apply: avoid using fixed-size buffer in write_out_one_reject()

On some systems PATH_MAX is not a hard limit.  Support longer paths by
building them on the heap instead of using static buffers.

Take care to work around (arguably buggy) implementations of free(3)
that change errno by calling it only after using the errno value.

Signed-off-by: René Scharfe <l.s.r@web.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: rscharfe

apply.c

@@ -4612,7 +4612,7 @@ static int write_out_one_result(struct apply_state *state,
 static int write_out_one_reject(struct apply_state *state, struct patch *patch)
 {
 	FILE *rej;
-	char namebuf[PATH_MAX];
+	char *namebuf;
 	struct fragment *frag;
 	int fd, cnt = 0;
 	struct strbuf sb = STRBUF_INIT;
@@ -4645,30 +4645,29 @@ static int write_out_one_reject(struct apply_state *state, struct patch *patch)
 		say_patch_name(stderr, sb.buf, patch);
 	strbuf_release(&sb);
 
-	cnt = strlen(patch->new_name);
-	if (ARRAY_SIZE(namebuf) <= cnt + 5) {
-		cnt = ARRAY_SIZE(namebuf) - 5;
-		warning(_("truncating .rej filename to %.*s.rej"),
-			cnt - 1, patch->new_name);
-	}
-	memcpy(namebuf, patch->new_name, cnt);
-	memcpy(namebuf + cnt, ".rej", 5);
+	namebuf = xstrfmt("%s.rej", patch->new_name);
 
 	fd = open(namebuf, O_CREAT | O_EXCL | O_WRONLY, 0666);
 	if (fd < 0) {
-		if (errno != EEXIST)
-			return error_errno(_("cannot open %s"), namebuf);
-		if (unlink(namebuf))
-			return error_errno(_("cannot unlink '%s'"), namebuf);
+		if (errno != EEXIST) {
+			error_errno(_("cannot open %s"), namebuf);
+			goto error;
+		}
+		if (unlink(namebuf)) {
+			error_errno(_("cannot unlink '%s'"), namebuf);
+			goto error;
+		}
 		fd = open(namebuf, O_CREAT | O_EXCL | O_WRONLY, 0666);
-		if (fd < 0)
-			return error_errno(_("cannot open %s"), namebuf);
+		if (fd < 0) {
+			error_errno(_("cannot open %s"), namebuf);
+			goto error;
+		}
 	}
 	rej = fdopen(fd, "w");
 	if (!rej) {
 		error_errno(_("cannot open %s"), namebuf);
 		close(fd);
-		return -1;
+		goto error;
 	}
 
 	/* Normal git tools never deal with .rej, so do not pretend
@@ -4693,6 +4692,8 @@ static int write_out_one_reject(struct apply_state *state, struct patch *patch)
 			fputc('\n', rej);
 	}
 	fclose(rej);
+error:
+	free(namebuf);
 	return -1;
 }