builtin/apply: make parse_chunk() return a negative integer on error

To libify `git apply` functionality we have to signal errors to the
caller instead of die()ing or exit()ing.

To do that in a compatible manner with the rest of the error handling
in builtin/apply.c, parse_chunk() should return a negative integer
instead of calling die() or exit().

As parse_chunk() is called only by apply_patch() which already
returns either -1 or -128 when an error happened, let's make it also
return -1 or -128.

This makes it compatible with what find_header() and parse_binary()
already return.

Helped-by: Eric Sunshine <sunshine@sunshineco.com>
Signed-off-by: Christian Couder <chriscool@tuxfamily.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/apply.c

@@ -1996,22 +1996,22 @@ static int use_patch(struct apply_state *state, struct patch *p)
 	return !state->has_include;
 }
 
-
 /*
  * Read the patch text in "buffer" that extends for "size" bytes; stop
  * reading after seeing a single patch (i.e. changes to a single file).
  * Create fragments (i.e. patch hunks) and hang them to the given patch.
- * Return the number of bytes consumed, so that the caller can call us
- * again for the next patch.
+ *
+ * Returns:
+ *   -1 if no header was found or parse_binary() failed,
+ *   -128 on another error,
+ *   the number of bytes consumed otherwise,
+ *     so that the caller can call us again for the next patch.
  */
 static int parse_chunk(struct apply_state *state, char *buffer, unsigned long size, struct patch *patch)
 {
 	int hdrsize, patchsize;
 	int offset = find_header(state, buffer, size, &hdrsize, patch);
 
-	if (offset == -128)
-		exit(128);
-
 	if (offset < 0)
 		return offset;
 
@@ -2071,8 +2071,10 @@ static int parse_chunk(struct apply_state *state, char *buffer, unsigned long si
 		 * empty to us here.
 		 */
 		if ((state->apply || state->check) &&
-		    (!patch->is_binary && !metadata_changes(patch)))
-			die(_("patch with only garbage at line %d"), state->linenr);
+		    (!patch->is_binary && !metadata_changes(patch))) {
+			error(_("patch with only garbage at line %d"), state->linenr);
+			return -128;
+		}
 	}
 
 	return offset + hdrsize + patchsize;
@@ -4455,6 +4457,10 @@ static int apply_patch(struct apply_state *state,
 		nr = parse_chunk(state, buf.buf + offset, buf.len - offset, patch);
 		if (nr < 0) {
 			free_patch(patch);
+			if (nr == -128) {
+				res = -128;
+				goto end;
+			}
 			break;
 		}
 		if (state->apply_in_reverse)