fix(cmdline): trigger autocorrection only if appending single character

Details:
- Although appending multiple characters with a single key stroke is
  possible (like with `:cnoremap <C-x> www` or `:nnoremap <C-y> :ehco`),
  making it work with autocorrection is problematic.

  Currently it just treats new text as a single "separator character"
  and tries to autocorrect the text that was prior to it. This is
  problematic for navigating through history: if previous command is
  `:Pick files`, typing `:P<Up>` will treat `ick files` as a separator
  character and autocorrect `P`->`p` (as it is a valid autocorrection).

  Ideally it would be nice to have autocorrect all words that were
  created after appending new text, but that is problematic. Mostly
  because there is (currently) no way to actually compute these words
  (`vim.fn.getcomplpat()` works only for current command line text and
  cursor; moving cursor for this case is not quite clean).

  So instead make it more explicit that autocorrection is triggered only
  if *a single character* is appended to the command line text. This was
  more or less the initial intention, so do not mark as a breaking
  change.

Author: echasnovski

doc/mini-cmdline.txt

@@ -188,9 +188,9 @@ Use `return vim.fn.getcmdtype() == ':'` as a predicate output.
 Autocorrect ~
 
 `config.autocorrect` is used to configure autocorrection: automatic adjustment
-of bad words as you type them. This works only when appending text at the end
-of the command line. Editing already typed words does not trigger autocorrect
-(allows correcting the autocorrection).
+of bad words as you type them. This works only when appending single character
+at the end of the command line. Editing already typed words does not trigger
+autocorrect (allows correcting the autocorrection).
 
 When to autocorrect is computed automatically based on |getcmdcomplpat()| after
 every key press: if it doesn't add the character to completion pattern, then

lua/mini/cmdline.lua

@@ -159,9 +159,9 @@ end
 ---# Autocorrect ~
 ---
 --- `config.autocorrect` is used to configure autocorrection: automatic adjustment
---- of bad words as you type them. This works only when appending text at the end
---- of the command line. Editing already typed words does not trigger autocorrect
---- (allows correcting the autocorrection).
+--- of bad words as you type them. This works only when appending single character
+--- at the end of the command line. Editing already typed words does not trigger
+--- autocorrect (allows correcting the autocorrection).
 ---
 --- When to autocorrect is computed automatically based on |getcmdcomplpat()| after
 --- every key press: if it doesn't add the character to completion pattern, then
@@ -759,13 +759,14 @@ H.autocorrect = function(is_final)
   local line, line_prev = state.line, state_prev.line
   local pos, pos_prev = state.pos, state_prev.pos
 
-  -- Act only when text is appended. It makes it natural to tweak autocorrected
-  -- text by going back and editing it. This is also easier to implement.
+  -- Act only when a char is appended. It makes tweaking autocorrected text
+  -- easier by going back and editing it. This is also easier to implement.
   local is_at_end, was_at_end = (pos - 1) == line:len(), (pos_prev - 1) == line_prev:len()
-  local is_text_append = vim.startswith(line, line_prev) and is_at_end and was_at_end
+  local new = line:sub(pos_prev)
+  local is_char_append = is_at_end and was_at_end and line == (line_prev .. new) and vim.fn.strchars(new) <= 1
   local is_word_finished = not vim.startswith(state.complpat, state_prev.complpat)
 
-  if not (is_text_append and (is_word_finished or is_final)) then return end
+  if not (is_char_append and (is_word_finished or is_final)) then return end
 
   -- Compute autocorrection
   local state_to_use = is_final and state or state_prev

tests/test_cmdline.lua

@@ -894,10 +894,19 @@ T['Autocorrect']['respects mappings'] = function()
   eq(ok, false)
   eq(err, 'E492: Not an editor command: ehco')
 
-  -- Should work if Command-line mode is only entered
-  child.cmd('nnoremap <C-y> :ehco')
-  type_keys('<C-y>', '<CR>')
-  eq(child.fn.histget('cmd', -1), 'echo')
+  -- Should act if text increases latest word by a single character
+  child.cmd('cnoremap <C-x> w')
+  type_keys(':', 'XX', '<C-x>')
+  validate_cmdline('XXw')
+  type_keys(' ')
+  validate_cmdline('bw ')
+  type_keys('<Esc>')
+
+  -- Should act if text finishes the last word
+  child.cmd('cnoremap <C-y> <Space>')
+  type_keys(':', 'XX', '<C-y>')
+  validate_cmdline('ex ')
+  type_keys('<Esc>')
 end
 
