patch 9.2.1240: crash when a clipboard provider returns a null tuple

Problem:  Crash when the "paste" callback of a clipboard provider returns
          a null tuple or a null list.
Solution: Check for a NULL tuple and a NULL list before using the
          returned value (Yegappan Lakshmanan).

fixes:  #21583
closes: #21584

Assisted-by: Claude Code (Claude Opus 5.5)
Signed-off-by: Yegappan Lakshmanan <yegappan@yahoo.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>

src/clipboard.c

@@ -3540,6 +3540,7 @@ clip_provider_paste(char_u *reg, char_u *provider)
     if (ret == FAIL)
 	goto exit;
     else if (rettv.v_type == VAR_TUPLE
+	    && rettv.vval.v_tuple != NULL
 	    && TUPLE_LEN(rettv.vval.v_tuple) == 2
 	    && TUPLE_ITEM(rettv.vval.v_tuple, 0)->v_type == VAR_STRING
 	    && TUPLE_ITEM(rettv.vval.v_tuple, 1)->v_type == VAR_LIST)
@@ -3548,6 +3549,7 @@ clip_provider_paste(char_u *reg, char_u *provider)
 	lines = TUPLE_ITEM(rettv.vval.v_tuple, 1)->vval.v_list;
     }
     else if (rettv.v_type == VAR_LIST
+	    && rettv.vval.v_list != NULL
 	    && rettv.vval.v_list->lv_len == 2
 	    && rettv.vval.v_list->lv_first->li_tv.v_type == VAR_STRING
 	    && rettv.vval.v_list->lv_first->li_next->li_tv.v_type == VAR_LIST)

src/testdir/test_registers.vim

@@ -1358,4 +1358,36 @@ func Test_writing_readonly_regs()
   call assert_fails('let @~ = "foo"', 'E354:')
 endfunc
 
+func s:ProviderPaste(reg)
+  return g:provider_paste_ret
+endfunc
+
+" A clipboard provider "paste" callback returning a null tuple or a null list
+" used to cause a crash.  The register should not change.
+func Test_clipboard_provider_paste_null_value()
+  CheckFeature clipboard_provider
+
+  let v:clipproviders['Xnull'] = {
+        \ 'paste': {'+': function('s:ProviderPaste'),
+        \           '*': function('s:ProviderPaste')}}
+  set clipmethod=Xnull
+
+  try
+    let g:provider_paste_ret = ('', ['one', 'two'])
+    call assert_equal(['one', 'two'], getreg('+', 1, 1))
+    let g:provider_paste_ret = test_null_tuple()
+    call assert_equal(['one', 'two'], getreg('+', 1, 1))
+    let g:provider_paste_ret = test_null_list()
+    call assert_equal(['one', 'two'], getreg('+', 1, 1))
+
+  finally
+    call remove(v:clipproviders, 'Xnull')
+    unlet g:provider_paste_ret
+    call setreg('"', [])
+    call setreg('+', [])
+    call setreg('*', [])
+    set clipmethod&
+  endtry
+endfunc
+
 " vim: shiftwidth=2 sts=2 expandtab

src/version.c

@@ -743,6 +743,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1240,
 /**/
     1239,
 /**/