From ac772706cccbcfbd05699368492b51a34d78bcbd Mon Sep 17 00:00:00 2001
From: zeertzjq <zeertzjq@outlook.com>
Date: Wed, 11 Jun 2025 06:38:40 +0800
Subject: [PATCH] vim-patch:9.1.1447: completion: crash when backspacing with
 fuzzy completion

Problem:  completion: crash when backspacing with fuzzy completion
Solution: Don't dereference compl_first_match when it's NULL
          (zeertzjq).

related: neovim/neovim#34419
closes: vim/vim#17511

https://github.com/vim/vim/commit/91782b4aeb62043739138903f30cad2fe79238ab
---
 src/nvim/insexpand.c                   | 14 ++++++++------
 test/old/testdir/test_ins_complete.vim | 25 +++++++++++++++++++++++++
 2 files changed, 33 insertions(+), 6 deletions(-)

diff --git a/src/nvim/insexpand.c b/src/nvim/insexpand.c
index 19bfd726e4..1f0e3b54d8 100644
--- a/src/nvim/insexpand.c
+++ b/src/nvim/insexpand.c
@@ -1339,13 +1339,15 @@ static int cp_compare_nearest(const void *a, const void *b)
 /// Set fuzzy score.
 static void set_fuzzy_score(void)
 {
-  if (compl_leader.data != NULL && compl_leader.size > 0) {
-    compl_T *comp = compl_first_match;
-    do {
-      comp->cp_score = fuzzy_match_str(comp->cp_str.data, compl_leader.data);
-      comp = comp->cp_next;
-    } while (comp != NULL && !is_first_match(comp));
+  if (!compl_first_match || compl_leader.data == NULL || compl_leader.size == 0) {
+    return;
   }
+
+  compl_T *comp = compl_first_match;
+  do {
+    comp->cp_score = fuzzy_match_str(comp->cp_str.data, compl_leader.data);
+    comp = comp->cp_next;
+  } while (comp != NULL && !is_first_match(comp));
 }
 
 /// Sort completion matches, excluding the node that contains the leader.
diff --git a/test/old/testdir/test_ins_complete.vim b/test/old/testdir/test_ins_complete.vim
index aa2f2569d1..14a917376c 100644
--- a/test/old/testdir/test_ins_complete.vim
+++ b/test/old/testdir/test_ins_complete.vim
@@ -4835,4 +4835,29 @@ func Test_complete_unloaded_buf_refresh_always()
   delfunc TestComplete
 endfunc
 
+func Test_complete_fuzzy_omnifunc_backspace()
+  let g:do_complete = v:false
+  func Omni_test(findstart, base)
+    if a:findstart
+      let g:do_complete = !g:do_complete
+    endif
+    if g:do_complete
+      return a:findstart ? 0 : [#{word: a:base .. 'def'}, #{word: a:base .. 'ghi'}]
+    endif
+    return a:findstart ? -3 : {}
+  endfunc
+
+  new
+  redraw  " need this to prevent NULL dereference in Nvim
+  setlocal omnifunc=Omni_test
+  setlocal completeopt=menuone,fuzzy,noinsert
+  call setline(1, 'abc')
+  call feedkeys("A\<C-X>\<C-O>\<BS>\<Esc>0", 'tx!')
+  call assert_equal('ab', getline(1))
+
+  bwipe!
+  delfunc Omni_test
+  unlet g:do_complete
+endfunc
+
 " vim: shiftwidth=2 sts=2 expandtab nofoldenable