Update zsh history substring search plugin
authorJoerg Jaspert <joerg@debian.org>
Thu, 3 Nov 2016 08:34:09 +0000 (09:34 +0100)
committerJoerg Jaspert <joerg@debian.org>
Thu, 3 Nov 2016 08:34:09 +0000 (09:34 +0100)
.zsh/plugins/history-substring-search.zsh

index c977cd5..e29c9b1 100644 (file)
@@ -6,6 +6,7 @@
 # Copyright (c) 2011 Suraj N. Kurapati
 # Copyright (c) 2011 Sorin Ionescu
 # Copyright (c) 2011 Vincent Guerci
+# Copyright (c) 2016 Geza Lore
 # All rights reserved.
 #
 # Redistribution and use in source and binary forms, with or without
 HISTORY_SUBSTRING_SEARCH_HIGHLIGHT_FOUND='bg=magenta,fg=white,bold'
 HISTORY_SUBSTRING_SEARCH_HIGHLIGHT_NOT_FOUND='bg=red,fg=white,bold'
 HISTORY_SUBSTRING_SEARCH_GLOBBING_FLAGS='i'
+HISTORY_SUBSTRING_SEARCH_ENSURE_UNIQUE=''
 
 #-----------------------------------------------------------------------------
 # the main ZLE widgets
 #-----------------------------------------------------------------------------
 
-function history-substring-search-up() {
+history-substring-search-up() {
   _history-substring-search-begin
 
   _history-substring-search-up-history ||
@@ -59,7 +61,7 @@ function history-substring-search-up() {
   _history-substring-search-end
 }
 
-function history-substring-search-down() {
+history-substring-search-down() {
   _history-substring-search-begin
 
   _history-substring-search-down-history ||
@@ -72,25 +74,6 @@ function history-substring-search-down() {
 zle -N history-substring-search-up
 zle -N history-substring-search-down
 
-#-----------------------------------------------------------------------------
-# shortcut key bindings
-#-----------------------------------------------------------------------------
-
-# bind P and N for EMACS mode
-bindkey -M emacs '^P' history-substring-search-up
-bindkey -M emacs '^N' history-substring-search-down
-
-# bind k and j for VI mode
-bindkey -M vicmd 'k' history-substring-search-up
-bindkey -M vicmd 'j' history-substring-search-down
-
-# bind up and down arrow keys
-for keycode in '[' '0'; do
-  bindkey "^[${keycode}A" history-substring-search-up
-  bindkey "^[${keycode}B" history-substring-search-down
-done
-unset keycode
-
 #-----------------------------------------------------------------------------
 # implementation details
 #-----------------------------------------------------------------------------
@@ -109,7 +92,7 @@ if [[ $+functions[_zsh_highlight] -eq 0 ]]; then
   # simply removes any existing highlights when the
   # user inserts printable characters into $BUFFER.
   #
-  function _zsh_highlight() {
+  _zsh_highlight() {
     if [[ $KEYS == [[:print:]] ]]; then
       region_highlight=()
     fi
@@ -162,7 +145,7 @@ if [[ $+functions[_zsh_highlight] -eq 0 ]]; then
 
     # Override ZLE widgets to make them invoke _zsh_highlight.
     local cur_widget
-    for cur_widget in ${${(f)"$(builtin zle -la)"}:#(.*|_*|orig-*|run-help|which-command|beep)}; do
+    for cur_widget in ${${(f)"$(builtin zle -la)"}:#(.*|_*|orig-*|run-help|which-command|beep|yank*)}; do
       case $widgets[$cur_widget] in
 
         # Already rebound event: do nothing.
@@ -192,20 +175,39 @@ if [[ $+functions[_zsh_highlight] -eq 0 ]]; then
   _zsh_highlight_bind_widgets
 fi
 
-function _history-substring-search-begin() {
+_history-substring-search-begin() {
   setopt localoptions extendedglob
 
   _history_substring_search_refresh_display=
   _history_substring_search_query_highlight=
 
