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I am editing a source code in language1.

It doesn't have a built-in syntax highliting configuration into my vim.

However, its syntax is very similar to language2, which has. I think, syntax highliting the sources as language2 would be pretty okay for me. Thus, I tried to set up the syntax highliting of language2 to the files with extensions of language1.

Checking the syntax highliting configuration of my distribution-provided vim (filetype.vim), I found the line

au BufNewFile,BufRead *.<ext2>  setf language2

Thus, I inserted a line

au BufNewFile,BufRead *.<ext1>  setf language2

into my local .vimrc.

However, nothing happened. My source files - in language1 - are still un-syntax highlited.

Why is it so? How could I make it working?

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  • In my specific case: I am trying to syntax hightlig Typescript files (.ts) as if they would be Javascript, on a vim provided by debian/ubuntu. This is why I am trying to avoid to overwrite the distro-provided /usr/share/vim/vim74/filetype.vim. However, I tried to make the question as general as possible (I think not the question and also not the answer won't be specific to my environment). – peterh says reinstate Monica Feb 18 '18 at 22:55
  • If I overwrite /usr/share/vim/vim74/filetype.vim, then it works, but I am trying to use a local config, as overwriting distro-provided file is a bad thing on debian. – peterh says reinstate Monica Feb 18 '18 at 22:57
  • Does set filetype=language2 work (i.e., not using setf)? – Mass Feb 18 '18 at 23:23
  • @Mass Wow! Yes, it works. But why the au command didn't work in my local vimrc? – peterh says reinstate Monica Feb 18 '18 at 23:31
  • Did you try au BufNewFile,BufRead *.<ext1> set filetype=language2 in your vimrc already? The reason set filetype works and setf doesn't is because vim already knows .ts as having filetype=xml. setf will not change the filetype if it's already set (I will add an answer if the code works in your vimrc). – Mass Feb 18 '18 at 23:34
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A quick solution is to just replace setf with set filetype in the line in your vimrc:

au BufNewFile,BufRead *.<ext1>  set filetype=language2

This is explained in :help ftdetect but it is quite difficult understand. In this specific case the reason is very simple- that vim has already used setf to set a file type for ext1.

Suppose ext1=ts. In /usr/share/vim/vim80/filetype.vim, we see,

" Qt Linguist translation source and Qt User Interface Files are XML
au BufNewFile,BufRead *.ts,*.ui         setf xml

This means any following setf issued in autocmds will fail:

:setf[iletype] [FALLBACK] {filetype}            *:setf* *:setfiletype*
        Set the 'filetype' option to {filetype}, but only if
        not done yet in a sequence of (nested) autocommands.
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