WIP: remerge-diff: suppress conflict marker labels

TODO: Deliberate whether this makes sense only optionally, e.g. with
`range-diff --diff-merges=remerge`. If so: How to do that? Do we need to
avoid the spawned `git log` calls in `range-diff.c` for that, in which
case we face a then-again-premature optimization again that I fixed in
ab75a56 (log: --remerge-diff needs to keep around commit parents,
2024-11-08). Besides, that would need to be refactored into its own
patch as it would otherwise over-extend the scope.

TODO: add a test case that demonstrates how this is useful.

TODO: explain in the commit message why this is useful.

Signed-off-by: Johannes Schindelin <[email protected]>

log-tree.c

@@ -1025,6 +1025,7 @@ static int do_remerge_diff(struct rev_info *opt,
 	init_ui_merge_options(&o, the_repository);
 	o.show_rename_progress = 0;
 	o.record_conflict_msgs_as_headers = 1;
+	o.suppress_conflict_labels = 1;
 	o.msg_header_prefix = "remerge";
 
 	ctx.abbrev = DEFAULT_ABBREV;

merge-ort.c

@@ -2085,7 +2085,11 @@ static int merge_3way(struct merge_options *opt,
 	}
 
 	assert(pathnames[0] && pathnames[1] && pathnames[2] && opt->ancestor);
-	if (pathnames[0] == pathnames[1] && pathnames[1] == pathnames[2]) {
+	if (opt->suppress_conflict_labels) {
+		base = xstrdup("");
+		name1 = xstrdup("");
+		name2 = xstrdup("");
+	} else if (pathnames[0] == pathnames[1] && pathnames[1] == pathnames[2]) {
 		base  = mkpathdup("%s", opt->ancestor);
 		name1 = mkpathdup("%s", opt->branch1);
 		name2 = mkpathdup("%s", opt->branch2);

merge-recursive.h

@@ -48,6 +48,7 @@ struct merge_options {
 	const char *subtree_shift;
 	unsigned renormalize : 1;
 	unsigned record_conflict_msgs_as_headers : 1;
+	unsigned suppress_conflict_labels : 1;
 	const char *msg_header_prefix;
 
 	/* internal fields used by the implementation */