fix(prompt): wrong cursor col after prompt_setprompt, no on_lines

Problem: prompt_setprompt calls coladvance with a byte column, but it expects a
screen column. on_lines buffer-updates aren't fired when fixing the prompt line.

Solution: don't use coladvance. Call changed_lines, which also simplifies the
redraw logic. (and calls changed_cline_bef_curs if needed; added test checks
this)

Unlike https://github.com/neovim/neovim/pull/37743/changes#r2775398744, this
means &modified is set by prompt_setprompt if it fixes the prompt line.
Not setting &modified is inconsistent anyway -- even init_prompt sets it if it
fixes the prompt line.

src/nvim/eval/buffer.c

@@ -801,10 +801,9 @@ void f_prompt_setprompt(typval_T *argvars, typval_T *rettv, EvalFuncData fptr)
     }
 
     if (curwin->w_buffer == buf && curwin->w_cursor.lnum == prompt_lno) {
-      coladvance(curwin, cursor_col);
+      curwin->w_cursor.col = cursor_col;
     }
-    changed_lines_redraw_buf(buf, prompt_lno, prompt_lno + 1, 0);
-    redraw_buf_later(buf, UPD_INVERTED);
+    changed_lines(buf, prompt_lno, 0, prompt_lno + 1, 0, true);
   }
 
   // Clear old prompt text and replace with the new one

test/functional/legacy/prompt_buffer_spec.lua

@@ -62,7 +62,7 @@ describe('prompt buffer', function()
     screen:expect([[
       cmd: ^                    |
       {1:~                        }|*3
-      {3:[Prompt]                 }|
+      {3:[Prompt] [+]             }|
       other buffer             |
       {1:~                        }|*3
       {5:-- INSERT --}             |
@@ -149,7 +149,7 @@ describe('prompt buffer', function()
     screen:expect([[
       cmd:                     |
       {1:~                        }|*3
-      {2:[Prompt]                 }|
+      {2:[Prompt] [+]             }|
       ^other buffer             |
       {1:~                        }|*3
                                |
@@ -158,7 +158,7 @@ describe('prompt buffer', function()
     screen:expect([[
       cmd: ^                    |
       {1:~                        }|*3
-      {3:[Prompt]                 }|
+      {3:[Prompt] [+]             }|
       other buffer             |
       {1:~                        }|*3
       {5:-- INSERT --}             |
@@ -167,7 +167,7 @@ describe('prompt buffer', function()
     screen:expect([[
       cmd:^                     |
       {1:~                        }|*3
-      {3:[Prompt]                 }|
+      {3:[Prompt] [+]             }|
       other buffer             |
       {1:~                        }|*3
                                |
@@ -892,10 +892,42 @@ describe('prompt buffer', function()
       {1:~                        }|*7
                                |
     ]])
+    -- Correct col when prompt has multi-cell chars.
+    feed('i<Left><Left>')
+    screen:expect([[
+      new-prompt > user input  |
+      <>< user inp^ut           |
+      {1:~                        }|*7
+      {5:-- INSERT --}             |
+    ]])
+    set_prompt('\t > ')
+    screen:expect([[
+      new-prompt > user input  |
+               > user inp^ut    |
+      {1:~                        }|*7
+      {5:-- INSERT --}             |
+    ]])
+    -- Works with 'virtualedit': coladd remains sensible. Cursor is redrawn correctly.
+    -- Tab size visually changes due to multiples of 'tabstop'.
+    command('set virtualedit=all')
+    feed('<C-O>Sa<Tab>b<C-O>3h')
+    screen:expect([[
+      new-prompt > user input  |
+               > a  ^  b        |
+      {1:~                        }|*7
+      {5:-- INSERT --}             |
+    ]])
+    set_prompt('😊 > ')
+    screen:expect([[
+      new-prompt > user input  |
+      😊 > a ^ b                |
+      {1:~                        }|*7
+      {5:-- INSERT --}             |
+    ]])
 
     -- No crash when setting shorter prompt than curbuf's in other buffer.
-    feed('i<C-O>zt')
-    command('new | setlocal buftype=prompt')
+    feed('<C-O>zt')
+    command('set virtualedit& | new | setlocal buftype=prompt')
     set_prompt('looooooooooooooooooooooooooooooooooooooooooooong > ', '') -- curbuf
     set_prompt('foo > ')
     screen:expect([[
@@ -904,7 +936,7 @@ describe('prompt buffer', function()
        ^                        |
       {1:~                        }|
       {3:[Prompt] [+]             }|
-      foo > user input         |
+      foo > a b                |
       {1:~                        }|*3
       {5:-- INSERT --}             |
     ]])

test/functional/lua/buffer_updates_spec.lua

@@ -422,6 +422,48 @@ describe('lua: nvim_buf_attach on_lines', function()
     feed('<C-v>I <ESC>')
     eq({ api.nvim_get_current_buf(), 0, 1, 1 }, exec_lua('return _G.res'))
   end)
+
+  it('prompt buffer', function()
+    local check_events = setup_eventcheck(false, nil, {})
+    api.nvim_set_option_value('buftype', 'prompt', {})
+    feed('i')
+    check_events {
+      { 'test1', 'lines', 1, 4, 0, 1, 1, 1 },
+    }
+    fn.prompt_setprompt('', 'foo > ')
+    check_events {
+      { 'test1', 'lines', 1, 5, 0, 1, 1, 3 },
+    }
+    feed('hello')
+    check_events {
+      { 'test1', 'lines', 1, 6, 0, 1, 1, 7 },
+    }
+    fn.prompt_setprompt('', 'super-foo > ')
+    check_events {
+      { 'test1', 'lines', 1, 7, 0, 1, 1, 12 },
+    }
+    eq({ 'super-foo > hello' }, api.nvim_buf_get_lines(0, 0, -1, true))
+    -- Do this in the same event.
+    exec_lua(function()
+      vim.fn.setpos("':", { 0, 1, 999, 0 })
+      vim.fn.prompt_setprompt('', 'discard > ')
+    end)
+    check_events {
+      { 'test1', 'lines', 1, 8, 0, 1, 1, 18 },
+    }
+    eq({ 'discard > ' }, api.nvim_buf_get_lines(0, 0, -1, true))
+    feed('hello<S-CR>there')
+    check_events {
+      { 'test1', 'lines', 1, 9, 0, 1, 1, 11 },
+      { 'test1', 'lines', 1, 10, 0, 1, 2, 16 },
+      { 'test1', 'lines', 1, 11, 1, 2, 2, 1 },
+    }
+    fn.prompt_setprompt('', 'foo > ')
+    check_events {
+      { 'test1', 'lines', 1, 12, 0, 1, 1, 16 },
+    }
+    eq({ 'foo > hello', 'there' }, api.nvim_buf_get_lines(0, 0, -1, true))
+  end)
 end)
 
 describe('lua: nvim_buf_attach on_bytes', function()