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In TypeScript and Node.js, you can import a file `./directory/index.ts`
by importing `./directory`.
I wanted `gf` and friends to open the `index` file if the import refers
to a directory. By default, `gf` opens the directory using Netrw.
At first tried to do this by setting 'includeexpr' as follows:
setlocal includeexpr=<SID>FindFile(v:fname)
function! s:FindFile(fname)
echom 'FindFile: ' . a:fname
if filereadable(a:fname)
return a:fname
endif
return a:fname . '/index'
endfunction
This gave me the following error:
E120: Using <SID> not in a script context: <SID>FindFile
so I tried removing `<SID>`:
setlocal includeexpr=FindFile(v:fname)
function! FindFile(fname)
echom 'FindFile: ' . a:fname
if filereadable(a:fname)
return a:fname
endif
return a:fname . '/index.ts'
endfunction
The problem was, my 'includeexpr' function wasn't getting executed every
time I used `gf`, only some times. And it never ran when I used `gf` on
a directory.
After asking on Freenode#vim, 'crose' made the following suggestion:
augroup typescript_maybe_append_filename
au!
au BufEnter * if expand('<amatch>')->isdirectory()
\ | call s:maybe_append_filename()
\ | endif
augroup END
fu s:maybe_append_filename() abort
if getbufvar('#', '&ft', '') == 'typescript'
exe 'e ' .. expand('%:p') .. 'index.ts'
endif
endfu
This works, but it adds the Netrw directory buffer to the jumplist, and
feels more like a mitigation than a solution.
I looked at the following language ftplugins for inspiration:
* .../vim/8.2.1650/share/vim/vim82/ftplugin/ruby.vim
* https://github.com/moll/vim-node/blob/master/autoload/node.vim
These prompted me to override `gf` with a custom mapping since it looked
like 'includeexpr' wasn't going to be the right tool for this. The
`s:FindFile()` function has similar logic, but is now written as a map
rhs function, taking into account the different ways of invoking `gf`.
When defined as a script-local function, I at first kept getting this
error using `gf` on a directory:
E127: Cannot redefine function <SNR>111_FindFile: It is in use
Thanks to Ingo Karkat
(https://stackoverflow.com/users/813602/ingo-karkat) and this Stack
Overflow answer which describes how to keep the function in the same
file (so I didn't have to move it to an autoload function) and still
prevent it from being redefined:
https://stackoverflow.com/questions/22633115/why-do-i-get-e127-from-this-vimscript/22633702#22633702
I needed to prepend `<C-v>` to the `<C-w>` characters in the map
function calls because these would actually run in the command line,
deleting the preceding word, and messing up the mapping. In order to
pass those `<C-w>` characters in the string arguments, I needed to
escape them with `<C-v>`, even though it resulted in non-obvious looking
code.
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