[MITgcm-devel] makedepend and indirect dependencies

[Oliver Jahn]

Below is an interesting excerpt from the makedepend man page. 
Basically, makedepend caches indirect dependencies from include files it 
has already looked at.  This is a problem, since includes within ifdef's 
in header files may change depending on which .F file the header file 
was included from (an example is the dependence on SIZE.h in LAND_SIZE.h)


ALGORITHM
...
It parses each source and include file
exactly once, maintaining an internal symbol table for each.  Thus, the
first file on the command line will take an amount of time proportional
to the amount of time that a normal C preprocessor takes.  But on  sub-
sequent  files,  if  it  encounters an include file that it has already
parsed, it does not parse it again.

For example, imagine you are compiling two files, file1.c and  file2.c,
they  each  include  the header file header.h, and the file header.h in
turn includes the files def1.h and def2.h.  When you run the command

    makedepend file1.c file2.c

makedepend will parse  file1.c  and  consequently,  header.h  and  then
def1.h and def2.h.  It then decides that the dependencies for this file
are

    file1.o: header.h def1.h def2.h

But when the  program  parses  file2.c  and  discovers  that  it,  too,
includes  header.h,  it  does  not  parse  the  file,  but  simply adds
header.h, def1.h and def2.h to the list of dependencies for file2.o.

...

BUGS
...
Imagine  you  are  parsing  two  files,  say  file1.c and file2.c, each
includes the file def.h.  The list of files that def.h  includes  might
truly  be  different  when def.h is included by file1.c than when it is
included by file2.c.  But once makedepend arrives at a list  of  depen-
dencies for a file, it is cast in concrete.