   #
-  # Continue using the previous $_history_substring_search_result by default,
-  # unless the current query was cleared or a new/different query was entered.
+  # If the buffer is the same as the previously displayed history substring
+  # search result, then just keep stepping through the match list. Otherwise
+  # start a new search.
+  #
+  if [[ -n $BUFFER && $BUFFER == ${_history_substring_search_result:-} ]]; then
+    return;
+  fi
+
+  #
+  # Clear the previous result.
   #
-  if [[ -z $BUFFER || $BUFFER != $_history_substring_search_result ]]; then
+  _history_substring_search_result=''
+
+  if [[ -z $BUFFER ]]; then
+    #
+    # If the buffer is empty, we will just act like up-history/down-history
+    # in ZSH, so we do not need to actually search the history. This should
+    # speed things up a little.
     #
-    # For the purpose of highlighting we will also keep
-    # a version without doubly-escaped meta characters.
+    _history_substring_search_query=
+    _history_substring_search_raw_matches=()
+
+  else
+    #
+    # For the purpose of highlighting we keep a copy of the original
+    # query string.
     #
     _history_substring_search_query=$BUFFER
 
@@ -214,58 +216,68 @@ function _history-substring-search-begin() {
     # we put an extra "\\" before meta characters such as "\(" and "\)",
     # so that they become "\\\(" and "\\\)".
     #
-    _history_substring_search_query_escaped=${BUFFER//(#m)[\][()|\\*?#<>~^]/\\$MATCH}
+    local escaped_query=${BUFFER//(#m)[\][()|\\*?#<>~^]/\\$MATCH}
 
     #
     # Find all occurrences of the search query in the history file.
     #
-    # (k) turns it an array of line numbers.
-    #
-    # (on) seems to remove duplicates, which are default
-    #      options. They can be turned off by (ON).
+    # (k) returns the "keys" (history index numbers) instead of the values
+    # (R) returns values in reverse older, so the index of the youngest
+    # matching history entry is at the head of the list.
     #
-    _history_substring_search_matches=(${(kon)history[(R)(#$HISTORY_SUBSTRING_SEARCH_GLOBBING_FLAGS)*${_history_substring_search_query_escaped}*]})
+    _history_substring_search_raw_matches=(${(k)history[(R)(#$HISTORY_SUBSTRING_SEARCH_GLOBBING_FLAGS)*${escaped_query}*]})
+  fi
 
-    #
-    # Define the range of values that $_history_substring_search_match_index
-    # can take: [0, $_history_substring_search_matches_count_plus].
-    #
-    _history_substring_search_matches_count=$#_history_substring_search_matches
-    _history_substring_search_matches_count_plus=$(( _history_substring_search_matches_count + 1 ))
-    _history_substring_search_matches_count_sans=$(( _history_substring_search_matches_count - 1 ))
+  #
+  # In order to stay as responsive as possible, we will process the raw
+  # matches lazily (when the user requests the next match) to choose items
+  # that need to be displayed to the user.
+  # _history_substring_search_raw_match_index holds the index of the last
+  # unprocessed entry in _history_substring_search_raw_matches. Any items
+  # that need to be displayed will be added to
+  # _history_substring_search_matches.
+  #
+  # We use an associative array (_history_substring_search_unique_filter) as
+  # a 'set' data structure to ensure uniqueness of the results if desired.
+  # If an entry (key) is in the set (non-empty value), then we have already
+  # added that entry to _history_substring_search_matches.
+  #
+  _history_substring_search_raw_match_index=0
+  _history_substring_search_matches=()
+  unset _history_substring_search_unique_filter
+  typeset -A -g _history_substring_search_unique_filter
 
-    #
-    # If $_history_substring_search_match_index is equal to
-    # $_history_substring_search_matches_count_plus, this indicates that we
-    # are beyond the beginning of $_history_substring_search_matches.
-    #
-    # If $_history_substring_search_match_index is equal to 0, this indicates
-    # that we are beyond the end of $_history_substring_search_matches.
-    #
-    # If we have initially pressed "up" we have to initialize
-    # $_history_substring_search_match_index to
-    # $_history_substring_search_matches_count_plus so that it will be
-    # decreased to $_history_substring_search_matches_count.
-    #
-    # If we have initially pressed "down" we have to initialize
-    # $_history_substring_search_match_index to
-    # $_history_substring_search_matches_count so that it will be increased to
-    # $_history_substring_search_matches_count_plus.
-    #
-    if [[ $WIDGET == history-substring-search-down ]]; then
-       _history_substring_search_match_index=$_history_substring_search_matches_count
-    else
-      _history_substring_search_match_index=$_history_substring_search_matches_count_plus
-    fi
+  #
+  # If $_history_substring_search_match_index is equal to
+  # $#_history_substring_search_matches + 1, this indicates that we
+  # are beyond the end of $_history_substring_search_matches and that we
+  # have also processed all entries in
+  # _history_substring_search_raw_matches.
+  #
+  # If $#_history_substring_search_match_index is equal to 0, this indicates
+  # that we are beyond the beginning of $_history_substring_search_matches.
+  #
+  # If we have initially pressed "up" we have to initialize
+  # $_history_substring_search_match_index to 0 so that it will be
+  # incremented to 1.
+  #
+  # If we have initially pressed "down" we have to initialize
+  # $_history_substring_search_match_index to 1 so that it will be
+  # decremented to 0.
+  #
+  if [[ $WIDGET == history-substring-search-down ]]; then
+     _history_substring_search_match_index=1
+  else
+    _history_substring_search_match_index=0
   fi
 }
 
