patch 9.1.1742: complete: preinsert does not work well with preinsert

Problem:  complete: preinsert does not work well with preinsert
Solution: Make "preinsert" completeopt value work with autocompletion
          (Girish Palya)

This change extends Insert mode autocompletion so that 'preinsert' also
works when 'autocomplete' is enabled.

Try: `:set ac cot=preinsert`

See `:help 'cot'` for more details.

closes: #18213

Signed-off-by: Girish Palya <girishji@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>

runtime/doc/insert.txt

@@ -1,4 +1,4 @@
-*insert.txt*    For Vim version 9.1.  Last change: 2025 Aug 25
+*insert.txt*    For Vim version 9.1.  Last change: 2025 Sep 08
 
 
 		  VIM REFERENCE MANUAL    by Bram Moolenaar
@@ -1150,7 +1150,26 @@ any of them at any time by typing |CTRL-X|, which temporarily suspends
 autocompletion.  To use |i_CTRL-N| or |i_CTRL-X_CTRL-N| specifically, press
 |CTRL-E| first to dismiss the popup menu (see |complete_CTRL-E|).
 
-See also 'autocomplete', 'autocompletetimeout' and 'autocompletedelay'.
+						*ins-autocompletion-example*
+Example setup~
+A typical configuration for automatic completion with a popup menu: >
+	set autocomplete
+	set complete=.^5,w^5,b^5,u^5
+	set completeopt=popup
+
+	inoremap <silent><expr> <Tab>   pumvisible() ? "\<C-n>" : "\<Tab>"
+	inoremap <silent><expr> <S-Tab> pumvisible() ? "\<C-p>" : "\<S-Tab>"
+<
+This enables automatic completion with suggestions from the current buffer,
+other windows, and listed buffers, displayed in a popup menu.  Each source is
+limited to 5 candidates.  <Tab> and <S-Tab> move through the items when the
+menu is visible.  Optionally, add "preinsert" to 'completeopt' to insert the
+longest common prefix automatically.  You can also add other completion
+sources to 'complete' as needed.
+
+See also 'autocomplete', 'autocompletedelay' and 'autocompletetimeout'.
+
+For command-line autocompletion, see |cmdline-autocompletion|.
 
 
 FUNCTIONS FOR FINDING COMPLETIONS			*complete-functions*

runtime/doc/options.txt

@@ -1,4 +1,4 @@
-*options.txt*	For Vim version 9.1.  Last change: 2025 Sep 02
+*options.txt*	For Vim version 9.1.  Last change: 2025 Sep 08
 
 
 		  VIM REFERENCE MANUAL	  by Bram Moolenaar
@@ -2124,10 +2124,11 @@ A jump table for the options with a short description can be found at |Q_op|.
 						*'complete'* *'cpt'* *E535*
 'complete' 'cpt'	string	(default: ".,w,b,u,t,i")
 			local to buffer
-	This option specifies how keyword completion |ins-completion| works
+	This option controls how completion |ins-completion| behaves when
-	when CTRL-P or CTRL-N are used.  It is also used for whole-line
+	using CTRL-P, CTRL-N, or |ins-autocompletion|.  It is also used for
-	completion |i_CTRL-X_CTRL-L|.  It indicates the type of completion
+	whole-line completion |i_CTRL-X_CTRL-L|.  It indicates the type of
-	and the places to scan.  It is a comma-separated list of flags:
+	completion and the places to scan.  It is a comma-separated list of
+	flags:
 	.	scan the current buffer ('wrapscan' is ignored)
 	w	scan buffers from other windows
 	b	scan other loaded buffers that are in the buffer list
@@ -2179,9 +2180,11 @@ A jump table for the options with a short description can be found at |Q_op|.
 	   5. tags
 	   6. included files
 
-	As you can see, CTRL-N and CTRL-P can be used to do any 'iskeyword'-
+	CTRL-N, CTRL-P, and |ins-autocompletion| can be used for any
-	based expansion (e.g., dictionary |i_CTRL-X_CTRL-K|, included patterns
+	'iskeyword'-based completion (dictionary |i_CTRL-X_CTRL-K|, included
-	|i_CTRL-X_CTRL-I|, tags |i_CTRL-X_CTRL-]| and normal expansions).
+	patterns |i_CTRL-X_CTRL-I|, tags |i_CTRL-X_CTRL-]|, and normal
+	expansions).  With the "F" and "o" flags in 'complete', non-keywords
+	can also be completed.
 
