vim-patch:9.1.1466: filetype: not all lex files are recognized

Problem:  filetype: not all lex files are recognized
Solution: detect *.ll as lex, llvm or lifelines filetype, depending on
          the content (Eisuke Kawashima)

closes: vim/vim#17560

48295111e5

Co-authored-by: Eisuke Kawashima <e-kwsm@users.noreply.github.com>

runtime/lua/vim/filetype/detect.lua

@@ -908,9 +908,13 @@ function M.ll(_, bufnr)
   local first_line = getline(bufnr, 1)
   if matchregex(first_line, [[;\|\<source_filename\>\|\<target\>]]) then
     return 'llvm'
-  else
-    return 'lifelines'
   end
+  for _, line in ipairs(getlines(bufnr, 1, 100)) do
+    if line:find('^%s*%%') then
+      return 'lex'
+    end
+  end
+  return 'lifelines'
 end
 
 --- @type vim.filetype.mapfn

test/old/testdir/test_filetype.vim

@@ -2600,6 +2600,12 @@ func Test_ll_file()
   call assert_equal('llvm', &filetype)
   bwipe!
 
+  " lex (C++)
+  call writefile(['%{', '#include <iostream>', '%}'], 'Xfile.ll', 'D')
+  split Xfile.ll
+  call assert_equal('lex', &filetype)
+  bwipe!
+
   " lifelines
   call writefile(['proc main() {}'], 'Xfile.ll', 'D')
   split Xfile.ll