Mesa 10.5 Is Branched, Still Lacks OpenGL 4.0+ Support
Mesa 10.5 was branched and there's been many changes implemented in the past few months -- including a number of OpenGL 4 extensions -- but unfortunately not enough yet to claim OpenGL 4.0 support. The Git-based TODO list still shows lacking from the GL 4.0 implementation is GL_ARB_gpu_shader_fp64, GL_ARB_shader_subroutine, and GL_ARB_tessellation_shader support.
With the OpenGL 4.0 work items not being done ahead of the 10.5 branching and Mesa releases coming quarterly, the next change to have OpenGL 4.0 via this open-source stack in released form is now another 3~4 months down the road. This also puts out the open-source Linux GPU drivers having OpenGL 4.0 out-of-the-box in the next round of distribution updates like Ubuntu 15.04 and Fedora 22 but most likely will not have this level of support until the fall distribution updates -- sans the rolling-release distributions getting their new versions right away out to users. At least when GL 4.0 is accomplished, a number of the work items in OpenGL 4.1 and OpenGL 4.2 are already completed in Mesa Git. It's possible that the follow-on release could jump from OpenGL 3.3 to OpenGL 4.2 if all goes well.
Left to do in Mesa's OpenGL 4.1 is GL_ARB_shader_precision and GL_ARB_vertex_attrib_64bit while OpenGL 4.2 has GL_ARB_shader_image_load_store. However, when it comes to OpenGL 4.3, 4.4, and 4.5 compliance, there's still numerous months of work left to be tackled. OpenGL ES 3.1 also isn't yet complete in Mesa. This all comes while next-generation OpenGL is being announced next month and will yield even more work for the Mesa TODO list.
Anyhow, for those wishing to test Mesa 10.5, you can fetch the code from this Git branch and there will be test releases ahead of the official 10.5.0 release in the weeks to come. In terms of what Mesa 10.5 does have is initial Intel Skylake support, many VC4 / Raspberry Pi driver improvements, various new extensions, and AMD RadeonSI driver improvements.