ESPIDF : C++ standard issue when compiling

[martinroger]

Hi,

Apologies in advance if this is a dumb one, as I am just getting in the process of trying to migrate from using pioarduino to ESP-IDF + VSCode. This might be a dumb and obvious one but I cannot really find anything else similar.

Context :

• ESP-IDF v5.4.2 fresh install + related esp-tools
• Updated VSCode
• Windows 11

I initially started an empty project with ESP-IDF and added ESP32_Display_Panel as a component, without editing the app_main. Upon compilation, I was hit by a bunch of C++ compilation standard errors that seemed to span from esp-lib-utils to esp32_display_panel such as:

...

C:/Users/Martin/Documents/GitHub/ESP32_Display_Panel/examples/esp_idf/lvgl_v8_port/managed_components/espressif__esp-lib-utils/src/log/esp_utils_log.hpp:28:20: error: defaulted 'constexpr bool esp_utils::detail::FixedString<N>::operator==(const esp_utils::detail::FixedString<N>&) const' only available with '-std=c++20' or '-std=gnu++20'
   28 |     constexpr bool operator==(const FixedString &) const = default;
      |                    ^~~~~~~~
C:/Users/Martin/Documents/GitHub/ESP32_Display_Panel/examples/esp_idf/lvgl_v8_port/managed_components/espressif__esp-lib-utils/src/log/esp_utils_log.hpp:50:22: error: non-type template parameters of deduced class type only available with '-std=c++20' or '-std=gnu++20'
   50 | template<FixedString file, int line, FixedString func>
      |                      ^~~~
C:/Users/Martin/Documents/GitHub/ESP32_Display_Panel/examples/esp_idf/lvgl_v8_port/managed_components/espressif__esp-lib-utils/src/log/esp_utils_log.hpp:50:50: error: non-type template parameters of deduced class type only available with '-std=c++20' or '-std=gnu++20'
   50 | template<FixedString file, int line, FixedString func>
      |                                                  ^~~~
ninja: build stopped: subcommand failed.

I thought it might be my dodgy empty template or something escaping my understanding, so I tried to re-compile the lvgl_v8_port ESP-IDF example from the repository. After checking that everything was fairly aligned with menuconfig, the compilation failed again with the same error messages.

I googled a bit and stumbled upon this section of the ESP32 documentation that specifies that the normal compilation standard for this version of the IDF should at least be C++23, which puzzled me even further.

Being confused, I went and edited the CMakeLists.txt file of esp-lib-utils, adding -std=gnu++20 to the target_compile_options section, and despite throwing a lot of warning it seems to successfully compile (I have not tested the functionality of the firmware though):

set(SRC_DIR ./src)
file(GLOB_RECURSE SRCS_C ${SRC_DIR}/*.c)
file(GLOB_RECURSE SRCS_CPP ${SRC_DIR}/*.cpp)

if(ESP_PLATFORM)
    idf_component_register(
        SRCS ${SRCS_C} ${SRCS_CPP}
        INCLUDE_DIRS ${SRC_DIR}
        PRIV_REQUIRES pthread
    )
else()
    set(COMPONENT_LIB esp-lib-utils)
    add_library(${COMPONENT_LIB} STATIC ${SRCS_C} ${SRCS_CPP})
    target_include_directories(${COMPONENT_LIB} PUBLIC ${SRC_DIR})
endif()

target_compile_options(${COMPONENT_LIB}
    PUBLIC
        -Wno-missing-field-initializers
        -std=gnu++20
)

if(NOT ESP_PLATFORM)
    target_compile_definitions(${COMPONENT_LIB} PUBLIC ESP_UTILS_KCONFIG_IGNORE)
endif()

So the question is : is this a bug, or have I missed something ?
I also tried this on Debian on a different machine, and I had the same compilation issue.

[james-l-key]

I'm encountering the same issue. I attempted to enable cxx exceptions as the documentation mentions in passing that these are enabled by default for Arduino.

Didn't help, not that I'm trying to use any Arduino libraries directly. This component is a dependency of the esp32_io_expander which is a dependency of eap32_display_panel.

[APF-MRoger]

I'm encountering the same issue. I attempted to enable cxx exceptions as the documentation mentions in passing that these are enabled by default for Arduino.

Didn't help, not that I'm trying to use any Arduino libraries directly. This component is a dependency of the esp32_io_expander which is a dependency of eap32_display_panel.

Hi @james-l-key , CXX Exceptions are for runtime, not for compilation time as far as I understood.

You can try a workaround while the pull request is ongoing on the dependency repository :

• do a full clean of your ESP-IDF project
• do idf.py reconfigure so it downloads the managed_components folder content
• in the managed_components folder, open the espressif__esp-lib-utils folder
• open CMakeLists.txt and add the line $<$<COMPILE_LANGUAGE:CXX>:-std=gnu++20> so it looks like that :

set(SRC_DIR ./src)
file(GLOB_RECURSE SRCS_C ${SRC_DIR}/*.c)
file(GLOB_RECURSE SRCS_CPP ${SRC_DIR}/*.cpp)

if(ESP_PLATFORM)
    idf_component_register(
        SRCS ${SRCS_C} ${SRCS_CPP}
        INCLUDE_DIRS ${SRC_DIR}
        PRIV_REQUIRES pthread
    )
else()
    set(COMPONENT_LIB esp-lib-utils)
    add_library(${COMPONENT_LIB} STATIC ${SRCS_C} ${SRCS_CPP})
    target_include_directories(${COMPONENT_LIB} PUBLIC ${SRC_DIR})
endif()

target_compile_options(${COMPONENT_LIB}
    PUBLIC
        -Wno-missing-field-initializers
        $<$<COMPILE_LANGUAGE:CXX>:-std=gnu++20>
)

if(NOT ESP_PLATFORM)
    target_compile_definitions(${COMPONENT_LIB} PUBLIC ESP_UTILS_KCONFIG_IGNORE)
endif()

Note that every time you update or fully clean your project, you will have to do this until the pull request on the lib utils repository goes through or another fix is brought...

[james-l-key]

I'll give that a try. I figured that might be a solution. But I was reluctant to go that way as I was hoping for a more elegant fix.

Thank you for the response!

[martinroger]

I'll give that a try. I figured that might be a solution. But I was reluctant to go that way as I was hoping for a more elegant fix.

Thank you for the response!

Ultimately if the PR is accepted it should be fairly easy... But @Lzw655 seems to have been away for a while, so it might not be quick. If you don't do full cleans of the build folder often, you don't need to do the workaround very often!

[Lzw655]

Hi guys,

Sorry for the late. Recently, I've been busy with something urgent.

@martinroger @APF-MRoger Thank you very much for helping identify this issue! I'll incorporate the changes right away.

[martinroger]

Can be closed with esp-arduino-libs/esp-lib-utils#14

[martinroger]

@james-l-key v0.2.3 of the esp-lib-utils is out, just tested on my projects and it's good. Run 'idf.py update-dependencies' and off you go ! Issue closed.