patch 8.2.2578: Lua cannot handle a passed in lambda

Problem:    Lua cannot handle a passed in lambda.
Solution:   Handle VAR_PARTIAL. (Prabir Shrestha, closes #7937, closes #7936)

src/if_lua.c

@@ -568,6 +568,11 @@ luaV_pushtypval(lua_State *L, typval_T *tv)
 	case VAR_FUNC:
 	    luaV_pushfuncref(L, tv->vval.v_string);
 	    break;
+	case VAR_PARTIAL:
+	    // TODO: handle partial arguments
+	    luaV_pushfuncref(L, partial_name(tv->vval.v_partial));
+	    break;
+
 	case VAR_BLOB:
 	    luaV_pushblob(L, tv->vval.v_blob);
 	    break;

src/testdir/test_lua.vim

@@ -121,6 +121,15 @@ func Test_lua_eval()
   lua v = nil
 endfunc
 
+" Test luaeval() with lambda
+func Test_luaeval_with_lambda()
+  lua function hello_luaeval_lambda(a, cb) return a .. cb() end
+  call assert_equal('helloworld',
+        \ luaeval('hello_luaeval_lambda(_A[1], _A[2])',
+        \         ['hello', {->'world'}]))
+  lua hello_luaeval_lambda = nil
+endfunc
+
 " Test vim.window()
 func Test_lua_window()
   e Xfoo2

src/version.c

@@ -750,6 +750,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    2578,
 /**/
     2577,
 /**/