builtin/apply: make apply_patch() return -1 or -128 instead of die()ing

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

As a first step in this direction, let's make apply_patch() return
-1 or -128 in case of errors instead of dying. For now its only
caller apply_all_patches() will exit(128) when apply_patch()
return -128 and it will exit(1) when it returns -1.

We exit() with code 128 because that was what die() was doing
and we want to keep the distinction between exiting with code 1
and exiting with code 128.

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

@@ -4404,6 +4404,15 @@ static struct lock_file lock_file;
 #define INACCURATE_EOF	(1<<0)
 #define RECOUNT		(1<<1)
 
+/*
+ * Try to apply a patch.
+ *
+ * Returns:
+ *  -128 if a bad error happened (like patch unreadable)
+ *  -1 if patch did not apply and user cannot deal with it
+ *   0 if the patch applied
+ *   1 if the patch did not apply but user might fix it
+ */
 static int apply_patch(struct apply_state *state,
 		       int fd,
 		       const char *filename,
@@ -4413,6 +4422,7 @@ static int apply_patch(struct apply_state *state,
 	struct strbuf buf = STRBUF_INIT; /* owns the patch text */
 	struct patch *list = NULL, **listp = &list;
 	int skipped_patch = 0;
+	int res = 0;
 
 	state->patch_input_file = filename;
 	read_patch_file(&buf, fd);
@@ -4445,8 +4455,11 @@ static int apply_patch(struct apply_state *state,
 		offset += nr;
 	}
 
-	if (!list && !skipped_patch)
+	if (!list && !skipped_patch) {
-		die(_("unrecognized input"));
+		error(_("unrecognized input"));
+		res = -128;
+		goto end;
+	}
 
 	if (state->whitespace_error && (state->ws_error_action == die_on_ws_error))
 		state->apply = 0;
@@ -4455,21 +4468,23 @@ static int apply_patch(struct apply_state *state,
 	if (state->update_index && state->newfd < 0)
 		state->newfd = hold_locked_index(state->lock_file, 1);
 
-	if (state->check_index) {
+	if (state->check_index && read_cache() < 0) {
-		if (read_cache() < 0)
+		error(_("unable to read index file"));
-			die(_("unable to read index file"));
+		res = -128;
+		goto end;
 	}
 
 	if ((state->check || state->apply) &&
 	    check_patch_list(state, list) < 0 &&
-	    !state->apply_with_reject)
+	    !state->apply_with_reject) {
-		exit(1);
+		res = -1;
+		goto end;
+	}
 
 	if (state->apply && write_out_results(state, list)) {
-		if (state->apply_with_reject)
-			exit(1);
 		/* with --3way, we still need to write the index out */
-		return 1;
+		res = state->apply_with_reject ? -1 : 1;
+		goto end;
 	}
 
 	if (state->fake_ancestor)
@@ -4484,10 +4499,11 @@ static int apply_patch(struct apply_state *state,
 	if (state->summary)
 		summary_patch_list(list);
 
+end:
 	free_patch_list(list);
 	strbuf_release(&buf);
 	string_list_clear(&state->fn_table, 0);
-	return 0;
+	return res;
 }
 
 static void git_apply_config(void)
@@ -4628,6 +4644,7 @@ static int apply_all_patches(struct apply_state *state,
 			     int options)
 {
 	int i;
+	int res;
 	int errs = 0;
 	int read_stdin = 1;
 
@@ -4636,7 +4653,10 @@ static int apply_all_patches(struct apply_state *state,
 		int fd;
 
 		if (!strcmp(arg, "-")) {
-			errs |= apply_patch(state, 0, "<stdin>", options);
+			res = apply_patch(state, 0, "<stdin>", options);
+			if (res < 0)
+				goto end;
+			errs |= res;
 			read_stdin = 0;
 			continue;
 		} else if (0 < state->prefix_length)
@@ -4649,12 +4669,19 @@ static int apply_all_patches(struct apply_state *state,
 			die_errno(_("can't open patch '%s'"), arg);
 		read_stdin = 0;
 		set_default_whitespace_mode(state);
-		errs |= apply_patch(state, fd, arg, options);
+		res = apply_patch(state, fd, arg, options);
+		if (res < 0)
+			goto end;
+		errs |= res;
 		close(fd);
 	}
 	set_default_whitespace_mode(state);
-	if (read_stdin)
+	if (read_stdin) {
-		errs |= apply_patch(state, 0, "<stdin>", options);
+		res = apply_patch(state, 0, "<stdin>", options);
+		if (res < 0)
+			goto end;
+		errs |= res;
+	}
 
 	if (state->whitespace_error) {
 		if (state->squelch_whitespace_errors &&
@@ -4690,6 +4717,9 @@ static int apply_all_patches(struct apply_state *state,
 	}
 
 	return !!errs;
+
+end:
+	exit(res == -1 ? 1 : 128);
 }
 
 int cmd_apply(int argc, const char **argv, const char *prefix)