 	An optional match limit can be specified for a completion source by
 	appending a caret ("^") followed by a {count} to the source flag.
@@ -2298,17 +2301,22 @@ A jump table for the options with a short description can be found at |Q_op|.
 		    {only works when compiled with the |+textprop| feature}
 
 	   preinsert
-		    Preinsert the portion of the first candidate word that is
+		    When autocompletion is not enabled, inserts the part of the
-		    not part of the current completion leader and using the
+		    first candidate word beyond the current completion leader,
-		    |hl-ComplMatchIns| highlight group.  In order for it to
+		    highlighted with |hl-ComplMatchIns|.  The cursor does not
-		    work, "fuzzy" must not be set and "menuone" must be set.
+		    move.  Requires 'fuzzy' unset and 'menuone' in 'completeopt'.
+
+		    When 'autocomplete' is enabled, inserts the longest common
+		    prefix of matches (from all shown items or buffer-specific
+		    matches), highlighted with |hl-PreInsert|.  This occurs only
+		    when no menu item is selected.  Press CTRL-Y to accept.
 
 	   preview  Show extra information about the currently selected
 		    completion in the preview window.  Only works in
 		    combination with "menu" or "menuone".
 
-	Only "fuzzy", "popup", "popuphidden" and "preview" have an effect when
+	Only "fuzzy", "popup", "popuphidden", "preinsert" and "preview" have
-	'autocomplete' is enabled.
+	an effect when 'autocomplete' is enabled.
 
 	This option does not apply to |cmdline-completion|. See 'wildoptions'
 	for that.
@@ -4654,7 +4662,7 @@ A jump table for the options with a short description can be found at |Q_op|.
 				     #:TabLineSel,_:TabLineFill,!:CursorColumn,
 				     .:CursorLine,o:ColorColumn,q:QuickFixLine,
 				     z:StatusLineTerm,Z:StatusLineTermNC,
-				     g:MsgArea,h:ComplMatchIns")
+				     g:MsgArea,h:ComplMatchIns,I:PreInsert")
 			global
 	This option can be used to set highlighting mode for various
 	occasions.  It is a comma-separated list of character pairs.  The
@@ -4717,6 +4725,7 @@ A jump table for the options with a short description can be found at |Q_op|.
 	|hl-PmenuThumb|	 X  popup menu scrollbar thumb
 	|hl-PmenuMatch|	 k  popup menu matched text
 	|hl-PmenuMatchSel| <  popup menu matched text in selected line
+	|hl-PreInsert|	 I  text inserted when "preinsert" and 'autocomplete'
 
 	The display modes are:
 		r	reverse		(termcap entry "mr" and "me")

runtime/doc/syntax.txt

@@ -1,4 +1,4 @@
-*syntax.txt*	For Vim version 9.1.  Last change: 2025 Aug 18
+*syntax.txt*	For Vim version 9.1.  Last change: 2025 Sep 08
 
 
 		  VIM REFERENCE MANUAL	  by Bram Moolenaar
@@ -5998,6 +5998,8 @@ PmenuMatchSel	Popup menu: Matched text in selected item. Applied in
 		combination with |hl-PmenuSel|.
 							*hl-ComplMatchIns*
 ComplMatchIns	Matched text of the currently inserted completion.
+							*hl-PreInsert*
+PreInsert	Text inserted during autocompletion when "preinsert".
 							*hl-PopupSelected*
 PopupSelected	Popup window created with |popup_menu()|.  Linked to
 		|hl-PmenuSel| by default.

runtime/doc/tags

@@ -8366,6 +8366,7 @@ hl-PmenuSel	syntax.txt	/*hl-PmenuSel*
 hl-PmenuThumb	syntax.txt	/*hl-PmenuThumb*
 hl-PopupNotification	syntax.txt	/*hl-PopupNotification*
 hl-PopupSelected	syntax.txt	/*hl-PopupSelected*
+hl-PreInsert	syntax.txt	/*hl-PreInsert*
 hl-Question	syntax.txt	/*hl-Question*
 hl-QuickFixLine	syntax.txt	/*hl-QuickFixLine*
 hl-Scrollbar	syntax.txt	/*hl-Scrollbar*
@@ -8627,6 +8628,7 @@ inputrestore()	builtin.txt	/*inputrestore()*
 inputsave()	builtin.txt	/*inputsave()*
 inputsecret()	builtin.txt	/*inputsecret()*
 ins-autocompletion	insert.txt	/*ins-autocompletion*
+ins-autocompletion-example	insert.txt	/*ins-autocompletion-example*
 ins-completion	insert.txt	/*ins-completion*
 ins-completion-menu	insert.txt	/*ins-completion-menu*
 ins-expandtab	insert.txt	/*ins-expandtab*

runtime/syntax/vim.vim

@@ -2,7 +2,7 @@
 " Language:	   Vim script
 " Maintainer:	   Hirohito Higashi <h.east.727 ATMARK gmail.com>
 "	   Doug Kearns <dougkearns@gmail.com>
-" Last Change:	   2025 Aug 29
+" Last Change:	   2025 Sep 08
 " Former Maintainer: Charles E. Campbell
 
 " DO NOT CHANGE DIRECTLY.
@@ -145,8 +145,8 @@ syn keyword vimGroup contained Added Bold BoldItalic Boolean Changed Character C
 