 T['Autocorrect']['respects abbreviations'] = function()
@@ -924,26 +933,6 @@ T['Autocorrect']['respects abbreviations'] = function()
   eq(child.lua_get('_G.log'), {})
 end
 
-T['Autocorrect']['can act after mappings appended text'] = function()
-  -- Should act if text increases latest word
-  child.cmd('cnoremap <C-x> www')
-  type_keys(':', 'XX', '<C-x>')
-  validate_cmdline('XXwww')
-  type_keys(' ')
-  validate_cmdline('below ')
-  type_keys('<Esc>')
-
-  -- Should act if text finishes the last word.
-  child.cmd('cnoremap <C-y> www<Space>')
-  type_keys(':', 'XX', '<C-y>')
-  -- Whole new text from the mapping is treated as "separator text" and is not
-  -- included into autocorrected word. It might be good to have the new text
-  -- also be part of the word to correct (`XXwww` here instead of `XX`), but it
-  -- seems too complex to implement (if reasonably possible even).
-  validate_cmdline('exwww ')
-  type_keys('<Esc>')
-end
-
 T['Autocorrect']['ignores editing previous text'] = function()
   type_keys(':', 'set ', '<Left>')
   type_keys('<BS>')
@@ -960,6 +949,14 @@ T['Autocorrect']['ignores editing previous text'] = function()
   validate_cmdline('sort ')
 end
 
+T['Autocorrect']['ignores navigating through history'] = function()
+  child.cmd('command Icommand echo "Hello"')
+  type_keys(':', 'Icommand ', '<Esc>')
+  -- Should not autocorrect `I` to `i` (as it happens in case of `:I<Space>`)
+  type_keys(':', 'I', '<Up>')
+  validate_cmdline('Icommand ')
+end
+
 T['Autocorrect']['correctly computes word to autocorrect'] = function()
   if child.fn.has('nvim-0.11') == 0 then MiniTest.skip('Requires `getcmdcomplpat()`, present in Neovim>=0.11') end
 
@@ -1065,7 +1062,7 @@ end
 
 T['Autocorrect']['works just before final <CR>'] = function()
   local validate = function(bad_word, ref_word)
-    type_keys(':', bad_word, '<CR>')
+    type_every_key(':', bad_word, '<CR>')
     eq(child.fn.histget('cmd', -1), ref_word)
     eq(child.fn.mode(), 'n')
   end
@@ -1101,19 +1098,19 @@ T['Autocorrect']['uses correct state before final <CR>'] = function()
   ]])
 
   -- Changing `type` just before `<CR>`
-  type_keys(':', 'cnoremap <C-x> www', '<CR>')
-  type_keys(':', 'cn', '<Up>')
-  validate_cmdline('cnoremap \24 www')
+  type_every_key(':', 'cnoremap <LT>C-x> www', '<CR>')
+  type_every_key(':', 'cnoremap <LT>C-x> ww', '<Up>')
+  validate_cmdline('cnoremap <C-x> www')
   child.lua('_G.log = {}')
   type_keys('<CR>')
-  local ref_word = child.fn.has('nvim-0.11') == 1 and '\24 www' or 'www'
+  local ref_word = child.fn.has('nvim-0.11') == 1 and '<C-x> www' or 'www'
   eq(child.lua_get('_G.log'), { { word = ref_word, type = 'mapping' } })
 
   -- Should include `!` in the word (when using `vim.fn.getcmdcomplpat()`)
   if child.fn.has('nvim-0.11') == 0 then return end
   child.cmd('split')
   child.lua('_G.log = {}')
-  type_keys(':', 'q!', '<CR>')
+  type_every_key(':', 'q!', '<CR>')
   eq(child.lua_get('_G.log'), { { word = 'q!', type = '' } })
 end