vim-patch:8.2.3050: cannot recognize elixir files

Problem:    Cannot recognize elixir files.
Solution:   Recognize Elixir-specific files.  Check if an .ex file is Euphoria
            or Elixir. (Austin Gatlin, closes vim/vim#8401, closes vim/vim#8446)
f3caeb63d6

src/nvim/testdir/test_filetype.vim

@@ -161,6 +161,8 @@ let s:filename_checks = {
     \ 'ecd': ['file.ecd'],
     \ 'edif': ['file.edf', 'file.edif', 'file.edo'],
     \ 'elinks': ['elinks.conf'],
+    \ 'elixir': ['file.ex', 'file.exs', 'mix.lock'],
+    \ 'eelixir': ['file.eex', 'file.leex'],
     \ 'elm': ['file.elm'],
     \ 'elmfilt': ['filter-rules'],
     \ 'epuppet': ['file.epp'],
@@ -765,5 +767,41 @@ func Test_pp_file()
   filetype off
 endfunc
 
+func Test_ex_file()
+  filetype on
+
+  call writefile(['arbitrary content'], 'Xfile.ex')
+  split Xfile.ex
+  call assert_equal('elixir', &filetype)
+  bwipe!
+  let g:filetype_euphoria = 'euphoria4'
+  split Xfile.ex
+  call assert_equal('euphoria4', &filetype)
+  bwipe!
+  unlet g:filetype_euphoria
+
+  call writefile(['-- filetype euphoria comment'], 'Xfile.ex')
+  split Xfile.ex
+  call assert_equal('euphoria3', &filetype)
+  bwipe!
+
+  call writefile(['--filetype euphoria comment'], 'Xfile.ex')
+  split Xfile.ex
+  call assert_equal('euphoria3', &filetype)
+  bwipe!
+
+  call writefile(['ifdef '], 'Xfile.ex')
+  split Xfile.ex
+  call assert_equal('euphoria3', &filetype)
+  bwipe!
+
+  call writefile(['include '], 'Xfile.ex')
+  split Xfile.ex
+  call assert_equal('euphoria3', &filetype)
+  bwipe!
+
+  call delete('Xfile.ex')
+  filetype off
+endfunc
 
 " vim: shiftwidth=2 sts=2 expandtab