Add automated ABI compatibility testing to the CI

[doug-walker]

OIIO already has this setup in their CI. It uses the abi-compliance-checker tool.

OCIO would benefit from a similar check.

[yosri-brh]

Hello ! I'd like to work on this issue.

[doug-walker]

Thank you @yosri-brh , I've assigned it to you!

[remia]

I did some tests on this here, using Claude I basically asked it to write the ABI check workflow, explaining its choice regarding which method / library to use for the check, which is visible as comments in the workflow file (it went for libabigail and not abi-compliance-checker, for reasons explained, whether they are sensible or not is to be reviewed).

Trying it on the RB-2.5 branch, it seems like it correctly detected the ABI break we introduced in 2.5.1, see the error, or below copy/paste:

Baseline library: /__w/_temp/old/install/lib64/libOpenColorIO.so.2.5.0
Proposed library: /__w/_temp/new/install/lib64/libOpenColorIO.so.2.5.2
Functions changes summary: 0 Removed, 1 Changed (6 filtered out), 0 Added functions
Variables changes summary: 0 Removed, 0 Changed, 0 Added variable
Function symbols changes summary: 0 Removed, 0 Added function symbol not referenced by debug info

1 function with some indirect sub-type change:

  [C] 'method OpenColorIO_v2_5::GpuShaderDesc::GpuShaderDesc()' at GpuShaderDesc.cpp:406:1 has some indirect sub-type changes:
    implicit parameter 0 of type 'OpenColorIO_v2_5::GpuShaderDesc*' has sub-type changes:
      in pointed to type 'class OpenColorIO_v2_5::GpuShaderDesc' at OpenColorIO.h:3725:1:
        type size hasn't changed
        2 member function insertions:
          'method virtual unsigned int OpenColorIO_v2_5::GpuShaderDesc::get3DTextureShaderBindingIndex(unsigned int) const' at OpenColorIO.h:3813:1, virtual at voffset 35/35
          'method virtual unsigned int OpenColorIO_v2_5::GpuShaderDesc::getTextureShaderBindingIndex(unsigned int) const' at OpenColorIO.h:3797:1, virtual at voffset 31/35
        3 member function changes (10 filtered):
          'method virtual unsigned int OpenColorIO_v2_5::GpuShaderDesc::getNum3DTextures() const' has some sub-type changes:
            the vtable offset of method virtual unsigned int OpenColorIO_v2_5::GpuShaderDesc::getNum3DTextures() const changed from 31 to 32
              note that this is an ABI incompatible change to the vtable of class OpenColorIO_v2_5::GpuShaderDesc
          'method virtual void OpenColorIO_v2_5::GpuShaderDesc::get3DTexture(unsigned int, const char*&, const char*&, unsigned int&, OpenColorIO_v2_5::Interpolation&) const' has some sub-type changes:
            the vtable offset of method virtual void OpenColorIO_v2_5::GpuShaderDesc::get3DTexture(unsigned int, const char*&, const char*&, unsigned int&, OpenColorIO_v2_5::Interpolation&) const changed from 32 to 33
              note that this is an ABI incompatible change to the vtable of class OpenColorIO_v2_5::GpuShaderDesc
          'method virtual void OpenColorIO_v2_5::GpuShaderDesc::get3DTextureValues(unsigned int, const float*&) const' has some sub-type changes:
            the vtable offset of method virtual void OpenColorIO_v2_5::GpuShaderDesc::get3DTextureValues(unsigned int, const float*&) const changed from 33 to 34
              note that this is an ABI incompatible change to the vtable of class OpenColorIO_v2_5::GpuShaderDesc

There is probably some cleanup / review to do but this seem promising.