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 85.00%. Comparing base (c0e97b0) to head (ca0c980).
⚠️ Report is 65 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%   85.00%   +0.88%     
==========================================
  Files         198      181      -17     
  Lines       22241    13074    -9167     
  Branches     4687     1206    -3481     
==========================================
- Hits        18709    11113    -7596     
+ Misses       2610     1778     -832     
+ Partials      922      183     -739     

Flag	Coverage Δ
py-unittests	85.00% <100.00%> (+0.88%)	⬆️

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% <100.00%> (+1.15%)	⬆️
src/opentime/timeRange.h	98.36% <100.00%> (-0.74%)	⬇️
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 115 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?

[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.

[meshula]

Hi Darby can you please separate the fabs from the GenerateExportHeader functionality? the fabs diff is easy to land, introducing a new meta-source generator needs some discussion. I'm not aware of any projects that use this facility, and I'd like to understand why that is.

[jlskuz]

#1919 describes in detail why this is needed. It's a problem we are facing with Kdenlive on clang based builds ie. macOS and FreeBSD. As it causes crashes it's a critical bug for us. There are workarounds, but these are, well workarounds and no proper fixes.

Further description of the Kdenlive issue can be found here: https://invent.kde.org/multimedia/kdenlive/-/issues/1992

[darbyjohnston]

@meshula provided some sample code for replacing the GenerateExportHeader functionality, I'm going to try integrating it and will change this PR to a "draft" while I work through it.