 " Default highlighting groups {{{2
 " GEN_SYN_VIM: vimHLGroup, START_STR='syn keyword vimHLGroup contained', END_STR=''
-syn keyword vimHLGroup contained ErrorMsg IncSearch ModeMsg NonText StatusLine StatusLineNC EndOfBuffer VertSplit VisualNOS DiffText DiffTextAdd PmenuSbar TabLineSel TabLineFill TabPanel TabPanelSel TabPanelFill Cursor lCursor QuickFixLine CursorLineSign CursorLineFold CurSearch PmenuKind PmenuKindSel PmenuMatch PmenuMatchSel PmenuExtra PmenuExtraSel PopupSelected MessageWindow PopupNotification Normal Directory LineNr CursorLineNr MoreMsg Question Search SpellBad SpellCap SpellRare SpellLocal PmenuThumb Pmenu PmenuSel SpecialKey Title WarningMsg WildMenu Folded FoldColumn SignColumn Visual DiffAdd DiffChange DiffDelete TabLine CursorColumn CursorLine ColorColumn MatchParen StatusLineTerm StatusLineTermNC ToolbarLine ToolbarButton Menu Tooltip Scrollbar CursorIM
+syn keyword vimHLGroup contained ErrorMsg IncSearch ModeMsg NonText StatusLine StatusLineNC EndOfBuffer VertSplit VisualNOS DiffText DiffTextAdd PmenuSbar TabLineSel TabLineFill TabPanel TabPanelSel TabPanelFill Cursor lCursor QuickFixLine CursorLineSign CursorLineFold CurSearch PmenuKind PmenuKindSel PmenuMatch PmenuMatchSel PmenuExtra PmenuExtraSel PopupSelected MessageWindow PopupNotification PreInsert Normal Directory LineNr CursorLineNr MoreMsg Question Search SpellBad SpellCap SpellRare SpellLocal PmenuThumb Pmenu PmenuSel SpecialKey Title WarningMsg WildMenu Folded FoldColumn SignColumn Visual DiffAdd DiffChange DiffDelete TabLine CursorColumn CursorLine ColorColumn MatchParen StatusLineTerm StatusLineTermNC ToolbarLine ToolbarButton Menu Tooltip Scrollbar
-syn keyword vimHLGroup contained ComplMatchIns LineNrAbove LineNrBelow MsgArea Terminal User1 User2 User3 User4 User5 User6 User7 User8 User9
+syn keyword vimHLGroup contained CursorIM ComplMatchIns LineNrAbove LineNrBelow MsgArea Terminal User1 User2 User3 User4 User5 User6 User7 User8 User9
 syn match vimHLGroup contained "\<Conceal\>"
 syn case match
 

src/edit.c

@@ -693,7 +693,11 @@ edit(
 			&& stop_arrow() == OK)
 		{
 		    ins_compl_delete();
-		    ins_compl_insert(FALSE);
+		    if (ins_compl_has_preinsert()
+			    && ins_compl_has_autocomplete())
+			(void)ins_compl_insert(FALSE, TRUE);
+		    else
+			(void)ins_compl_insert(FALSE, FALSE);
 		}
 		// Delete preinserted text when typing special chars
 		else if (IS_WHITE_NL_OR_NUL(c) && ins_compl_preinsert_effect())

src/highlight.c

@@ -269,6 +269,7 @@ static char *(highlight_init_both[]) = {
     "default link PopupSelected PmenuSel",
     "default link MessageWindow WarningMsg",
     "default link PopupNotification WarningMsg",
+    "default link PreInsert Added",
     CENT("Normal cterm=NONE", "Normal gui=NONE"),
     NULL
 };

src/insexpand.c

@@ -154,8 +154,9 @@ static string_T	  compl_leader = {NULL, 0};
 static int	  compl_get_longest = FALSE;	// put longest common string
 						// in compl_leader
 
-// Selected one of the matches.  When FALSE the match was edited or using the
+// This flag indicates that one of the items in the match list is currently
-// longest common string.
+// selected.  FALSE when no match is selected or the match was edited or using
+// the longest common string.
 static int	  compl_used_match;
 
 // didn't finish finding completions.
@@ -210,6 +211,7 @@ static int	  compl_autocomplete = FALSE;	    // whether autocompletion is active
 static int	  compl_timeout_ms = COMPL_INITIAL_TIMEOUT_MS;
 static int	  compl_time_slice_expired = FALSE; // time budget exceeded for current source
 static int	  compl_from_nonkeyword = FALSE;    // completion started from non-keyword
+static int	  compl_autocomplete_preinsert = FALSE;    // apply preinsert highlight
 
