Generalize and libify index_is_dirty() to index_differs_from(...)

index_is_dirty() in builtin-revert.c checks if the index is dirty.
This patch generalizes this function to check if the index differs
from a revision, i.e. the former index_is_dirty() behavior can now be
achieved by index_differs_from("HEAD", 0).

The second argument "diff_flags" allows to set further diff option
flags like DIFF_OPT_IGNORE_SUBMODULES. See DIFF_OPT_* macros in diff.h
for a list.

index_differs_from() seems to be useful for more than builtin-revert.c,
so it is moved into diff-lib.c and also used in builtin-commit.c.

Yet to mention:

 - "rev.abbrev = 0;" can be safely removed.
   This has no impact on performance or functioning of neither
   setup_revisions() nor run_diff_index().

 - rev.pending.objects is free()d because this fixes a leak.
   (Also see 295dd2ad "Fix memory leak in traverse_commit_list")

Mentored-by: Daniel Barkalow <barkalow@iabervon.org>
Mentored-by: Christian Couder <chriscool@tuxfamily.org>
Signed-off-by: Stephan Beyer <s-beyer@gmx.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 2 insertions, 11 deletions

diff --git a/builtin-commit.c b/builtin-commit.c
index d6a3a6203..46e649cd7 100644
--- a/builtin-commit.c
+++ b/builtin-commit.c
@@ -561,7 +561,6 @@ static int prepare_to_commit(const char *index_file, const char *prefix)
 		commitable = run_status(fp, index_file, prefix, 1);
 		wt_status_use_color = saved_color_setting;
 	} else {
-		struct rev_info rev;
 		unsigned char sha1[20];
 		const char *parent = "HEAD";
 
@@ -573,16 +572,8 @@ static int prepare_to_commit(const char *index_file, const char *prefix)
 
 		if (get_sha1(parent, sha1))
 			commitable = !!active_nr;
-		else {
-			init_revisions(&rev, "");
-			rev.abbrev = 0;
-			setup_revisions(0, NULL, &rev, parent);
-			DIFF_OPT_SET(&rev.diffopt, QUIET);
-			DIFF_OPT_SET(&rev.diffopt, EXIT_WITH_STATUS);
-			run_diff_index(&rev, 1 /* cached */);
-
-			commitable = !!DIFF_OPT_TST(&rev.diffopt, HAS_CHANGES);
-		}
+		else
+			commitable = index_differs_from(parent, 0);
 	}
 
 	fclose(fp);