fix: use non-interactive pager in fzf preview for TUI pagers (#498)

When users configure a TUI/interactive diff pager (e.g., diffnav, tig)
via `git config pager.diff`, fzf preview panes show blank output because
TUI pagers require a TTY that fzf previews don't provide.

Add FORGIT_PREVIEW_PAGER env var that overrides the diff pager only in
fzf preview context. Preview detection relies on a FORGIT_IN_PREVIEW
marker set by a new `_forgit_preview` wrapper, so the override applies
only to preview commands and leaves fullscreen behavior unchanged.

Fixes #491

README.md

@@ -299,6 +299,9 @@ variables:
 | `FORGIT_BLAME_PAGER`      | `git config pager.blame` _or_ `$FORGIT_PAGER`    |
 | `FORGIT_IGNORE_PAGER`     | `bat -l gitignore --color always` _or_ `cat`     |
 | `FORGIT_ATTRIBUTES_PAGER` | `bat -l gitattributes --color always` _or_ `cat` |
+| `FORGIT_PREVIEW_PAGER`    | Normal pager resolution<sup>*</sup>              |
+
+<sup>*</sup> If your pager is a TUI program (e.g., `diffnav`, `tig`), fzf preview panes will be blank because they run without a TTY. Set `FORGIT_PREVIEW_PAGER` to a non-interactive pager (e.g., `delta`) to fix this. When set, it overrides all other `FORGIT_*_PAGER` settings in fzf preview context.
 
 ### FZF Options
 

bin/git-forgit

@@ -131,11 +131,27 @@ _forgit_dir_view=${FORGIT_DIR_VIEW:-$(hash tree &> /dev/null && echo 'tree' || e
 
 _forgit_pager() {
     local pager
-    pager=$(_forgit_get_pager "$1")
+    # Preview mode must be marked explicitly by forgit. Inferred signals such
+    # as FZF_PREVIEW_COLUMNS or a non-TTY stdout also show up in execute/fullscreen
+    # paths, which would incorrectly route Enter actions to FORGIT_PREVIEW_PAGER.
+    if [[ -n "$FORGIT_IN_PREVIEW" ]] && [[ -n "$FORGIT_PREVIEW_PAGER" ]]; then
+        pager="$FORGIT_PREVIEW_PAGER"
+    else
+        pager=$(_forgit_get_pager "$1")
+    fi
     [[ -z "${pager}" ]] && exit 1
     eval "${pager} ${*:2}"
 }
 
