vim-patch:9.1.1056: Vim doesn't highlight to be inserted text when completing (#32251)

Problem:  Vim doesn't highlight to be inserted text when completing
Solution: Add support for the "preinsert" 'completeopt' value
          (glepnir)

Support automatically inserting the currently selected candidate word
that does not belong to the latter part of the leader.

fixes: vim/vim#3433
closes: vim/vim#16403

https://github.com/vim/vim/commit/edd4ac3e895ce16034c7e098f1d68e0155d97886

Co-authored-by: glepnir <glephunter@gmail.com>

10 files changed, 205 insertions, 9 deletions

diff --git a/runtime/doc/dev_vimpatch.txt b/runtime/doc/dev_vimpatch.txt
index 5119613b55..76be24878a 100644
--- a/runtime/doc/dev_vimpatch.txt
+++ b/runtime/doc/dev_vimpatch.txt
@@ -188,6 +188,7 @@ information.
   vim_strcat strncat                                     xstrlcat
   VIM_ISWHITE                                          ascii_iswhite
   IS_WHITE_OR_NUL                                  ascii_iswhite_or_nul
+  IS_WHITE_NL_OR_NUL                              ascii_iswhite_nl_or_nul
   vim_isalpha                                           mb_isalpha
   vim_isNormalIDc                                      ascii_isident
   vim_islower vim_isupper                          mb_islower mb_isupper
diff --git a/runtime/doc/news.txt b/runtime/doc/news.txt
index 65417971ab..2208428f75 100644
--- a/runtime/doc/news.txt
+++ b/runtime/doc/news.txt
@@ -309,6 +309,7 @@ LUA
 OPTIONS
 
 • 'completeopt' flag "fuzzy" enables |fuzzy-matching| during |ins-completion|.
+• 'completeopt' flag "preinsert" highlights text to be inserted.
 • 'messagesopt' configures |:messages| and |hit-enter| prompt.
 • 'tabclose' controls which tab page to focus when closing a tab page.
 
diff --git a/runtime/doc/options.txt b/runtime/doc/options.txt
index 1f19db5eb9..b4ae3cc8fd 100644
--- a/runtime/doc/options.txt
+++ b/runtime/doc/options.txt
@@ -1575,6 +1575,12 @@ A jump table for the options with a short description can be found at |Q_op|.
 		    scores when "fuzzy" is enabled. Candidates will appear
 		    in their original order.
 
+	   preinsert
+		    Preinsert the portion of the first candidate word that is
+		    not part of the current completion leader and using the
+		    |hl-ComplMatchIns| highlight group. Does not work when
+		    "fuzzy" is also included.
+
 						*'completeslash'* *'csl'*
 'completeslash' 'csl'	string	(default "")
 			local to buffer
diff --git a/runtime/lua/vim/_meta/options.lua b/runtime/lua/vim/_meta/options.lua
index f0f0d1a768..452959970d 100644
--- a/runtime/lua/vim/_meta/options.lua
+++ b/runtime/lua/vim/_meta/options.lua
@@ -1102,6 +1102,12 @@ vim.go.cia = vim.go.completeitemalign
 --- 	    scores when "fuzzy" is enabled. Candidates will appear
 --- 	    in their original order.
 ---
+---    preinsert
+--- 	    Preinsert the portion of the first candidate word that is
+--- 	    not part of the current completion leader and using the
+--- 	    `hl-ComplMatchIns` highlight group. Does not work when
+--- 	    "fuzzy" is also included.
+---
 --- @type string
 vim.o.completeopt = "menu,preview"
 vim.o.cot = vim.o.completeopt
diff --git a/src/nvim/ascii_defs.h b/src/nvim/ascii_defs.h
index 155a18fb95..86187b553c 100644
--- a/src/nvim/ascii_defs.h
+++ b/src/nvim/ascii_defs.h
@@ -103,6 +103,15 @@ static inline bool ascii_iswhite_or_nul(int c)
   return ascii_iswhite(c) || c == NUL;
 }
 
