vim-patch:9.0.1785: wrong cursor position with 'showbreak' and lcs-eol (#24852)

Problem:  wrong cursor position with 'showbreak' and lcs-eol
Solution: Add size of 'showbreak' before when 'listchars' "eol" is used.
          Also fix wrong cursor position with wrapping virtual text on
          empty line and 'showbreak'.

closes: vim/vim#12891

https://github.com/vim/vim/commit/1193951bebcff50d88403ce17dec5d3be14f131d

5 files changed, 73 insertions, 47 deletions

diff --git a/src/nvim/move.c b/src/nvim/move.c
index 3f4ba3c811..993e5bf495 100644
--- a/src/nvim/move.c
+++ b/src/nvim/move.c
@@ -879,7 +879,7 @@ void curs_columns(win_T *wp, int may_scroll)
       // column
       char *const sbr = get_showbreak_value(wp);
       if (*sbr && *get_cursor_pos_ptr() == NUL
-          && wp->w_wcol == vim_strsize(sbr)) {
+          && wp->w_wcol == (wp->w_width_inner - width2) + vim_strsize(sbr)) {
         wp->w_wcol = 0;
       }
     }
diff --git a/src/nvim/plines.c b/src/nvim/plines.c
index c2447103dc..c378b55413 100644
--- a/src/nvim/plines.c
+++ b/src/nvim/plines.c
@@ -404,8 +404,13 @@ int win_lbr_chartabsize(chartabsize_T *cts, int *headp)
     return win_chartabsize(wp, s, vcol);
   }
 
+  bool has_lcs_eol = wp->w_p_list && wp->w_p_lcs_chars.eol != NUL;
+
   // First get normal size, without 'linebreak' or inline virtual text
   int size = win_chartabsize(wp, s, vcol);
+  if (*s == NUL && !has_lcs_eol) {
+    size = 0;  // NUL is not displayed
+  }
 
   if (cts->cts_has_virt_text) {
     int tab_size = size;
@@ -491,14 +496,11 @@ int win_lbr_chartabsize(chartabsize_T *cts, int *headp)
   }
 
   // May have to add something for 'breakindent' and/or 'showbreak'
-  // string at start of line.
-  // Do not use 'showbreak' at the NUL after the text.
+  // string at the start of a screen line.
   int head = mb_added;
-  char *const sbr
-  // XXX: there should be a better check deeper below
-    = ((c == NUL && cts->cts_cur_text_width_left + cts->cts_cur_text_width_right == 0)
-       ? empty_option : get_showbreak_value(wp));
-  if ((*sbr != NUL || wp->w_p_bri) && wp->w_p_wrap) {
+  char *const sbr = get_showbreak_value(wp);
+  // When "size" is 0, no new screen line is started.
+  if (size > 0 && wp->w_p_wrap && (*sbr != NUL || wp->w_p_bri)) {
     int col_off_prev = win_col_off(wp);
     int width2 = wp->w_width_inner - col_off_prev + win_col_off2(wp);
     colnr_T wcol = vcol + col_off_prev;
@@ -542,35 +544,33 @@ int win_lbr_chartabsize(chartabsize_T *cts, int *headp)
       if (wp->w_p_bri) {
         head_mid += get_breakindent_win(wp, line);
       }
-      if (head_mid > 0) {
-        if (wcol + size > wp->w_width_inner) {
-          // Calculate effective window width.
-          int prev_rem = wp->w_width_inner - wcol;
-          int width = width2 - head_mid;
-
-          if (width <= 0) {
-            width = 1;
+      if (head_mid > 0 && wcol + size > wp->w_width_inner) {
+        // Calculate effective window width.
+        int prev_rem = wp->w_width_inner - wcol;
+        int width = width2 - head_mid;
+
+        if (width <= 0) {
+          width = 1;
+        }
+        // divide "size - prev_width" by "width", rounding up
+        int cnt = (size - prev_rem + width - 1) / width;
+        added += cnt * head_mid;
+
+        if (max_head_vcol == 0 || vcol + size + added < max_head_vcol) {
+          head += cnt * head_mid;
+        } else if (max_head_vcol > vcol + head_prev + prev_rem) {
+          head += (max_head_vcol - (vcol + head_prev + prev_rem)
+                   + width2 - 1) / width2 * head_mid;
+        } else if (max_head_vcol < 0) {
+          int off = 0;
+          if (c != NUL || !(State & MODE_NORMAL)) {
+            off += cts->cts_cur_text_width_left;
           }
-          // divide "size - prev_width" by "width", rounding up
-          int cnt = (size - prev_rem + width - 1) / width;
-          added += cnt * head_mid;
-
-          if (max_head_vcol == 0 || vcol + size + added < max_head_vcol) {
-            head += cnt * head_mid;
-          } else if (max_head_vcol > vcol + head_prev + prev_rem) {
-            head += (max_head_vcol - (vcol + head_prev + prev_rem)
-                     + width2 - 1) / width2 * head_mid;
-          } else if (max_head_vcol < 0) {
-            int off = 0;
-            if (c != NUL || !(State & MODE_NORMAL)) {
-              off += cts->cts_cur_text_width_left;
-            }
-            if (c != NUL && (State & MODE_NORMAL)) {
-              off += cts->cts_cur_text_width_right;
-            }
-            if (off >= prev_rem) {
-              head += (1 + (off - prev_rem) / width) * head_mid;
-            }
+          if (c != NUL && (State & MODE_NORMAL)) {
+            off += cts->cts_cur_text_width_right;
+          }
+          if (off >= prev_rem) {
+            head += (1 + (off - prev_rem) / width) * head_mid;
           }
         }
       }
diff --git a/test/functional/legacy/breakindent_spec.lua b/test/functional/legacy/breakindent_spec.lua
index d7779684a4..ecd2d47f47 100644
--- a/test/functional/legacy/breakindent_spec.lua
+++ b/test/functional/legacy/breakindent_spec.lua
@@ -1,6 +1,7 @@
 local helpers = require('test.functional.helpers')(after_each)
 local Screen = require('test.functional.ui.screen')
 local clear = helpers.clear
+local command = helpers.command
 local exec = helpers.exec
 local feed = helpers.feed
 
