feat: extract word from completion item for auto-insert preview (#341)

* feat: extract word from completion item for auto-insert preview

Use a modified version of nvim-cmp's word extraction algorithm from
expanded snippets for use in auto-insert preview textEdits.

For example, if a snippet expansion results in something like:

```
my_neat_function(int arg1, double arg2)
```

Then the floating window will show the above for that completion, but
when selecting it, the buffer will only insert `my_neat_function`. This
allows using the snippet completion item without actually _accepting_ it
by just selecting it in the preview window and then continuing to type.

So one could type "my_n", Ctrl-N/Tab (or whatever your keymap is) to
select `my_neat_function`, and then just continue with typing the ( and
args manually. Of course, accepting the completion will still work as
expected by expanding the snippet.

* refactor: word extraction for auto-insert preview

---------

Co-authored-by: Liam Dyer <[email protected]>

lua/blink/cmp/accept/preview.lua

@@ -6,22 +6,17 @@ local function preview(item, previous_text_edit)
   -- with auto_insert, we may have to undo the previous preview
   if previous_text_edit ~= nil then text_edit.range = text_edits_lib.get_undo_range(previous_text_edit) end
 
-  -- for snippets, expand them with the default property names
+  if item.insertTextFormat == vim.lsp.protocol.InsertTextFormat.Snippet then
+    local expanded_snippet = require('blink.cmp.sources.snippets.utils').safe_parse(text_edit.newText)
+    text_edit.newText = require('blink.cmp.utils').get_prefix_before_brackets_and_quotes(
+      expanded_snippet and tostring(expanded_snippet) or text_edit.newText
+    )
+  end
+
   local cursor_pos = {
     text_edit.range.start.line + 1,
     text_edit.range.start.character + #text_edit.newText,
   }
-  if item.insertTextFormat == vim.lsp.protocol.InsertTextFormat.Snippet then
-    local expanded_snippet = require('blink.cmp.sources.snippets.utils').safe_parse(text_edit.newText)
-    text_edit.newText = expanded_snippet and tostring(expanded_snippet) or text_edit.newText
-
-    -- place the cursor at the first tab stop
-    local tabstops = require('blink.cmp.sources.snippets.utils').get_tab_stops(text_edit.newText)
-    if tabstops and #tabstops > 0 then
-      cursor_pos[1] = text_edit.range.start.line + tabstops[1].line
-      cursor_pos[2] = text_edit.range.start.character + tabstops[1].character
-    end
-  end
 
   text_edits_lib.apply({ text_edit })
   vim.api.nvim_win_set_cursor(0, cursor_pos)

lua/blink/cmp/utils.lua

@@ -97,4 +97,61 @@ function utils.get_tailwind_hl(ctx)
   end
 end
 
+local PAIRS_AND_INVALID_CHARS = {}
+string.gsub('\'"=$()[]<>{} \t\n\r', '.', function(char) PAIRS_AND_INVALID_CHARS[string.byte(char)] = true end)
+
+local CLOSING_PAIR = {
+  [string.byte('<')] = string.byte('>'),
+  [string.byte('[')] = string.byte(']'),
+  [string.byte('(')] = string.byte(')'),
+  [string.byte('{')] = string.byte('}'),
+  [string.byte('"')] = string.byte('"'),
+  [string.byte("'")] = string.byte("'"),
+}
+
+local ALPHANUMERIC = {}
+string.gsub(
+  'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789',
+  '.',
+  function(char) ALPHANUMERIC[string.byte(char)] = true end
+)
+
+--- Gets the prefix of the given text, stopping at brackets and quotes
+--- @param text string
+--- @return string
+function utils.get_prefix_before_brackets_and_quotes(text)
+  local closing_pairs_stack = {}
+  local word = ''
+
+  local add = function(char)
+    word = word .. string.char(char)
+
+    -- if we've seen the opening pair, and we've just received the closing pair,
+    -- remove it from the closing pairs stack
+    if closing_pairs_stack[#closing_pairs_stack] == char then
+      table.remove(closing_pairs_stack, #closing_pairs_stack)
+    -- if the character is an opening pair, add it to the closing pairs stack
+    elseif CLOSING_PAIR[char] ~= nil then
+      table.insert(closing_pairs_stack, CLOSING_PAIR[char])
+    end
+  end
+
+  local has_alphanumeric = false
+  for i = 1, #text do
+    local char = string.byte(text, i)
+    if PAIRS_AND_INVALID_CHARS[char] == nil then
+      add(char)
+      has_alphanumeric = has_alphanumeric or ALPHANUMERIC[char]
+    elseif not has_alphanumeric or #closing_pairs_stack ~= 0 then
+      add(char)
+      -- if we had an alphanumeric, and the closing pairs stuck *just* emptied,
+      -- because the current character is a closing pair, we exit
+      if has_alphanumeric and #closing_pairs_stack == 0 then break end
+    else
+      break
+    end
+  end
+  return word
+end
+
 return utils