+/// Checks if `c` is a space or tab or newline character or NUL.
+///
+/// @see {ascii_isdigit}
+static inline bool ascii_iswhite_nl_or_nul(int c)
+  FUNC_ATTR_CONST FUNC_ATTR_ALWAYS_INLINE
+{
+  return ascii_iswhite(c) || c == '\n' || c == NUL;
+}
+
 /// Check whether character is a decimal digit.
 ///
 /// Library isdigit() function is officially locale-dependent and, for
diff --git a/src/nvim/edit.c b/src/nvim/edit.c
index e55cda1c21..9e17c93f3f 100644
--- a/src/nvim/edit.c
+++ b/src/nvim/edit.c
@@ -609,7 +609,10 @@ static int insert_execute(VimState *state, int key)
                && (s->c == CAR || s->c == K_KENTER || s->c == NL)))
           && stop_arrow() == OK) {
         ins_compl_delete(false);
-        ins_compl_insert(false);
+        ins_compl_insert(false, false);
+      } else if (ascii_iswhite_nl_or_nul(s->c) && ins_compl_preinsert_effect()) {
+        // Delete preinserted text when typing special chars
+        ins_compl_delete(false);
       }
     }
   }
diff --git a/src/nvim/insexpand.c b/src/nvim/insexpand.c
index 8eb1a49e7d..73b84175d7 100644
--- a/src/nvim/insexpand.c
+++ b/src/nvim/insexpand.c
@@ -1781,12 +1781,33 @@ int ins_compl_len(void)
   return compl_length;
 }
 
+/// Return true when preinsert is set otherwise FALSE.
+static bool ins_compl_has_preinsert(void)
+{
+  return (get_cot_flags() & (kOptCotFlagFuzzy|kOptCotFlagPreinsert)) == kOptCotFlagPreinsert;
+}
+
+/// Returns true if the pre-insert effect is valid and the cursor is within
+/// the `compl_ins_end_col` range.
+bool ins_compl_preinsert_effect(void)
+{
+  if (!ins_compl_has_preinsert()) {
+    return false;
+  }
+
+  return curwin->w_cursor.col < compl_ins_end_col;
+}
+
 /// Delete one character before the cursor and show the subset of the matches
 /// that match the word that is now before the cursor.
 /// Returns the character to be used, NUL if the work is done and another char
 /// to be got from the user.
 int ins_compl_bs(void)
 {
+  if (ins_compl_preinsert_effect()) {
+    ins_compl_delete(false);
+  }
+
   char *line = get_cursor_line_ptr();
   char *p = line + curwin->w_cursor.col;
   MB_PTR_BACK(line, p);
@@ -1872,8 +1893,13 @@ static void ins_compl_new_leader(void)
   ins_compl_show_pum();
 
   // 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.size > 0) {
+    ins_compl_insert(false, true);
+  }
   // Don't let Enter select when use user function and refresh_always is set
-  if (compl_match_array == NULL || ins_compl_refresh_always()) {
+  if (ins_compl_refresh_always()) {
     compl_enter_selects = false;
   }
 }
@@ -1896,6 +1922,10 @@ void ins_compl_addleader(int c)
 {
   int cc;
 
+  if (ins_compl_preinsert_effect()) {
+    ins_compl_delete(false);
+  }
+
   if (stop_arrow() == FAIL) {
     return;
   }
@@ -3696,6 +3726,12 @@ void ins_compl_delete(bool new_leader)
   // In insert mode: Delete the typed part.
   // In replace mode: Put the old characters back, if any.
   int col = compl_col + (compl_status_adding() ? compl_length : orig_col);
+  bool has_preinsert = ins_compl_preinsert_effect();
+  if (has_preinsert) {
+    col = compl_col + (int)ins_compl_leader_len() - compl_length;
+    curwin->w_cursor.col = compl_ins_end_col;
+  }
+
   if ((int)curwin->w_cursor.col > col) {
     if (stop_arrow() == FAIL) {
       return;
@@ -3713,15 +3749,24 @@ void ins_compl_delete(bool new_leader)
 
