[PATCH 1/2] xdiff: implement a zealous diff3, or "zdiff3"

@@ -34,6 +34,8 @@ int cmd_merge_file(int argc, const char **argv, const char *prefix)
 	struct option options[] = {
 		OPT_BOOL('p', "stdout", &to_stdout, N_("send results to standard output")),
 		OPT_SET_INT(0, "diff3", &xmp.style, N_("use a diff3 based merge"), XDL_MERGE_DIFF3),
+		OPT_SET_INT(0, "zdiff3", &xmp.style, N_("use a zealous diff3 based merge"),
+				XDL_MERGE_ZEALOUS_DIFF3),
 		OPT_SET_INT(0, "ours", &xmp.favor, N_("for conflicts, use our version"),
 			    XDL_MERGE_FAVOR_OURS),
 		OPT_SET_INT(0, "theirs", &xmp.favor, N_("for conflicts, use their version"),

@@ -1566,7 +1566,7 @@ _git_checkout ()
 
 	case "$cur" in
 	--conflict=*)
-		__gitcomp "diff3 merge" "" "${cur##--conflict=}"
+		__gitcomp "diff3 merge zdiff3" "" "${cur##--conflict=}"
 		;;
 	--*)
 		__gitcomp_builtin checkout

@@ -308,6 +308,8 @@ int git_xmerge_config(const char *var, const char *value, void *cb)
 			die("'%s' is not a boolean", var);
 		if (!strcmp(value, "diff3"))
 			git_xmerge_style = XDL_MERGE_DIFF3;
+		else if (!strcmp(value, "zdiff3"))
+			git_xmerge_style = XDL_MERGE_ZEALOUS_DIFF3;
 		else if (!strcmp(value, "merge"))
 			git_xmerge_style = 0;
 		/*

@@ -65,6 +65,7 @@ extern "C" {
 
 /* merge output styles */
 #define XDL_MERGE_DIFF3 1
+#define XDL_MERGE_ZEALOUS_DIFF3 2
 
 typedef struct s_mmfile {
 	char *ptr;

@@ -230,7 +230,7 @@ static int fill_conflict_hunk(xdfenv_t *xe1, const char *name1,
 	size += xdl_recs_copy(xe1, m->i1, m->chg1, needs_cr, 1,
 			      dest ? dest + size : NULL);
 
-	if (style == XDL_MERGE_DIFF3) {
+	if (style == XDL_MERGE_DIFF3 || style == XDL_MERGE_ZEALOUS_DIFF3) {
 		/* Shared preimage */
 		if (!dest) {
 			size += marker_size + 1 + needs_cr + marker3_size;

@@ -327,7 +327,7 @@ static int xdl_fill_merge_buffer(xdfenv_t *xe1, const char *name1,
  * lines. Try hard to show only these few lines as conflicting.
  */
 static int xdl_refine_conflicts(xdfenv_t *xe1, xdfenv_t *xe2, xdmerge_t *m,
-		xpparam_t const *xpp)
+				xpparam_t const *xpp, int style)
 {
 	for (; m; m = m->next) {
 		mmfile_t t1, t2;

@@ -368,6 +368,42 @@ static int xdl_refine_conflicts(xdfenv_t *xe1, xdfenv_t *xe2, xdmerge_t *m,
 			continue;
 		}
 		x = xscr;
+		if (style == XDL_MERGE_ZEALOUS_DIFF3) {
+			int advance1 = xscr->i1, advance2 = xscr->i2;
+
+			/*
+			 * Advance m->i1 and m->i2 so that conflict for sides
+			 * 1 and 2 start after common region.  Decrement
+			 * m->chg[12] since there are now fewer conflict lines
+			 * for those sides.
+			 */
+			m->i1 += advance1;
+			m->i2 += advance2;
+			m->chg1 -= advance1;
+			m->chg2 -= advance2;
+
+			/*
+			 * Splitting conflicts due to internal common regions
+			 * on the two sides would be inappropriate since we
+			 * are also showing the merge base and have no
+			 * reasonable way to split the merge base text.
+			 */
+			while (xscr->next)
+				xscr = xscr->next;
+
+			/*
+			 * Lower the number of conflict lines to not include
+			 * the final common lines, if any.  Do this by setting
+			 * number of conflict lines to
+			 *   (line offset for start of conflict in xscr) +
+			 *   (number of lines in the conflict in xscr)
+			 */
+			m->chg1 = (xscr->i1 - advance1) + (xscr->chg1);
+			m->chg2 = (xscr->i2 - advance2) + (xscr->chg2);
+			xdl_free_env(&xe);
+			xdl_free_script(x);
+			continue;
+		}
 		m->i1 = xscr->i1 + i1;
 		m->chg1 = xscr->chg1;
 		m->i2 = xscr->i2 + i2;

@@ -482,6 +518,16 @@ static int xdl_do_merge(xdfenv_t *xe1, xdchange_t *xscr1,
 	int style = xmp->style;
 	int favor = xmp->favor;
 
+	/*
+	 * XDL_MERGE_DIFF3 does not attempt to refine conflicts by looking
+	 * at common areas of sides 1 & 2, because the base (side 0) does
+	 * not match and is being shown.
+	 *
+	 * XDL_MERGE_ZEALOUS_DIFF3 will attempt to refine conflicts
+	 * looking for common areas of sides 1 & 2, despite the base
+	 * not matching and being shown, but will only look for common
+	 * areas at the beginning or ending of the conflict block.
+	 */
 	if (style == XDL_MERGE_DIFF3) {
 		/*
 		 * "diff3 -m" output does not make sense for anything

@@ -604,7 +650,7 @@ static int xdl_do_merge(xdfenv_t *xe1, xdchange_t *xscr1,
 		changes = c;
 	/* refine conflicts */
 	if (XDL_MERGE_ZEALOUS <= level &&
-	    (xdl_refine_conflicts(xe1, xe2, changes, xpp) < 0 ||
+	    (xdl_refine_conflicts(xe1, xe2, changes, xpp, style) < 0 ||
 	     xdl_simplify_non_conflicts(xe1, changes,
 					XDL_MERGE_ZEALOUS < level) < 0)) {
 		xdl_cleanup_merge(changes);