@@ -17,20 +18,15 @@ describe('breakindent', function()
     })
     screen:attach()
     exec([[
+      set listchars=eol:$
       let &signcolumn = 'yes'
-      let &showbreak = '+'
+      let &showbreak = '++'
+      let &breakindent = v:true
+      let &breakindentopt = 'shift:2'
       let leftcol = win_getid()->getwininfo()->get(0, {})->get('textoff')
       eval repeat('x', &columns - leftcol - 1)->setline(1)
       eval 'second line'->setline(2)
     ]])
-    screen:expect([[
-      {1:  }^xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx |
-      {1:  }second line                                                              |
-      {0:~                                                                          }|
-      {0:~                                                                          }|
-      {0:~                                                                          }|
-                                                                                 |
-    ]])
     feed('AX')
     screen:expect([[
       {1:  }xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxX|
@@ -40,5 +36,18 @@ describe('breakindent', function()
       {0:~                                                                          }|
       {2:-- INSERT --}                                                               |
     ]])
+    -- No line wraps, so changing 'showbreak' should lead to the same screen.
+    command('setlocal showbreak=+')
+    screen:expect_unchanged()
+    -- The first line now wraps because of "eol" in 'listchars'.
+    command('setlocal list')
+    screen:expect{grid=[[
+      {1:  }xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxX|
+      {1:  }  {0:+^$}                                                                     |
+      {1:  }second line{0:$}                                                             |
+      {0:~                                                                          }|
+      {0:~                                                                          }|
+      {2:-- INSERT --}                                                               |
+    ]]}
   end)
 end)
diff --git a/test/functional/ui/decorations_spec.lua b/test/functional/ui/decorations_spec.lua
index 4e3214da71..6c1a7a6a2c 100644
--- a/test/functional/ui/decorations_spec.lua
+++ b/test/functional/ui/decorations_spec.lua
@@ -2886,6 +2886,15 @@ bbbbbbb]])
       {1:~                             }|
                                     |
     ]]}
+    feed('zbx')
+    screen:expect{grid=[[
+        1 ^12312312312312312312312312|
+            {1:+}31231231231231231231231|
+            {1:+}23123123123123123123   |
+      {1:~                             }|
+      {1:~                             }|
+                                    |
+    ]]}
   end
 
   describe('with showbreak, smoothscroll', function()
diff --git a/test/old/testdir/test_breakindent.vim b/test/old/testdir/test_breakindent.vim
index 8d64c0dc90..3ce7d1386b 100644
--- a/test/old/testdir/test_breakindent.vim
+++ b/test/old/testdir/test_breakindent.vim
@@ -937,7 +937,9 @@ func Test_cursor_position_with_showbreak()
   let lines =<< trim END
       vim9script
       &signcolumn = 'yes'
-      &showbreak = '+ '
+      &showbreak = '++'
+      &breakindent = true
+      &breakindentopt = 'shift:2'
       var leftcol: number = win_getid()->getwininfo()->get(0, {})->get('textoff')
       repeat('x', &columns - leftcol - 1)->setline(1)
       'second line'->setline(2)
@@ -946,7 +948,13 @@ func Test_cursor_position_with_showbreak()
   let buf = RunVimInTerminal('-S XscriptShowbreak', #{rows: 6})
 
   call term_sendkeys(buf, "AX")
-  call VerifyScreenDump(buf, 'Test_cursor_position_with_showbreak', {})
+  call VerifyScreenDump(buf, 'Test_cursor_position_with_showbreak_1', {})
+  " No line wraps, so changing 'showbreak' should lead to the same screen.
+  call term_sendkeys(buf, "\<C-\>\<C-O>:setlocal showbreak=+\<CR>")
+  call VerifyScreenDump(buf, 'Test_cursor_position_with_showbreak_1', {})
+  " The first line now wraps because of "eol" in 'listchars'.
+  call term_sendkeys(buf, "\<C-\>\<C-O>:setlocal list\<CR>")
+  call VerifyScreenDump(buf, 'Test_cursor_position_with_showbreak_2', {})
 
   call StopVimInTerminal(buf)
 endfunc