+_forgit_preview() {
+    local cmd=$1
+    shift
+    # Funnel all fzf --preview commands through a single wrapper so preview-only
+    # pager behavior is controlled by an explicit marker instead of ambient env.
+    export FORGIT_IN_PREVIEW=1
+    _forgit_"${cmd}" "$@"
+}
+
 _forgit_get_pager() {
     local pager
     pager=${1:-core}
@@ -225,7 +241,7 @@ _forgit_log() {
         +s +m --tiebreak=index
         --bind=\"enter:execute($FORGIT log_enter {} $quoted_files)\"
         --bind=\"ctrl-y:execute-silent($FORGIT yank_sha {})\"
-        --preview=\"$FORGIT log_preview {} $quoted_files\"
+        --preview=\"$FORGIT preview log_preview {} $quoted_files\"
         $FORGIT_LOG_FZF_OPTS
     "
     graph=()
@@ -252,7 +268,7 @@ _forgit_reflog() {
         +s +m --tiebreak=index
         --bind=\"enter:execute($FORGIT log_enter {})\"
         --bind=\"ctrl-y:execute-silent($FORGIT yank_sha {})\"
-        --preview=\"$FORGIT log_preview {}\"
+        --preview=\"$FORGIT preview log_preview {}\"
         $FORGIT_REFLOG_FZF_OPTS
     "
     reflog_format=${FORGIT_GRL_FORMAT:-$_forgit_log_format}
@@ -357,7 +373,7 @@ _forgit_diff() {
     opts="
         $FORGIT_FZF_DEFAULT_OPTS
         +m -0 --bind=\"enter:execute($FORGIT diff_enter {} $escaped_commits | $FORGIT pager enter)\"
-        --preview=\"$FORGIT diff_view {} '$_forgit_preview_context' $escaped_commits\"
+        --preview=\"$FORGIT preview diff_view {} '$_forgit_preview_context' $escaped_commits\"
         --bind=\"alt-e:execute($FORGIT edit_diffed_file {})+refresh-preview\"
         $FORGIT_DIFF_FZF_OPTS
         --prompt=\"${commits[*]} > \"
@@ -427,7 +443,7 @@ _forgit_show() {
     opts="
         $FORGIT_FZF_DEFAULT_OPTS
         +m -0 --bind=\"enter:execute($FORGIT show_enter {} $escaped_commit | $FORGIT pager enter)\"
-        --preview=\"$FORGIT show_preview {} '$_forgit_preview_context' $escaped_commit\"
+        --preview=\"$FORGIT preview show_preview {} '$_forgit_preview_context' $escaped_commit\"
         --preview-label=\" Diff \"
         --bind=\"alt-e:execute($FORGIT edit_diffed_file {})+refresh-preview\"
         --bind=\"alt-t:transform:[[ ! \\\"\$FZF_PREVIEW_LABEL\\\" =~ 'Diff' ]] &&
@@ -499,7 +515,7 @@ _forgit_add() {
     opts="
         $FORGIT_FZF_DEFAULT_OPTS
         -0 -m --nth 2..,..
-        --preview=\"$FORGIT add_preview {}\"
+        --preview=\"$FORGIT preview add_preview {}\"
         --bind=\"alt-e:execute($FORGIT edit_add_file {})+refresh-preview\"
         $FORGIT_ADD_FZF_OPTS
     "
@@ -536,7 +552,7 @@ _forgit_reset_head() {
     opts="
         $FORGIT_FZF_DEFAULT_OPTS
         -m -0
-        --preview=\"$FORGIT reset_head_preview '$rootdir'/{}\"
+        --preview=\"$FORGIT preview reset_head_preview '$rootdir'/{}\"
         $FORGIT_RESET_HEAD_FZF_OPTS
     "
     files=()
@@ -576,7 +592,7 @@ _forgit_stash_show() {
         $FORGIT_FZF_DEFAULT_OPTS
         +s +m -0 --tiebreak=index --bind=\"enter:execute($FORGIT stash_show_enter {})\"
         --bind=\"ctrl-y:execute-silent($FORGIT yank_stash_name {})\"
-        --preview=\"$FORGIT stash_show_preview {}\"
+        --preview=\"$FORGIT preview stash_show_preview {}\"
         $FORGIT_STASH_FZF_OPTS
     "
     git stash list "${_forgit_stash_show_git_opts[@]}" | FZF_DEFAULT_OPTS="$opts" fzf
@@ -622,7 +638,7 @@ _forgit_stash_push() {
     opts="
         $FORGIT_FZF_DEFAULT_OPTS
         -m
-        --preview=\"$FORGIT stash_push_preview {}\"
+        --preview=\"$FORGIT preview stash_push_preview {}\"
         $FORGIT_STASH_PUSH_FZF_OPTS
     "
     # Show both modified and untracked files
@@ -649,7 +665,7 @@ _forgit_clean_select_files() {
     local opts
     opts="
         $FORGIT_FZF_DEFAULT_OPTS
-        --preview=\"$FORGIT clean_preview {}\"
+        --preview=\"$FORGIT preview clean_preview {}\"
         -m -0
         $FORGIT_CLEAN_FZF_OPTS
     "
@@ -693,7 +709,7 @@ _forgit_cherry_pick() {
 