 // Halve the current completion timeout, simulating exponential decay.
 #define COMPL_MIN_TIMEOUT_MS	5
@@ -252,6 +254,7 @@ typedef struct cpt_source_T
 #ifdef ELAPSED_FUNC
     elapsed_T	compl_start_tv;	    // Timestamp when match collection starts
 #endif
+    char_u  cs_flag;	    // flag indicating the type of source
 } cpt_source_T;
 
 static cpt_source_T *cpt_sources_array; // Pointer to the array of completion sources
@@ -1067,7 +1070,11 @@ ins_compl_col_range_attr(linenr_T lnum, int col)
     int	    attr;
 
     if ((get_cot_flags() & COT_FUZZY)
-	    || (attr = syn_name2attr((char_u *)"ComplMatchIns")) == 0)
+	    || (!compl_autocomplete
+		&& (attr = syn_name2attr((char_u *)"ComplMatchIns")) == 0)
+	    || (compl_autocomplete
+		&& (!compl_autocomplete_preinsert
+		    || (attr = syn_name2attr((char_u *)"PreInsert")) == 0)))
 	return -1;
 
     start_col = compl_col + (int)ins_compl_leader_len();
@@ -1624,13 +1631,13 @@ ins_compl_build_pum(void)
     {
 	compl->cp_in_match_array = FALSE;
 
-	// Apply 'smartcase' behavior during normal mode
-	if (ctrl_x_mode_normal() && !p_inf && compl_leader.string
-		&& !ignorecase(compl_leader.string) && !fuzzy_filter)
-	    compl->cp_flags &= ~CP_ICASE;
-
 	leader = get_leader_for_startcol(compl, TRUE);
 
+	// Apply 'smartcase' behavior during normal mode
+	if (ctrl_x_mode_normal() && !p_inf && leader->string
+		&& !ignorecase(leader->string) && !fuzzy_filter)
+	    compl->cp_flags &= ~CP_ICASE;
+
 	if (!match_at_original_text(compl)
 		&& (leader->string == NULL
 		    || ins_compl_equal(compl, leader->string,
@@ -2339,12 +2346,14 @@ ins_compl_len(void)
  * Return TRUE when the 'completeopt' "preinsert" flag is in effect,
  * otherwise return FALSE.
  */
-    static int
+    int
 ins_compl_has_preinsert(void)
 {
     int cur_cot_flags = get_cot_flags();
-    return (cur_cot_flags & (COT_PREINSERT | COT_FUZZY | COT_MENUONE))
+    return !compl_autocomplete
-	== (COT_PREINSERT | COT_MENUONE) && !compl_autocomplete;
+	? (cur_cot_flags & (COT_PREINSERT | COT_FUZZY | COT_MENUONE))
+		== (COT_PREINSERT | COT_MENUONE)
+	: (cur_cot_flags & (COT_PREINSERT | COT_FUZZY)) == COT_PREINSERT;
 }
 
 /*
@@ -2360,6 +2369,15 @@ ins_compl_preinsert_effect(void)
     return curwin->w_cursor.col < compl_ins_end_col;
 }
 
+/*
+ * Returns TRUE if autocompletion is active.
+ */
+    int
+ins_compl_has_autocomplete(void)
+{
+    return compl_autocomplete;
+}
+
 /*
  * Delete one character before the cursor and show the subset of the matches
  * that match the word that is now before the cursor.
@@ -2505,11 +2523,23 @@ ins_compl_new_leader(void)
     if (!compl_interrupted)
 	show_pum(save_w_wrow, save_w_leftcol);
 
+    compl_autocomplete_preinsert = FALSE;
     // Don't let Enter select the original text when there is no popup menu.
     if (compl_match_array == NULL)
 	compl_enter_selects = FALSE;
     else if (ins_compl_has_preinsert() && compl_leader.length > 0)
-	ins_compl_insert(TRUE);
+    {
+	if (compl_started && compl_autocomplete
+		&& !ins_compl_preinsert_effect())
+	{
+	    if (ins_compl_insert(TRUE, TRUE) != OK)
+		(void)ins_compl_insert(FALSE, FALSE);
+	    else
+		compl_autocomplete_preinsert = TRUE;
+	}
+	else
+	    (void)ins_compl_insert(TRUE, FALSE);
+    }
 }
 
 /*
@@ -2956,6 +2986,7 @@ ins_compl_stop(int c, int prev_mode, int retval)
     compl_autocomplete = FALSE;
     compl_from_nonkeyword = FALSE;
     compl_best_matches = 0;
+    compl_ins_end_col = 0;
 
     if (c == Ctrl_C && cmdwin_type != 0)
 	// Avoid the popup menu remains displayed when leaving the
@@ -5057,9 +5088,10 @@ get_next_default_completion(ins_compl_next_state_T *st, pos_T *start_pos)
 	    continue;
 
