feat(runtime)!: enable filetype.lua by default (#19216)

* revert to filetype.vim by setting `g:do_legacy_filetype`
* skip either filetype.lua or filetype.vim via `g:did_load_filetypes`

(Running both is no longer required and therefore no longer supported.)

8 files changed, 45 insertions, 63 deletions

diff --git a/runtime/doc/filetype.txt b/runtime/doc/filetype.txt
index 7f88216f43..7fff74a963 100644
--- a/runtime/doc/filetype.txt
+++ b/runtime/doc/filetype.txt
@@ -177,7 +177,9 @@ This means that the contents of compressed files are not inspected.
 If a file type that you want to use is not detected yet, there are a few ways
 to add it.  In any way, it's better not to modify the $VIMRUNTIME/filetype.lua
 or $VIMRUNTIME/filetype.vim files.  They will be overwritten when installing a
-new version of Nvim.
+new version of Nvim. The following explains the legacy Vim mechanism (enabled
+if |do_legacy_filetype| is set). For Nvim's default mechanism, see
+|vim.filetype.add()|.
 
 A. If you want to overrule all default file type checks.
    This works by writing one file for each filetype.  The disadvantage is that
@@ -236,39 +238,8 @@ C. If your file type can be detected by the file name or extension.
       Write this file as "filetype.vim" in your user runtime directory.  For
       example, for Unix: >
 	:w ~/.config/nvim/filetype.vim
-<
-      Alternatively, create a file called "filetype.lua" that adds new
-      filetypes.
-      Example: >
-	vim.filetype.add({
-	  extension = {
-	    foo = "fooscript",
-	  },
-	  filename = {
-	    [".foorc"] = "foorc",
-	  },
-	  pattern = {
-	    [".*/etc/foo/.*%.conf"] = "foorc",
-	  },
-	})
-<
-      See |vim.filetype.add()|.
-						     *g:do_filetype_lua*
-      For now, Lua filetype detection is opt-in. You can enable it by adding
-      the following to your |init.vim|: >
-        let g:do_filetype_lua = 1
-<						     *g:did_load_filetypes*
-      In either case, the builtin filetype detection provided by Nvim can be
-      disabled by setting the did_load_filetypes global variable. If this
-      variable exists, $VIMRUNTIME/filetype.vim will not run.
-      Example: >
-	" Disable filetype.vim (but still load filetype.lua if enabled)
-	let g:did_load_filetypes = 0
 
-	" Disable filetype.vim and filetype.lua
-	let g:did_load_filetypes = 1
-
-<  3. To use the new filetype detection you must restart Vim.
+<   3. To use the new filetype detection you must restart Vim.
 
    Your filetype.vim will be sourced before the default FileType autocommands
    have been installed.  Your autocommands will match first, and the
@@ -315,6 +286,16 @@ the 'runtimepath' for a directory to use.  If there isn't one, set
 'runtimepath' in the |system-vimrc|.  Be careful to keep the default
 directories!
 
+						     *g:do_legacy_filetype*
+To disable Nvim's default filetype detection and revert to Vim's legacy
+filetype detection, add the following to your |init.vim|: >
+  let g:do_legacy_filetype = 1
+<						     *g:did_load_filetypes*
+The builtin filetype detection provided by Nvim can be disabled by setting
+the `did_load_filetypes` global variable. If this variable exists, neither
+the default `$VIMRUNTIME/filetype.lua` nor the legacy `$VIMRUNTIME/filetype.vim`
+will run.
+
 							*plugin-details*
 The "plugin" directory can be in any of the directories in the 'runtimepath'
 option.  All of these directories will be searched for plugins and they are
diff --git a/runtime/doc/lua.txt b/runtime/doc/lua.txt
index 3372bc90f7..089cf0ce9d 100644
--- a/runtime/doc/lua.txt
+++ b/runtime/doc/lua.txt
@@ -2022,8 +2022,8 @@ add({filetypes})                                          *vim.filetype.add()*
 
                 See $VIMRUNTIME/lua/vim/filetype.lua for more examples.
 
-                Note that Lua filetype detection is only enabled when
-                |g:do_filetype_lua| is set to 1.
+                Note that Lua filetype detection is disabled when
+                |g:do_legacy_filetype| is set.
 
