Minor fixes, cleanups, and clarifications

There are three actual changes in this commit:

1. When the trailing newline of a file is removed in a diff, the
   change will now be reported with `GIT_DIFF_LINE_DEL_EOFNL` passed
   to the callback.  Previously, the `ADD_EOFNL` constant was given
   which was just an error in my understanding of when the various
   circumstances arose.  `GIT_DIFF_LINE_ADD_EOFNL` is deprecated and
   should never be generated.  A new newline is simply an `ADD`.
2. Rewrote the `diff_delta__merge_like_cgit` function that contains
   the core logic of the `git_diff_merge` implementation.  The new
   version doesn't actually have significantly different behavior,
   but the logic should be much more obvious, I think.
3. Fixed a bug in `git_diff_merge` where it freed a string pool
   while some of the string data was still in use.  This led to
   `git_diff_print_patch` accessing memory that had been freed.

The rest of this commit contains improved documentation in `diff.h`
to make the behavior and the equivalencies with core git clearer,
and a bunch of new tests to cover the various cases, oh and a minor
simplification of `examples/diff.c`.

1 files changed, 6 insertions, 5 deletions

diff --git a/src/diff_output.c b/src/diff_output.c
index d1aa910b3..92f7f8f2f 100644
--- a/src/diff_output.c
+++ b/src/diff_output.c
@@ -83,12 +83,13 @@ static int diff_output_cb(void *priv, mmbuffer_t *bufs, int len)
 			info->cb_data, info->delta, &info->range, origin, bufs[1].ptr, bufs[1].size) < 0)
 			return -1;
 
-		/* deal with adding and removing newline at EOF */
+		/* This should only happen if we are adding a line that does not
+		 * have a newline at the end and the old code did.  In that case,
+		 * we have a ADD with a DEL_EOFNL as a pair.
+		 */
 		if (len == 3) {
-			if (origin == GIT_DIFF_LINE_ADDITION)
-				origin = GIT_DIFF_LINE_ADD_EOFNL;
-			else
-				origin = GIT_DIFF_LINE_DEL_EOFNL;
+			origin = (origin == GIT_DIFF_LINE_ADDITION) ?
+				GIT_DIFF_LINE_DEL_EOFNL : GIT_DIFF_LINE_ADD_EOFNL;
 
 			return info->line_cb(
 				info->cb_data, info->delta, &info->range, origin, bufs[2].ptr, bufs[2].size);