 	if (!in_fuzzy_collect)
-	    ptr = ins_compl_get_next_word_or_line(st->ins_buf, st->cur_match_pos,
+	    ptr = ins_compl_get_next_word_or_line(st->ins_buf,
-							       &len, &cont_s_ipos);
+		    st->cur_match_pos, &len, &cont_s_ipos);
-	if (ptr == NULL || (ins_compl_has_preinsert() && STRCMP(ptr, compl_pattern.string) == 0))
+	if (ptr == NULL || (!compl_autocomplete && ins_compl_has_preinsert()
+		    && STRCMP(ptr, compl_pattern.string) == 0))
 	    continue;
 
 	if (is_nearest_active() && in_curbuf)
@@ -5677,8 +5709,8 @@ ins_compl_delete(void)
     int col = compl_col + (compl_status_adding() ? compl_length : 0);
     string_T	remaining = {NULL, 0};
     int	    orig_col;
-    int	has_preinsert = ins_compl_preinsert_effect();
+
-    if (has_preinsert)
+    if (ins_compl_preinsert_effect())
     {
 	col += (int)ins_compl_leader_len();
 	curwin->w_cursor.col = compl_ins_end_col;
@@ -5770,13 +5802,111 @@ ins_compl_expand_multiple(char_u *str)
     compl_ins_end_col = curwin->w_cursor.col;
 }
 
+/*
+ * Find the longest common prefix among the current completion matches.
+ * Returns a pointer to the first match string, with *prefix_len set to
+ * the length of the common prefix.
+ * If "curbuf_only" is TRUE, restrict matches to the current buffer
+ * ('.' source in 'complete').
+ */
+    static char_u *
+find_common_prefix(size_t *prefix_len, int curbuf_only)
+{
+    compl_T     *compl;
+    int		*match_count;
+    char_u	*first = NULL;
+    int		len = -1;
+    int		is_cpt_completion = (cpt_sources_array != NULL);
+
+    if (!is_cpt_completion)
+	return NULL;
+
+    match_count = ALLOC_CLEAR_MULT(int, cpt_sources_count);
+    if (match_count == NULL)
+	return NULL;
+
+    (void)get_leader_for_startcol(NULL, TRUE); // Clear the cache
+
+    compl = compl_first_match;
+    do
+    {
+	string_T *leader = get_leader_for_startcol(compl, TRUE);
+
+	// Apply 'smartcase' behavior during normal mode
+	if (ctrl_x_mode_normal() && !p_inf && leader->string
+		&& !ignorecase(leader->string))
+	    compl->cp_flags &= ~CP_ICASE;
+
+	if (!match_at_original_text(compl)
+		&& (leader->string == NULL
+		    || ins_compl_equal(compl, leader->string,
+			(int)leader->length)))
+	{
+	    // Limit number of items from each source if max_items is set.
+	    int match_limit_exceeded = FALSE;
+	    int cur_source = compl->cp_cpt_source_idx;
+
+	    if (cur_source != -1)
+	    {
+		match_count[cur_source]++;
+		int max_matches = cpt_sources_array[cur_source].cs_max_matches;
+		if (max_matches > 0 && match_count[cur_source] > max_matches)
+		    match_limit_exceeded = TRUE;
+	    }
+
+	    if (!match_limit_exceeded && (!curbuf_only
+			|| cpt_sources_array[cur_source].cs_flag == '.'))
+	    {
+		if (first == NULL)
+		{
+		    first = compl->cp_str.string;
+		    len = (int)STRLEN(first);
+		}
+		else
+		{
+		    int j = 0;  // count in bytes
+		    char_u *s1 = first;
+		    char_u *s2 = compl->cp_str.string;
+
+		    while (j < len && *s1 != NUL && *s2 != NUL)
+		    {
+			if (MB_BYTE2LEN(*s1) != MB_BYTE2LEN(*s2)
+				|| memcmp(s1, s2, MB_BYTE2LEN(*s1)) != 0)
+			    break;
+
+			j += MB_BYTE2LEN(*s1);
+			MB_PTR_ADV(s1);
+			MB_PTR_ADV(s2);
+		    }
+		    len = j;
+
+		    if (len == 0)
+			break;
+		}
+	    }
+	}
+	compl = compl->cp_next;
+    } while (compl != NULL && !is_first_match(compl));
+
+    vim_free(match_count);
+
+    if (len > get_compl_len())
+    {
+	*prefix_len = (size_t)len;
+	return first;
+    }
+    return NULL;
+}
+
 /*
  * Insert the new text being completed.
  * "move_cursor" is used when 'completeopt' includes "preinsert" and when TRUE
  * cursor needs to move back from the inserted text to the compl_leader.
+ * When "preinsert_prefix" is TRUE the longest common prefix is inserted
+ * instead of shown match.
  */
-    void
+    int
-ins_compl_insert(int move_cursor)
+ins_compl_insert(int move_cursor, int preinsert_prefix)
 {
     int		compl_len = get_compl_len();
     int		preinsert = ins_compl_has_preinsert();
@@ -5785,10 +5915,20 @@ ins_compl_insert(int move_cursor)
     size_t	leader_len = ins_compl_leader_len();
     char_u	*has_multiple = vim_strchr(cp_str, '\n');
 
