fix(ghost_text): ensure multiline indent is correct

lua/blink/cmp/completion/windows/ghost_text.lua

@@ -71,7 +71,8 @@ function ghost_text.draw_preview(bufnr)
 
   if ghost_text.selected_item.insertTextFormat == vim.lsp.protocol.InsertTextFormat.Snippet then
     local expanded_snippet = snippets_utils.safe_parse(text_edit.newText)
-    text_edit.newText = expanded_snippet and tostring(expanded_snippet) or text_edit.newText
+    text_edit.newText = expanded_snippet and table.concat(snippets_utils.to_static_text(expanded_snippet), '\n')
+      or text_edit.newText
   end
 
   local display_lines = vim.split(get_still_untyped_text(text_edit), '\n', { plain = true }) or {}

lua/blink/cmp/sources/snippets/utils.lua

@@ -65,6 +65,137 @@ function utils.read_snippet(snippet, fallback)
   return snippets
 end
 
+--@see https://github.com/neovim/neovim/blob/9afa1fd35510c5fe485f4a1dfdabf94e5f051a1c/runtime/lua/vim/snippet.lua#L59
+
+--- Transforms the given text into an array of lines (so no line contains `\n`).
+---
+--- @param text string|string[]
+--- @return string[]
+local function text_to_lines(text)
+  text = type(text) == 'string' and { text } or text
+  --- @cast text string[]
+  return vim.split(table.concat(text), '\n', { plain = true })
+end
+
+--@see https://github.com/neovim/neovim/blob/b67fcd0488746b079a3b721ae4800af94cd126e1/runtime/lua/vim/snippet.lua#L26
+--- Resolves variables (like `$name` or `${name:default}`) as follows:
+--- - When a variable is unknown (i.e.: its name is not recognized in any of the cases below), return `nil`.
+--- - When a variable isn't set, return its default (if any) or an empty string.
+---
+--- Note that in some cases, the default is ignored since it's not clear how to distinguish an empty
+--- value from an unset value (e.g.: `TM_CURRENT_LINE`).
+---
+--- @param var string
+--- @param default string
+--- @return string?
+local function resolve_variable(var, default)
+  --- @param str string
+  --- @return string
+  local function expand_or_default(str)
+    local expansion = vim.fn.expand(str) --[[@as string]]
+    return expansion == '' and default or expansion
+  end
+
+  if var == 'TM_SELECTED_TEXT' then
+    -- Snippets are expanded in insert mode only, so there's no selection.
+    return default
+  elseif var == 'TM_CURRENT_LINE' then
+    return vim.api.nvim_get_current_line()
+  elseif var == 'TM_CURRENT_WORD' then
+    return expand_or_default('<cword>')
+  elseif var == 'TM_LINE_INDEX' then
+    return tostring(vim.fn.line('.') - 1)
+  elseif var == 'TM_LINE_NUMBER' then
+    return tostring(vim.fn.line('.'))
+  elseif var == 'TM_FILENAME' then
+    return expand_or_default('%:t')
+  elseif var == 'TM_FILENAME_BASE' then
+    return expand_or_default('%:t:r')
+  elseif var == 'TM_DIRECTORY' then
+    return expand_or_default('%:p:h:t')
+  elseif var == 'TM_FILEPATH' then
+    return expand_or_default('%:p')
+  end
+
+  -- Unknown variable.
+  return nil
+end
+
+--@see https://github.com/neovim/neovim/blob/b67fcd0488746b079a3b721ae4800af94cd126e1/runtime/lua/vim/snippet.lua#L477
+function utils.to_static_text(node)
+  local snippet = node
+  local snippet_text = {}
+  local base_indent = vim.api.nvim_get_current_line():match('^%s*') or ''
+
+  local grammar = require('vim.lsp._snippet_grammar')
+  -- Get the placeholders we should use for each tabstop index.
+  --- @type table<integer, string>
+  local placeholders = {}
+  for _, child in ipairs(snippet.data.children) do
+    local type, data = child.type, child.data
+    if type == grammar.NodeType.Placeholder then
+      --- @cast data vim.snippet.PlaceholderData
+      local tabstop, value = data.tabstop, tostring(data.value)
+      if placeholders[tabstop] and placeholders[tabstop] ~= value then
+        error('Snippet has multiple placeholders for tabstop $' .. tabstop)
+      end
+      placeholders[tabstop] = value
+    end
+  end
+
+  --- Appends the given text to the snippet, taking care of indentation.
+  ---
+  --- @param text string|string[]
+  local function append_to_snippet(text)
+    local snippet_lines = text_to_lines(snippet_text)
+    -- Get the base indentation based on the current line and the last line of the snippet.
+    if #snippet_lines > 0 then
+      base_indent = base_indent .. (snippet_lines[#snippet_lines]:match('(^%s+)%S') or '') --- @type string
+    end
+
+    local shiftwidth = vim.fn.shiftwidth()
+    local curbuf = vim.api.nvim_get_current_buf()
+    local expandtab = vim.bo[curbuf].expandtab
+
+    local lines = {} --- @type string[]
+    for i, line in ipairs(text_to_lines(text)) do
+      -- Replace tabs by spaces.
+      if expandtab then
+        line = line:gsub('\t', (' '):rep(shiftwidth)) --- @type string
+      end
+      -- Add the base indentation.
+      if i > 1 then line = base_indent .. line end
+      lines[#lines + 1] = line
+    end
+
+    table.insert(snippet_text, table.concat(lines, '\n'))
+  end
+
+  for _, child in ipairs(snippet.data.children) do
+    local type, data = child.type, child.data
+    if type == grammar.NodeType.Tabstop then
+      --- @cast data vim.snippet.TabstopData
+      local placeholder = placeholders[data.tabstop]
+      if placeholder then append_to_snippet(placeholder) end
+    elseif type == grammar.NodeType.Placeholder then
+      --- @cast data vim.snippet.PlaceholderData
+      local value = placeholders[data.tabstop]
+      append_to_snippet(value)
+    elseif type == grammar.NodeType.Variable then
+      --- @cast data vim.snippet.VariableData
+      -- Try to get the variable's value.
+      local value = resolve_variable(data.name, data.default and tostring(data.default) or '')
+      if value ~= nil then append_to_snippet(value) end
+    elseif type == grammar.NodeType.Text then
+      --- @cast data vim.snippet.TextData
+      append_to_snippet(data.text)
+    end
+  end
+
+  snippet_text = text_to_lines(snippet_text)
+  return snippet_text
+end
+
 function utils.get_tab_stops(snippet)
   local expanded_snippet = require('blink.cmp.sources.snippets.utils').safe_parse(snippet)
   if not expanded_snippet then return end