[vim/vim] cannot use vim9 block inside nested autocmd (Issue #20918)

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lacygoill

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8:25 AM (12 hours ago) 8:25 AM

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lacygoill created an issue (vim/vim#20918)

Steps to reproduce

Run this shell command:

vim -Nu NONE -S <(tee <<'EOF'
    vim9script
    autocmd FileType fzf autocmd BufWinEnter * ++once {
        autocmd SafeState * ++once if true
            |     echo
            | endif
    }
EOF
)

An error is given:

E1128: } without {: }

Expected behavior

No error is given.

Version of Vim

9.2 Included patches: 1-894

Environment

Operating system: Debian GNU/Linux 13 (trixie)
Terminal: XTerm(398)
Value of $TERM: xterm-256color
Shell: GNU bash, version 5.2.37

Additional context

This works:

vim9script
autocmd BufWinEnter * ++once {
    autocmd SafeState * ++once if true
        |     echo
        | endif
}

It's a regression because the original code used to work a long time ago.
But I don't know when it broke, and I can't bisect the issue because I can't compile old Vim versions.
When I try, I get this error:

checking for tgetent()... configure: error: NOT FOUND!
      You need to install a terminal library; for example ncurses.
      Or specify the name of the library with --with-tlib.

Which I don't understand, because I have libncurses-dev installed.

If someone could tell me how to compile old Vim versions, I could bisect the issue.

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h_east

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5:30 PM (3 hours ago) 5:30 PM

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h-east left a comment (vim/vim#20918)

At script level the block is only read when the argument of :autocmd starts
with "{". In your example the argument of the outer :autocmd is

autocmd BufWinEnter * ++once {

which ends with "{" but does not start with it, so the outer :autocmd keeps
just that one line. The lines after it are executed as ordinary script lines
and the final "}" gives E1128.

This is the documented limitation: |:autocmd-block| points at |:command-repl|,
which says "No nesting is supported". It is also not a regression. The check
has been "the argument starts with {" since patch 8.2.3268, which added blocks
for :autocmd in 2021.

In a :def function it does work, because there the block is recognized by a
trailing "{" instead. That went in as patch 8.2.3271, on the same day. So
this is a workaround for now:

    vim9script
    def Setup()

autocmd FileType fzf autocmd BufWinEnter * ++once {
          autocmd SafeState * ++once if true
              |     echo
              | endif

      }
    enddef
    Setup()

The registered autocmd then holds the whole block, and it fires as you expect.

Two rules for the same syntax is not a good state, and I will have a look at
making the script level accept a trailing "{" as well.

About building older versions: on Debian tgetent is in libtinfo, not in
libncurses. Configure with

./configure --with-tlib=tinfo