     opts="
         $FORGIT_FZF_DEFAULT_OPTS
-        --preview=\"$FORGIT cherry_pick_preview {}\"
+        --preview=\"$FORGIT preview cherry_pick_preview {}\"
         --multi --ansi --with-nth 2.. -0 --tiebreak=index
         $FORGIT_CHERRY_PICK_FZF_OPTS
     "
@@ -736,7 +752,7 @@ _forgit_cherry_pick_from_branch() {
     opts="
         $FORGIT_FZF_DEFAULT_OPTS
         +s +m --tiebreak=index --header-lines=1
-        --preview=\"$FORGIT cherry_pick_from_branch_preview '$base' {}\"
+        --preview=\"$FORGIT preview cherry_pick_from_branch_preview '$base' {}\"
         $FORGIT_CHERRY_PICK_FROM_BRANCH_FZF_OPTS
         "
     # loop until either the branch selector is closed or a commit to be cherry
@@ -771,7 +787,7 @@ _forgit_rebase() {
         $FORGIT_FZF_DEFAULT_OPTS
         +s +m --tiebreak=index
         --bind=\"ctrl-y:execute-silent($FORGIT yank_sha {})\"
-        --preview=\"$FORGIT file_preview {}\"
+        --preview=\"$FORGIT preview file_preview {}\"
         $FORGIT_REBASE_FZF_OPTS
     "
     target_commit=$(
@@ -818,7 +834,7 @@ _forgit_edit_commit() {
         $FORGIT_FZF_DEFAULT_OPTS
         +s +m --tiebreak=index
         --bind=\"ctrl-y:execute-silent($FORGIT yank_sha {})\"
-        --preview=\"$FORGIT file_preview {} $quoted_files\"
+        --preview=\"$FORGIT preview file_preview {} $quoted_files\"
         $fzf_opts
     "
     target_commit=$(
@@ -847,7 +863,7 @@ _forgit_reword() {
         $FORGIT_FZF_DEFAULT_OPTS
         +s +m --tiebreak=index
         --bind=\"ctrl-y:execute-silent($FORGIT yank_sha {})\"
-        --preview=\"$FORGIT file_preview {} $quoted_files\"
+        --preview=\"$FORGIT preview file_preview {} $quoted_files\"
         $FORGIT_REWORD_FZF_OPTS
     "
     target_commit=$(
@@ -882,7 +898,7 @@ _forgit_checkout_file() {
     opts="
         $FORGIT_FZF_DEFAULT_OPTS
         -m -0
-        --preview=\"$FORGIT checkout_file_preview {}\"
+        --preview=\"$FORGIT preview checkout_file_preview {}\"
         $FORGIT_CHECKOUT_FILE_FZF_OPTS
     "
     files=()
@@ -918,7 +934,7 @@ _forgit_checkout_branch() {
     opts="
         $FORGIT_FZF_DEFAULT_OPTS
         +s +m --tiebreak=index --header-lines=1
-        --preview=\"$FORGIT branch_preview {}\"
+        --preview=\"$FORGIT preview branch_preview {}\"
         $FORGIT_CHECKOUT_BRANCH_FZF_OPTS
         "
     _forgit_checkout_branch_branch_git_opts=()
@@ -964,7 +980,7 @@ _forgit_switch_branch() {
     opts="
         $FORGIT_FZF_DEFAULT_OPTS
         +s +m --tiebreak=index --header-lines=1
-        --preview=\"$FORGIT branch_preview {}\"
+        --preview=\"$FORGIT preview branch_preview {}\"
         $FORGIT_SWITCH_BRANCH_FZF_OPTS
         "
     _forgit_switch_branch_branch_git_opts=()
@@ -1001,7 +1017,7 @@ _forgit_checkout_tag() {
     opts="
         $FORGIT_FZF_DEFAULT_OPTS
         +s +m --tiebreak=index
-        --preview=\"$FORGIT branch_preview {}\"
+        --preview=\"$FORGIT preview branch_preview {}\"
         $FORGIT_CHECKOUT_TAG_FZF_OPTS
     "
     tag="$(git tag -l --sort=-v:refname | FZF_DEFAULT_OPTS="$opts" fzf)"
@@ -1030,7 +1046,7 @@ _forgit_checkout_commit() {
         $FORGIT_FZF_DEFAULT_OPTS
         +s +m --tiebreak=index
         --bind=\"ctrl-y:execute-silent($FORGIT yank_sha {})\"
-        --preview=\"$FORGIT checkout_commit_preview {}\"
+        --preview=\"$FORGIT preview checkout_commit_preview {}\"
         $FORGIT_CHECKOUT_COMMIT_FZF_OPTS
     "
     graph=()
@@ -1063,7 +1079,7 @@ _forgit_branch_delete() {
     opts="
         $FORGIT_FZF_DEFAULT_OPTS
         +s --multi --tiebreak=index --header-lines=1
-        --preview=\"$FORGIT branch_preview {}\"
+        --preview=\"$FORGIT preview branch_preview {}\"
         $FORGIT_BRANCH_DELETE_FZF_OPTS
     "
     for branch in $(_forgit_branch_list | FZF_DEFAULT_OPTS="$opts" fzf | _forgit_extract_branch_name)
@@ -1094,7 +1110,7 @@ _forgit_revert_commit() {
         $FORGIT_FZF_DEFAULT_OPTS
         -m +s --tiebreak=index
         --ansi --with-nth 2..
-        --preview=\"$FORGIT revert_preview {}\"
+        --preview=\"$FORGIT preview revert_preview {}\"
         $FORGIT_REVERT_COMMIT_FZF_OPTS
     "
     graph=()
@@ -1149,7 +1165,7 @@ _forgit_blame() {
     done < <(git rev-parse --flags "$@")
     opts="
         $FORGIT_FZF_DEFAULT_OPTS
-        --preview=\"$FORGIT blame_preview {} ${flags[*]}\"
+        --preview=\"$FORGIT preview blame_preview {} ${flags[*]}\"
         $FORGIT_BLAME_FZF_OPTS
     "
     # flags is not quoted here, which is fine given that they are retrieved
@@ -1184,7 +1200,7 @@ _forgit_ignore() {
     opts="
         $FORGIT_FZF_DEFAULT_OPTS
         -m --preview-window='right:70%'
-        --preview=\"$FORGIT path_preview $FORGIT_GI_TEMPLATES {2} .gitignore ignore\"
+        --preview=\"$FORGIT preview path_preview $FORGIT_GI_TEMPLATES {2} .gitignore ignore\"
         $FORGIT_IGNORE_FZF_OPTS
     "
     args=("$@")
@@ -1212,7 +1228,7 @@ _forgit_attributes() {
     opts="
         $FORGIT_FZF_DEFAULT_OPTS
         -m --preview-window='right:70%'
-        --preview=\"$FORGIT path_preview $FORGIT_ATTR_TEMPLATES {2} .gitattributes attributes\"
+        --preview=\"$FORGIT preview path_preview $FORGIT_ATTR_TEMPLATES {2} .gitattributes attributes\"
         $FORGIT_ATTRIBUTES_FZF_OPTS
     "
     args=("$@")
@@ -1371,7 +1387,7 @@ _forgit_worktree() {
     opts="
         $FORGIT_FZF_DEFAULT_OPTS
         +s +m --tiebreak=index
-        --preview=\"$FORGIT worktree_preview {}\"
+        --preview=\"$FORGIT preview worktree_preview {}\"
         --bind=\"ctrl-y:execute-silent($FORGIT worktree_yank_path {})\"
         --bind=\"alt-l:execute-silent($FORGIT worktree_toggle_lock {})+reload($FORGIT worktree_list)\"
         $FORGIT_WORKTREE_FZF_OPTS
@@ -1397,7 +1413,7 @@ _forgit_worktree_delete() {
     opts="
         $FORGIT_FZF_DEFAULT_OPTS
         +s --multi --tiebreak=index
-        --preview=\"$FORGIT worktree_preview {}\"
+        --preview=\"$FORGIT preview worktree_preview {}\"
         --bind=\"ctrl-y:execute-silent($FORGIT worktree_yank_path {})\"
         --bind=\"alt-l:execute-silent($FORGIT worktree_toggle_lock {})+reload($FORGIT worktree_list_deletable)\"
         $FORGIT_WORKTREE_DELETE_FZF_OPTS
@@ -1551,6 +1567,7 @@ PRIVATE_COMMANDS=(
     "exec_show"
     "file_preview"
     "path_preview"
+    "preview"
     "revert_preview"
     "reset_head_preview"
     "show_enter"

