Automatically detect script filetype when typing

Makefile

@@ -7,4 +7,4 @@ test:
 	@ scripts/test
 
 dev:
-	@ echo "packages.yaml\nheuristics.yaml\nscripts/test\nscripts/build\nscripts/test_extensions.vim" | DEV=1 entr bash -c 'make && make test'
+	@ (ls && find scripts) | DEV=1 entr bash -c 'make && make test'

autoload/polyglot.vim

@@ -4,11 +4,13 @@ set cpo&vim
 
 func! polyglot#Heuristics()
   " Try to detect filetype from shebang
-  let l:filetype = polyglot#Shebang()
-  if l:filetype != ""
-    exec "setf " . l:filetype
-    return
+  let filetype = polyglot#Shebang()
+  if filetype != ""
+    exec "setf " . filetype
+    return 1
   endif
+
+  return 0
 endfunc
 
 let s:interpreters = {
@@ -86,37 +88,41 @@ let s:r_envflag = '%(\S\+=\S\+\|-[iS]\|--ignore-environment\|--split-string\)'
 let s:r_env = '^\%(\' . s:r_envflag . '\s\+\)*\(\S\+\)'
 
 func! polyglot#Shebang()
-  let l:line1 = getline(1)
+  let line1 = getline(1)
 
-  if l:line1 !~# "^#!"
+  if line1 !~# "^#!"
     return
   endif
 
-  let l:pathrest = matchlist(l:line1, s:r_hashbang)
+  let pathrest = matchlist(line1, s:r_hashbang)
 
-  if len(l:pathrest) == 0
+  if len(pathrest) == 0
     return 
   endif
 
-  let [_, l:path, l:rest; __] = l:pathrest
+  let [_, path, rest; __] = pathrest
 
-  let l:script = split(l:path, "/")[-1]
+  let script = split(path, "/")[-1]
 
-  if l:script == "env"
-    let l:argspath = matchlist(l:rest, s:r_env)
-    if len(l:argspath) == 0
+  if len(script) == 0
     return
   endif
 
-    let l:script = l:argspath[1]
+  if script == "env"
+    let argspath = matchlist(rest, s:r_env)
+    if len(argspath) == 0
+      return
     endif
 
-  if has_key(s:interpreters, l:script)
-    return s:interpreters[l:script]
+    let script = argspath[1]
+  endif
+
+  if has_key(s:interpreters, script)
+    return s:interpreters[script]
   endif
 
   for interpreter in keys(s:interpreters)
-    if l:script =~# '^' . interpreter
+    if script =~# '^' . interpreter
       return s:interpreters[interpreter]
     endif
   endfor

ftdetect/polyglot.vim

@@ -1911,12 +1911,11 @@ endif
 
 " end filetypes
 
-augroup END
-
 au BufNewFile,BufRead,StdinReadPost * 
   \ if !did_filetype() && expand("<afile>") !~ g:ft_ignore_pat 
   \ | call polyglot#Heuristics() | endif
 
+augroup END
 
 if !has_key(s:disabled_packages, 'autoindent')
   " Code below re-implements sleuth for vim-polyglot
@@ -2088,10 +2087,10 @@ if !has_key(s:disabled_packages, 'autoindent')
     endif
   endfunction
 
-  augroup polyglot
-    autocmd!
-    autocmd FileType * call s:detect_indent()
-    autocmd User Flags call Hoist('buffer', 5, 'SleuthIndicator')
+  augroup polyglot-sleuth
+    au!
+    au FileType * call s:detect_indent()
+    au User Flags call Hoist('buffer', 5, 'SleuthIndicator')
   augroup END
 
   command! -bar -bang Sleuth call s:detect_indent()
@@ -2109,7 +2108,17 @@ func! s:verify()
   endif
 endfunc
 
-autocmd VimEnter * call s:verify()
+au VimEnter * call s:verify()
+
+func! s:observe_filetype()
+  augroup polyglot-observer
+    au! CursorHold,CursorHoldI <buffer>
+      \ if polyglot#Heuristics() | au! polyglot-observer CursorHold,CursorHoldI | endif
+  augroup END
+endfunc
+
+au BufEnter * if &ft == "" && expand("<afile>") !~ g:ft_ignore_pat
+      \ | call s:observe_filetype() | endif
 
 " restore Vi compatibility settings
 let &cpo = s:cpo_save

scripts/build

@@ -559,8 +559,10 @@ def generate_ftdetect(packages, heuristics)
       let l:filetype = polyglot#Shebang()
       if l:filetype != ""
         exec "setf " . l:filetype
-        return
+        return 1
       endif
+
+      return 0
     endfunc
     
     let s:interpreters = {