xdiff: add hunk_func()

Add a way to register a callback function that is gets passed the
start line and line count of each hunk of a diff.  Only standard
types are used.

Signed-off-by: Rene Scharfe <rene.scharfe@lsrfire.ath.cx>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

xdiff/xdiff.h

@@ -86,13 +86,18 @@ typedef struct s_xdemitcb {
 
 typedef long (*find_func_t)(const char *line, long line_len, char *buffer, long buffer_size, void *priv);
 
+typedef int (*xdl_emit_hunk_consume_func_t)(long start_a, long count_a,
+					    long start_b, long count_b,
+					    void *cb_data);
+
 typedef struct s_xdemitconf {
 	long ctxlen;
 	long interhunkctxlen;
 	unsigned long flags;
 	find_func_t find_func;
 	void *find_func_priv;
 	void (*emit_func)();
+	xdl_emit_hunk_consume_func_t hunk_func;
 } xdemitconf_t;
 
 typedef struct s_bdiffparam {

xdiff/xdiffi.c

@@ -538,6 +538,20 @@ void xdl_free_script(xdchange_t *xscr) {
 	}
 }
 
+static int xdl_call_hunk_func(xdfenv_t *xe, xdchange_t *xscr, xdemitcb_t *ecb,
+			      xdemitconf_t const *xecfg)
+{
+	xdchange_t *xch, *xche;
+
+	for (xch = xscr; xch; xch = xche->next) {
+		xche = xdl_get_hunk(xch, xecfg);
+		if (xecfg->hunk_func(xch->i1, xche->i1 + xche->chg1 - xch->i1,
+				     xch->i2, xche->i2 + xche->chg2 - xch->i2,
+				     ecb->priv) < 0)
+			return -1;
+	}
+	return 0;
+}
 
 int xdl_diff(mmfile_t *mf1, mmfile_t *mf2, xpparam_t const *xpp,
 	     xdemitconf_t const *xecfg, xdemitcb_t *ecb) {
@@ -546,6 +560,9 @@ int xdl_diff(mmfile_t *mf1, mmfile_t *mf2, xpparam_t const *xpp,
 	emit_func_t ef = xecfg->emit_func ?
 		(emit_func_t)xecfg->emit_func : xdl_emit_diff;
 
+	if (xecfg->hunk_func)
+		ef = xdl_call_hunk_func;
+
 	if (xdl_do_diff(mf1, mf2, xpp, &xe) < 0) {
 
 		return -1;