New warning on gcc 13

[mikekryjak]

Compiling on gcc 13 adds a new warning. It's harmless, but since warnings will stop compilation by default, you will need to suppress warnings to compile until this is resolved if you're on gcc 13 or above.

/home/mike/work/hermes-3/src/izn_rec_reaction.cxx: In member function ‘virtual void hermes::IznRecReaction::transform_additional(GuardedOptions&, const hermes::RateData&)’:
/home/mike/work/hermes-3/src/izn_rec_reaction.cxx:108:18: warning: possibly dangling reference to a temporary [-Wdangling-reference]
  108 |   const Field3D& n_rh = hr["density"].GetRef<Field3D>();
      |                  ^~~~
/home/mike/work/hermes-3/src/izn_rec_reaction.cxx:108:54: note: the temporary was destroyed at the end of the full expression ‘GuardedOptions::operator[](const char*) const(((const char*)"density")).GuardedOptions::GetRef<Field3D>(Regions::All)’
  108 |   const Field3D& n_rh = hr["density"].GetRef<Field3D>();
      |                         ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~
/home/mike/work/hermes-3/src/izn_rec_reaction.cxx:109:18: warning: possibly dangling reference to a temporary [-Wdangling-reference]
  109 |   const Field3D& v_rh = hr["velocity"].GetRef<Field3D>();
      |                  ^~~~
/home/mike/work/hermes-3/src/izn_rec_reaction.cxx:109:55: note: the temporary was destroyed at the end of the full expression ‘GuardedOptions::operator[](const char*) const(((const char*)"velocity")).GuardedOptions::GetRef<Field3D>(Regions::All)’
  109 |   const Field3D& v_rh = hr["velocity"].GetRef<Field3D>();
      |                         ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~
/home/mike/work/hermes-3/src/izn_rec_reaction.cxx:113:18: warning: possibly dangling reference to a temporary [-Wdangling-reference]
  113 |   const Field3D& v_hp = hp["velocity"].GetRef<Field3D>();
      |                  ^~~~
/home/mike/work/hermes-3/src/izn_rec_reaction.cxx:113:55: note: the temporary was destroyed at the end of the full expression ‘GuardedOptions::operator[](const char*) const(((const char*)"velocity")).GuardedOptions::GetRef<Field3D>(Regions::All)’
  113 |   const Field3D& v_hp = hp["velocity"].GetRef<Field3D>();
      |                         ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~
/home/mike/work/hermes-3/src/izn_rec_reaction.cxx:149:18: warning: possibly dangling reference to a temporary [-Wdangling-reference]
  149 |   const Field3D& T_e = electron["temperature"].GetRef<Field3D>();
      |                  ^~~
/home/mike/work/hermes-3/src/izn_rec_reaction.cxx:149:63: note: the temporary was destroyed at the end of the full expression ‘GuardedOptions::operator[](const char*) const(((const char*)"temperature")).GuardedOptions::GetRef<Field3D>(Regions::All)’
  149 |   const Field3D& T_e = electron["temperature"].GetRef<Field3D>();
      |                        ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~
/home/mike/work/hermes-3/src/izn_rec_reaction.cxx:161:22: warning: possibly dangling reference to a temporary [-Wdangling-reference]
  161 |       const Field3D& v_e = electron["velocity"].GetRef<Field3D>();
      |                      ^~~
/home/mike/work/hermes-3/src/izn_rec_reaction.cxx:161:64: note: the temporary was destroyed at the end of the full expression ‘GuardedOptions::operator[](const char*) const(((const char*)"velocity")).GuardedOptions::GetRef<Field3D>(Regions::All)’
  161 |       const Field3D& v_e = electron["velocity"].GetRef<Field3D>();
      |                            ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~
/home/mike/work/hermes-3/src/izn_rec_reaction.cxx:168:18: warning: possibly dangling reference to a temporary [-Wdangling-reference]
  168 |   const Field3D& n_e = electron["density"].GetRef<Field3D>();
      |                  ^~~
/home/mike/work/hermes-3/src/izn_rec_reaction.cxx:168:59: note: the temporary was destroyed at the end of the full expression ‘GuardedOptions::operator[](const char*) const(((const char*)"density")).GuardedOptions::GetRef<Field3D>(Regions::All)’
  168 |   const Field3D& n_e = electron["density"].GetRef<Field3D>();

[dschwoerer]

Rather then suppress warnings, it is better to remove -Werror.
-Werror is only for developers useful, you should not use that as a user. If the compiler developer would think this should error, rather than warn, it would be an error, not a warning, after all.

[mikekryjak]

I like that warnings are errors, because it gives us motivation to fix warnings. Previously there were far too many. I already have the fix for this and I'll raise a PR.

[dschwoerer]

Because you are a developer.

For a user, -Werror is bad.

[mikekryjak]

Is it though? They would be more likely to raise an issue so we can fix the warning, and in the meantime they can still override it with the CMake flag.