feat: output preview with ghost text, including for snippets

lua/blink/cmp/config.lua

@@ -90,6 +90,7 @@
 --- @field autocomplete? blink.cmp.AutocompleteConfig
 --- @field documentation? blink.cmp.DocumentationConfig
 --- @field signature_help? blink.cmp.SignatureHelpConfig
+--- @field ghost_text_preview? blink.cmp.GhostTextPreviewConfig
 
 --- @class blink.cmp.HighlightConfig
 --- @field ns? number
@@ -137,6 +138,9 @@
 --- @field border? blink.cmp.WindowBorder
 --- @field winhighlight? string
 
+--- @class blink.cmp.GhostTextPreviewConfig
+--- @field enabled? boolean
+
 --- @class blink.cmp.Config
 --- @field keymap? blink.cmp.KeymapConfig
 --- @field accept? blink.cmp.AcceptConfig

lua/blink/cmp/init.lua

@@ -99,6 +99,8 @@ cmp.add_default_highlights = function()
     set_hl('BlinkCmpKind' .. kind, { link = use_nvim_cmp and 'CmpItemKind' .. kind or 'BlinkCmpKind' })
   end
 
+  set_hl('BlinkCmpGhostText', { link = use_nvim_cmp and 'CmpGhostText' or 'Comment' })
+
   set_hl('BlinkCmpMenu', { link = 'Pmenu' })
   set_hl('BlinkCmpMenuBorder', { link = 'Pmenu' })
   set_hl('BlinkCmpMenuSelection', { link = 'PmenuSel' })

lua/blink/cmp/windows/autocomplete.lua

@@ -10,6 +10,8 @@ local config = require('blink.cmp.config')
 local renderer = require('blink.cmp.windows.lib.render')
 local text_edits_lib = require('blink.cmp.accept.text-edits')
 local autocmp_config = config.windows.autocomplete
+local ghost_text_preview = require('blink.cmp.windows.ghost-text-preview')
+
 local autocomplete = {
   ---@type blink.cmp.CompletionItem[]
   items = {},
@@ -79,6 +81,7 @@ function autocomplete.open_with_items(context, items)
 
   autocomplete.update_position(context)
   autocomplete.set_has_selected(autocmp_config.selection == 'preselect')
+  ghost_text_preview.show_preview(autocomplete.get_selected_item())
 
   -- todo: some logic to maintain the selection if the user moved the cursor?
   vim.api.nvim_win_set_cursor(autocomplete.win:get_win(), { 1, 0 })
@@ -89,6 +92,8 @@ function autocomplete.open()
   if autocomplete.win:is_open() then return end
   vim.iter(autocomplete.event_targets.on_open):each(function(callback) callback() end)
   autocomplete.win:open()
+
+  -- ghost_text_preview.show_preview(auto)
   autocomplete.set_has_selected(autocmp_config.selection == 'preselect')
 end
 
@@ -98,6 +103,7 @@ function autocomplete.close()
   autocomplete.win:close()
   autocomplete.set_has_selected(autocmp_config.selection == 'preselect')
 
+  ghost_text_preview.clear_preview()
   vim.iter(autocomplete.event_targets.on_close):each(function(callback) callback() end)
 end
 
@@ -181,6 +187,7 @@ local function select(line, skip_auto_insert)
   vim.api.nvim_win_set_cursor(autocomplete.win:get_win(), { line, 0 })
 
   local selected_item = autocomplete.get_selected_item()
+  ghost_text_preview.show_preview(selected_item)
 
   -- when auto_insert is enabled, we immediately apply the text edit
   if config.windows.autocomplete.selection == 'auto_insert' and selected_item ~= nil and not skip_auto_insert then

lua/blink/cmp/windows/ghost-text-preview.lua

@@ -0,0 +1,68 @@
+local config = require('blink.cmp.config')
+
+local ghost_text_preview_config = config.windows.ghost_text_preview
+
+local ghost_text_preview = {
+  enabled = ghost_text_preview_config and ghost_text_preview_config.enabled or false,
+  extmark_id = 1,
+  ns_id = config.highlight.ns,
+}
+
+local function get_text_before_cursor()
+  local current_line = vim.api.nvim_get_current_line()
+  local _, col = unpack(vim.api.nvim_win_get_cursor(0))
+
+  return string.gsub(string.sub(current_line, 1, col), '^%s*', '')
+end
+
+--- @param str1 string
+--- @param str2 string
+--- @return string
+local function get_overlapping_text_from(str1, str2)
+  for i = 1, #str2 do
+    local sub_str2 = string.sub(str2, i)
+    if string.sub(str1, 1, #sub_str2) == sub_str2 then return sub_str2 end
+  end
+  return ''
+end
+
+--- @param selected_item? blink.cmp.CompletionItem
+function ghost_text_preview.show_preview(selected_item)
+  if ghost_text_preview.enabled ~= true then return end
+  if selected_item == nil then return end
+
+  local text_to_display = selected_item.insertText or selected_item.label
+
+  if selected_item.insertTextFormat == vim.lsp.protocol.InsertTextFormat.Snippet then
+    local expanded_snippet = require('blink.cmp.sources.snippets.utils').safe_parse(text_to_display)
+    text_to_display = expanded_snippet and tostring(expanded_snippet) or text_to_display
+  end
+
+  local display_lines = vim.split(text_to_display, '\n', { plain = true }) or {}
+  display_lines[1] =
+    string.gsub(display_lines[1], '^' .. get_overlapping_text_from(display_lines[1], get_text_before_cursor()), '')
+
+  --- @type vim.api.keyset.set_extmark
+  local extmark = {
+    id = ghost_text_preview.extmark_id,
+    virt_text_pos = 'inline',
+    virt_text = { { display_lines[1], 'BlinkCmpGhostText' } },
+    hl_mode = 'combine',
+  }
+
+  if #display_lines > 1 then
+    extmark.virt_lines = {}
+    for i = 2, #display_lines do
+      extmark.virt_lines[i - 1] = { { display_lines[i], 'BlinkCmpGhostText' } }
+    end
+  end
+
+  local row, col = unpack(vim.api.nvim_win_get_cursor(0))
+  vim.api.nvim_buf_set_extmark(0, ghost_text_preview.ns_id, row - 1, col, extmark)
+end
+
+function ghost_text_preview.clear_preview()
+  vim.api.nvim_buf_del_extmark(0, ghost_text_preview.ns_id, ghost_text_preview.extmark_id)
+end
+
+return ghost_text_preview