Prevent segfaults for partial 0-D objects

[ischoegl]

Changes proposed in this pull request

• Prevent segfaults in reactors with no contents
• Prevent segfaults for unconnected walls
• Add google tests

Currently existing guards are largely specific to the implementation of the Python API (example: retrieving temperature for an empty reactor fails when attempting to load the current reactor state into a thermo object). As underlying C++ code is difficult to reach from Python (but may be exposed elsewhere), unit tests are added for C++ directly.

If applicable, fill in the issue number this pull request is fixing

Fixes #1623

If applicable, provide an example illustrating new features this pull request is introducing

Example taken from #1623:

In [1]: import cantera as ct
   ...:
   ...: r1 = ct.Reactor()
   ...: r2 = ct.Reactor()
   ...:
   ...: w = ct.Wall(r1,r2)

In [2]: w.heat_rate
---------------------------------------------------------------------------
CanteraError                              Traceback (most recent call last)
Cell In[2], line 1
----> 1 w.heat_rate

File /Volumes/Data/work/GitHub/cantera/build/python/cantera/reactor.pyx:1066, in cantera.reactor.WallBase.heat_rate.__get__()
   1064 .. versionadded:: 3.0
   1065 """
-> 1066 return self.wall.heatRate()
   1067
   1068

CanteraError:
*******************************************************************************
CanteraError thrown by ReactorBase::temperature:
Reactor state empty and/or contents not defined.
*******************************************************************************

Other thoughts

An alternative to the added guards is to prevent the creation of empty (or unconnected) 0-D objects altogether (which should likely be done when moving from raw pointers to shared pointers for various held objects - m_thermo, etc.). As this is more involved and will require a deprecation cycle, the guards proposed in this PR are still appropriate.

Checklist

• The pull request includes a clear description of this code change
• Commit messages have short titles and reference relevant issues
• Build passes (scons build & scons test) and unit tests address code coverage
• Style & formatting of contributed code follows contributing guidelines
• The pull request is ready for review

[codecov]

Codecov Report

Attention: 7 lines in your changes are missing coverage. Please review.

Comparison is base (01a0284) 72.75% compared to head (faddc8f) 72.78%.

Files	Patch %	Lines
include/cantera/zeroD/ReactorBase.h	58.33%	0 Missing and 5 partials ⚠️
src/zeroD/Wall.cpp	83.33%	0 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1661      +/-   ##
==========================================
+ Coverage   72.75%   72.78%   +0.02%     
==========================================
  Files         375      375              
  Lines       56584    56610      +26     
  Branches    20494    20510      +16     
==========================================
+ Hits        41168    41201      +33     
+ Misses      12401    12389      -12     
- Partials     3015     3020       +5     

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[speth]

Thanks, @ischoegl, all the changes here look good to me, and I appreciate the thoughts on longer-term options to eliminate the need for these checks.

My only request here is to document what upstream deprecation warning is resolved by installing pyarrow as part of the commit message. Do we need to update the dependencies of some of the examples?

[ischoegl]

My only request here is to document what upstream deprecation warning is resolved by installing pyarrow as part of the commit message.

👍 done

Do we need to update the dependencies of some of the examples?

I don't think so - it's just pandas complaining that it will require pyarrow down the line.