A strange parsing error with heredoc without whitespace (`lua<<EOF` instead of `lua << EOF`)

[wookayin]

Neovim version (nvim -v)

v0.6.0-dev+1976-gcb15055c2

Vim (not Nvim) behaves the same?

Yes, Vim 8.2.0000

Operating system/version

macOS 11.6

Terminal name/version

xterm

$TERM environment variable

xterm-256color

Installation

homebrew

How to reproduce the issue

nvim --clean
source foo.vim

foo.vim:

function! s:setup_gitsigns() abort
lua<<EOF
require('gitsigns').setup {
  signs = {
    change       = {hl = 'GitSignsChange', text = '~', numhl='GitSignsChangeNr', linehl='GitSignsChangeLn'},
  },
}
EOF
endfunction

Expected behavior

There should be no errors in parsing.

Actual behavior

Error detected while processing f.vim:                                                                                                         
line   10:
E126: Missing :endfunction

Note: removing the following line, or replacing the word change with something else will make the error not happen.

    change       = {hl = 'GitSignsChange', text = '~', numhl='GitSignsChangeNr', linehl='GitSignsChangeLn'},

Is there any special thing about change in parsing heredoc?

[wookayin]

This looks like a core vim bug. Other words like append, insert also trigger the same parsing error. (Note: NOT :append, :insert as per help :lua-heredoc)

Releavant line: https://github.com/vim/vim/blob/master/src/userfunc.c#L940

Should I file a bug for upstream vim as well?

[zeertzjq]

When lua<<EOF is changed to lua <<EOF the error can no longer be reproduced in either Vim or Nvim.

And this is also what the documentation says:

:[range]lua << [endmarker]
{script}
{endmarker}

[zeertzjq]

Although :lua<<EOF is an undocumented usage, its behavior is indeed confusing in this case. I'm not sure what should be changed.