[Tarantool-patches] [PATCH] box: always promote error created via box.error() to diag

[Nikita Pettik <korablev@tarantool.org>]

Note that it is vital that box.error() now promotes error to diag, since
otherwise user is unable to set to diag custom error, which in turn is
linked with other errors:

e1 = box.error.new({code = 111, reason = "cause"})
e2 = box.error.new({code = 111, reason = "err"})
e2:set_prev(e1)
-- There's no means to set e2 to diagnostic area.

This patch makes box.error() always promote error to the diagnostic
area despite of passed arguments.

Closes #4829

@TarantoolBot document
Title: always promote error created via box.error() to diag

box.error() is able to accept two types of argument: either pair of code
+ reason (box.error{code = 555, reason = 'Arbitrary message'}) or error
object (box.error(err)). In the first case error is promoted to
diagnostic area, meanwhile in the latter - it is not:
```
e1 = box.error.new({code = 111, reason = "cause"})
box.error({code = 111, reason = "err"})
- error: err
box.error.last()
- err
box.error(e1)
- error: cause
box.error.last()
- err
```
From now box.error(e1) sets error to diagnostic area as well:
```
box.error(e1)
- error: cause
box.error.last()
- cause
```
---
Patch is located on branch with stacked diagnostics since patch
is required to write correct tests for it.

Branch: https://github.com/tarantool/tarantool/commit/cb1010c1497f1d134e576b5bbbd6c1d0520ff7f4
Issue: https://github.com/tarantool/tarantool/issues/4829

 src/box/lua/error.cc    | 13 ++++++++++---
 test/box/error.result   | 22 ++++++++++++++++++++++
 test/box/error.test.lua |  8 ++++++++
 3 files changed, 40 insertions(+), 3 deletions(-)

diff --git a/src/box/lua/error.cc b/src/box/lua/error.cc
index 08c2d983d..b2625bf5f 100644
--- a/src/box/lua/error.cc
+++ b/src/box/lua/error.cc
@@ -114,9 +114,16 @@ luaT_error_call(lua_State *L)
 			return luaT_error(L);
 		return 0;
 	}
-	if (lua_gettop(L) == 2 && luaL_iserror(L, 2))
-		return lua_error(L);
-	struct error *e = luaT_error_create(L, 2);
+	struct error *e = NULL;
+	if (lua_gettop(L) == 2) {
+		e = luaL_iserror(L, 2);
+		if (e != NULL) {
+			/* Re-set error to diag area. */
+			diag_set_error(&fiber()->diag, e);
+			return lua_error(L);
+		}
+	}
+	e = luaT_error_create(L, 2);
 	if (e == NULL)
 		return luaL_error(L, "box.error(): bad arguments");
 	diag_set_error(&fiber()->diag, e);
diff --git a/test/box/error.result b/test/box/error.result
index 4f0f30491..9ab4d1f6d 100644
--- a/test/box/error.result
+++ b/test/box/error.result
@@ -786,6 +786,28 @@ assert(e1.prev == e2)
  | - true
  | ...
 
+-- gh-4829: always promote error created via box.error() to
+-- diagnostic area.
+e1 = box.error.new({code = 111, reason = "cause"})
+ | ---
+ | ...
+box.error({code = 111, reason = "err"})
+ | ---
+ | - error: err
+ | ...
+box.error.last()
+ | ---
+ | - err
+ | ...
+box.error(e1)
+ | ---
+ | - error: cause
+ | ...
+assert(box.error.last() == e1)
+ | ---
+ | - true
+ | ...
+
 space:drop()
  | ---
  | ...
diff --git a/test/box/error.test.lua b/test/box/error.test.lua
index 66a22db90..c4783031e 100644
--- a/test/box/error.test.lua
+++ b/test/box/error.test.lua
@@ -213,4 +213,12 @@ box.error.set(e1)
 box.error.clear()
 assert(e1.prev == e2)
 
+-- gh-4829: always promote error created via box.error() to
+-- diagnostic area.
+e1 = box.error.new({code = 111, reason = "cause"})
+box.error({code = 111, reason = "err"})
+box.error.last()
+box.error(e1)
+assert(box.error.last() == e1)
+
 space:drop()
-- 
2.17.1