fix(lsp): do not cancel snippet when selecting placeholder (#25835)

runtime/lua/vim/snippet.lua

@@ -278,6 +278,11 @@ local function setup_autocmds(bufnr)
     desc = 'Update snippet state when the cursor moves',
     buffer = bufnr,
     callback = function()
+      -- Just update the tabstop in insert and select modes.
+      if not vim.fn.mode():match('^[isS]') then
+        return
+      end
+
       local cursor_row, cursor_col = cursor_pos()
 
       -- The cursor left the snippet region.
@@ -292,11 +297,6 @@ local function setup_autocmds(bufnr)
         return true
       end
 
-      -- Just update the tabstop in insert and select modes.
-      if not vim.fn.mode():match('^[isS]') then
-        return
-      end
-
       -- Update the current tabstop to be the one containing the cursor.
       for tabstop_index, tabstops in pairs(M._session.tabstops) do
         for _, tabstop in ipairs(tabstops) do

test/functional/lua/snippet_spec.lua

@@ -165,10 +165,10 @@ describe('vim.snippet', function()
     eq(false, exec_lua('return vim.snippet.active()'))
   end)
 
-  it('cancels session when leaving snippet region', function()
+  it('cancels session when inserting outside snippet region', function()
     feed('i<cr>')
     test_success({ 'local function $1()', '  $0', 'end' }, { '', 'local function ()', '  ', 'end' })
-    feed('<esc>k')
+    feed('<esc>O-- A comment')
     eq(false, exec_lua('return vim.snippet.active()'))
   end)
 end)