Re: Use a *real* built-in diff generator

On Sat, 25 Mar 2006, Davide Libenzi wrote:

Btw, git-apply does it, and it's actually quite simple: the code to handle the "\ No newline" case is literally just this:

                /*
                 * "plen" is how much of the line we should use for 
                 * the actual patch data. Normally we just remove the
                 * first character on the line, but if the line is
                 * followed by "\ No newline", then we also remove the
                 * last one (which is the newline, of course).
                 */
                plen = len-1;
                if (len < size && patch[len] == '\\')
                        plen--;

if we just remove the last '\n' on a line, if the _next_ line starts with a '\\' (so the git-apply code actually depends on knowing that the patch text is dense, and that it's also padded out so that you can look one byte past the end of the diff and it won't be a '\\').

I don't know how well that fits into xpatch (I never looked at the patch side, since I already had my own ;), but my point being that handling this special case _can_ be very simple if the data structures are just set up for it.

It's also important to realize that (a) you can't actually check the "No newline" string, because that depends on your locale and (b) it's not necessarily at the _end_ of the patch, because you can have a patch that looks like

	-	next-to-last-line
	-	last-line
	\ No newline at end of file
	+	new-end-of-file
	+	new-last-line
	\ No newline at end of file

ie the first "\ No newline" is in the middle, because it relates to the last removed line (while the second one obviously relates to the last added one).

The xdiff patch I sent out automatically does that when generating these things, of course.

			Linus