Commit: patch 9.2.0030: completion: non-prefix matches shown when leader is NULL

[Christian Brabandt]

patch 9.2.0030: completion: non-prefix matches shown when leader is NULL

Commit: https://github.com/vim/vim/commit/a04ae0210b18795d05d26609b6ba9fb9bf88caff
Author: Hirohito Higashi <h.eas...@gmail.com>
Date: Thu Feb 19 17:06:43 2026 +0000

patch 9.2.0030: completion: non-prefix matches shown when leader is NULL

Problem: When 'autocomplete' fires before compl_leader is initialized,
the prefix filter is bypassed. This allows non-prefix matches
(e.g. from fuzzy omnifuncs) to be shown in the popup menu and
incorrectly preinserted.
Solution: In get_leader_for_startcol(), if compl_leader.string is NULL,
fall back to using compl_orig_text as a filter for matches
starting at or after the completion column (Hirohito Higashi).

When 'autocomplete' first fires, compl_leader is NULL because
ins_compl_start() has not set it yet. This caused the prefix filter in
ins_compl_build_pum(), find_next_completion_match() and
find_common_prefix() to be bypassed, allowing non-prefix fuzzy omnifunc
matches to appear in the PUM and be preinserted.

Extend get_leader_for_startcol() to fall back to compl_orig_text when
compl_leader.string is NULL: if the match's cpt source startcol is less
than compl_col the match includes pre-compl_col text, so return
&compl_leader (NULL string) to signal "pass through"; otherwise return
&compl_orig_text so callers filter by the original text. The compl_col
<= 0 guard is kept only for the prepend-text path to avoid it
interfering with the NULL-leader fallback when compl_col is zero.

With this change all callers of get_leader_for_startcol() automatically
receive the correct filter string without additional helpers.

Also update Test_autocomplete_trigger Test 9 to reflect the new
behavior: 'faberge' is no longer shown when completing 'foo' because
it does not start with the current prefix.

Add Test_autocomplete_preinsert_null_leader() to verify that only
prefix-matching candidates appear in the PUM and are preinserted.

fixes: #19328
closes: #19447

Co-Authored-By: Claude Sonnet 4.6 <nor...@anthropic.com>
Signed-off-by: Hirohito Higashi <h.eas...@gmail.com>
Signed-off-by: Christian Brabandt <c...@256bit.org>

diff --git a/src/insexpand.c b/src/insexpand.c
index 2117427cf..38e92dacf 100644
--- a/src/insexpand.c
+++ b/src/insexpand.c
@@ -1520,14 +1520,30 @@ get_leader_for_startcol(compl_T *match, int cached)
return NULL;
}

- if (cpt_sources_array == NULL || compl_leader.string == NULL)
+ if (cpt_sources_array == NULL)
goto theend;

int cpt_idx = match->cp_cpt_source_idx;
- if (cpt_idx < 0 || compl_col <= 0)
+ if (cpt_idx < 0)
goto theend;
int startcol = cpt_sources_array[cpt_idx].cs_startcol;

+ if (compl_leader.string == NULL)
+ {
+ // When leader is not set (e.g. 'autocomplete' first fires before
+ // compl_leader is initialised), fall back to compl_orig_text for
+ // matches starting at or after compl_col. Matches starting before
+ // compl_col carry pre-compl_col text and must not be compared with
+ // compl_orig_text, so return &compl_leader (NULL string) to signal
+ // "pass through" (no prefix filter).
+ if (startcol < 0 || startcol >= compl_col)
+ return &compl_orig_text;
+ return &compl_leader; // pass through (startcol < compl_col)
+ }
+
+ if (compl_col <= 0)
+ goto theend;
+
if (startcol >= 0 && startcol < compl_col)
{
int prepend_len = compl_col - startcol;
diff --git a/src/testdir/test_ins_complete.vim b/src/testdir/test_ins_complete.vim
index 37553e6db..5d93a4248 100644
--- a/src/testdir/test_ins_complete.vim
+++ b/src/testdir/test_ins_complete.vim
@@ -5486,10 +5486,13 @@ func Test_autocomplete_trigger()
call assert_equal(['fooze', 'faberge'], b:matches->mapnew('v:val.word'))

" Test 9: Trigger autocomplete immediately upon entering Insert mode
+ " 'faberge' is filtered out because it doesn't start with the current prefix
+ " 'foo'; non-prefix omnifunc matches are excluded from the PUM when leader
+ " is NULL (compl_orig_text is used as a fallback filter).
call feedkeys("Sprefix->foo\<Esc>a\<F2>\<Esc>0", 'tx!')
- call assert_equal(['foobar', 'fooze', 'faberge'], b:matches->mapnew('v:val.word'))
+ call assert_equal(['foobar', 'fooze'], b:matches->mapnew('v:val.word'))
call feedkeys("Sprefix->fooxx\<Esc>hcw\<F2>\<Esc>0", 'tx!')
- call assert_equal(['foobar', 'fooze', 'faberge'], b:matches->mapnew('v:val.word'))
+ call assert_equal(['foobar', 'fooze'], b:matches->mapnew('v:val.word'))

bw!
call test_override("char_avail", 0)
@@ -6196,4 +6199,45 @@ func Test_helptags_autocomplete_timeout()
bw!
endfunc

+func Test_autocomplete_preinsert_null_leader()
+ " Test that non-prefix matches from omnifunc are filtered when leader is NULL.
+ " When autocomplete first fires, compl_leader is NULL. Previously the prefix
+ " filter was bypassed, allowing non-prefix fuzzy matches to be incorrectly
+ " shown in the PUM and preinserted.
+ func NonPrefixOmni(findstart, base)
+ if a:findstart
+ return col(".") - 1
+ endif
+ " Return "key" (doesn't start with 'y') and "yellow" (starts with 'y').
+ " Simulates what a fuzzy omnifunc returns (e.g. vimcomplete#Complete with
+ " wildoptions=fuzzy).
+ return ["key", "yellow"]
+ endfunc
+
+ call test_override("char_avail", 1)
+ new
+ set omnifunc=NonPrefixOmni complete=o
+ set completeopt=preinsert autocomplete
+
+ func GetState()
+ let g:line = getline('.')
+ let g:col = col('.')
+ let g:matches = complete_info(['matches']).matches->mapnew('v:val.word')
+ endfunc
+ inoremap <buffer> <F5> <C-R>=GetState()<CR>
+
+ " Type 'y': "key" should be filtered out (doesn't start with 'y'),
+ " "yellow" should be the only PUM entry and preinserted with cursor after 'y'.
+ call feedkeys("iy\<F5>\<C-E>\<Esc>", 'tx')
+ call assert_equal("yellow", g:line)
+ call assert_equal(2, g:col)
+ call assert_equal(['yellow'], g:matches)
+
+ bw!
+ set omnifunc& complete& completeopt& autocomplete&
+ call test_override("char_avail", 0)
+ delfunc NonPrefixOmni
+ delfunc GetState
+endfunc
+
" vim: shiftwidth=2 sts=2 expandtab nofoldenable
diff --git a/src/version.c b/src/version.c
index 66e7169c3..5df5e5dcc 100644
--- a/src/version.c
+++ b/src/version.c
@@ -734,6 +734,8 @@ static char *(features[]) =

static int included_patches[] =
{ /* Add new patch number below this line */
+/**/
+ 30,
/**/
29,
/**/