                 Example: >
 
diff --git a/runtime/filetype.lua b/runtime/filetype.lua
index f1885a8b95..9f5b5fd0dc 100644
--- a/runtime/filetype.lua
+++ b/runtime/filetype.lua
@@ -1,11 +1,8 @@
-if vim.g.did_load_filetypes and vim.g.did_load_filetypes ~= 0 then
-  return
-end
-
--- For now, make this opt-in with a global variable
-if vim.g.do_filetype_lua ~= 1 then
+-- Skip if legacy filetype is enabled or filetype detection is disabled
+if vim.g.do_legacy_filetype or vim.g.did_load_filetypes then
   return
 end
+vim.g.did_load_filetypes = 1
 
 vim.api.nvim_create_augroup('filetypedetect', { clear = false })
 
@@ -38,21 +35,16 @@ if not vim.g.did_load_ftdetect then
   ]])
 end
 
--- Set a marker so that the ftdetect scripts are not sourced a second time by filetype.vim
-vim.g.did_load_ftdetect = 1
-
--- If filetype.vim is disabled, set up the autocmd to use scripts.vim
-if vim.g.did_load_filetypes then
-  vim.api.nvim_create_autocmd({ 'BufRead', 'BufNewFile' }, {
-    group = 'filetypedetect',
-    command = "if !did_filetype() && expand('<amatch>') !~ g:ft_ignore_pat | runtime! scripts.vim | endif",
-  })
+-- Set up the autocmd for user scripts.vim
+vim.api.nvim_create_autocmd({ 'BufRead', 'BufNewFile' }, {
+  group = 'filetypedetect',
+  command = "if !did_filetype() && expand('<amatch>') !~ g:ft_ignore_pat | runtime! scripts.vim | endif",
+})
 
-  vim.api.nvim_create_autocmd('StdinReadPost', {
-    group = 'filetypedetect',
-    command = 'if !did_filetype() | runtime! scripts.vim | endif',
-  })
-end
+vim.api.nvim_create_autocmd('StdinReadPost', {
+  group = 'filetypedetect',
+  command = 'if !did_filetype() | runtime! scripts.vim | endif',
+})
 
 if not vim.g.ft_ignore_pat then
   vim.g.ft_ignore_pat = '\\.\\(Z\\|gz\\|bz2\\|zip\\|tgz\\)$'
diff --git a/runtime/filetype.vim b/runtime/filetype.vim
index 44a3567983..7469f86cf5 100644
--- a/runtime/filetype.vim
+++ b/runtime/filetype.vim
@@ -3,6 +3,11 @@
 " Maintainer:	Bram Moolenaar <Bram@vim.org>
 " Last Change:	2022 Jul 5
 
+" Only run this if enabled
+if !exists("do_legacy_filetype")
+  finish
+endif
+
 " Listen very carefully, I will say this only once
 if exists("did_load_filetypes")
   finish
diff --git a/runtime/lua/vim/filetype.lua b/runtime/lua/vim/filetype.lua
index fd47e12f07..8e86812347 100644
--- a/runtime/lua/vim/filetype.lua
+++ b/runtime/lua/vim/filetype.lua
@@ -2227,8 +2227,7 @@ end
 ---
 --- See $VIMRUNTIME/lua/vim/filetype.lua for more examples.
 ---
---- Note that Lua filetype detection is only enabled when |g:do_filetype_lua| is
---- set to 1.
+--- Note that Lua filetype detection is disabled when |g:do_legacy_filetype| is set.
 ---
 --- Example:
 --- <pre>
diff --git a/runtime/scripts.vim b/runtime/scripts.vim
index a129c3467e..2d8bfdcb05 100644
--- a/runtime/scripts.vim
+++ b/runtime/scripts.vim
@@ -11,9 +11,13 @@
 " 'ignorecase' option making a difference.  Where case is to be ignored use
 " =~? instead.  Do not use =~ anywhere.
 
-" Only do the rest when not using Lua filetype detection
-" and the FileType autocommand has not been triggered yet.
-if exists("g:do_filetype_lua") && g:do_filetype_lua || did_filetype()
+" Only run when using legacy filetype
+if !exists('g:do_legacy_filetype')
+  finish
+endif
+
+" Only do the rest when the FileType autocommand has not been triggered yet.
+if did_filetype()
   finish
 endif
 
diff --git a/src/nvim/testdir/test_filetype_lua.vim b/src/nvim/testdir/test_filetype_lua.vim
deleted file mode 100644
index d9c0dcba9c..0000000000
--- a/src/nvim/testdir/test_filetype_lua.vim
+++ /dev/null
@@ -1,3 +0,0 @@
-let g:do_filetype_lua = 1
-let g:did_load_filetypes = 0
-source test_filetype.vim
diff --git a/src/nvim/testdir/test_legacy_filetype.vim b/src/nvim/testdir/test_legacy_filetype.vim
new file mode 100644
index 0000000000..772faaadb0
--- /dev/null
+++ b/src/nvim/testdir/test_legacy_filetype.vim
@@ -0,0 +1,4 @@
+let g:do_legacy_filetype = 1
+filetype on
+
+source test_filetype.vim