tests/preview-context.test.sh

@@ -0,0 +1,68 @@
+#!/usr/bin/env bash
+
+function set_up_before_script() {
+    source bin/git-forgit
+    FORGIT="bin/git-forgit"
+
+    # Ignore global git config files
+    export GIT_CONFIG_SYSTEM=/dev/null
+    export GIT_CONFIG_GLOBAL=/dev/null
+
+    cd "$(bashunit::temp_dir)" || return 1
+    git init --quiet
+    git config user.name "Test User"
+    git config user.email "test@example.com"
+    touch tracked.txt
+    git add tracked.txt
+    git commit -m "init" --quiet
+}
+
+function test_forgit_pager_uses_preview_pager_only_in_explicit_preview_context() {
+    local without_marker with_marker
+
+    without_marker=$(
+        FORGIT_DIFF_PAGER="printf diff" \
+        FORGIT_PREVIEW_PAGER="printf preview" \
+        FZF_PREVIEW_COLUMNS=80 \
+        _forgit_pager diff
+    )
+    with_marker=$(
+        FORGIT_DIFF_PAGER="printf diff" \
+        FORGIT_PREVIEW_PAGER="printf preview" \
+        FORGIT_IN_PREVIEW=1 \
+        _forgit_pager diff
+    )
+
+    assert_same "diff" "$without_marker"
+    assert_same "preview" "$with_marker"
+}
+
+function _forgit_capture_preview_flag() {
+    printf '%s' "${FORGIT_IN_PREVIEW:-unset}"
+}
+
+function test_forgit_preview_wrapper_marks_preview_context() {
+    local actual
+
+    actual=$(_forgit_preview capture_preview_flag 2>/dev/null || true)
+
+    assert_same "1" "$actual"
+}
+
+function test_forgit_diff_preview_command_uses_preview_wrapper() {
+    bashunit::mock "fzf" 'printf "%s" "$FZF_DEFAULT_OPTS"'
+
+    local output
+    output=$(_forgit_diff)
+
+    assert_contains "--preview=\"$FORGIT preview diff_view {}" "$output"
+}
+
+function test_forgit_show_preview_command_uses_preview_wrapper() {
+    bashunit::mock "fzf" 'printf "%s" "$FZF_DEFAULT_OPTS"'
+
+    local output
+    output=$(_forgit_show HEAD)
+
+    assert_contains "--preview=\"$FORGIT preview show_preview {}" "$output"
+}