Introduce status/diff TYPECHANGE flags

When I wrote the diff code, I based it on core git's diff output
which tends to split a type change into an add and a delete.  But
core git's status has the notion of a T (typechange) flag for a
file.  This introduces that into our status APIs and modifies the
diff code so it can be forced to not split type changes.

include/git2/diff.h

@@ -49,6 +49,7 @@ enum {
 	GIT_DIFF_DISABLE_PATHSPEC_MATCH = (1 << 11),
 	GIT_DIFF_DELTAS_ARE_ICASE = (1 << 12),
 	GIT_DIFF_INCLUDE_UNTRACKED_CONTENT = (1 << 13),
+	GIT_DIFF_DONT_SPLIT_TYPECHANGE = (1 << 14),
 };
 
 /**
@@ -116,7 +117,8 @@ typedef enum {
 	GIT_DELTA_RENAMED = 4,
 	GIT_DELTA_COPIED = 5,
 	GIT_DELTA_IGNORED = 6,
-	GIT_DELTA_UNTRACKED = 7
+	GIT_DELTA_UNTRACKED = 7,
+	GIT_DELTA_TYPECHANGE = 8,
 } git_delta_t;
 
 /**

include/git2/status.h

@@ -19,19 +19,22 @@
  */
 GIT_BEGIN_DECL
 
-enum {
+typedef enum {
 	GIT_STATUS_CURRENT = 0,
 
-	GIT_STATUS_INDEX_NEW = (1 << 0),
-	GIT_STATUS_INDEX_MODIFIED = (1 << 1),
-	GIT_STATUS_INDEX_DELETED = (1 << 2),
+	GIT_STATUS_INDEX_NEW        = (1u << 0),
+	GIT_STATUS_INDEX_MODIFIED   = (1u << 1),
+	GIT_STATUS_INDEX_DELETED    = (1u << 2),
+	GIT_STATUS_INDEX_RENAMED    = (1u << 3),
+	GIT_STATUS_INDEX_TYPECHANGE = (1u << 4),
 
-	GIT_STATUS_WT_NEW = (1 << 3),
-	GIT_STATUS_WT_MODIFIED = (1 << 4),
-	GIT_STATUS_WT_DELETED = (1 << 5),
+	GIT_STATUS_WT_NEW           = (1u << 7),
+	GIT_STATUS_WT_MODIFIED      = (1u << 8),
+	GIT_STATUS_WT_DELETED       = (1u << 9),
+	GIT_STATUS_WT_TYPECHANGE    = (1u << 10),
 
-	GIT_STATUS_IGNORED = (1 << 6),
-};
+	GIT_STATUS_IGNORED          = (1u << 14),
+} git_status_t;
 
 /**
  * Gather file statuses and run a callback for each one.

src/diff.c

@@ -508,6 +508,7 @@ static int maybe_modified(
 	git_delta_t status = GIT_DELTA_MODIFIED;
 	unsigned int omode = oitem->mode;
 	unsigned int nmode = nitem->mode;
+	bool new_is_workdir = (new_iter->type == GIT_ITERATOR_WORKDIR);
 
 	GIT_UNUSED(old_iter);
 
@@ -515,15 +516,14 @@ static int maybe_modified(
 		return 0;
 
 	/* on platforms with no symlinks, preserve mode of existing symlinks */
-	if (S_ISLNK(omode) && S_ISREG(nmode) &&
-		!(diff->diffcaps & GIT_DIFFCAPS_HAS_SYMLINKS) &&
-		new_iter->type == GIT_ITERATOR_WORKDIR)
+	if (S_ISLNK(omode) && S_ISREG(nmode) && new_is_workdir &&
+		!(diff->diffcaps & GIT_DIFFCAPS_HAS_SYMLINKS))
 		nmode = omode;
 
 	/* on platforms with no execmode, just preserve old mode */
 	if (!(diff->diffcaps & GIT_DIFFCAPS_TRUST_MODE_BITS) &&
 		(nmode & MODE_BITS_MASK) != (omode & MODE_BITS_MASK) &&
-		new_iter->type == GIT_ITERATOR_WORKDIR)
+		new_is_workdir)
 		nmode = (nmode & ~MODE_BITS_MASK) | (omode & MODE_BITS_MASK);
 
 	/* support "assume unchanged" (poorly, b/c we still stat everything) */
@@ -537,11 +537,15 @@ static int maybe_modified(
 