+    if (preinsert_prefix)
+    {
+	cp_str = find_common_prefix(&cp_str_len, FALSE);
+	if (cp_str == NULL)
+	{
+	    cp_str = find_common_prefix(&cp_str_len, TRUE);
+	    if (cp_str == NULL)
+		return FAIL;
+	}
+    }
     // Since completion sources may provide matches with varying start
     // positions, insert only the portion of the match that corresponds to the
     // intended replacement range.
-    if (cpt_sources_array != NULL)
+    else if (cpt_sources_array != NULL)
     {
 	int	cpt_idx = compl_shown_match->cp_cpt_source_idx;
 	if (cpt_idx >= 0 && compl_col >= 0)
@@ -5814,7 +5954,8 @@ ins_compl_insert(int move_cursor)
 	    ins_compl_expand_multiple(cp_str + compl_len);
 	else
 	{
-	    ins_compl_insert_bytes(cp_str + compl_len, -1);
+	    ins_compl_insert_bytes(cp_str + compl_len,
+		    preinsert_prefix ? (int)cp_str_len - compl_len : -1);
 	    if (preinsert && move_cursor)
 		curwin->w_cursor.col -= (colnr_T)(cp_str_len - leader_len);
 	}
@@ -5830,6 +5971,7 @@ ins_compl_insert(int move_cursor)
 	set_vim_var_dict(VV_COMPLETED_ITEM, dict);
     }
 #endif
+    return OK;
 }
 
 /*
@@ -6084,16 +6226,39 @@ ins_compl_next(
 	return -1;
     }
 
+    compl_autocomplete_preinsert = FALSE;
+
     // Insert the text of the new completion, or the compl_leader.
-    if (compl_no_insert && !started && !compl_preinsert)
+    if (compl_no_insert && !started)
     {
-	ins_compl_insert_bytes(compl_orig_text.string + get_compl_len(), -1);
+	int insert_orig = !compl_preinsert;
+	if (compl_preinsert && compl_autocomplete)
+	{
+	    if (ins_compl_insert(TRUE, TRUE) == OK)
+		compl_autocomplete_preinsert = TRUE;
+	    else
+		insert_orig = TRUE;
+	}
+	if (insert_orig)
+	    ins_compl_insert_bytes(compl_orig_text.string + get_compl_len(), -1);
 	compl_used_match = FALSE;
     }
     else if (insert_match)
     {
 	if (!compl_get_longest || compl_used_match)
-	    ins_compl_insert(TRUE);
+	{
+	    int none_selected = match_at_original_text(compl_shown_match);
+	    if (compl_preinsert && compl_autocomplete
+		    && none_selected)
+	    {
+		if (ins_compl_insert(none_selected, TRUE) == OK)
+		    compl_autocomplete_preinsert = none_selected;
+		else
+		    (void)ins_compl_insert(FALSE, FALSE);
+	    }
+	    else
+		(void)ins_compl_insert(!compl_autocomplete, FALSE);
+	}
 	else
 	    ins_compl_insert_bytes(compl_leader.string + get_compl_len(), -1);
     }
@@ -7360,6 +7525,7 @@ setup_cpt_sources(void)
 	    p++;
 	if (*p) // If not end of string, count this segment
 	{
+	    cpt_sources_array[idx].cs_flag = *p;
 	    slen = copy_option_part(&p, buf, LSIZE, ","); // Advance p
 	    if (slen > 0)
 	    {

src/optiondefs.h

@@ -309,7 +309,7 @@ struct vimoption
 # define ISP_LATIN1 (char_u *)"@,161-255"
 #endif
 