 /// Insert the new text being completed.
 /// "in_compl_func" is true when called from complete_check().
-void ins_compl_insert(bool in_compl_func)
+/// "move_cursor" is used when 'completeopt' includes "preinsert" and when true
+/// cursor needs to move back from the inserted text to the compl_leader.
+void ins_compl_insert(bool in_compl_func, bool move_cursor)
 {
   int compl_len = get_compl_len();
+  bool preinsert = ins_compl_has_preinsert();
+  char *str = compl_shown_match->cp_str.data;
+  size_t leader_len = ins_compl_leader_len();
+
   // Make sure we don't go over the end of the string, this can happen with
   // illegal bytes.
   if (compl_len < (int)compl_shown_match->cp_str.size) {
-    ins_compl_insert_bytes(compl_shown_match->cp_str.data + compl_len, -1);
+    ins_compl_insert_bytes(str + compl_len, -1);
+    if (preinsert && move_cursor) {
+      curwin->w_cursor.col -= (colnr_T)(strlen(str) - leader_len);
+    }
   }
-  compl_used_match = !match_at_original_text(compl_shown_match);
+  compl_used_match = !(match_at_original_text(compl_shown_match) || preinsert);
 
   dict_T *dict = ins_compl_dict_alloc(compl_shown_match);
   set_vim_var_dict(VV_COMPLETED_ITEM, dict);
@@ -3923,6 +3968,7 @@ static int ins_compl_next(bool allow_get_expansion, int count, bool insert_match
   unsigned cur_cot_flags = get_cot_flags();
   bool compl_no_insert = (cur_cot_flags & kOptCotFlagNoinsert) != 0;
   bool compl_fuzzy_match = (cur_cot_flags & kOptCotFlagFuzzy) != 0;
+  bool compl_preinsert = ins_compl_has_preinsert();
 
   // When user complete function return -1 for findstart which is next
   // time of 'always', compl_shown_match become NULL.
@@ -3967,13 +4013,13 @@ static int ins_compl_next(bool allow_get_expansion, int count, bool insert_match
   }
 
