Export C++ symbols

[darbyjohnston]

Fixes #1919

This change uses the CMake GenerateExportHeader functionality to explicitly export C++ symbols. In addition to fixing #1919, this can also potentially make the use of OTIO shared libraries more efficient.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 84.86%. Comparing base (c0e97b0) to head (5ed86fe).
⚠️ Report is 63 commits behind head on main.

❌ Your changes status has failed because you have indirect coverage changes. Learn more about Unexpected Coverage Changes and reasons for indirect coverage changes.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1920      +/-   ##
==========================================
+ Coverage   84.11%   84.86%   +0.74%     
==========================================
  Files         198      181      -17     
  Lines       22241    13054    -9187     
  Branches     4687     1206    -3481     
==========================================
- Hits        18709    11078    -7631     
+ Misses       2610     1790     -820     
+ Partials      922      186     -736     

Flag	Coverage Δ
py-unittests	84.86% <ø> (+0.74%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
src/opentime/errorStatus.h	100.00% <ø> (ø)
src/opentime/rationalTime.h	95.83% <ø> (+1.15%)	⬆️
src/opentime/timeRange.h	98.30% <ø> (-0.79%)	⬇️
src/opentime/timeTransform.h	100.00% <ø> (+8.33%)	⬆️
src/opentimelineio/anyDictionary.h	96.92% <ø> (+5.39%)	⬆️
src/opentimelineio/anyVector.h	91.42% <ø> (+7.55%)	⬆️
src/opentimelineio/color.h	41.66% <ø> (ø)
src/opentimelineio/composable.h	100.00% <ø> (ø)
src/opentimelineio/composition.h	83.87% <ø> (+18.35%)	⬆️
src/opentimelineio/effect.h	83.33% <ø> (-16.67%)	⬇️
... and 16 more

... and 114 files with indirect coverage changes

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[jlskuz]

LGTM.

I wonder if [CMAKE_]CXX_VISIBILITY_PRESET should be set to hidden now so that everything that is not explicitly marked as exported will be hidden.

[ssteinbach]

Couple of questions! Thanks for putting this together though. Did you check to see if the DSO sizes or load times change at all after this?

[ssteinbach]

Do we need to export the fabs symbol?

[ssteinbach]

Also, @darbyjohnston I suspect this is a question for another PR, but is this still true?

#1047 (comment)

[darbyjohnston]

Good point, we should probably remove it from the public API entirely. @meshula thought it was a worthwhile optimization, and when we upgrade to C++ 23 we can replace it with the std library version.

[ssteinbach]

Agreed - @meshula let us know if you think it should stay in this public header and be exported

[darbyjohnston]

Did you check to see if the DSO sizes or load times change at all after this?

I checked and the sizes were the same, but I exported all of the symbols so I didn't expect any difference. Hopefully it's a feature we can take more advantage of in the future, for example the C++ OTIOZ PR has some code that might not need to be part of the public API.