patch 9.1.0484: Sorting of completeopt+=fuzzy is not stable

Problem:  Sorting of completeopt+=fuzzy is not stable.
Solution: Compare original indexes when scores are the same.
          (zeertzjq)

closes: #14988

Signed-off-by: zeertzjq <zeertzjq@outlook.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>

src/insexpand.c

@@ -1203,11 +1203,13 @@ trigger_complete_changed_event(int cur)
  * pumitem qsort compare func
  */
     static int
-ins_compl_fuzzy_sort(const void *a, const void *b)
+ins_compl_fuzzy_cmp(const void *a, const void *b)
 {
     const int sa = (*(pumitem_T *)a).pum_score;
     const int sb = (*(pumitem_T *)b).pum_score;
-    return sa == sb ? 0 : sa < sb ? 1 : -1;
+    const int ia = (*(pumitem_T *)a).pum_idx;
+    const int ib = (*(pumitem_T *)b).pum_idx;
+    return sa == sb ? (ia == ib ? 0 : (ia < ib ? -1 : 1)) : (sa < sb ? 1 : -1);
 }
 
 /*
@@ -1355,8 +1357,13 @@ ins_compl_build_pum(void)
     } while (compl != NULL && !is_first_match(compl));
 
     if (compl_fuzzy_match && compl_leader != NULL && lead_len > 0)
+    {
+	for (i = 0; i < compl_match_arraysize; i++)
+	    compl_match_array[i].pum_idx = i;
 	// sort by the largest score of fuzzy match
-	qsort(compl_match_array, (size_t)compl_match_arraysize, sizeof(pumitem_T), ins_compl_fuzzy_sort);
+	qsort(compl_match_array, (size_t)compl_match_arraysize,
+				       sizeof(pumitem_T), ins_compl_fuzzy_cmp);
+    }
 
     if (!shown_match_ok)    // no displayed match at all
 	cur = -1;

src/structs.h

@@ -4470,7 +4470,8 @@ typedef struct
     char_u	*pum_kind;	// extra kind text (may be truncated)
     char_u	*pum_extra;	// extra menu text (may be truncated)
     char_u	*pum_info;	// extra info
-    int		 pum_score;	// fuzzy match score
+    int		pum_score;	// fuzzy match score
+    int		pum_idx;	// index of item before sorting by score
 } pumitem_T;
 
 /*

src/testdir/test_ins_complete.vim

@@ -2578,4 +2578,24 @@ func Test_complete_fuzzy_match()
   unlet g:word
 endfunc
 
+" Check that tie breaking is stable for completeopt+=fuzzy (which should
+" behave the same on different platforms).
+func Test_complete_fuzzy_match_tie()
+  new
+  set completeopt+=fuzzy,noselect
+  call setline(1, ['aaabbccc', 'aaabbCCC', 'aaabbcccc', 'aaabbCCCC', ''])
+
+  call feedkeys("Gcc\<C-X>\<C-N>ab\<C-N>\<C-Y>", 'tx')
+  call assert_equal('aaabbccc', getline('.'))
+  call feedkeys("Gcc\<C-X>\<C-N>ab\<C-N>\<C-N>\<C-Y>", 'tx')
+  call assert_equal('aaabbCCC', getline('.'))
+  call feedkeys("Gcc\<C-X>\<C-N>ab\<C-N>\<C-N>\<C-N>\<C-Y>", 'tx')
+  call assert_equal('aaabbcccc', getline('.'))
+  call feedkeys("Gcc\<C-X>\<C-N>ab\<C-N>\<C-N>\<C-N>\<C-N>\<C-Y>", 'tx')
+  call assert_equal('aaabbCCCC', getline('.'))
+
+  bwipe!
+  set completeopt&
+endfunc
+
 " vim: shiftwidth=2 sts=2 expandtab nofoldenable

src/version.c

@@ -704,6 +704,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    484,
 /**/
     483,
 /**/