refactor: source ftplugin.vim separately from filetype.vim (#17129)

This is a follow-on to #17040. The real benefit of #17040 was ensuring
that the ftplugin FileType autocommand was defined first and thus always
fired first. A side effect of the implementation in #17040 was that
setting variables that modified the state of filetype detection (such as
g:did_load_filetypes or g:do_filetype_lua) could no longer be set in the
user's init file. Filetype detection can also no longer be prevented
from loading by using `:filetype off`.

This PR addresses both of those side effects by unconditionally sourcing
ftplugin.vim and indent.vim before the user's init file (which ensures
that these autocommands run first) and sourcing filetype.vim *after* the
user's init file (thus allowing it to be blocked or modified).

1 files changed, 17 insertions, 9 deletions

diff --git a/src/nvim/ex_docmd.c b/src/nvim/ex_docmd.c
index 3a285cdf90..b33a17c631 100644
--- a/src/nvim/ex_docmd.c
+++ b/src/nvim/ex_docmd.c
@@ -9546,16 +9546,12 @@ static void ex_filetype(exarg_T *eap)
   }
 }
 
-/// Set all :filetype options ON if user did not explicitly set any to OFF.
-void filetype_maybe_enable(void)
+/// Source ftplugin.vim and indent.vim to create the necessary FileType
+/// autocommands. We do this separately from filetype.vim so that these
+/// autocommands will always fire first (and thus can be overriden) while still
+/// allowing general filetype detection to be disabled in the user's init file.
+void filetype_plugin_enable(void)
 {
-  if (filetype_detect == kNone) {
-    // Normally .vim files are sourced before .lua files when both are
-    // supported, but we reverse the order here because we want the Lua
-    // autocommand to be defined first so that it runs first
-    source_runtime(FILETYPE_FILE, DIP_ALL);
-    filetype_detect = kTrue;
-  }
   if (filetype_plugin == kNone) {
     source_runtime(FTPLUGIN_FILE, DIP_ALL);
     filetype_plugin = kTrue;
@@ -9566,6 +9562,18 @@ void filetype_maybe_enable(void)
   }
 }
 
+/// Enable filetype detection if the user did not explicitly disable it.
+void filetype_maybe_enable(void)
+{
+  if (filetype_detect == kNone) {
+    // Normally .vim files are sourced before .lua files when both are
+    // supported, but we reverse the order here because we want the Lua
+    // autocommand to be defined first so that it runs first
+    source_runtime(FILETYPE_FILE, DIP_ALL);
+    filetype_detect = kTrue;
+  }
+}
+
 /// ":setfiletype [FALLBACK] {name}"
 static void ex_setfiletype(exarg_T *eap)
 {