-function _history-substring-search-end() {
+_history-substring-search-end() {
   setopt localoptions extendedglob
 
   _history_substring_search_result=$BUFFER
 
-  # the search was succesful so display the result properly by clearing away
+  # the search was successful so display the result properly by clearing away
   # existing highlights and moving the cursor to the end of the result buffer
   if [[ $_history_substring_search_refresh_display -eq 1 ]]; then
     region_highlight=()
@@ -280,7 +292,7 @@ function _history-substring-search-end() {
     #
     # The following expression yields a variable $MBEGIN, which
     # indicates the begin position + 1 of the first occurrence
-    # of _history_substring_search_query_escaped in $BUFFER.
+    # of _history_substring_search_query in $BUFFER.
     #
     : ${(S)BUFFER##(#m$HISTORY_SUBSTRING_SEARCH_GLOBBING_FLAGS)($_history_substring_search_query##)}
     local begin=$(( MBEGIN - 1 ))
@@ -296,7 +308,7 @@ function _history-substring-search-end() {
   return 0
 }
 
-function _history-substring-search-up-buffer() {
+_history-substring-search-up-buffer() {
   #
   # Check if the UP arrow was pressed to move the cursor within a multi-line
   # buffer. This amounts to three tests:
@@ -325,7 +337,7 @@ function _history-substring-search-up-buffer() {
   return 1
 }
 
-function _history-substring-search-down-buffer() {
+_history-substring-search-down-buffer() {
   #
   # Check if the DOWN arrow was pressed to move the cursor within a multi-line
   # buffer. This amounts to three tests:
@@ -354,7 +366,7 @@ function _history-substring-search-down-buffer() {
   return 1
 }
 
-function _history-substring-search-up-history() {
+_history-substring-search-up-history() {
   #
   # Behave like up in ZSH, except clear the $BUFFER
   # when beginning of history is reached like in Fish.
@@ -376,7 +388,7 @@ function _history-substring-search-up-history() {
   return 1
 }
 
-function _history-substring-search-down-history() {
+_history-substring-search-down-history() {
   #
   # Behave like down-history in ZSH, except clear the
   # $BUFFER when end of history is reached like in Fish.
@@ -399,180 +411,313 @@ function _history-substring-search-down-history() {
   return 1
 }
 
