Add a placeholder in version.h for the URL and revision to be stored

[jmlait]

When distributing an OpenVDB package that is forked from the official it can be useful to provide the URL and commit hash that was used so people can re-create it or derive from it if they wish.

What we do for USD is have a define that we replace when we download the library from github with our particular URL and revision. This seems like a useful thing to have in the master branch with the placeholder values, so others can follow a similar protocol if they wish. If we eventually distribute binaries we may also ensure our binary build process likewise patches this.

[Idclip]

We should update the CMake to try and automatically populate these. Something like the below (untested, typed into comment):

set(OPENVDB_PACKAGE_URL "unknown")
set(OPENVDB_PACKAGE_REVISION  "unknown")
find_package(Git)

if(TARGET Git::Git)
  execute_process(COMMAND ${GIT_EXECUTABLE} rev-parse HEAD
  ERROR_QUIET 
  RESULT_VARIABLE code
  OUTPUT_VARIABLE result
  )
  if(NOT ${code} AND ${result})
     set(OPENVDB_PACKAGE_REVISION ${result})
  endif()

  execute_process(COMMAND ${GIT_EXECUTABLE} remote get-url origin
  ERROR_QUIET 
  RESULT_VARIABLE code
  OUTPUT_VARIABLE result
  )
  if(NOT ${code} AND ${result})
     set(OPENVDB_PACKAGE_URL ${result})
  endif()
endif()

[jmlait]

I like the idea of it being built into the CMake, but then it occurred to me that this might be a security issue? It might not be expected that the git URL is auto-published by our cmake, so someone could leak their URL unexpectedly?

[Idclip]

Very good point - we could add a parent option which turns on this behaviour which is off by default.

[Idclip]

@jmlait did you mention you were going to try and solve this with options in the CMake build?

[jmlait]

As mentioned, we'd ideally have options in Cmake, but we can make that a separate PR if we get there.