[Tarantool-patches] [PATCH 2/3] lua: table.deepcopy ignores __pairs metamethod

[olegrok@tarantool.org]

From: Oleg Babin <babinoleg@mail.ru>

After 1d85144a9b4bbbb026402848efde1ab98bf72633
table.deepcopy changed the behaviour and started
iterate through tables considering __pairs metamethod.
In some cases it broke backward compatibility.
To avoid such problem let's ignore __pairs
and iterate through tables as it was before

Closes #4770
Follow-up #4560
---
Issue: https://github.com/tarantool/tarantool/issues/4770
Branch: https://github.com/tarantool/tarantool/tree/olegrok/table-fixes
 src/lua/table.lua           |  7 ++++++-
 test/app-tap/table.test.lua | 26 +++++++++++++++++++++++++-
 2 files changed, 31 insertions(+), 2 deletions(-)

diff --git a/src/lua/table.lua b/src/lua/table.lua
index d83217dcb..4fa9c421c 100644
--- a/src/lua/table.lua
+++ b/src/lua/table.lua
@@ -1,3 +1,8 @@
+-- This pairs implementation doesn't trigger __pairs metamethod
+local function internal_pairs(tbl)
+    return next, tbl, nil
+end
+
 local function table_deepcopy_internal(orig, cyclic)
     cyclic = cyclic or {}
     local copy = orig
@@ -10,7 +15,7 @@ local function table_deepcopy_internal(orig, cyclic)
                 copy = cyclic[orig]
             else
                 cyclic[orig] = copy
-                for orig_key, orig_value in pairs(orig) do
+                for orig_key, orig_value in internal_pairs(orig) do
                     local key = table_deepcopy_internal(orig_key, cyclic)
                     copy[key] = table_deepcopy_internal(orig_value, cyclic)
                 end
diff --git a/test/app-tap/table.test.lua b/test/app-tap/table.test.lua
index 07894f69e..3faf2ed23 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(33)
+test:plan(35)
 
 do -- check basic table.copy (deepcopy)
     local example_table = {
@@ -241,4 +241,28 @@ do -- gh-4340: deepcopy doesn't handle __metatable correctly.
     )
 end
 
+do -- gh-4770: deepcopy uses __pairs for iteration over table.
+    local original = { a = 1, b = 2 }
+
+    local function custom_pairs(self)
+        local function step(tbl, k)
+            local k, v = next(tbl, k)
+            if v ~= nil then
+                v = v + 1
+            end
+            return k, v
+        end
+        return step, self, nil
+    end
+
+    setmetatable(original, {__pairs = custom_pairs })
+
+    -- Don't use is deeply as it could use pairs for check
+    local copy = table.deepcopy(original)
+    test:is(original.a, copy.a,
+            "checking that the first values is correctly copied")
+    test:is(original.b, copy.b,
+            "checking that the second values is correctly copied")
+end
+
 os.exit(test:check() == true and 0 or 1)
-- 
2.23.0