From e2656c82fd836a3d410230c98f6a725368f15642 Mon Sep 17 00:00:00 2001 From: Johan Herland Date: Tue, 9 Nov 2010 22:49:41 +0100 Subject: 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 Signed-off-by: Junio C Hamano --- notes.h | 16 +++++++++++++++- 1 file changed, 15 insertions(+), 1 deletion(-) (limited to 'notes.h') 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. -- cgit v1.2.1