constexpr is invalid on is2D()

[scourge411]

The WLED_DISABLE_2D build flag fails to compile, because the is2D() member of the Segment is not a literal type:

In file included from wled00/fcn_declare.h:222:0,
    from wled00/wled.h:189,
    from wled00/FX.cpp:13:
     wled00/FX.h:714:27: error: 
     enclosing class of constexpr non-static member function 'bool Segment::is2D() const' is not a literal type
             inline constexpr bool is2D() const                                            { return false; }
                                  ^
In file included from wled00/fcn_declare.h:222:0,
    from wled00/wled.h:189,
    from wled00/FX.cpp:13:
        wled00/FX.h:361:16: note: 'Segment' is not literal because:
                 typedef struct Segment {
                                ^
wled00/FX.h:361:16: note:   'Segment' has a non-trivial destructor

Removing the constexpr allows it to compile

[DedeHai]

compiles fine for me. what version and what env?

[scourge411]

Not sure what you need for env; let me know if you need more. Basically running vsode/platformIO on the current tip of main, only change is adding the -D WLED_DISABLE_2D flag to the esp32dev config and building:

vscode 1.97
platformio: 6.1.16

(3.11.4) scourge411@ubuntu:~/WLED (main)$ git branch
* main

(3.11.4) scourge411@ubuntu:~/WLED (main)$ git log | head -5
commit 8c717537c489aae54c0f03091efc44fd6db0965e
Author: Blaž Kristan <blaz@kristan-sp.si>
Date:   Thu Feb 6 15:12:04 2025 +0100

    Lambda XY()

(3.11.4) scourge411@ubuntu:~/WLED (main)$ git st
## main...origin/main
 M platformio.ini

(3.11.4) scourge411@ubuntu:~/WLED (main)$ git diff platformio.ini
diff --git a/platformio.ini b/platformio.ini
index e775c61f..0534ad03 100644
--- a/platformio.ini
+++ b/platformio.ini

@@ -436,7 +437,7 @@ platform = ${esp32.platform}
 platform_packages = ${esp32.platform_packages}
 build_unflags = ${common.build_unflags}
 build_flags = ${common.build_flags} ${esp32.build_flags} -D WLED_RELEASE_NAME=\"ESP32\" #-D WLED_DISABLE_BROWNOUT_DET
-  ${esp32.AR_build_flags}
+  ${esp32.AR_build_flags} -D WLED_DISABLE_2D
 lib_deps = ${esp32.lib_deps}
   ${esp32.AR_lib_deps}
 monitor_filters = esp32_exception_decoder

(3.11.4) scourge411@ubuntu:~/WLED (main)$ npm --loglevel error  --no-fund --no-audit install
added 238 packages in 3s

(3.11.4) scourge411@ubuntu:~/WLED (main)$ platformio run --environment esp32dev 
Processing esp32dev (board: esp32dev; platform: espressif32@3.5.0; framework: arduino)
-----------------------------------------------------------------------------------------------------------------
Verbose mode can be enabled via `-v, --verbose` option
*** use existing my_config.h ***
npm run build
<<platformio doing platformio things>>
Compiling .pio/build/esp32dev/src/FX_fcn.cpp.o
Compiling .pio/build/esp32dev/src/alexa.cpp.o
In file included from wled00/fcn_declare.h:222:0,
                 from wled00/wled.h:189,
                 from wled00/FX_2Dfcn.cpp:10:
wled00/FX.h:713:27: error: enclosing class of constexpr non-static member function 'bool Segment::is2D() const' is not a literal type
     inline constexpr bool is2D() const                                            { return false; }
                           ^
In file included from wled00/fcn_declare.h:222:0,
                 from wled00/wled.h:189,
                 from wled00/FX_2Dfcn.cpp:10:
wled00/FX.h:361:16: note: 'Segment' is not literal because:
 typedef struct Segment {
                ^
wled00/FX.h:361:16: note:   'Segment' has a non-trivial destructor
*** [.pio/build/esp32dev/src/FX_2Dfcn.cpp.o] Error 1
*** [.pio/build/esp32dev/src/alexa.cpp.o] Error 1
*** [.pio/build/esp32dev/src/FX.cpp.o] Error 1
*** [.pio/build/esp32dev/src/FX_fcn.cpp.o] Error 1
==== [FAILED] Took 11.84 seconds ====
Environment    Status    Duration
-------------  --------  ------------
esp32dev       FAILED    00:00:11.836

[DedeHai]

thanks for the feedback. I can see the error but only on ESP32dev env, the _V4 version does work so it seems to be compiler(setting) related. Also other envs based on V4 work fine.
@willmmiles any idea what is going on and what fix should be applied?

[willmmiles]

It is likely a C++ version thing -- IIRC, constexpr rules were substantially extended in C++14.

I'd probably recommend removing constexpr for now, at least until we can enforce a specific newer C++ standard. It won't make any difference to the resulting binary -- the function call should be inlined to a constant anyways. I'm not sure that constexpr is helpful here anyways, as I don't think we'll ever be calling this function in some other constexpr context.

[DedeHai]

please fix the alignment of indentation and I will merge this.

[DedeHai]

@scourge411 can you also update to latest main to resolve conflict?

[scourge411]

Should be good now.

[DedeHai]

thanks. for future reference: don't force push on branches in a PR, it can mess up the review.