mini_custom_debug/NeoPixelBus/src/internal/NeoEsp8266I2sDmx512Method.h:161:35: error: expected ')' before '[' token

The problem lies in NeoEsp8266DmaMethod.h and NeoEsp8266I2sDmx512Method.h with compiler directive [[maybe_unused]] which does not compile for some odd reason.
Commenting out those 2 directives resolves the issue.

To Reproduce
try to compile sample code

Expected behavior
No errors during compilation.

Development environment (please complete the following information):

• OS: [macOS 10.14]
• Build Environment [PlatformIO 6.1.6]
• Board target [ESP8266 v4.1.0]
• Library version [v2.7.3]

Minimal Sketch that reproduced the problem:

NeoPixelBrightnessBus<NeoGrbFeature, NeoEsp8266Dma800KbpsMethod> *busPtr = new NeoPixelBrightnessBus<NeoGrbFeature, NeoEsp8266Dma800KbpsMethod>(len, pin);

Additional context
Above sample code from WLED bus_wrapper.h.

[Frank]

At least in the "gcc world", there would be an alternative:
__attribute__((unused)) or [[gnu::unused]]

https://gcc.gnu.org/onlinedocs/gcc-10.4.0/gcc/Attribute-Syntax.html#Attribute-Syntax

Another option could be to create a macro like MAYBE_UNUSED, which is either empty, or defined as the keyword that is supported by the compiler.

[Michael Miller]

GCC does support [[maybe_unused]].

I believe this is due to the older compiler you are using or a compile flag that states to use older rules.
The latest Arduino board support for ESP8266 does not have this issue. (-std=gnu17)

Why are you not trying to fix your build environment?

[Blaž Kristan]

I am using PlatformIO 6.1.6 (+VSC) using supplied ESP8266 platform 4.1.0 using the following build flags:

build_flags =
  -DMQTT_MAX_PACKET_SIZE=1024
  -DSECURE_CLIENT=SECURE_CLIENT_BEARSSL
  -DBEARSSL_SSL_BASIC
  -D CORE_DEBUG_LEVEL=0
  -D NDEBUG
  #build_flags for the IRremoteESP8266 library (enabled decoders have to appear here)
  -D _IR_ENABLE_DEFAULT_=false
  -D DECODE_HASH=true
  -D DECODE_NEC=true
  -D DECODE_SONY=true
  -D DECODE_SAMSUNG=true
  -D DECODE_LG=true
  -DWLED_USE_MY_CONFIG
  -DESP8266
  -DFP_IN_IROM
  -DPIO_FRAMEWORK_ARDUINO_ESPRESSIF_SDK22x_190703
  -DPIO_FRAMEWORK_ARDUINO_LWIP_HIGHER_BANDWIDTH
  -DVTABLES_IN_FLASH
  -DMIMETYPE_MINIMAL

So no special compiler specific build flags and it will not compile.

I would appreciate any hint on how to fix it myself (other than forking and removing [[maybe_unused]]). I did not manipulate default installation in any way.

[Michael Miller]

try adding

-std=gnu17

this is what the Arduino builds use.

[Blaž Kristan]

Thank you. Will try it ASAP.

[Michael Miller]

also found a similiar flag

-std=gnu++17

[Oliver Westermann]

Hey,

since I searched way too long to "just use c17", here is a link for whoever else struggles:

https://community.platformio.org/t/how-to-use-c-17-with-esp8266/18950/6

Short form to solve this for me:

# https://github.com/Makuna/NeoPixelBus/issues/649
platform = espressif8266
board = nodemcuv2
platform_packages = 
    toolchain-xtensa@>=2.100300.220621
    framework-arduinoespressif8266 @ https://github.com/esp8266/Arduino.git

[Blaž Kristan]

I have now thoroughly tested compiling with PlatformIO platform = espressif8266@4.1.0 with

platform_packages = platformio/framework-arduinoespressif8266 ;latest
                    platformio/toolchain-xtensa ;@2.100300.220621
                    platformio/tool-esptool
                    platformio/tool-esptoolpy

And can report that compiling NeoPixelBus v2.7.0 or above compiles without major issues.
I am closing this issue as it appears latest platform and toolchain resolves compiling.