merge options: add a conflict style member

Add a conflict_style member to `struct merge_options` and `struct
ll_merge_options` to allow callers to override the default conflict
style. This will be used in the next commit.

Signed-off-by: Phillip Wood <phillip.wood@dunelm.org.uk>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

merge-ll.c

@@ -128,7 +128,9 @@ static enum ll_merge_result ll_xdl_merge(const struct ll_merge_driver *drv_unuse
 	xmp.level = XDL_MERGE_ZEALOUS;
 	xmp.favor = opts->variant;
 	xmp.xpp.flags = opts->xdl_opts;
-	if (git_xmerge_style >= 0)
+	if (opts->conflict_style >= 0)
+		xmp.style = opts->conflict_style;
+	else if (git_xmerge_style >= 0)
 		xmp.style = git_xmerge_style;
 	if (marker_size > 0)
 		xmp.marker_size = marker_size;

merge-ll.h

@@ -78,11 +78,14 @@ struct ll_merge_options {
 	 */
 	unsigned extra_marker_size;
 
+	/* Override the global conflict style. */
+	int conflict_style;
+
 	/* Extra xpparam_t flags as defined in xdiff/xdiff.h. */
 	long xdl_opts;
 };
 
-#define LL_MERGE_OPTIONS_INIT {0}
+#define LL_MERGE_OPTIONS_INIT { .conflict_style = -1 }
 
 enum ll_merge_result {
 	LL_MERGE_ERROR = -1,

merge-ort.c

@@ -1966,6 +1966,7 @@ static int merge_3way(struct merge_options *opt,
 	ll_opts.renormalize = opt->renormalize;
 	ll_opts.extra_marker_size = extra_marker_size;
 	ll_opts.xdl_opts = opt->xdl_opts;
+	ll_opts.conflict_style = opt->conflict_style;
 
 	if (opt->priv->call_depth) {
 		ll_opts.virtual_ancestor = 1;

merge-recursive.c

@@ -1054,6 +1054,7 @@ static int merge_3way(struct merge_options *opt,
 	ll_opts.renormalize = opt->renormalize;
 	ll_opts.extra_marker_size = extra_marker_size;
 	ll_opts.xdl_opts = opt->xdl_opts;
+	ll_opts.conflict_style = opt->conflict_style;
 
 	if (opt->priv->call_depth) {
 		ll_opts.virtual_ancestor = 1;
@@ -3899,6 +3900,8 @@ void init_merge_options(struct merge_options *opt,
 
 	opt->renormalize = 0;
 
+	opt->conflict_style = -1;
+
 	merge_recursive_config(opt);
 	merge_verbosity = getenv("GIT_MERGE_VERBOSITY");
 	if (merge_verbosity)

merge-recursive.h

@@ -31,6 +31,7 @@ struct merge_options {
 
 	/* xdiff-related options (patience, ignore whitespace, ours/theirs) */
 	long xdl_opts;
+	int conflict_style;
 	enum {
 		MERGE_VARIANT_NORMAL = 0,
 		MERGE_VARIANT_OURS,