fix(eval_lambda): cherry-pick leak fix from v8.1.2107

That patch also includes a test using test_refcount() for lambdas, but
such test functions are N/A for Nvim.

2 files changed, 17 insertions, 3 deletions

diff --git a/src/nvim/eval.c b/src/nvim/eval.c
index 5c8f90c490..a6becb4765 100644
--- a/src/nvim/eval.c
+++ b/src/nvim/eval.c
@@ -4186,7 +4186,7 @@ static int eval_lambda(char_u **const arg, typval_T *const rettv,
   typval_T base = *rettv;
   rettv->v_type = VAR_UNKNOWN;
 
-  const int ret = get_lambda_tv(arg, rettv, evaluate);
+  int ret = get_lambda_tv(arg, rettv, evaluate);
   if (ret == NOTDONE) {
     return FAIL;
   } else if (**arg != '(') {
@@ -4198,9 +4198,18 @@ static int eval_lambda(char_u **const arg, typval_T *const rettv,
       }
     }
     tv_clear(rettv);
-    return FAIL;
+    ret = FAIL;
+  } else {
+    ret = call_func_rettv(arg, rettv, evaluate, NULL, &base, NULL);
   }
-  return call_func_rettv(arg, rettv, evaluate, NULL, &base, NULL);
+
+  // Clear the funcref afterwards, so that deleting it while
+  // evaluating the arguments is possible (see test55).
+  if (evaluate) {
+    tv_clear(&base);
+  }
+
+  return ret;
 }
 
 /// Evaluate "->method()".
diff --git a/src/nvim/testdir/test_method.vim b/src/nvim/testdir/test_method.vim
index 5ad1d47e71..7a6e6aa19d 100644
--- a/src/nvim/testdir/test_method.vim
+++ b/src/nvim/testdir/test_method.vim
@@ -145,6 +145,11 @@ func Test_method_lambda()
 
   " todo: lambda accepts more arguments than it consumes
   " call assert_fails('eval "text"->{x -> x .. " extended"}("more")', 'E99:')
+
+  " Nvim doesn't include test_refcount().
+  " let l = [1, 2, 3]
+  " eval l->{x -> x}()
+  " call assert_equal(1, test_refcount(l))
 endfunc
 
 func Test_method_not_supported()