box/lua: allow to set error cause via prev argument

Currently, it's only possible to set an error cause with the set_prev
method. This isn't very convenient, because one has to construct a new
error without raising it, then set its cause, and only then raise it.
To simplify this, a new argument `prev` is added to the error constructor.

Closes tarantool#9103

@TarantoolBot document
Title: Document `prev` argument to table constructor of `box.error.new`
Product: Tarantool
Since: 3.1
Root documents: https://www.tarantool.io/en/doc/latest/reference/reference_lua/box_error/new/
and https://www.tarantool.io/en/doc/latest/reference/reference_lua/box_error/error/

[Link to the design document](https://www.notion.so/tarantool/Error-subsystem-improvements-90faa0a4714b4143abaf8bed2c10b2fc?pvs=4#c72c870f24734020aae1fbf34e2b8569)

Author: Gumix

changelogs/unreleased/gh-9103-error-new-prev-arg.md

@@ -0,0 +1,3 @@
+## feature/lua
+
+* Added a `prev` argument to the table constructor of `box.error.new` (gh-9103).

src/box/lua/error.cc

@@ -129,6 +129,7 @@ luaT_error_create(lua_State *L, int top_base)
 	const char *file = "";
 	unsigned line = 0;
 	lua_Debug info;
+	struct error *prev = NULL;
 	int top = lua_gettop(L);
 	int top_type = lua_type(L, top_base);
 	if (top >= top_base && (top_type == LUA_TNUMBER ||
@@ -175,6 +176,15 @@ luaT_error_create(lua_State *L, int top_base)
 		lua_getfield(L, top_base, "type");
 		if (!lua_isnil(L, -1))
 			custom_type = lua_tostring(L, -1);
+		lua_getfield(L, top_base, "prev");
+		if (!lua_isnil(L, -1)) {
+			prev = luaL_iserror(L, -1);
+			if (prev == NULL) {
+				luaL_error(L, "Invalid argument 'prev' (error "
+					   "expected, got %s)",
+					   lua_typename(L, lua_type(L, -1)));
+			}
+		}
 	} else {
 		return NULL;
 	}
@@ -192,6 +202,13 @@ luaT_error_create(lua_State *L, int top_base)
 	}
 	struct error *error;
 	error = box_error_new(file, line, code, custom_type, "%s", reason);
+	/*
+	 * Set the previous error, if it was specified.
+	 */
+	if (prev != NULL) {
+		/* Cycle is not possible for the newly created error. */
+		VERIFY(error_set_prev(error, prev) == 0);
+	}
 	/*
 	 * Add custom payload fields to the `error' if any.
 	 */

test/box-luatest/error_subsystem_improvements_test.lua

@@ -1,6 +1,22 @@
 local t = require('luatest')
 local g = t.group()
 
+-- Test the `prev' argument to the table constructor of `box.error.new'
+-- (gh-9103).
+g.test_error_new_prev_arg = function()
+    local e1 = box.error.new({"errare"})
+    local e2 = box.error.new({"humanum", prev = e1})
+    local _, e3 = pcall(box.error, {"est", prev = e2})
+
+    t.assert_equals(e3.prev.prev.message, "errare")
+    t.assert_equals(e3.prev.message, "humanum")
+    t.assert_equals(e3.message, "est")
+
+    t.assert_error_msg_equals(
+        "Invalid argument 'prev' (error expected, got number)",
+        box.error.new, {prev = 333})
+end
+
 -- Test custom error payload (gh-9104).
 g.test_custom_payload = function()
     local uuid = require('uuid')
@@ -67,7 +83,6 @@ g.test_custom_payload = function()
         custom_type = "MyCustomType",
         errno = "MyErrno",
         trace = "MyTrace",
-        prev = "MyPrev",
     })
     unpacked = e:unpack()
     unpacked.trace = nil