Add "as_path" parameters to blob and buffer diffs

This adds parameters to the four functions that allow for blob-to-
blob and blob-to-buffer differencing (either via callbacks or by
making a git_diff_patch object).  These parameters let you say
that filename we should pretend the blob has while doing the diff.
If you pass NULL, there should be no change from the existing
behavior, which is to skip using attributes for file type checks
and just look at content.  With the parameters, you can plug into
the new diff driver functionality and get binary or non-binary
behavior, plus function context regular expressions, etc.

This commit also fixes things so that the git_diff_delta that is
generated by these functions will actually be populated with the
data that we know about the blobs (or buffers) so you can use it
appropriately.  It also fixes a bug in generating patches from
the git_diff_patch objects created via these functions.

Lastly, there is one other behavior change that may matter.  If
there is no difference between the two blobs, these functions no
longer generate any diff callbacks / patches unless you have
passed in GIT_DIFF_INCLUDE_UNMODIFIED.  This is pretty natural,
but could potentially change the behavior of existing usage.

1 files changed, 13 insertions, 9 deletions

diff --git a/src/diff_print.c b/src/diff_print.c
index 6fc7425eb..30f221a62 100644
--- a/src/diff_print.c
+++ b/src/diff_print.c
@@ -21,14 +21,15 @@ static int diff_print_info_init(
 	diff_print_info *pi,
 	git_buf *out, git_diff_list *diff, git_diff_data_cb cb, void *payload)
 {
-	assert(diff && diff->repo);
-
 	pi->diff     = diff;
 	pi->print_cb = cb;
 	pi->payload  = payload;
 	pi->buf      = out;
 
-	if (git_repository__cvar(&pi->oid_strlen, diff->repo, GIT_CVAR_ABBREV) < 0)
+	if (!diff || !diff->repo)
+		pi->oid_strlen = GIT_ABBREV_DEFAULT;
+	else if (git_repository__cvar(
+		&pi->oid_strlen, diff->repo, GIT_CVAR_ABBREV) < 0)
 		return -1;
 
 	pi->oid_strlen += 1; /* for NUL byte */
@@ -82,6 +83,8 @@ static int diff_print_one_compact(
 	diff_print_info *pi = data;
 	git_buf *out = pi->buf;
 	char old_suffix, new_suffix, code = git_diff_status_char(delta->status);
+	int (*strcomp)(const char *, const char *) =
+		pi->diff ? pi->diff->strcomp : git__strcmp;
 
 	GIT_UNUSED(progress);
 
@@ -94,7 +97,7 @@ static int diff_print_one_compact(
 	git_buf_clear(out);
 
 	if (delta->old_file.path != delta->new_file.path &&
-		pi->diff->strcomp(delta->old_file.path,delta->new_file.path) != 0)
+		strcomp(delta->old_file.path,delta->new_file.path) != 0)
 		git_buf_printf(out, "%c\t%s%c -> %s%c\n", code,
 			delta->old_file.path, old_suffix, delta->new_file.path, new_suffix);
 	else if (delta->old_file.mode != delta->new_file.mode &&
@@ -229,10 +232,11 @@ static int diff_print_patch_file(
 	const git_diff_delta *delta, float progress, void *data)
 {
 	diff_print_info *pi = data;
-	const char *oldpfx = pi->diff->opts.old_prefix;
+	const char *oldpfx = pi->diff ? pi->diff->opts.old_prefix : NULL;
 	const char *oldpath = delta->old_file.path;
-	const char *newpfx = pi->diff->opts.new_prefix;
+	const char *newpfx = pi->diff ? pi->diff->opts.new_prefix : NULL;
 	const char *newpath = delta->new_file.path;
+	uint32_t opts_flags = pi->diff ? pi->diff->opts.flags : GIT_DIFF_NORMAL;
 
 	GIT_UNUSED(progress);
 
@@ -240,17 +244,17 @@ static int diff_print_patch_file(
 		delta->status == GIT_DELTA_UNMODIFIED ||
 		delta->status == GIT_DELTA_IGNORED ||
 		(delta->status == GIT_DELTA_UNTRACKED &&
-		 (pi->diff->opts.flags & GIT_DIFF_INCLUDE_UNTRACKED_CONTENT) == 0))
+		 (opts_flags & GIT_DIFF_INCLUDE_UNTRACKED_CONTENT) == 0))
 		return 0;
 
 	if (!oldpfx)
 		oldpfx = DIFF_OLD_PREFIX_DEFAULT;
-
 	if (!newpfx)
 		newpfx = DIFF_NEW_PREFIX_DEFAULT;
 
 	git_buf_clear(pi->buf);
-	git_buf_printf(pi->buf, "diff --git %s%s %s%s\n", oldpfx, delta->old_file.path, newpfx, delta->new_file.path);
+	git_buf_printf(pi->buf, "diff --git %s%s %s%s\n",
+		oldpfx, delta->old_file.path, newpfx, delta->new_file.path);
 
 	if (diff_print_oid_range(pi, delta) < 0)
 		return -1;