TUI pagers (diffnav, etc.) break fzf preview panes

[jetm]

Problem

When a user configures a TUI/interactive diff pager via git config pager.diff (e.g., diffnav, tig), all fzf preview panes in forgit show blank output or "Loading..." indefinitely.

This affects every command that uses _forgit_pager diff (or show/blame) inside a preview function — forgit add, forgit log, forgit stash, etc.

Root cause

fzf runs preview commands as subprocesses connected via pipes — there is no TTY. TUI pagers require a terminal to render their interface, so they either:

• Hang waiting for terminal capabilities that don't exist
• Exit immediately with no output
• Produce garbled/empty output

This is not a bug in fzf or the pager — it's a fundamental incompatibility. TUI pagers need a terminal; fzf preview provides a pipe.

The pager resolution chain in _forgit_get_pager reads git config pager.diff, which returns the TUI pager, and there's no distinction between "interactive context" (where TUI pagers work fine) and "preview context" (where they can't work).

Reproduction

# Set a TUI pager
git config pager.diff diffnav

# Run any forgit command with a preview pane
git forgit add    # preview is blank/Loading
git forgit log    # preview is blank/Loading

Current workaround

Setting FORGIT_PAGER or FORGIT_DIFF_PAGER to a non-TUI pager works:

export FORGIT_DIFF_PAGER="delta"
# or
export FORGIT_PAGER="delta"

This overrides the git config pager.diff lookup in _forgit_get_pager, so the TUI pager is never used.

However, this workaround has poor discoverability — users hitting blank previews have no indication of what's wrong or how to fix it.

Questions for discussion

• Should _forgit_pager detect non-TTY context and automatically fall back? (e.g., check [ -t 1 ])
• Should preview functions use a separate pager resolution that skips TUI pagers?
• Or is documenting the FORGIT_*_PAGER workaround sufficient?

I had a PR (#490) attempting one approach (dedicated preview pager function) but it broke per-command pager configurability, so I'm closing it in favor of this discussion.

[sandr01d]

Thanks for the detailed issue @jetm 👍

This is a limitation of how our preview works. We make use of fzfs preview window, which does not support anything interactive. My guess to why you see blank output would be that these tools probably spawn a subshell themselves, so fzf does not receive any of their output.

Should _forgit_pager detect non-TTY context and automatically fall back? (e.g., check [ -t 1 ])

I don't think checking [ -t 1 ] helps here. Wouldn't stdout always be opened in any case?

Should preview functions use a separate pager resolution that skips TUI pagers?

Unfortunately there is no way to tell whether or not the pager in the git config is a TUI pager or not, we just see what's written in the configuration without any context.

Or is documenting the FORGIT_*_PAGER workaround sufficient?

Documentation never hurts :)

From my knowledge documenting this as a limitation is the only option here, but maybe somebody else has a better idea...

[wfxr]

I think we can actually make this work with a small change.

@sandr01d [ -t 1 ] does help here — in fzf --preview, stdout is a pipe (not a TTY), while in execute(...) (Enter key) it's a real terminal. So the detection is reliable.

Based on this, how about adding a FORGIT_PREVIEW_PAGER env var that only kicks in when stdout is not a TTY?

_forgit_pager() {
    local pager
    if [[ ! -t 1 ]] && [[ -n "$FORGIT_PREVIEW_PAGER" ]]; then
        pager="$FORGIT_PREVIEW_PAGER"
    else
        pager=$(_forgit_get_pager "$1")
    fi
    [[ -z "${pager}" ]] && exit 1
    eval "${pager} ${*:2}"
}

Usage would be:

git config pager.diff diffnav        # keep your TUI pager for normal git
export FORGIT_PREVIEW_PAGER="delta"   # pipe-friendly pager for forgit previews

This is better than the existing FORGIT_DIFF_PAGER workaround because:

• One variable covers all preview types (diff, show, blame) instead of setting each separately
• Only affects non-TTY context, so Enter-key fullscreen viewing is untouched
• The name makes it obvious what it's for

The change is tiny — just the _forgit_pager function, no preview call sites need modification. And it's fully backward compatible — if unset, behavior is identical to today.

[sandr01d]

Sounds good @wfxr