[tarantool-patches] [PATCH] table: fix incorrect __metatable handling

[Oleg Babin <olegrok@tarantool.org>]

From: Oleg Babin <babinoleg@mail.ru>

Closes #4340

Before this patch we get metatabe of original table
using "getmetatable" function. It leads to the error
if original table contained __metatable.
To fix this problem getmetatable was replaced to debug.getmetatable
---
 src/lua/table.lua           |  2 +-
 test/app-tap/table.test.lua | 20 +++++++++++++++++++-
 2 files changed, 20 insertions(+), 2 deletions(-)

diff --git a/src/lua/table.lua b/src/lua/table.lua
index 7e8ba7aae..d83217dcb 100644
--- a/src/lua/table.lua
+++ b/src/lua/table.lua
@@ -2,7 +2,7 @@ local function table_deepcopy_internal(orig, cyclic)
     cyclic = cyclic or {}
     local copy = orig
     if type(orig) == 'table' then
-        local mt, copy_function = getmetatable(orig), nil
+        local mt, copy_function = debug.getmetatable(orig), nil
         if mt then copy_function = mt.__copy end
         if copy_function == nil then
             copy = {}
diff --git a/test/app-tap/table.test.lua b/test/app-tap/table.test.lua
index 60c095fdf..07894f69e 100755
--- a/test/app-tap/table.test.lua
+++ b/test/app-tap/table.test.lua
@@ -8,7 +8,7 @@ yaml.cfg{
     encode_invalid_as_nil  = true,
 }
 local test = require('tap').test('table')
-test:plan(31)
+test:plan(33)
 
 do -- check basic table.copy (deepcopy)
     local example_table = {
@@ -223,4 +223,22 @@ do -- check usage of not __copy metamethod on second level + shallow
     )
 end
 
+do -- gh-4340: deepcopy doesn't handle __metatable correctly.
+    local original = {
+        content = 'string'
+    }
+    setmetatable(original, { __metatable = 'protection' })
+    local copy = table.deepcopy(original)
+    test:is(
+            copy.content,
+            original.content,
+            "checking that original string was copied"
+    )
+    test:is(
+            getmetatable(copy),
+            'protection',
+            "checking that __metatable was correctly copied"
+    )
+end
+
 os.exit(test:check() == true and 0 or 1)
-- 
2.21.0