patch 8.2.0269: Vim9: operator after list index does not work

Problem:    Vim9: operator after list index does not work. (Yasuhiro
            Matsumoto)
Solution:   After indexing a list change the type to the list member type.
            (closes #5651)

Author: brammool

src/testdir/test_vim9_expr.vim

@@ -478,6 +478,17 @@ def Test_expr6()
   assert_equal(2, g:anint % g:alsoint)
 
   assert_equal(4, 6 * 4 / 6)
+
+  let x = [2]
+  let y = [3]
+  assert_equal(5, x[0] + y[0])
+  assert_equal(6, x[0] * y[0])
+  if has('float')
+    let xf = [2.0]
+    let yf = [3.0]
+    assert_equal(5.0, xf[0] + yf[0])
+    assert_equal(6.0, xf[0] * yf[0])
+  endif
 enddef
 
 def Test_expr6_float()
@@ -538,6 +549,10 @@ func Test_expr6_fails()
   call CheckDefFailure("let x = #{one: 1} / #{two: 2}", 'E1036:')
   call CheckDefFailure("let x = #{one: 1} % #{two: 2}", 'E1035:')
 
+  call CheckDefFailure("let x = 0xff[1]", 'E714:')
+  if has('float')
+    call CheckDefFailure("let x = 0.7[1]", 'E714:')
+  endif
 endfunc
 
 func Test_expr6_float_fails()

src/version.c

@@ -742,6 +742,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    269,
 /**/
     268,
 /**/

src/vim9compile.c

@@ -2330,6 +2330,9 @@ compile_subscript(
 	}
 	else if (**arg == '[')
 	{
+	    garray_T	*stack;
+	    type_T	**typep;
+
 	    // list index: list[123]
 	    // TODO: more arguments
 	    // TODO: dict member  dict['name']
@@ -2346,6 +2349,14 @@ compile_subscript(
 
 	    if (generate_instr_drop(cctx, ISN_INDEX, 1) == FAIL)
 		return FAIL;
+	    stack = &cctx->ctx_type_stack;
+	    typep = ((type_T **)stack->ga_data) + stack->ga_len - 1;
+	    if ((*typep)->tt_type != VAR_LIST && *typep != &t_any)
+	    {
+		emsg(_(e_listreq));
+		return FAIL;
+	    }
+	    *typep = (*typep)->tt_member;
 	}
 	else if (**arg == '.' && (*arg)[1] != '.')
 	{