Using neovim as $MANPAGER fails when stderr is redirected

[ybc37]

Hey there!

I'm using neovim as manpager (as described in :h man -> MANPAGER='nvim +Man!') and while it works great, I ran into an issue using fish-shells' Alt+h/F1 functionality. This shortcut jumps directly into the man page of the command under the cursor. Using it, neovim flashes up and it seems it tries to execute a lot of commands (they're all failing with E21: Cannot make changes, 'modifiable' is off, which is expected with +Man!).

After looking at the fish function I pinned it down to using man with a redirection: man ls 2>/dev/null, or more generally: echo "foo" | nvim -u NORC 2>/dev/null.

stderr of man ls 2>./log:

Vim: Error reading input, exiting...

Vim: Finished.
man: command exited with status 1: sed -e '/^[[:space:]]*$/{ N; /^[[:space:]]*\n[[:space:]]*$/D; }' | LESS=-ix8RmPm Manual page ls(1) ?ltline %lt?L/%L.:byte %bB?s/%s..?e (END):?pB %pB\%.. (press h for help or q to quit)$PM Manual page ls(1) ?ltline %lt?L/%L.:byte %bB?s/%s..?e (END):?pB %pB\%.. (press h for help or q to quit)$ MAN_PN=ls(1) nvim +Man!

stderr of echo "foo" | nvim -u NORC 2>./log:

Vim: Error reading input, exiting...

Vim: preserving files...
Vim: Finished.

With vim as manpager (MANPAGER="vim -M +MANPAGER -") it behaves more or less the same, but outputs some errors/warnings to stdout, too.

• nvim --version: NVIM v0.5.0-dev+1055-g8950f4e94
• vim -u DEFAULTS (version: 8.2) behaves differently? very similar
• Operating system/version: Arch Linux
• Terminal name/version: alacritty
• $TERM: tmux-256color

Steps to reproduce

# set nvim as manpager
# bash: `export MANPAGER='nvim +Man!'`
# fish: `set -x MANPAGER "nvim +Man!"`
man ls 2>/dev/null
# or
echo "foo" | nvim -u NORC 2>/dev/null

Actual behaviour

• nvim starts
• nvim tries to execute commands, failing with E21: Cannot make changes, 'modifiable' is off
• nvim closes

Expected behaviour

• nvim opens man page/piped text
• errors are redirected