Allow alternate "low-level" emit function from xdl_diff

For some users (e.g. git blame), getting textual patch output is just
extra work, as they can get all the information they need from the low-
level diff structures.  Allow for an alternate low-level emit function
to be defined to allow bypassing the textual patch generation; set
xemitconf_t's emit_func member to enable this.

The (void (*)()) type is pretty ugly, but the alternative would be to
include most of the private xdiff headers in xdiff.h to get the types
required for the "proper" function prototype.  Also, a (void *) won't
work, as ANSI C doesn't allow a function pointer to be cast to an
object pointer.

Signed-off-by: Brian Downing <bdowning@lavos.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

xdiff/xdiff.h

@@ -87,6 +87,7 @@ typedef struct s_xdemitconf {
 	unsigned long flags;
 	find_func_t find_func;
 	void *find_func_priv;
+	void (*emit_func)();
 } xdemitconf_t;
 
 typedef struct s_bdiffparam {

xdiff/xdiffi.c

@@ -538,6 +538,8 @@ int xdl_diff(mmfile_t *mf1, mmfile_t *mf2, xpparam_t const *xpp,
 	     xdemitconf_t const *xecfg, xdemitcb_t *ecb) {
 	xdchange_t *xscr;
 	xdfenv_t xe;
+	emit_func_t ef = xecfg->emit_func ?
+		(emit_func_t)xecfg->emit_func : xdl_emit_diff;
 
 	if (xdl_do_diff(mf1, mf2, xpp, &xe) < 0) {
 
@@ -551,7 +553,7 @@ int xdl_diff(mmfile_t *mf1, mmfile_t *mf2, xpparam_t const *xpp,
 		return -1;
 	}
 	if (xscr) {
-		if (xdl_emit_diff(&xe, xscr, ecb, xecfg) < 0) {
+		if (ef(&xe, xscr, ecb, xecfg) < 0) {
 
 			xdl_free_script(xscr);
 			xdl_free_env(&xe);

xdiff/xemit.c

@@ -27,7 +27,6 @@
 
 static long xdl_get_rec(xdfile_t *xdf, long ri, char const **rec);
 static int xdl_emit_record(xdfile_t *xdf, long ri, char const *pre, xdemitcb_t *ecb);
-static xdchange_t *xdl_get_hunk(xdchange_t *xscr, xdemitconf_t const *xecfg);
 
 
 
@@ -58,7 +57,7 @@ static int xdl_emit_record(xdfile_t *xdf, long ri, char const *pre, xdemitcb_t *
  * Starting at the passed change atom, find the latest change atom to be included
  * inside the differential hunk according to the specified configuration.
  */
-static xdchange_t *xdl_get_hunk(xdchange_t *xscr, xdemitconf_t const *xecfg) {
+xdchange_t *xdl_get_hunk(xdchange_t *xscr, xdemitconf_t const *xecfg) {
 	xdchange_t *xch, *xchp;
 
 	for (xchp = xscr, xch = xscr->next; xch; xchp = xch, xch = xch->next)

xdiff/xemit.h

@@ -24,7 +24,10 @@
 #define XEMIT_H
 
 
+typedef int (*emit_func_t)(xdfenv_t *xe, xdchange_t *xscr, xdemitcb_t *ecb,
+			   xdemitconf_t const *xecfg);
 
+xdchange_t *xdl_get_hunk(xdchange_t *xscr, xdemitconf_t const *xecfg);
 int xdl_emit_diff(xdfenv_t *xe, xdchange_t *xscr, xdemitcb_t *ecb,
 		  xdemitconf_t const *xecfg);