3 files changed, 21 insertions, 1 deletions
diff --git a/runtime/doc/filetype.txt b/runtime/doc/filetype.txt
index 9952ef6415..8de91ed3ae 100644
--- a/runtime/doc/filetype.txt
+++ b/runtime/doc/filetype.txt
@@ -148,6 +148,7 @@ variables can be used to overrule the filetype used for certain extensions:
 	*.fs		g:filetype_fs	|ft-forth-syntax|
 	*.i		g:filetype_i	|ft-progress-syntax|
 	*.inc		g:filetype_inc
+	*.lsl		g:filetype_lsl
 	*.m		g:filetype_m	|ft-mathematica-syntax|
 	*.mod		g:filetype_mod
 	*.p		g:filetype_p	|ft-pascal-syntax|
diff --git a/runtime/lua/vim/filetype.lua b/runtime/lua/vim/filetype.lua
index 28d13cf270..7dd1d7cd25 100644
--- a/runtime/lua/vim/filetype.lua
+++ b/runtime/lua/vim/filetype.lua
@@ -611,7 +611,9 @@ local extension = {
   c = function(path, bufnr)
     return require('vim.filetype.detect').lpc(bufnr)
   end,
-  lsl = 'lsl',
+  lsl = function(path, bufnr)
+    return require('vim.filetype.detect').lsl(bufnr)
+  end,
   lss = 'lss',
   nse = 'lua',
   rockspec = 'lua',
@@ -674,6 +676,7 @@ local extension = {
   DEF = 'modula2',
   ['m2'] = 'modula2',
   mi = 'modula2',
+  lm3 = 'modula3',
   ssc = 'monk',
   monk = 'monk',
   tsc = 'monk',
@@ -1459,6 +1462,9 @@ local filename = {
   ['.sawfishrc'] = 'lisp',
   ['/etc/login.access'] = 'loginaccess',
   ['/etc/login.defs'] = 'logindefs',
+  ['.lsl'] = function(path, bufnr)
+    return require('vim.filetype.detect').lsl(bufnr)
+  end,
   ['.luacheckrc'] = 'lua',
   ['lynx.cfg'] = 'lynx',
   ['m3overrides'] = 'm3build',
diff --git a/runtime/lua/vim/filetype/detect.lua b/runtime/lua/vim/filetype/detect.lua
index 23fa1c5068..51ea1971cb 100644
--- a/runtime/lua/vim/filetype/detect.lua
+++ b/runtime/lua/vim/filetype/detect.lua
@@ -634,6 +634,19 @@ function M.lpc(bufnr)
   return 'c'
 end
 
+function M.lsl(bufnr)
+  if vim.g.filetype_lsl then
+    return vim.g.filetype_lsl
+  end
+
+  local line = nextnonblank(bufnr, 1)
+  if findany(line, { '^%s*%%', ':%s*trait%s*$' }) then
+    return 'larch'
+  else
+    return 'lsl'
+  end
+end
+
 function M.m(bufnr)
   if vim.g.filetype_m then
     return vim.g.filetype_m