vim-patch:8.0.0613: the conf filetype is used before ftdetect from packages

Problem:    The conf filetype detection is done before ftdetect scripts from
            packages that are added later.
Solution:   Add the FALLBACK argument to :setfiletype. (closes vim/vim#1679,
            closes vim/vim#1693)

https://github.com/vim/vim/commit/3e54569b17683318e0cb6693ab0024c2ad1e3e8f

3 files changed, 55 insertions, 4 deletions

diff --git a/src/nvim/ex_docmd.c b/src/nvim/ex_docmd.c
index bd46c65c15..aebc395f56 100644
--- a/src/nvim/ex_docmd.c
+++ b/src/nvim/ex_docmd.c
@@ -9743,13 +9743,20 @@ void filetype_maybe_enable(void)
   }
 }
 
-/*
- * ":setfiletype {name}"
- */
+/// ":setfiletype [FALLBACK] {name}"
 static void ex_setfiletype(exarg_T *eap)
 {
   if (!did_filetype) {
-    set_option_value("filetype", 0L, (char *)eap->arg, OPT_LOCAL);
+    char_u *arg = eap->arg;
+
+    if (STRNCMP(arg, "FALLBACK ", 9) == 0) {
+      arg += 9;
+    }
+
+    set_option_value("filetype", 0L, (char *)arg, OPT_LOCAL);
+    if (arg != eap->arg) {
+      did_filetype = false;
+    }
   }
 }
 
diff --git a/src/nvim/testdir/test_alot.vim b/src/nvim/testdir/test_alot.vim
index 91da0d9566..1d979a924f 100644
--- a/src/nvim/testdir/test_alot.vim
+++ b/src/nvim/testdir/test_alot.vim
@@ -19,6 +19,7 @@ source test_ga.vim
 source test_goto.vim
 source test_jumps.vim
 source test_fileformat.vim
+source test_filetype.vim
 source test_lambda.vim
 source test_menu.vim
 source test_mapping.vim
diff --git a/src/nvim/testdir/test_filetype.vim b/src/nvim/testdir/test_filetype.vim
new file mode 100644
index 0000000000..818603b180
--- /dev/null
+++ b/src/nvim/testdir/test_filetype.vim
@@ -0,0 +1,43 @@
+" Test :setfiletype
+
+func Test_detection()
+  filetype on
+  augroup filetypedetect
+    au BufNewFile,BufRead *	call assert_equal(1, did_filetype())
+  augroup END
+  new something.vim
+  call assert_equal('vim', &filetype)
+
+  bwipe!
+  filetype off
+endfunc
+
+func Test_conf_type()
+  filetype on
+  call writefile(['# some comment', 'must be conf'], 'Xfile')
+  augroup filetypedetect
+    au BufNewFile,BufRead *	call assert_equal(0, did_filetype())
+  augroup END
+  split Xfile
+  call assert_equal('conf', &filetype)
+
+  bwipe!
+  call delete('Xfile')
+  filetype off
+endfunc
+
+func Test_other_type()
+  filetype on
+  augroup filetypedetect
+    au BufNewFile,BufRead *	call assert_equal(0, did_filetype())
+    au BufNewFile,BufRead Xfile	setf testfile
+    au BufNewFile,BufRead *	call assert_equal(1, did_filetype())
+  augroup END
+  call writefile(['# some comment', 'must be conf'], 'Xfile')
+  split Xfile
+  call assert_equal('testfile', &filetype)
+
+  bwipe!
+  call delete('Xfile')
+  filetype off
+endfunc