Fix env behavior to return true on empty vars

[mjcarroll]

Empty environment variables are valid on Linux (and other posix systems), we should return true in those cases.

Closes #96

Signed-off-by: Michael Carroll michael@openrobotics.org

[codecov]

Codecov Report

Merging #97 into ign-common3 will increase coverage by 0.01%.
The diff coverage is 85.00%.

@@               Coverage Diff               @@
##           ign-common3      #97      +/-   ##
===============================================
+ Coverage        73.94%   73.95%   +0.01%     
===============================================
  Files               69       69              
  Lines             9390     9408      +18     
===============================================
+ Hits              6943     6958      +15     
- Misses            2447     2450       +3     

Impacted Files	Coverage Δ
include/ignition/common/Util.hh	100.00% <ø> (ø)
src/Util.cc	83.75% <85.00%> (-0.05%)	⬇️

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[chapulina]

Due to the different behavior on Windows, it sounds like we shouldn't rely on empty env vars for any cross-platform code 😕

Besides that and the ABI issue, the rest looks good to me.

[mjcarroll]

Due to the different behavior on Windows, it sounds like we shouldn't rely on empty env vars for any cross-platform code confused

I believe that is true, but it also breaks expectations on Linux a bit if you are just checking for a value to be set rather than checking the value itself.

[chapulina]

Code checker is angry:

   ./src/Util_TEST.cc:181:  Line ends in whitespace.  Consider deleting these extra spaces.  [whitespace/end_of_line] [4]
  ./src/Util.cc:342:  Missing space before ( in if(  [whitespace/parens] [5]
  ./src/Util.cc:355:  Line ends in whitespace.  Consider deleting these extra spaces.  [whitespace/end_of_line] [4]
  ./include/ignition/common/Util.hh:220:  Line ends in whitespace.  Consider deleting these extra spaces.  

And Windows CI failed:

D:\Jenkins\workspace\ignition_common-ci-pr_any-windows7-amd64\ws\ign-common\src\Util_TEST.cc(179): error C3861: 'setenv': identifier not found