If this happened to be Python, there is no such thing. Two pieces of Python code that have different semantics can look identical under a whitespace-excluding diff, so you must not habitually use such a thing as your go-to comparison method.

For instance if we edit:

   if condition:                     if condition:
     blah                              blah
     blah                   ->       blah
     blah                            blah

then nothing shows under "diff -b" or "diff -w". With a different kind of language there will be a non-white-space difference due to the changing position of a brace or other delimiting token.

Otherwise, exactly the remark I was thinking of making.

If it was Python then it would be highly unlikely to have used tabs in the first place.