[Search History] slightly improve performance, add test and comments

Author: PatrickF1

functions/_fzf_search_history.fish

@@ -10,6 +10,10 @@ function _fzf_search_history --description "Search command history. Replace the
         set -f fzf_history_time_format "%m-%d %H:%M:%S"
     end
 
+    # Delinate time from command in history entries using the vertical box drawing char (U+2502).
+    # Then, to get raw command from history entries, delete everything up to it. The ? on regex is
+    # necessary to make regex non-greedy so it won't match into commands containing the char.
+    set -f time_prefix_regex '^.*? │ '
     # Delinate commands throughout pipeline using null rather than newlines because commands can be multi-line
     set -f commands_selected (
         builtin history --null --show-time="$fzf_history_time_format │ " |
@@ -19,12 +23,12 @@ function _fzf_search_history --description "Search command history. Replace the
             --scheme=history \
             --prompt="Search History> " \
             --query=(commandline) \
-            --preview="echo -- {} | string replace --regex '^.*? │ ' '' | fish_indent --ansi" \
+            --preview="string replace --regex $time_prefix_regex '' {} | fish_indent --ansi" \
             --preview-window="bottom:3:wrap" \
             $fzf_history_opts |
         string split0 |
         # remove timestamps from commands selected
-        string replace --regex '^.*? │ ' ''
+        string replace --regex $time_prefix_regex ''
     )
 
     if test $status -eq 0

tests/search_history/cmd_with_box_char.fish

@@ -0,0 +1,14 @@
+set fish_history test
+set history_file_path ~/.local/share/fish/test_history
+printf "%s" "- cmd: echo 'lots of │ chars
+  when: 1612201487" >$history_file_path
+
+mock commandline "--replace --" "echo \$argv"
+mock commandline \* ""
+set --export --append FZF_DEFAULT_OPTS --select-1
+
+set actual (_fzf_search_history)
+set expected "echo 'lots of │ chars"
+@test "doesn't erase commands containing box drawing char delineator" "$actual" = "$expected"
+
+rm $history_file_path

tests/search_history/multi_line_cmd.fish

@@ -1,4 +1,5 @@
 # force history to read from a file with pre-populated history
+# https://fishshell.com/docs/current/cmds/history.html#customizing-the-name-of-the-history-file
 set fish_history test
 set history_file_path ~/.local/share/fish/test_history
 printf "%s" "- cmd: z fzf