[Search Git Log][Search Git Status] enable integration with diff high…

…lighters

If fzf_diff_highlighter is set, fzf.fish will pipe git diff-like output through its value. This enables integration with delta, diff-so-fancy, diff-highlighter, or https://github.com/walles/riff. Resolves #202.

README.md

@@ -179,6 +179,16 @@ set fzf_git_log_format "%H %s"
 
 The format must be one line per commit and the hash must be the first field, or else Search Git Log will fail to determine which commits you selected.
 
+### Integrate with a diff highlighter
+
+To pipe the git diff previews from [Search Git Log][] and [Search Git Status][] through a highlighter tool (e.g. [delta](https://github.com/dandavison/delta) or [diff-so-fancy](https://github.com/so-fancy/diff-so-fancy)), set a command invoking the highlighter in `fzf_diff_highlighter`. It should not pipe its output to a pager:
+
+```fish
+set fzf_diff_highlighter delta --paging=never --line-numbers
+# Or, if using DFS
+set fzf_diff_highlighter diff-so-fancy
+```
+
 ### Change the date time format used by Search History
 
 [Search History][] shows the date time each command was executed. To change how its formatted, set your [strftime format string](https://devhints.io/strftime) in `fzf_history_time_format`. For example, this shows the date time as DD-MM-YY:
@@ -209,5 +219,6 @@ Find answers to these questions and more in the [project Wiki](https://github.co
 [latest release badge]: https://img.shields.io/github/v/release/patrickf1/fzf.fish
 [search directory]: #-search-directory
 [search git log]: #-search-git-log
+[search git status]: #-search-git-status
 [search history]: #-search-history
 [var scope]: https://fishshell.com/docs/current/#variable-scope

functions/_fzf_search_git_log.fish

@@ -6,13 +6,19 @@ function _fzf_search_git_log --description "Search the output of git log and pre
             # %h gives you the abbreviated commit hash, which is useful for saving screen space, but we will have to expand it later below
             set -f fzf_git_log_format '%C(bold blue)%h%C(reset) - %C(cyan)%ad%C(reset) %C(yellow)%d%C(reset) %C(normal)%s%C(reset)  %C(dim normal)[%an]%C(reset)'
         end
+
+        set -f preview_cmd 'git show --color=always --stat --patch {1}'
+        if set --query fzf_diff_highlighter
+            set preview_cmd "$preview_cmd | $fzf_diff_highlighter"
+        end
+
         set -f selected_log_lines (
             git log --no-show-signature --color=always --format=format:$fzf_git_log_format --date=short | \
             _fzf_wrapper --ansi \
                 --multi \
                 --scheme=history \
                 --prompt="Search Git Log> " \
-                --preview='git show --color=always --stat --patch {1}' \
+                --preview=$preview_cmd \
                 --query=(commandline --current-token) \
                 $fzf_git_log_opts
         )

functions/_fzf_search_git_status.fish

@@ -2,14 +2,19 @@ function _fzf_search_git_status --description "Search the output of git status.
     if not git rev-parse --git-dir >/dev/null 2>&1
         echo '_fzf_search_git_status: Not in a git repository.' >&2
     else
+        set -f preview_cmd '_fzf_preview_changed_file {}'
+        if set --query fzf_diff_highlighter
+            set preview_cmd "$preview_cmd | $fzf_diff_highlighter"
+        end
+
         set -f selected_paths (
             # Pass configuration color.status=always to force status to use colors even though output is sent to a pipe
             git -c color.status=always status --short |
             _fzf_wrapper --ansi \
                 --multi \
                 --prompt="Search Git Status> " \
                 --query=(commandline --current-token) \
-                --preview='_fzf_preview_changed_file {}' \
+                --preview=$preview_cmd \
                 --nth="2.." \
                 $fzf_git_status_opts
         )