lua: allow deepcopy of functions (#12136)

runtime/doc/lua.txt

@@ -908,7 +908,10 @@ deep_equal({a}, {b})                                        *vim.deep_equal()*
 deepcopy({orig})                                              *vim.deepcopy()*
                 Returns a deep copy of the given object. Non-table objects are
                 copied as in a typical Lua assignment, whereas table objects
-                are copied recursively.
+                are copied recursively. Functions are naively copied, so
+                functions in the copied table point to the same functions as
+                those in the input table. Userdata and threads are not copied
+                and will throw an error.
 
                 Parameters: ~
                     {orig}  Table to copy

runtime/lua/vim/shared.lua

@@ -8,6 +8,9 @@ local vim = vim or {}
 
 --- Returns a deep copy of the given object. Non-table objects are copied as
 --- in a typical Lua assignment, whereas table objects are copied recursively.
+--- Functions are naively copied, so functions in the copied table point to the
+--- same functions as those in the input table. Userdata and threads are not
+--- copied and will throw an error.
 ---
 --@param orig Table to copy
 --@returns New table of copied keys and (nested) values.
@@ -34,10 +37,16 @@ vim.deepcopy = (function()
     string = _id,
     ['nil'] = _id,
     boolean = _id,
+    ['function'] = _id,
   }
 
   return function(orig)
-    return deepcopy_funcs[type(orig)](orig)
+    local f = deepcopy_funcs[type(orig)]
+    if f then
+      return f(orig)
+    else
+      error("Cannot deepcopy object of type "..type(orig))
+    end
   end
 end)()
 

test/functional/lua/vim_spec.lua

@@ -341,6 +341,22 @@ describe('lua stdlib', function()
         and vim.tbl_count(b) == 2
         and tostring(a) ~= tostring(b)
     ]]))
+
+    ok(exec_lua([[
+      local f1 = function() return 1 end
+      local f2 = function() return 2 end
+      local t1 = {f = f1}
+      local t2 = vim.deepcopy(t1)
+      t1.f = f2
+      return t1.f() ~= t2.f()
+    ]]))
+
+    eq('Error executing lua: .../shared.lua: Cannot deepcopy object of type thread',
+      pcall_err(exec_lua, [[
+        local thread = coroutine.create(function () return 0 end)
+        local t = {thr = thread}
+        vim.deepcopy(t)
+      ]]))
   end)
 
   it('vim.pesc', function()