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)

3e54569b17

runtime/filetype.vim

@@ -1183,14 +1183,21 @@ au BufNewFile,BufRead *.markdown,*.mdown,*.mkd,*.mkdn,*.mdwn,*.md  setf markdown
 " Mason
 au BufNewFile,BufRead *.mason,*.mhtml,*.comp	setf mason
 
-" Matlab or Objective C
+" Mathematica, Matlab, Murphi or Objective C
 au BufNewFile,BufRead *.m			call s:FTm()
 
 func! s:FTm()
   let n = 1
-  while n < 10
+  let saw_comment = 0 " Whether we've seen a multiline comment leader.
+  while n < 100
     let line = getline(n)
-    if line =~ '^\s*\(#\s*\(include\|import\)\>\|@import\>\|/\*\|//\)'
+    if line =~ '^\s*/\*'
+      " /* ... */ is a comment in Objective C and Murphi, so we can't conclude
+      " it's either of them yet, but track this as a hint in case we don't see
+      " anything more definitive.
+      let saw_comment = 1
+    endif
+    if line =~ '^\s*\(#\s*\(include\|import\)\>\|@import\>\|//\)'
       setf objc
       return
     endif
@@ -1202,11 +1209,23 @@ func! s:FTm()
       setf mma
       return
     endif
+    if line =~ '^\c\s*\(\(type\|var\)\>\|--\)'
+      setf murphi
+      return
+    endif
     let n = n + 1
   endwhile
-  if exists("g:filetype_m")
+
+  if saw_comment
+    " We didn't see anything definitive, but this looks like either Objective C
+    " or Murphi based on the comment leader. Assume the former as it is more
+    " common.
+    setf objc
+  elseif exists("g:filetype_m")
+    " Use user specified default filetype for .m
     exe "setf " . g:filetype_m
   else
+    " Default is matlab
     setf matlab
   endif
 endfunc
@@ -2792,12 +2811,12 @@ runtime! ftdetect/*.vim
 " state.
 augroup END
 
-" Generic configuration file (check this last, it's just guessing!)
+" Generic configuration file. Use FALLBACK, it's just guessing!
 au filetypedetect BufNewFile,BufRead,StdinReadPost *
 	\ if !did_filetype() && expand("<amatch>") !~ g:ft_ignore_pat
 	\    && (getline(1) =~ '^#' || getline(2) =~ '^#' || getline(3) =~ '^#'
 	\	|| getline(4) =~ '^#' || getline(5) =~ '^#') |
-	\   setf conf |
+	\   setf FALLBACK conf |
 	\ endif
 
 

src/nvim/ex_docmd.c

@@ -9743,13 +9743,20 @@ void filetype_maybe_enable(void)
   }
 }
 
-/*
+/// ":setfiletype [FALLBACK] {name}"
- * ":setfiletype {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;
+    }
   }
 }
 

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

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