[Tarantool-patches] [PATCH v2 1/2] lua: introduce table.equals method

[Serge Petrenko via Tarantool-patches <tarantool-patches@dev.tarantool.org>]

Introduce table.equals for comparing tables.
The method respects __eq metamethod, if provided.

Needed-for #5894
---
 src/lua/table.lua           | 26 ++++++++++++++++++++++++++
 test/app-tap/table.test.lua | 31 ++++++++++++++++++++++++++++++-
 2 files changed, 56 insertions(+), 1 deletion(-)

diff --git a/src/lua/table.lua b/src/lua/table.lua
index 8fa9b876a..5f35a30f6 100644
--- a/src/lua/table.lua
+++ b/src/lua/table.lua
@@ -57,6 +57,31 @@ local function table_shallowcopy(orig)
     return copy
 end
 
+--- Compare two lua tables
+-- Supports __eq metamethod for comparing custom tables with metatables
+-- @function equals
+-- @return true when the two tables are equal (false otherwise).
+local function table_equals(a, b)
+    if type(a) ~= 'table' or type(b) ~= 'table' then
+        return a == b
+    end
+    local mt = getmetatable(a)
+    if mt and mt.__eq then
+        return a == b
+    end
+    for k, v in pairs(a) do
+        if not table_equals(v, b[k]) then
+            return false
+        end
+    end
+    for k, _ in pairs(b) do
+        if not a[k] then
+            return false
+        end
+    end
+    return true
+end
+
 -- table library extension
 local table = require('table')
 -- require modifies global "table" module and adds "clear" function to it.
@@ -65,3 +90,4 @@ require('table.clear')
 
 table.copy     = table_shallowcopy
 table.deepcopy = table_deepcopy
+table.equals   = table_equals
diff --git a/test/app-tap/table.test.lua b/test/app-tap/table.test.lua
index 60c095fdf..a3c9aa123 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(38)
 
 do -- check basic table.copy (deepcopy)
     local example_table = {
@@ -223,4 +223,33 @@ do -- check usage of not __copy metamethod on second level + shallow
     )
 end
 
+do -- check table.equals
+    test:ok(table.equals({}, {}), "table.equals for empty tables")
+    test:is(table.equals({}, {1}), false, "table.equals with one empty table")
+    test:is(table.equals({1}, {}), false, "table.equals with one empty table")
+    local tbl_a = {
+        first = {
+            1,
+            2,
+            {},
+        },
+        second = {
+            a = {
+                {'something'},
+            },
+            b = 'something else',
+        },
+        [3] = 'some value',
+    }
+    local tbl_b = table.deepcopy(tbl_a)
+    local tbl_c = table.copy(tbl_a)
+    test:ok(table.equals(tbl_a, tbl_b), "table.equals for complex tables")
+    test:ok(table.equals(tbl_a, tbl_c),
+            "table.equals for shallow copied tables")
+    tbl_c.second.a = 'other thing'
+    test:ok(table.equals(tbl_a, tbl_c),
+            "table.equals for shallow copied tables after modification")
+    test:is(table.equals(tbl_a, tbl_b), false, "table.equals does a deep check")
+end
+
 os.exit(test:check() == true and 0 or 1)
-- 
2.30.1 (Apple Git-130)