better handling of non-git builds

cmake/Version.cmake

@@ -45,10 +45,7 @@ if (NOT DEFINED BARRIER_REVISION)
         string (SUBSTRING $ENV{GIT_COMMIT} 0 8 BARRIER_REVISION)
     else()
         find_program (GIT_BINARY git)
-        if (GIT_BINARY STREQUAL "GIT_BINARY-NOTFOUND")
-            set (BARRIER_REVISION "00000000")
-            message (WARNING "git not found. revision hash set to ${BARRIER_REVISION}")
-        else()
+        if (NOT GIT_BINARY STREQUAL "GIT_BINARY-NOTFOUND")
             execute_process (
                 COMMAND git rev-parse --short=8 HEAD
                 WORKING_DIRECTORY ${CMAKE_SOURCE_DIR}
@@ -59,15 +56,12 @@ if (NOT DEFINED BARRIER_REVISION)
     endif()
 endif()
 
-if (DEFINED BARRIER_REVISION)
-    string(LENGTH ${BARRIER_REVISION} BARRIER_REVISION_LENGTH)
-    if (NOT ((BARRIER_REVISION MATCHES "^[a-f0-9]+") AND (BARRIER_REVISION_LENGTH EQUAL "8")))
-        message (FATAL_ERROR "BARRIER_REVISION ('${BARRIER_REVISION}') should be a short commit hash")
-    endif()
-    unset (BARRIER_REVISION_LENGTH)
-else()
-	set (BARRIER_REVISION "0badc0de")
+string(LENGTH "${BARRIER_REVISION}" BARRIER_REVISION_LENGTH)
+if (NOT BARRIER_REVISION_LENGTH EQUAL 8 OR NOT BARRIER_REVISION MATCHES "^[a-f0-9]+")
+    set (BARRIER_REVISION "00000000")
+    message (WARNING "revision not found. setting to ${BARRIER_REVISION}")
 endif()
+unset (BARRIER_REVISION_LENGTH)
 
 if (DEFINED ENV{BUILD_NUMBER})
     set (BARRIER_BUILD_NUMBER $ENV{BUILD_NUMBER})