feature: create ocamlinterface filetype for mli files

This is needed for supporting the tree-sitter parsers in ocaml because
the interface parser is different from the implementation one one.

Author: undu

README.md

@@ -17,7 +17,7 @@ NeoBundleInstall ocaml/vim-ocaml'
 
 " or use NeoBundleLazy
 NeoBundleLazy 'rgrinberg/vim-ocaml', {'autoload' : {'filetypes' :
-    \ ['ocaml', 'dune', 'opam', 'oasis', 'omake', 'ocamlbuild_tags', 'sexplib']}}
+    \ ['ocaml', 'ocamlinterface', 'dune', 'opam', 'oasis', 'omake', 'ocamlbuild_tags', 'sexplib']}}
 ```
 
 ## History

ftdetect/ocaml.vim

@@ -1 +1 @@
-au BufRead,BufNewFile *.ml,*.mli,*.mll,*.mly,.ocamlinit,*.mlt,*.mlp,*.mlip,*.mli.cppo,*.ml.cppo set ft=ocaml
+au BufRead,BufNewFile *.ml,*.mll,*.mly,.ocamlinit,*.mlt,*.mlp,*.ml.cppo set ft=ocaml

ftdetect/ocamlinterface.vim

@@ -0,0 +1 @@
+au BufRead,BufNewFile *.mli,*.mlip,*.mli.cppo set ft=ocamlinterface

ftplugin/ocamlinterface.vim

@@ -0,0 +1,11 @@
+" Language:    OCaml Interface
+" Maintainer:  vim-ocaml maintainers
+" URL:         http://www.github.com/ocaml/vim-ocaml
+
+if exists("b:did_ftplugin")
+  finish
+endif
+
+runtime! ftplugin/ocaml.vim ftplugin/ocaml_*.vim ftplugin/ocaml/*.vim
+
+" vim:sw=2 fdm=indent

syntax/ocamlinterface.vim

@@ -0,0 +1,17 @@
+" Vim syntax file
+" Language:     OCaml Interface
+" Filenames:    *.mli
+" Maintainers:  vim-ocaml maintainers
+" URL:          http://www.github.com/ocaml/vim-ocaml
+
+" Quit when a syntax file was already loaded
+if exists("b:current_syntax")
+  finish
+endif
+
+runtime! syntax/ocaml.vim
+unlet b:current_syntax
+
+let b:current_syntax = "ocamlinterface"
+
+" vim: ts=8