code: def get_standard_vars(cls, context, variant, build_type, install,
                            build_path, install_path=None):
          
          from rez.config import config
  
          package = variant.parent
          variant_requires = map(str, variant.variant_requires)
  
          if variant.index is None:
              variant_subpath = ''
          else:
              variant_subpath = variant._non_shortlinked_subpath
  
          vars_ = {
              'REZ_BUILD_ENV': 1,
              'REZ_BUILD_PATH': build_path,
              'REZ_BUILD_THREAD_COUNT': package.config.build_thread_count,
              'REZ_BUILD_VARIANT_INDEX': variant.index or 0,
              'REZ_BUILD_VARIANT_REQUIRES': ' '.join(variant_requires),
              'REZ_BUILD_VARIANT_SUBPATH': variant_subpath,
              'REZ_BUILD_PROJECT_VERSION': str(package.version),
              'REZ_BUILD_PROJECT_NAME': package.name,
              'REZ_BUILD_PROJECT_DESCRIPTION': (package.description or '').strip(),
              'REZ_BUILD_PROJECT_FILE': package.filepath,
              'REZ_BUILD_SOURCE_PATH': os.path.dirname(package.filepath),
              'REZ_BUILD_REQUIRES': ' '.join(
                  str(x) for x in context.requested_packages(True)
              ),
              'REZ_BUILD_REQUIRES_UNVERSIONED': ' '.join(
                  x.name for x in context.requested_packages(True)
              ),
              'REZ_BUILD_TYPE': build_type.name,
              'REZ_BUILD_INSTALL': 1 if install else 0,
          }
  
          if install_path:
              vars_['REZ_BUILD_INSTALL_PATH'] = install_path
  
          if config.rez_1_environment_variables and \
                  not config.disable_rez_1_compatibility and \
                  build_type == BuildType.central:
              vars_['REZ_IN_REZ_RELEASE'] = 1
  
          return vars_
docs: Returns a standard set of environment variables that can be set
          for the build system to use