box/error: introduce box.error.set() method

box.error.set(err) sets err to instance's diagnostics area. Argument err
is supposed to be instance of error object. This method is required
since we are going to avoid adding created via box.error.new() errors to
Tarantool's diagnostic area.

Needed for #1148
Part of #4778

src/box/lua/error.cc

@@ -154,6 +154,16 @@ luaT_error_clear(lua_State *L)
 	return 0;
 }
 
+static int
+luaT_error_set(struct lua_State *L)
+{
+	if (lua_gettop(L) == 0)
+		return luaL_error(L, "Usage: box.error.set(error)");
+	struct error *e = luaL_checkerror(L, 1);
+	diag_set_error(&fiber()->diag, e);
+	return 0;
+}
+
 static int
 lbox_errinj_set(struct lua_State *L)
 {
@@ -268,6 +278,10 @@ box_lua_error_init(struct lua_State *L) {
 			lua_pushcfunction(L, luaT_error_new);
 			lua_setfield(L, -2, "new");
 		}
+		{
+			lua_pushcfunction(L, luaT_error_set);
+			lua_setfield(L, -2, "set");
+		}
 		lua_setfield(L, -2, "__index");
 	}
 	lua_setmetatable(L, -2);

src/lua/error.c

@@ -53,7 +53,7 @@ luaL_iserror(struct lua_State *L, int narg)
 	return e;
 }
 
-static struct error *
+struct error *
 luaL_checkerror(struct lua_State *L, int narg)
 {
 	struct error *error = luaL_iserror(L, narg);

src/lua/error.h

@@ -65,6 +65,9 @@ luaT_pusherror(struct lua_State *L, struct error *e);
 struct error *
 luaL_iserror(struct lua_State *L, int narg);
 
+struct error *
+luaL_checkerror(struct lua_State *L, int narg);
+
 void
 tarantool_lua_error_init(struct lua_State *L);
 

test/box/error.result

@@ -436,6 +436,42 @@ test_run:cmd("setopt delimiter ''");
  | ---
  | - true
  | ...
+
+-- gh-4778: don't add created via box.error.new() errors to
+-- Tarantool's diagnostic area.
+--
+err = box.error.new({code = 111, reason = "cause"})
+ | ---
+ | ...
+assert(box.error.last() ~= err)
+ | ---
+ | - error: assertion failed!
+ | ...
+box.error.set(err)
+ | ---
+ | ...
+assert(box.error.last() == err)
+ | ---
+ | - true
+ | ...
+-- Consider wrong or tricky inputs to box.error.set()
+--
+box.error.set(1)
+ | ---
+ | - error: 'Invalid argument #1 (error expected, got number)'
+ | ...
+box.error.set(nil)
+ | ---
+ | - error: 'Invalid argument #1 (error expected, got nil)'
+ | ...
+box.error.set(box.error.last())
+ | ---
+ | ...
+assert(box.error.last() == err)
+ | ---
+ | - true
+ | ...
+
 space:drop()
  | ---
  | ...

test/box/error.test.lua

@@ -77,4 +77,19 @@ end;
 t;
 
 test_run:cmd("setopt delimiter ''");
+
+-- gh-4778: don't add created via box.error.new() errors to
+-- Tarantool's diagnostic area.
+--
+err = box.error.new({code = 111, reason = "cause"})
+assert(box.error.last() ~= err)
+box.error.set(err)
+assert(box.error.last() == err)
+-- Consider wrong or tricky inputs to box.error.set()
+--
+box.error.set(1)
+box.error.set(nil)
+box.error.set(box.error.last())
+assert(box.error.last() == err)
+
 space:drop()