xdiff-interface: replace discard_hunk_line() with a flag

Remove the dummy discard_hunk_line() function added in
3b40a090fd4 (diff: avoid generating unused hunk header lines,
2018-11-02) in favor of having a new XDL_EMIT_NO_HUNK_HDR flag, for
use along with the two existing and similar XDL_EMIT_* flags.

Unlike the recently amended xdiff_emit_line_fn interface which'll be
called in a loop in xdl_emit_diff(), the hunk header is only emitted
once.

It makes more sense to pass this as a flag than provide a dummy
callback because that function may be able to skip doing certain work
if it knows the caller is doing nothing with the hunk header.

It would be possible to do so in the case of -U0 now, but the benefit
of doing so is so small that I haven't bothered. But this leaves the
door open to that, and more importantly makes the API use more
intuitive.

The reason we're putting a flag in the gap between 1<<0 and 1<<2 is
that the old 1<<1 flag was removed in 907681e940d (xdiff: drop
XDL_EMIT_COMMON, 2016-02-23) without re-ordering the remaining flags.

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

6 files changed, 9 insertions, 19 deletions

diff --git a/diff.c b/diff.c
index 7a03c581c7..fe3abac79f 100644
--- a/diff.c
+++ b/diff.c
@@ -3725,7 +3725,8 @@ static void builtin_diffstat(const char *name_a, const char *name_b,
 		xpp.anchors_nr = o->anchors_nr;
 		xecfg.ctxlen = o->context;
 		xecfg.interhunkctxlen = o->interhunkcontext;
-		if (xdi_diff_outf(&mf1, &mf2, discard_hunk_line,
+		xecfg.flags = XDL_EMIT_NO_HUNK_HDR;
+		if (xdi_diff_outf(&mf1, &mf2, NULL,
 				  diffstat_consume, diffstat, &xpp, &xecfg))
 			die("unable to generate diffstat for %s", one->path);
 
@@ -6233,8 +6234,8 @@ static int diff_get_patch_id(struct diff_options *options, struct object_id *oid
 
 		xpp.flags = 0;
 		xecfg.ctxlen = 3;
-		xecfg.flags = 0;
-		if (xdi_diff_outf(&mf1, &mf2, discard_hunk_line,
+		xecfg.flags = XDL_EMIT_NO_HUNK_HDR;
+		if (xdi_diff_outf(&mf1, &mf2, NULL,
 				  patch_id_consume, &data, &xpp, &xecfg))
 			return error("unable to generate patch-id diff for %s",
 				     p->one->path);
diff --git a/diffcore-pickaxe.c b/diffcore-pickaxe.c
index 96183f4cfa..c88e50c632 100644
--- a/diffcore-pickaxe.c
+++ b/diffcore-pickaxe.c
@@ -53,6 +53,7 @@ static int diff_grep(mmfile_t *one, mmfile_t *two,
 	memset(&xecfg, 0, sizeof(xecfg));
 	ecbdata.regexp = regexp;
 	ecbdata.hit = 0;
+	xecfg.flags = XDL_EMIT_NO_HUNK_HDR;
 	xecfg.ctxlen = o->context;
 	xecfg.interhunkctxlen = o->interhunkcontext;
 
@@ -60,7 +61,7 @@ static int diff_grep(mmfile_t *one, mmfile_t *two,
 	 * An xdiff error might be our "data->hit" from above. See the
 	 * comment for xdiff_emit_line_fn in xdiff-interface.h
 	 */
-	ret = xdi_diff_outf(one, two, discard_hunk_line, diffgrep_consume,
+	ret = xdi_diff_outf(one, two, NULL, diffgrep_consume,
 			    &ecbdata, &xpp, &xecfg);
 	if (ecbdata.hit)
 		return 1;
diff --git a/xdiff-interface.c b/xdiff-interface.c
index 50c0ef759d..95f13a93ff 100644
--- a/xdiff-interface.c
+++ b/xdiff-interface.c
@@ -126,12 +126,6 @@ int xdi_diff(mmfile_t *mf1, mmfile_t *mf2, xpparam_t const *xpp, xdemitconf_t co
 	return xdl_diff(&a, &b, xpp, xecfg, xecb);
 }
 
-void discard_hunk_line(void *priv,
-		       long ob, long on, long nb, long nn,
-		       const char *func, long funclen)
-{
-}
-
 int xdi_diff_outf(mmfile_t *mf1, mmfile_t *mf2,
 		  xdiff_emit_hunk_fn hunk_fn,
 		  xdiff_emit_line_fn line_fn,
diff --git a/xdiff-interface.h b/xdiff-interface.h
index 3b6819586d..4301a7eef2 100644
--- a/xdiff-interface.h
+++ b/xdiff-interface.h
@@ -54,14 +54,6 @@ int git_xmerge_config(const char *var, const char *value, void *cb);
 extern int git_xmerge_style;
 
 /*
- * Can be used as a no-op hunk_fn for xdi_diff_outf(), since a NULL
- * one just sends the hunk line to the line_fn callback).
- */
-void discard_hunk_line(void *priv,
-		       long ob, long on, long nb, long nn,
-		       const char *func, long funclen);
-
-/*
  * Compare the strings l1 with l2 which are of size s1 and s2 respectively.
  * Returns 1 if the strings are deemed equal, 0 otherwise.
  * The `flags` given as XDF_WHITESPACE_FLAGS determine how white spaces
diff --git a/xdiff/xdiff.h b/xdiff/xdiff.h
index 7a04605146..b29deca5de 100644
--- a/xdiff/xdiff.h
+++ b/xdiff/xdiff.h
@@ -50,6 +50,7 @@ extern "C" {
 
 /* xdemitconf_t.flags */
 #define XDL_EMIT_FUNCNAMES (1 << 0)
+#define XDL_EMIT_NO_HUNK_HDR (1 << 1)
 #define XDL_EMIT_FUNCCONTEXT (1 << 2)
 
 /* merge simplification levels */
diff --git a/xdiff/xemit.c b/xdiff/xemit.c
index 9d7d6c5087..1cbf2b9829 100644
--- a/xdiff/xemit.c
+++ b/xdiff/xemit.c
@@ -278,7 +278,8 @@ pre_context_calculation:
 				      s1 - 1, funclineprev);
 			funclineprev = s1 - 1;
 		}
-		if (xdl_emit_hunk_hdr(s1 + 1, e1 - s1, s2 + 1, e2 - s2,
+		if (!(xecfg->flags & XDL_EMIT_NO_HUNK_HDR) &&
+		    xdl_emit_hunk_hdr(s1 + 1, e1 - s1, s2 + 1, e2 - s2,
 				      func_line.buf, func_line.len, ecb) < 0)
 			return -1;