support cpying self-referenced table (#2076)

lua/cmp/utils/misc.lua

@@ -156,28 +156,39 @@ misc.set = function(t, keys, v)
   c[keys[#keys]] = v
 end
 
----Copy table
----@generic T
----@param tbl T
----@return T
-misc.copy = function(tbl)
-  if type(tbl) ~= 'table' then
-    return tbl
-  end
+do
+  local function do_copy(tbl, seen)
+    if type(tbl) ~= 'table' then
+      return tbl
+    end
+    if seen[tbl] then
+      return seen[tbl]
+    end
+
+    if islist(tbl) then
+      local copy = {}
+      seen[tbl] = copy
+      for i, value in ipairs(tbl) do
+        copy[i] = do_copy(value, seen)
+      end
+      return copy
+    end
 
-  if islist(tbl) then
     local copy = {}
-    for i, value in ipairs(tbl) do
-      copy[i] = misc.copy(value)
+    seen[tbl] = copy
+    for key, value in pairs(tbl) do
+      copy[key] = do_copy(value, seen)
     end
     return copy
   end
 
-  local copy = {}
-  for key, value in pairs(tbl) do
-    copy[key] = misc.copy(value)
+  ---Copy table
+  ---@generic T
+  ---@param tbl T
+  ---@return T
+  misc.copy = function(tbl)
+    return do_copy(tbl, {})
   end
-  return copy
 end
 
 ---Safe version of vim.str_utfindex

lua/cmp/utils/misc_spec.lua

@@ -5,6 +5,33 @@ local misc = require('cmp.utils.misc')
 describe('misc', function()
   before_each(spec.before)
 
+  it('copy', function()
+    -- basic.
+    local tbl, copy
+    tbl = {
+      a = {
+        b = 1,
+      },
+    }
+    copy = misc.copy(tbl)
+    assert.are_not.equal(tbl, copy)
+    assert.are_not.equal(tbl.a, copy.a)
+    assert.are.same(tbl, copy)
+
+    -- self reference.
+    tbl = {
+      a = {
+        b = 1,
+      },
+    }
+    tbl.a.c = tbl.a
+    copy = misc.copy(tbl)
+    assert.are_not.equal(tbl, copy)
+    assert.are_not.equal(tbl.a, copy.a)
+    assert.are_not.equal(tbl.a.c, copy.a.c)
+    assert.are.same(tbl, copy)
+  end)
+
   it('merge', function()
     local merged
     merged = misc.merge({