merge-recursive --patience

Teach the merge-recursive strategy a --patience option to use the
"patience diff" algorithm, which tends to improve results when
cherry-picking a patch that reorders functions at the same time as
refactoring them.

To support this, struct merge_options and ll_merge_options gain an
xdl_opts member, so programs can use arbitrary xdiff flags (think
"XDF_IGNORE_WHITESPACE") in a git-aware merge.

git merge and git rebase can be passed the -Xpatience option to
use this.

[jn: split from --ignore-space patch; with documentation]

Signed-off-by: Justin Frankel <justin@cockos.com>
Signed-off-by: Jonathan Nieder <jrnieder@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/merge-strategies.txt

@@ -40,6 +40,13 @@ the other tree did, declaring 'our' history contains all that happened in it.
 theirs;;
 	This is opposite of 'ours'.
 
+patience;;
+	With this option, 'merge-recursive' spends a little extra time
+	to avoid mismerges that sometimes occur due to unimportant
+	matching lines (e.g., braces from distinct functions).  Use
+	this when the branches to be merged have diverged wildly.
+	See also linkgit:git-diff[1] `--patience`.
+
 renormalize;;
 	This runs a virtual check-out and check-in of all three stages
 	of a file when resolving a three-way merge.  This option is

builtin/merge-recursive.c

@@ -2,6 +2,7 @@
 #include "commit.h"
 #include "tag.h"
 #include "merge-recursive.h"
+#include "xdiff-interface.h"
 
 static const char *better_branch_name(const char *branch)
 {

ll-merge.c

@@ -86,6 +86,7 @@ static int ll_xdl_merge(const struct ll_merge_driver *drv_unused,
 	memset(&xmp, 0, sizeof(xmp));
 	xmp.level = XDL_MERGE_ZEALOUS;
 	xmp.favor = opts->variant;
+	xmp.xpp.flags = opts->xdl_opts;
 	if (git_xmerge_style >= 0)
 		xmp.style = git_xmerge_style;
 	if (marker_size > 0)

ll-merge.h

@@ -9,6 +9,7 @@ struct ll_merge_options {
 	unsigned virtual_ancestor : 1;
 	unsigned variant : 2;	/* favor ours, favor theirs, or union merge */
 	unsigned renormalize : 1;
+	long xdl_opts;
 };
 
 int ll_merge(mmbuffer_t *result_buf,

merge-recursive.c

@@ -613,6 +613,7 @@ static int merge_3way(struct merge_options *o,
 	int merge_status;
 
 	ll_opts.renormalize = o->renormalize;
+	ll_opts.xdl_opts = o->xdl_opts;
 
 	if (o->call_depth) {
 		ll_opts.virtual_ancestor = 1;
@@ -1512,6 +1513,8 @@ int parse_merge_opt(struct merge_options *o, const char *s)
 		o->subtree_shift = "";
 	else if (!prefixcmp(s, "subtree="))
 		o->subtree_shift = s + strlen("subtree=");
+	else if (!strcmp(s, "patience"))
+		o->xdl_opts |= XDF_PATIENCE_DIFF;
 	else if (!strcmp(s, "renormalize"))
 		o->renormalize = 1;
 	else if (!strcmp(s, "no-renormalize"))

merge-recursive.h

@@ -15,6 +15,7 @@ struct merge_options {
 	const char *subtree_shift;
 	unsigned buffer_output : 1;
 	unsigned renormalize : 1;
+	long xdl_opts;
 	int verbosity;
 	int diff_rename_limit;
 	int merge_rename_limit;