-# define HIGHLIGHT_INIT "8:SpecialKey,~:EndOfBuffer,@:NonText,d:Directory,e:ErrorMsg,i:IncSearch,l:Search,y:CurSearch,m:MoreMsg,M:ModeMsg,n:LineNr,a:LineNrAbove,b:LineNrBelow,N:CursorLineNr,G:CursorLineSign,O:CursorLineFold,r:Question,s:StatusLine,S:StatusLineNC,c:VertSplit,t:Title,v:Visual,V:VisualNOS,w:WarningMsg,W:WildMenu,f:Folded,F:FoldColumn,A:DiffAdd,C:DiffChange,D:DiffDelete,T:DiffText,E:DiffTextAdd,>:SignColumn,-:Conceal,B:SpellBad,P:SpellCap,R:SpellRare,L:SpellLocal,+:Pmenu,=:PmenuSel,k:PmenuMatch,<:PmenuMatchSel,[:PmenuKind,]:PmenuKindSel,{:PmenuExtra,}:PmenuExtraSel,x:PmenuSbar,X:PmenuThumb,*:TabLine,#:TabLineSel,_:TabLineFill,!:CursorColumn,.:CursorLine,o:ColorColumn,q:QuickFixLine,z:StatusLineTerm,Z:StatusLineTermNC,g:MsgArea,h:ComplMatchIns,%:TabPanel,^:TabPanelSel,&:TabPanelFill"
+# define HIGHLIGHT_INIT "8:SpecialKey,~:EndOfBuffer,@:NonText,d:Directory,e:ErrorMsg,i:IncSearch,l:Search,y:CurSearch,m:MoreMsg,M:ModeMsg,n:LineNr,a:LineNrAbove,b:LineNrBelow,N:CursorLineNr,G:CursorLineSign,O:CursorLineFold,r:Question,s:StatusLine,S:StatusLineNC,c:VertSplit,t:Title,v:Visual,V:VisualNOS,w:WarningMsg,W:WildMenu,f:Folded,F:FoldColumn,A:DiffAdd,C:DiffChange,D:DiffDelete,T:DiffText,E:DiffTextAdd,>:SignColumn,-:Conceal,B:SpellBad,P:SpellCap,R:SpellRare,L:SpellLocal,+:Pmenu,=:PmenuSel,k:PmenuMatch,<:PmenuMatchSel,[:PmenuKind,]:PmenuKindSel,{:PmenuExtra,}:PmenuExtraSel,x:PmenuSbar,X:PmenuThumb,*:TabLine,#:TabLineSel,_:TabLineFill,!:CursorColumn,.:CursorLine,o:ColorColumn,q:QuickFixLine,z:StatusLineTerm,Z:StatusLineTermNC,g:MsgArea,h:ComplMatchIns,%:TabPanel,^:TabPanelSel,&:TabPanelFill,I:PreInsert"
 
 // Default python version for pyx* commands
 #if defined(FEAT_PYTHON) && defined(FEAT_PYTHON3)

src/proto/insexpand.pro

@@ -69,9 +69,11 @@ void f_complete_check(typval_T *argvars, typval_T *rettv);
 void f_complete_match(typval_T *argvars, typval_T *rettv);
 void f_complete_info(typval_T *argvars, typval_T *rettv);
 void ins_compl_delete(void);
-void ins_compl_insert(int move_cursor);
+int ins_compl_insert(int move_cursor, int insert_longest_prefix);
 void ins_compl_check_keys(int frequency, int in_compl_func);
 int ins_complete(int c, int enable_pum);
 void ins_compl_enable_autocomplete(void);
 void free_insexpand_stuff(void);
+int ins_compl_has_autocomplete(void);
+int ins_compl_has_preinsert(void);
 /* vim: set ft=c : */

src/testdir/test_cmdline.vim

@@ -489,6 +489,7 @@ func Test_highlight_completion()
   call assert_equal("\"hi link Aardig NONE", getreg(':'))
 
   " A cleared group does not show up in completions.
+  hi clear Added
   hi Anders ctermfg=green
   call assert_equal(['Aardig', 'Anders'], getcompletion('A', 'highlight'))
   hi clear Aardig

src/testdir/test_ins_complete.vim

@@ -5359,7 +5359,7 @@ func Test_autocomplete_timer()
   call assert_equal(-1, b:selected)
 
   " Test 7: Following 'cot' option values have no effect
-  set completeopt=menu,menuone,noselect,noinsert,longest,preinsert
+  set completeopt=menu,menuone,noselect,noinsert,longest
   set complete=.,Ffunction('TestComplete'\\,\ [0\\,\ 0\\,\ 0])
   let g:CallCount = 0
   call feedkeys("Sab\<c-n>\<F2>\<F3>\<Esc>0", 'tx!')
@@ -5578,4 +5578,109 @@ func Test_autocompletedelay()
   call StopVimInTerminal(buf)
 endfunc
 
