sigh, is this filed upstream?

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  mesa 18.0.0 will cause rendering errors in Qt applications

Status in mesa package in Ubuntu:
Status in qtbase-opensource-src package in Ubuntu:
Status in mesa source package in Bionic:
Status in qtbase-opensource-src source package in Bionic:

Bug description:

  ** extract **

  The `QOpenGLShaderProgram` class in Qt can be used to compile and link
  OpenGL shaders. If the `GL_ARB_get_program_binary` OpenGL extension is
  available, it can cache those shaders on disk
  (~/.cache/qtshadercache). The i965 driver in Mesa supports this
  extension since version 18.0.0.

  When the shader is loaded using the `glProgramBinary` function, OpenGL
  can refuse it if for example some hardware or software component
  changed. Mesa refuses binaries that were created by any other build of
  Mesa (using among other things the build_id of the library).

  If the shader is refused, Qt should fallback to compiling it from
  sources, but it incorrectly calls glLinkProgram first. The
  glLinkProgram succeeds, because it actually links 0 shaders together.
  That is allowed in OpenGL compatibility profile and the resulting
  program works as a fixed pipeline. Which of course does not render as

  This causes rendering errors in Qt applications every time Mesa is
  updated since version 18.0.0. For example white screen in sddm.

  This issue was originally reported in openSUSE

  ** end extract **

  As this potentially effects Qt applications, and could even render
  display manager login unusable, this should be a blocking bug in mesa
  and Qt until Qt mitigations patches pass codereview and can be
  included in Qtbase for 18.04.

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