 	/* if basic type of file changed, then split into delete and add */
 	else if (GIT_MODE_TYPE(omode) != GIT_MODE_TYPE(nmode)) {
+		if ((diff->opts.flags & GIT_DIFF_DONT_SPLIT_TYPECHANGE) != 0)
+			status = GIT_DELTA_TYPECHANGE;
+		else {
 			if (diff_delta__from_one(diff, GIT_DELTA_DELETED, oitem) < 0 ||
 				diff_delta__from_one(diff, GIT_DELTA_ADDED, nitem) < 0)
 				return -1;
 			return 0;
 		}
+	}
 
 	/* if oids and modes match, then file is unmodified */
 	else if (git_oid_cmp(&oitem->oid, &nitem->oid) == 0 &&
@@ -551,9 +555,7 @@ static int maybe_modified(
 	/* if we have an unknown OID and a workdir iterator, then check some
 	 * circumstances that can accelerate things or need special handling
 	 */
-	else if (git_oid_iszero(&nitem->oid) &&
-			 new_iter->type == GIT_ITERATOR_WORKDIR)
-	{
+	else if (git_oid_iszero(&nitem->oid) && new_is_workdir) {
 		/* TODO: add check against index file st_mtime to avoid racy-git */
 
 		/* if the stat data looks exactly alike, then assume the same */
@@ -600,7 +602,7 @@ static int maybe_modified(
 	/* if we got here and decided that the files are modified, but we
 	 * haven't calculated the OID of the new item, then calculate it now
 	 */
-	if (status == GIT_DELTA_MODIFIED && git_oid_iszero(&nitem->oid)) {
+	if (status != GIT_DELTA_UNMODIFIED && git_oid_iszero(&nitem->oid)) {
 		if (oid_for_workdir_item(diff->repo, nitem, &noid) < 0)
 			return -1;
 		else if (omode == nmode && git_oid_equal(&oitem->oid, &noid))

src/status.c

@@ -25,7 +25,6 @@ static unsigned int index_delta2status(git_delta_t index_status)
 	switch (index_status) {
 	case GIT_DELTA_ADDED:
 	case GIT_DELTA_COPIED:
-	case GIT_DELTA_RENAMED:
 		st = GIT_STATUS_INDEX_NEW;
 		break;
 	case GIT_DELTA_DELETED:
@@ -34,6 +33,12 @@ static unsigned int index_delta2status(git_delta_t index_status)
 	case GIT_DELTA_MODIFIED:
 		st = GIT_STATUS_INDEX_MODIFIED;
 		break;
+	case GIT_DELTA_RENAMED:
+		st = GIT_STATUS_INDEX_RENAMED;
+		break;
+	case GIT_DELTA_TYPECHANGE:
+		st = GIT_STATUS_INDEX_TYPECHANGE;
+		break;
 	default:
 		break;
 	}
@@ -47,8 +52,8 @@ static unsigned int workdir_delta2status(git_delta_t workdir_status)
 
 	switch (workdir_status) {
 	case GIT_DELTA_ADDED:
-	case GIT_DELTA_COPIED:
 	case GIT_DELTA_RENAMED:
+	case GIT_DELTA_COPIED:
 	case GIT_DELTA_UNTRACKED:
 		st = GIT_STATUS_WT_NEW;
 		break;
@@ -61,6 +66,9 @@ static unsigned int workdir_delta2status(git_delta_t workdir_status)
 	case GIT_DELTA_IGNORED:
 		st = GIT_STATUS_IGNORED;
 		break;
+	case GIT_DELTA_TYPECHANGE:
+		st = GIT_STATUS_WT_TYPECHANGE;
+		break;
 	default:
 		break;
 	}
@@ -92,6 +100,8 @@ int git_status_foreach_ext(
 	memset(&diffopt, 0, sizeof(diffopt));
 	memcpy(&diffopt.pathspec, &opts->pathspec, sizeof(diffopt.pathspec));
 
+	diffopt.flags = GIT_DIFF_DONT_SPLIT_TYPECHANGE;
+
 	if ((opts->flags & GIT_STATUS_OPT_INCLUDE_UNTRACKED) != 0)
 		diffopt.flags = diffopt.flags | GIT_DIFF_INCLUDE_UNTRACKED;
 	if ((opts->flags & GIT_STATUS_OPT_INCLUDE_IGNORED) != 0)