   // Insert the text of the new completion, or the compl_leader.
-  if (compl_no_insert && !started) {
+  if (compl_no_insert && !started && !compl_preinsert) {
     ins_compl_insert_bytes(compl_orig_text.data + get_compl_len(), -1);
     compl_used_match = false;
     restore_orig_extmarks();
   } else if (insert_match) {
     if (!compl_get_longest || compl_used_match) {
-      ins_compl_insert(in_compl_func);
+      ins_compl_insert(in_compl_func, true);
     } else {
       assert(compl_leader.data != NULL);
       ins_compl_insert_bytes(compl_leader.data + get_compl_len(), -1);
diff --git a/src/nvim/options.lua b/src/nvim/options.lua
index c6f5221c8b..fdd5799b46 100644
--- a/src/nvim/options.lua
+++ b/src/nvim/options.lua
@@ -1494,6 +1494,7 @@ local options = {
         'noselect',
         'fuzzy',
         'nosort',
+        'preinsert',
       },
       flags = true,
       deny_duplicates = true,
@@ -1542,6 +1543,12 @@ local options = {
            nosort   Disable sorting of completion candidates based on fuzzy
         	    scores when "fuzzy" is enabled. Candidates will appear
         	    in their original order.
+
+           preinsert
+        	    Preinsert the portion of the first candidate word that is
+        	    not part of the current completion leader and using the
+        	    |hl-ComplMatchIns| highlight group. Does not work when
+        	    "fuzzy" is also included.
       ]=],
       full_name = 'completeopt',
       list = 'onecomma',
diff --git a/test/old/testdir/gen_opt_test.vim b/test/old/testdir/gen_opt_test.vim
index bcb0f3d4c4..f9fcc4ae1b 100644
--- a/test/old/testdir/gen_opt_test.vim
+++ b/test/old/testdir/gen_opt_test.vim
@@ -87,7 +87,7 @@ let test_values = {
       \		['xxx', 'help,nofile']],
       \ 'clipboard': [['', 'unnamed'], ['xxx', '\ze*', 'exclude:\\%(']],
       \ 'completeopt': [['', 'menu', 'menuone', 'longest', 'preview', 'popup',
-      \		'noinsert', 'noselect', 'fuzzy', 'menu,longest'],
+      \		'noinsert', 'noselect', 'fuzzy', 'preinsert', 'menu,longest'],
       \		['xxx', 'menu,,,longest,']],
       \ 'encoding': [['utf8'], []],
       \ 'foldcolumn': [[0, 1, 4, 'auto', 'auto:1', 'auto:9'], [-1, 13, 999]],
@@ -186,7 +186,7 @@ let test_values = {
       \		['xxx']],
       \ 'concealcursor': [['', 'n', 'v', 'i', 'c', 'nvic'], ['xxx']],
       "\ 'completeopt': [['', 'menu', 'menuone', 'longest', 'preview', 'popup',
-      "\ "		'popuphidden', 'noinsert', 'noselect', 'fuzzy', 'menu,longest'],
+      "\ "		'popuphidden', 'noinsert', 'noselect', 'fuzzy', 'preinsert', 'menu,longest'],
       "\ "		['xxx', 'menu,,,longest,']],
       \ 'completeitemalign': [['abbr,kind,menu', 'menu,abbr,kind'],
       \		['', 'xxx', 'abbr', 'abbr,menu', 'abbr,menu,kind,abbr',
diff --git a/test/old/testdir/test_ins_complete.vim b/test/old/testdir/test_ins_complete.vim
index 1c63e8f4cc..969d5012f4 100644
--- a/test/old/testdir/test_ins_complete.vim
+++ b/test/old/testdir/test_ins_complete.vim
@@ -2964,4 +2964,121 @@ func Test_complete_info_completed()
   set cot&
 endfunc
 
