Vim highlights valid shell parameter expansion syntax as an error

Question

#!/bin/bash
echo ${2:-"-l -p"}

Having some bash parameter-substitution fun and (Neo) Vim complains about it, while the code is perfectly fine.

I know I can suppress errors totally by doing sort of like hi Error ctermbg=None, but that's quick and dirty. (I can live with the red background, but it's ugly).

I did :h error [[ press Tab 20 times ]], but didn't find anything interesting about the topic.

Can I fix (or should I report) such misbehaviour?

Pure Vim highlights the same way, running:

vim -u NONE -c "set nocp | set filetype=sh | syn on"

vim --version
VIM - Vi IMproved 8.0 (2016 Sep 12, compiled Nov 15 2016 18:06:04)
Included patches: 1-86
Compiled by Arch Linux
Huge version without GUI.

Update

Doesn't work in urxvt. Neither in neo nor pure Vim.
Doesn't work in NeoVim. Neither in urxvt nor xterm.
Works only in xterm, pure Vim.

works == no red background, I mean
All of the above happens with -u NONE.

Answer 1

Vim also used to display this as an error, but the latest version no longer does. It looks like the syntax file for Vim has been updated in a fairly recent version Vim, which isn't in Neovim yet.

I downloaded the Vim source and did:

git checkout v7.4.1900

To get an older Vim version. We're only interested in the syntax file (runtime/syntax/sh.vim) so we don't need to re-compile Vim.

After opening a simple a.sh file which contains echo ${2:-"-l -p"} I did:

:unlet b:current_syntax
:source /home/martin/src/vim/runtime/syntax/sh.vim

to load the Vim 7.4.1900 syntax file from the source tree, and now I have the same red text as you do.

So now we need to isolate the patch that fixes this. Unfortunately the git commits for runtime directories don't contain a helpful description (just "update runtime directory") but we know that:

• v8.0.0142 does not have this problem;
• v7.4.1900 does have this problem;
• that the fix is in runtime/syntax/sh.vim

Checking the history for that file we see there aren't that many recent changes, so I simply did git checkout <commit-id> until I managed to reproduce the problem. The commit after that one will have fixed the problem, which is e4a3bcf.

if you look at the diff, we see a number of changes to the shDeref* syntax groups, which seem fix the error.

There are two things you can do:

• Copy the latest syntax/sh.vim from the Vim source to to ~/.config/nvim/syntax/sh.vim (Neovim) or ~/.vim/syntax/sh.vim (Vim) so it will override the default. Neovim doesn't seem to have made any changes to this file, so you won't lose anything.

  The downside of this is that you won't get any future updates made to the system-wide syntax/sh.vim.

• You can also try to locally amend the syntax/sh.vim file with just the fixes using the after directory. This will take more time, but you will get future updates made to the system-wide syntax/sh.vim.