+func Test_autocomplete_completeopt_preinsert()
+  func GetLine()
+    let g:line = getline('.')
+    let g:col = col('.')
+  endfunc
+
+  call test_override("char_avail", 1)
+  new
+  inoremap <buffer><F5> <C-R>=GetLine()<CR>
+  set completeopt=preinsert autocomplete
+  call setline(1, ["foobar", "foozbar"])
+  call feedkeys("Go\<ESC>", 'tx')
+
+  func DoTest(typed, line, col)
+    call feedkeys($"S{a:typed}\<F5>\<ESC>", 'tx')
+    call assert_equal(a:line, g:line)
+    call assert_equal(a:col, g:col)
+  endfunc
+
+  call DoTest("f", 'foo', 2)
+  call DoTest("fo", 'foo', 3)
+  call DoTest("foo", 'foo', 4)
+  call DoTest("foob", 'foobar', 5)
+  call DoTest("foob\<BS>", 'foo', 4)
+  call DoTest("foob\<BS>\<BS>", 'foo', 3)
+  call DoTest("foo\<BS>", 'foo', 3)
+  call DoTest("foo\<BS>\<BS>", 'foo', 2)
+  call DoTest("foo\<BS>\<BS>\<BS>", '', 1)
+
+  call DoTest("foo \<BS>", 'foo', 4)
+  call DoTest("foo \<BS>\<BS>", 'foo', 3)
+
+  call DoTest("f\<C-N>", 'foozbar', 8)
+  call DoTest("f\<C-N>\<C-N>", 'foobar', 7)
+  call DoTest("f\<C-N>\<C-N>\<C-N>", 'foo', 2)
+  call DoTest("f\<C-N>\<C-N>\<C-N>\<C-N>", 'foozbar', 8)
+  call DoTest("f\<C-N>\<C-N>\<C-N>\<C-N>\<C-P>", 'foo', 2)
+  call DoTest("f\<C-N>\<C-N>\<C-N>\<C-N>\<C-P>\<C-P>", 'foobar', 7)
+  call DoTest("f\<C-P>", 'foobar', 7)
+  call DoTest("fo\<BS>\<C-P>", 'foobar', 7)
+
+  call DoTest("zar\<C-O>0f", 'foozar', 2)
+  call DoTest("zar\<C-O>0f\<C-Y>", 'foozar', 4)
+  call DoTest("zar\<C-O>0f\<C-Y>\<BS>", 'foozar', 3)
+
+  call DoTest("zar\<C-O>0f\<C-N>", 'foozbarzar', 8)
+  call DoTest("zar\<C-O>0f\<C-N>\<C-N>", 'foobarzar', 7)
+  call DoTest("zar\<C-O>0f\<C-N>\<C-N>\<C-N>", 'foozar', 2)
+  call DoTest("zar\<C-O>0f\<C-N>\<C-N>\<C-N>\<C-N>", 'foozbarzar', 8)
+  call DoTest("zar\<C-O>0f\<C-N>\<C-N>\<C-N>\<C-N>\<C-P>", 'foozar', 2)
+  call DoTest("zar\<C-O>0f\<C-N>\<C-N>\<C-N>\<C-N>\<C-P>\<C-P>", 'foobarzar', 7)
+  call DoTest("zar\<C-O>0f\<C-P>", 'foobarzar', 7)
+
+  " Should not work with fuzzy
+  set cot+=fuzzy
+  call DoTest("f", 'f', 2)
+
+  %delete _
+  let &l:undolevels = &l:undolevels
+  normal! ifoo
+  let &l:undolevels = &l:undolevels
+  normal! ofoobar
+  let &l:undolevels = &l:undolevels
+  normal! ofoobaz
+  let &l:undolevels = &l:undolevels
+
+  func CheckUndo()
+    let g:errmsg = ''
+    call assert_equal(['foo', 'foobar', 'foobaz'], getline(1, '$'))
+    undo
+    call assert_equal(['foo', 'foobar'], getline(1, '$'))
+    undo
+    call assert_equal(['foo'], getline(1, '$'))
+    undo
+    call assert_equal([''], getline(1, '$'))
+    later 3
+    call assert_equal(['foo', 'foobar', 'foobaz'], getline(1, '$'))
+    call assert_equal('', v:errmsg)
+  endfunc
+
+  " Check that switching buffer with "preinsert" doesn't corrupt undo.
+  new
+  setlocal bufhidden=wipe
+  inoremap <buffer> <F2> <Cmd>enew!<CR>
+  call feedkeys("if\<F2>\<Esc>", 'tx')
+  bwipe!
+  call CheckUndo()
+
+  " Check that closing window with "preinsert" doesn't corrupt undo.
+  new
+  setlocal bufhidden=wipe
+  inoremap <buffer> <F2> <Cmd>close!<CR>
+  call feedkeys("if\<F2>\<Esc>", 'tx')
+  call CheckUndo()
+
+  %delete _
+  delfunc CheckUndo
+
+  bw!
+  set cot& autocomplete&
+  delfunc GetLine
+  delfunc DoTest
+  call test_override("char_avail", 0)
+endfunc
+
 " vim: shiftwidth=2 sts=2 expandtab nofoldenable

src/version.c

@@ -724,6 +724,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1742,
 /**/
     1741,
 /**/

src/vim.h

@@ -1587,6 +1587,7 @@ typedef enum
     , HLF_TPL	    // tabpanel
     , HLF_TPLS	    // tabpanel selected
     , HLF_TPLF	    // tabpanel filler
+    , HLF_PRI	    // "preinsert" in 'completeopt'
     , HLF_COUNT	    // MUST be the last one
 } hlf_T;
 
@@ -1599,7 +1600,7 @@ typedef enum
 		  '+', '=', 'k', '<','[', ']', '{', '}', 'x', 'X', \
 		  '*', '#', '_', '!', '.', 'o', 'q', \
 		  'z', 'Z', 'g', \
-		  '%', '^', '&' }
+		  '%', '^', '&', 'I'}
 
 /*
  * Values for behaviour in spell_move_to