Fix the finite element dual assignment operators

[jamiebramwell]

This fixes a memory leak as reported by @tepperly .

[codecov-commenter]

Codecov Report

Attention: 4 lines in your changes are missing coverage. Please review.

Comparison is base (b2ab378) 88.95% compared to head (c3962f1) 88.88%.

Files	Patch %	Lines
src/serac/physics/state/finite_element_dual.hpp	42.85%	4 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #1032      +/-   ##
===========================================
- Coverage    88.95%   88.88%   -0.08%     
===========================================
  Files          153      153              
  Lines        12325    12344      +19     
===========================================
+ Hits         10964    10972       +8     
- Misses        1361     1372      +11     

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[jamiebramwell]

@tepperly , I added a few extras to your patch. Let me know if this works for you.

[samuelpmishLLNL]

out of curiosity, what was the cause of the underlying leak?

[jamiebramwell]

out of curiosity, what was the cause of the underlying leak?

I defer to @tepperly as he developed and tested this patch.

[tepperly]

out of curiosity, what was the cause of the underlying leak?

I believe it's the operator=(&& rhs) variant. After an invocation of the move operator, the compiler assumes that the rhs has been completely pilfered (i.e., all of the allocated resources owned by rhs have been moved into this or freed). When rhs is an upcast, it doesn't properly deal with all the parts of rhs leaving some orphaned pointers. This is what my valgrind logs suggested at least. Applying this patch, plugged some leaks.

In particular, I believe it was when the right hand side was an instead of FiniteElementDual, the rhs.linear_form_ was leaked.

[tepperly]

The comments saying this seems like the wrong way to be doing this assignment drew my attention.

[tepperly]

It would be nice if this could get in soon, so LiDO's next TPL could have it. Without this patch, my uncertain bracket problem crashes in 10-20 MMA iterations do to the Linux OOM killler which sometimes crashes my desktop.