vim - Is there a way to configure vimdiff to ignore ALL whitespaces?

Question

I'm using vim -d file1 file2 in order to see the differences between them. This works fine, but I want to ignore whitespace changes - they are irrelevant for source code files.

Vim help states that the following command will do the magic:

set diffopt+=iwhite

But unfortunately, this command only adds -b to diff tool command line, and that only ignores trailing whitespaces. The correct command line key for diff should be -w, to ignore all whitespace changes. But I can't find how to modify the diff command line directly from Vim. Of course I can compile a custom diff, or replace diff with diff.sh, but that looks kinda ugly :(.

Is there a better way to modify how Vim interacts with the diff tool for displaying file differences?

Answer 1

This implements what you want (taken from the diffexpr docs with -b changed to -w):

set diffopt+=iwhite
set diffexpr=DiffW()
function DiffW()
  let opt = ""
   if &diffopt =~ "icase"
     let opt = opt . "-i "
   endif
   if &diffopt =~ "iwhite"
     let opt = opt . "-w " " swapped vim's -b with -w
   endif
   silent execute "!diff -a --binary " . opt .
      v:fname_in . " " . v:fname_new .  " > " . v:fname_out
endfunction

... I'm still looking for a better diffexpr helper with respect to handling which lines map to which (GNU diff, even with -w instead of -b, is rather baffled by combining extra whitespace with minor edits like commented lines). Maybe diffchar?