+function Test_completeopt_preinsert()
+  func Omni_test(findstart, base)
+    if a:findstart
+      return col(".")
+    endif
+    return [#{word: "fobar"}, #{word: "foobar"}, #{word: "你的"}, #{word: "你好世界"}]
+  endfunc
+  set omnifunc=Omni_test
+  set completeopt=menu,menuone,preinsert
+
+  new
+  call feedkeys("S\<C-X>\<C-O>f", 'tx')
+  call assert_equal("fobar", getline('.'))
+  call feedkeys("\<C-E>\<ESC>", 'tx')
+
+  call feedkeys("S\<C-X>\<C-O>foo", 'tx')
+  call assert_equal("foobar", getline('.'))
+  call feedkeys("\<C-E>\<ESC>", 'tx')
+
+  call feedkeys("S\<C-X>\<C-O>foo\<BS>\<BS>\<BS>", 'tx')
+  call assert_equal("", getline('.'))
+  call feedkeys("\<C-E>\<ESC>", 'tx')
+
+  " delete a character and input new leader
+  call feedkeys("S\<C-X>\<C-O>foo\<BS>b", 'tx')
+  call assert_equal("fobar", getline('.'))
+  call feedkeys("\<C-E>\<ESC>", 'tx')
+
+  " delete preinsert when prepare completion
+  call feedkeys("S\<C-X>\<C-O>f\<Space>", 'tx')
+  call assert_equal("f ", getline('.'))
+  call feedkeys("\<C-E>\<ESC>", 'tx')
+
+  call feedkeys("S\<C-X>\<C-O>你", 'tx')
+  call assert_equal("你的", getline('.'))
+  call feedkeys("\<C-E>\<ESC>", 'tx')
+
+  call feedkeys("S\<C-X>\<C-O>你好", 'tx')
+  call assert_equal("你好世界", getline('.'))
+  call feedkeys("\<C-E>\<ESC>", 'tx')
+
+  call feedkeys("Shello   wo\<Left>\<Left>\<Left>\<C-X>\<C-O>f", 'tx')
+  call assert_equal("hello  fobar wo", getline('.'))
+  call feedkeys("\<C-E>\<ESC>", 'tx')
+
+  call feedkeys("Shello   wo\<Left>\<Left>\<Left>\<C-X>\<C-O>f\<BS>", 'tx')
+  call assert_equal("hello   wo", getline('.'))
+  call feedkeys("\<C-E>\<ESC>", 'tx')
+
+  call feedkeys("Shello   wo\<Left>\<Left>\<Left>\<C-X>\<C-O>foo", 'tx')
+  call assert_equal("hello  foobar wo", getline('.'))
+  call feedkeys("\<C-E>\<ESC>", 'tx')
+
+  call feedkeys("Shello   wo\<Left>\<Left>\<Left>\<C-X>\<C-O>foo\<BS>b", 'tx')
+  call assert_equal("hello  fobar wo", getline('.'))
+  call feedkeys("\<C-E>\<ESC>", 'tx')
+
+  " confrim
+  call feedkeys("S\<C-X>\<C-O>f\<C-Y>", 'tx')
+  call assert_equal("fobar", getline('.'))
+  call assert_equal(5, col('.'))
+
+  " cancel
+  call feedkeys("S\<C-X>\<C-O>fo\<C-E>", 'tx')
+  call assert_equal("fo", getline('.'))
+  call assert_equal(2, col('.'))
+
+  call feedkeys("S hello hero\<CR>h\<C-X>\<C-N>", 'tx')
+  call assert_equal("hello", getline('.'))
+  call assert_equal(1, col('.'))
+
+  call feedkeys("Sh\<C-X>\<C-N>\<C-Y>", 'tx')
+  call assert_equal("hello", getline('.'))
+  call assert_equal(5, col('.'))
+
+  " delete preinsert part
+  call feedkeys("S\<C-X>\<C-O>fo ", 'tx')
+  call assert_equal("fo ", getline('.'))
+  call assert_equal(3, col('.'))
+
+  " whole line
+  call feedkeys("Shello hero\<CR>\<C-X>\<C-L>", 'tx')
+  call assert_equal("hello hero", getline('.'))
+  call assert_equal(1, col('.'))
+
+  call feedkeys("Shello hero\<CR>he\<C-X>\<C-L>", 'tx')
+  call assert_equal("hello hero", getline('.'))
+  call assert_equal(2, col('.'))
+
+  " can not work with fuzzy
+  set cot+=fuzzy
+  call feedkeys("S\<C-X>\<C-O>", 'tx')
+  call assert_equal("fobar", getline('.'))
+  call assert_equal(5, col('.'))
+
+  " test for fuzzy and noinsert
+  set cot+=noinsert
+  call feedkeys("S\<C-X>\<C-O>fb", 'tx')
+  call assert_equal("fb", getline('.'))
+  call assert_equal(2, col('.'))
+
+  call feedkeys("S\<C-X>\<C-O>你", 'tx')
+  call assert_equal("你", getline('.'))
+  call assert_equal(1, col('.'))
+
+  call feedkeys("S\<C-X>\<C-O>fb\<C-Y>", 'tx')
+  call assert_equal("fobar", getline('.'))
+  call assert_equal(5, col('.'))
+
+  bw!
+  bw!
+  set cot&
+  set omnifunc&
+  delfunc Omni_test
+  autocmd! CompleteChanged
+endfunc
+
 " vim: shiftwidth=2 sts=2 expandtab nofoldenable