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authorJohan Herland <johan@herland.net>2010-11-09 22:49:41 +0100
committerJunio C Hamano <gitster@pobox.com>2010-11-10 10:25:52 -0800
commite2656c82fd836a3d410230c98f6a725368f15642 (patch)
tree340dfa322efafa49212b5cc9ba2f157e76614f9a /notes.h
parenta5cdebea55d53406e117d9a1fd4cc316ef036553 (diff)
downloadgit-e2656c82fd836a3d410230c98f6a725368f15642.tar.gz
notes.h/c: Allow combine_notes functions to remove notes
Allow combine_notes functions to request that a note be removed, by setting the resulting note SHA1 to null_sha1 (0000000...). For consistency, also teach note_tree_insert() to skip insertion of an empty note (a note with entry->val_sha1 equal to null_sha1) when there is no note to combine it with. In general, an empty note (null_sha1) is treated identically to no note at all, but when adding an empty note where there already exists a non-empty note, we allow the combine_notes function to potentially record a new/changed note. Document this behaviour, and clearly specify how combine_notes functions are expected to handle null_sha1 in input. Before this patch, storing null_sha1s in the notes tree were silently allowed, causing an invalid notes tree (referring to blobs with null_sha1) to be produced by write_notes_tree(). Signed-off-by: Johan Herland <johan@herland.net> Signed-off-by: Junio C Hamano <gitster@pobox.com>
Diffstat (limited to 'notes.h')
-rw-r--r--notes.h16
1 files changed, 15 insertions, 1 deletions
diff --git a/notes.h b/notes.h
index 20db42fe95..79ea7976ab 100644
--- a/notes.h
+++ b/notes.h
@@ -12,7 +12,10 @@
* resulting SHA1 into the first SHA1 argument (cur_sha1). A non-zero return
* value indicates failure.
*
- * The two given SHA1s must both be non-NULL and different from each other.
+ * The two given SHA1s shall both be non-NULL and different from each other.
+ * Either of them (but not both) may be == null_sha1, which indicates an
+ * empty/non-existent note. If the resulting SHA1 (cur_sha1) is == null_sha1,
+ * the note will be removed from the notes tree.
*
* The default combine_notes function (you get this when passing NULL) is
* combine_notes_concatenate(), which appends the contents of the new note to
@@ -90,6 +93,17 @@ void init_notes(struct notes_tree *t, const char *notes_ref,
/*
* Add the given note object to the given notes_tree structure
*
+ * If there already exists a note for the given object_sha1, the given
+ * combine_notes function is invoked to break the tie. If not given (i.e.
+ * combine_notes == NULL), the default combine_notes function for the given
+ * notes_tree is used.
+ *
+ * Passing note_sha1 == null_sha1 indicates the addition of an
+ * empty/non-existent note. This is a (potentially expensive) no-op unless
+ * there already exists a note for the given object_sha1, AND combining that
+ * note with the empty note (using the given combine_notes function) results
+ * in a new/changed note.
+ *
* IMPORTANT: The changes made by add_note() to the given notes_tree structure
* are not persistent until a subsequent call to write_notes_tree() returns
* zero.