Check that self%perturbation is allocated before trying to apply perturbations

[dougiesquire]

This PR adds a check to libforcing/src/forcing_field.F90::forcing_field_apply_perturbations to ensure that that self%perturbation is allocated before trying to apply perturbations.

This prevents errors like:

Program received signal SIGSEGV: Segmentation fault - invalid memory reference.

when running with GCC-compiled binaries

[dougiesquire]

@anton-seaice could please review.

This allows building and running ACCESS-OM2 with GCC (see here) and doesn't change answers with oneapi (see here)

[anton-seaice]

I'm sure i've over thought this

Here:

libaccessom2/libforcing/src/forcing_config.F90

Lines 176 to 182 in 23f82af

	call self%core%get_child(field_jv_ptr, "perturbations", perturbation_list, found)
	if (.not. found) then
	return
	endif
	num_perturbations = self%core%count(perturbation_list)
	allocate(field_ptr%perturbations(num_perturbations))

if num_perturbations is 0, then it should return (and not allocate perturbations)

The change lined in this PR could just be

if (.not. allocated(self%perturbations)) then

[anton-seaice]

We almost need a config / repro test with some perturbations included

[dougiesquire]

I'm possibly not understanding what you're saying, but I think:

allocate(field_ptr%perturbations(0)) 

will still allocate the array, but it's size will be zero.

To be clear, I didn't add the check that size(self%perturbations) == 0.

[anton-seaice]

Yeah - that's right. But why allocate an array that's not needed? Feels neater just not to allocate it and treat all cases of having no pertubations to apply the same ?

[dougiesquire]

I think I'm fine with what I currently have. It's less code changes and, more importantly, it's what I've tested and I'm not that interested in spending more time on this 😅

[anton-seaice]

Yeah - its also probably lowest risk

[anton-seaice]

Thanks Dougie - it looks like if no peturbations section is provided in the forcing.json then this array isn't allocated, so this make sense