fix(lsp): fix cursor position after snippet expansion (#30659)

Problem: on `CompleteDone` cursor can jump to the end of line instead of
the end of the completed word.

Solution: remove only inserted word for snippet expansion instead of everything
until eol.

Fixes #30656

Co-authored-by: Mathias Fussenegger <f.mathias@zignar.net>
Co-authored-by: Justin M. Keyes <justinkz@gmail.com>

runtime/lua/vim/lsp/completion.lua

@@ -113,12 +113,11 @@ local function parse_snippet(input)
 end
 
 --- @param item lsp.CompletionItem
---- @param suffix? string
-local function apply_snippet(item, suffix)
+local function apply_snippet(item)
   if item.textEdit then
-    vim.snippet.expand(item.textEdit.newText .. suffix)
+    vim.snippet.expand(item.textEdit.newText)
   elseif item.insertText then
-    vim.snippet.expand(item.insertText .. suffix)
+    vim.snippet.expand(item.insertText)
   end
 end
 
@@ -539,15 +538,12 @@ local function on_complete_done()
 
     -- Remove the already inserted word.
     local start_char = cursor_col - #completed_item.word
-    local line = api.nvim_buf_get_lines(bufnr, cursor_row, cursor_row + 1, true)[1]
-    api.nvim_buf_set_text(bufnr, cursor_row, start_char, cursor_row, #line, { '' })
-    return line:sub(cursor_col + 1)
+    api.nvim_buf_set_text(bufnr, cursor_row, start_char, cursor_row, cursor_col, { '' })
   end
 
-  --- @param suffix? string
-  local function apply_snippet_and_command(suffix)
+  local function apply_snippet_and_command()
     if expand_snippet then
-      apply_snippet(completion_item, suffix)
+      apply_snippet(completion_item)
     end
 
     local command = completion_item.command
@@ -565,9 +561,9 @@ local function on_complete_done()
   end
 
   if completion_item.additionalTextEdits and next(completion_item.additionalTextEdits) then
-    local suffix = clear_word()
+    clear_word()
     lsp.util.apply_text_edits(completion_item.additionalTextEdits, bufnr, offset_encoding)
-    apply_snippet_and_command(suffix)
+    apply_snippet_and_command()
   elseif resolve_provider and type(completion_item) == 'table' then
     local changedtick = vim.b[bufnr].changedtick
 
@@ -577,7 +573,7 @@ local function on_complete_done()
         return
       end
 
-      local suffix = clear_word()
+      clear_word()
       if err then
         vim.notify_once(err.message, vim.log.levels.WARN)
       elseif result and result.additionalTextEdits then
@@ -587,11 +583,11 @@ local function on_complete_done()
         end
       end
 
-      apply_snippet_and_command(suffix)
+      apply_snippet_and_command()
     end, bufnr)
   else
-    local suffix = clear_word()
-    apply_snippet_and_command(suffix)
+    clear_word()
+    apply_snippet_and_command()
   end
 end
 

test/functional/plugin/lsp/completion_spec.lua

@@ -471,25 +471,9 @@ describe('vim.lsp.completion: item conversion', function()
   )
 end)
 
-describe('vim.lsp.completion: protocol', function()
-  before_each(function()
-    clear()
-    exec_lua(create_server_definition)
-    exec_lua(function()
-      _G.capture = {}
-      --- @diagnostic disable-next-line:duplicate-set-field
-      vim.fn.complete = function(col, matches)
-        _G.capture.col = col
-        _G.capture.matches = matches
-      end
-    end)
-  end)
-
-  after_each(clear)
-
-  --- @param completion_result lsp.CompletionList
-  --- @return integer
-  local function create_server(completion_result)
+--- @param completion_result lsp.CompletionList
+--- @return integer
+local function create_server(completion_result)
   return exec_lua(function()
     local server = _G._create_server({
       capabilities = {
@@ -518,7 +502,23 @@ describe('vim.lsp.completion: protocol', function()
       end,
     })
   end)
+end
+
+describe('vim.lsp.completion: protocol', function()
+  before_each(function()
+    clear()
+    exec_lua(create_server_definition)
+    exec_lua(function()
+      _G.capture = {}
+      --- @diagnostic disable-next-line:duplicate-set-field
+      vim.fn.complete = function(col, matches)
+        _G.capture.col = col
+        _G.capture.matches = matches
       end
+    end)
+  end)
+
+  after_each(clear)
 
   local function assert_matches(fn)
     retry(nil, nil, function()
@@ -726,3 +726,58 @@ describe('vim.lsp.completion: protocol', function()
     end)
   end)
 end)
+
+describe('vim.lsp.completion: integration', function()
+  before_each(function()
+    clear()
+    exec_lua(create_server_definition)
+    exec_lua(function()
+      vim.fn.complete = vim.schedule_wrap(vim.fn.complete)
+    end)
+  end)
+
+  after_each(clear)
+
+  it('puts cursor at the end of completed word', function()
+    local completion_list = {
+      isIncomplete = false,
+      items = {
+        {
+          label = 'hello',
+          insertText = '${1:hello} friends',
+          insertTextFormat = 2,
+        },
+      },
+    }
+    exec_lua(function()
+      vim.o.completeopt = 'menuone,noselect'
+    end)
+    create_server(completion_list)
+    feed('i world<esc>0ih<c-x><c-o>')
+    retry(nil, nil, function()
+      eq(
+        1,
+        exec_lua(function()
+          return vim.fn.pumvisible()
+        end)
+      )
+    end)
+    feed('<C-n><C-y>')
+    eq(
+      { true, { 'hello friends world' } },
+      exec_lua(function()
+        return {
+          vim.snippet.active({ direction = 1 }),
+          vim.api.nvim_buf_get_lines(0, 0, -1, true),
+        }
+      end)
+    )
+    feed('<tab>')
+    eq(
+      #'hello friends',
+      exec_lua(function()
+        return vim.api.nvim_win_get_cursor(0)[2]
+      end)
+    )
+  end)
+end)