37.4 Caveats and Annoyances

The machinery drift uses to intercept calls to Grid_releaseBlkPtr is lacking in sophistication, and as such can put some unwanted constraints on the code base. The technique used is to declare a preprocessor #define in Flash.h to expand occurrences of Grid_releaseBlkPtr to something larger that includes __FILE__ and __LINE__. This is how drift is able to correlate calls to Grid_releaseBlkPtr with the originating line of source code. Unfortunately this technique places a very specific restriction on the code once drift is enabled. The trouble comes from the types of source lines that may refer to a subroutine without calling it. The primary offender being use statements with only clauses listing the module members to import into scope. Because macro expansion is dumb with respect to context, it will expand occurrences of Grid_releaseBlkPtr in these use statements, turning them into syntactic rubbish. The remedy for this issue is to make sure the line #include "Flash.h" comes after all statements involving Grid_releaseBlkPtr but not calling it, and before all statements that are calls to Grid_releaseBlkPtr. In practice this is quite easy. With only one subroutine per file, there will only be one line like:  
use Grid_interface, only: ..., Grid_releaseBlkPtr, ...
and it will come before all calls to Grid_releaseBlkPtr, so just move the #include "Flash.h" after the use statements. The following is an example:



Incorrect Correct
 
#include "Flash.h"
subroutine Flash_subroutine()
  use Grid_interface, only: Grid_releaseBlkPtr
  implicit none
  [...]
  call Grid_releaseBlkPtr(...)
  [...]
end subroutine Flash_subroutine
 
subroutine Flash_subroutine()
  use Grid_interface, only: Grid_releaseBlkPtr
  implicit none
#include "Flash.h"
  [...]
  call Grid_releaseBlkPtr(...)
  [...]
end subroutine Flash_subroutine



If such a solution is not possible because no separation between all use and call statements exists, then there are two remaining courses of action to get the source file to compile. One, hide these calls to Grid_releaseBlkPtr from drift by forceably disabling the macro expansion. To do so, just add the line #undef Grid_releaseBlkPtr after #include "Flash.h". The second option is to carry out the macro expansion by hand. This also requires disabling the macro with the undef just mentioned, but then also rewriting each call to Grid_releaseBlkPtr just as the preprocessor would. Please consult Flash.h to see the text that gets substituted in for Grid_releaseBlkPtr.