hashmap.h: compare function has access to a data field

When using the hashmap a common need is to have access to caller provided
data in the compare function. A couple of times we abuse the keydata field
to pass in the data needed. This happens for example in patch-ids.c.

This patch changes the function signature of the compare function
to have one more void pointer available. The pointer given for each
invocation of the compare function must be defined in the init function
of the hashmap and is just passed through.

Documentation of this new feature is deferred to a later patch.
This is a rather mechanical conversion, just adding the new pass-through
parameter.  However while at it improve the naming of the fields of all
compare functions used by hashmaps by ensuring unused parameters are
prefixed with 'unused_' and naming the parameters what they are (instead
of 'unused' make it 'unused_keydata').

Signed-off-by: Stefan Beller <sbeller@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 4 insertions, 2 deletions

diff --git a/patch-ids.c b/patch-ids.c
index 9c0ab9e67a..815c115811 100644
--- a/patch-ids.c
+++ b/patch-ids.c
@@ -35,7 +35,8 @@ int commit_patch_id(struct commit *commit, struct diff_options *options,
  * the side of safety.  The actual value being negative does not have
  * any significance; only that it is non-zero matters.
  */
-static int patch_id_cmp(struct patch_id *a,
+static int patch_id_cmp(const void *unused_cmp_data,
+			struct patch_id *a,
 			struct patch_id *b,
 			struct diff_options *opt)
 {
@@ -57,7 +58,8 @@ int init_patch_ids(struct patch_ids *ids)
 	ids->diffopts.detect_rename = 0;
 	DIFF_OPT_SET(&ids->diffopts, RECURSIVE);
 	diff_setup_done(&ids->diffopts);
-	hashmap_init(&ids->patches, (hashmap_cmp_fn)patch_id_cmp, 256);
+	hashmap_init(&ids->patches, (hashmap_cmp_fn)patch_id_cmp,
+		     NULL, 256);
 	return 0;
 }