-function _history-substring-search-not-found() {
+_history_substring_search_process_raw_matches() {
+  #
+  # Process more outstanding raw matches and append any matches that need to
+  # be displayed to the user to _history_substring_search_matches.
+  # Return whether there were any more results appended.
+  #
+
+  #
+  # While we have more raw matches. Process them to see if there are any more
+  # matches that need to be displayed to the user.
+  #
+  while [[ $_history_substring_search_raw_match_index -lt $#_history_substring_search_raw_matches ]]; do
+    #
+    # Move on to the next raw entry and get its history index.
+    #
+    (( _history_substring_search_raw_match_index++ ))
+    local index=${_history_substring_search_raw_matches[$_history_substring_search_raw_match_index]}
+
+    #
+    # If HISTORY_SUBSTRING_SEARCH_ENSURE_UNIQUE is set to a non-empty value,
+    # then ensure that only unique matches are presented to the user.
+    # When HIST_IGNORE_ALL_DUPS is set, ZSH already ensures a unique history,
+    # so in this case we do not need to do anything.
+    #
+    if [[ ! -o HIST_IGNORE_ALL_DUPS && -n $HISTORY_SUBSTRING_SEARCH_ENSURE_UNIQUE ]]; then
+      #
+      # Get the actual history entry at the new index, and check if we have
+      # already added it to _history_substring_search_matches.
+      #
+      local entry=${history[$index]}
+
+      if [[ -z ${_history_substring_search_unique_filter[$entry]} ]]; then
+        #
+        # This is a new unique entry. Add it to the filter and append the
+        # index to _history_substring_search_matches.
+        #
+        _history_substring_search_unique_filter[$entry]=1
+        _history_substring_search_matches+=($index)
+
+        #
+        # Indicate that we did find a match.
+        #
+        return 0
+      fi
+
+    else
+      #
+      # Just append the new history index to the processed matches.
+      #
+      _history_substring_search_matches+=($index)
+
+      #
+      # Indicate that we did find a match.
+      #
+      return 0
+    fi
+
+  done
+
+  #
+  # We are beyond the end of the list of raw matches. Indicate that no
+  # more matches are available.
+  #
+  return 1
+}
+
+_history-substring-search-has-next() {
+  #
+  # Predicate function that returns whether any more older matches are
+  # available.
+  #
+
+  if  [[ $_history_substring_search_match_index -lt $#_history_substring_search_matches ]]; then
+    #
+    # We did not reach the end of the processed list, so we do have further
+    # matches.
+    #
+    return 0
+
+  else
+    #
+    # We are at the end of the processed list. Try to process further
+    # unprocessed matches. _history_substring_search_process_raw_matches
+    # returns whether any more matches were available, so just return
+    # that result.
+    #
+    _history_substring_search_process_raw_matches
+    return $?
+  fi
+}
+
+_history-substring-search-has-prev() {
+  #
+  # Predicate function that returns whether any more younger matches are
+  # available.
+  #
+
+  if [[ $_history_substring_search_match_index -gt 1 ]]; then
+    #
+    # We did not reach the beginning of the processed list, so we do have
+    # further matches.
+    #
+    return 0
+
+  else
+    #
+    # We are at the beginning of the processed list. We do not have any more
+    # matches.
+    #
+    return 1
+  fi
+}
+
+_history-substring-search-found() {
   #
-  # Nothing matched the search query, so put it back into the $BUFFER while
-  # highlighting it accordingly so the user can revise it and search again.
+  # A match is available. The index of the match is held in
+  # $_history_substring_search_match_index
+  #
+  # 1. Make $BUFFER equal to the matching history entry.
+  #
+  # 2. Use $HISTORY_SUBSTRING_SEARCH_HIGHLIGHT_FOUND
+  #    to highlight the current buffer.
+  #
+  BUFFER=$history[$_history_substring_search_matches[$_history_substring_search_match_index]]
+  _history_substring_search_query_highlight=$HISTORY_SUBSTRING_SEARCH_HIGHLIGHT_FOUND
+}
+
+_history-substring-search-not-found() {
+  #
+  # No more matches are available.
+  #
+  # 1. Make $BUFFER equal to $_history_substring_search_query so the user can
+  #    revise it and search again.
+  #
+  # 2. Use $HISTORY_SUBSTRING_SEARCH_HIGHLIGHT_NOT_FOUND
+  #    to highlight the current buffer.
   #
-  _history_substring_search_old_buffer=$BUFFER
   BUFFER=$_history_substring_search_query
   _history_substring_search_query_highlight=$HISTORY_SUBSTRING_SEARCH_HIGHLIGHT_NOT_FOUND
 }
 
-function _history-substring-search-up-search() {
+_history-substring-search-up-search() {
   _history_substring_search_refresh_display=1
 
   #
-  # Highlight matches during history-substring-up-search:
+  # Select history entry during history-substring-down-search:
   #
-  # The following constants have been initialized in
+  # The following variables have been initialized in
   # _history-substring-search-up/down-search():
   #
-  # $_history_substring_search_matches is the current list of matches
-  # $_history_substring_search_matches_count is the current number of matches
-  # $_history_substring_search_matches_count_plus is the current number of matches + 1
-  # $_history_substring_search_matches_count_sans is the current number of matches - 1
+  # $_history_substring_search_matches is the current list of matches that
+  # need to be displayed to the user.
   # $_history_substring_search_match_index is the index of the current match
+  # that is being displayed to the user.
   #
   # The range of values that $_history_substring_search_match_index can take
-  # is: [0, $_history_substring_search_matches_count_plus].  A value of 0
-  # indicates that we are beyond the end of
+  # is: [0, $#_history_substring_search_matches + 1].  A value of 0
+  # indicates that we are beyond the beginning of
   # $_history_substring_search_matches. A value of
-  # $_history_substring_search_matches_count_plus indicates that we are beyond
-  # the beginning of $_history_substring_search_matches.
+  # $#_history_substring_search_matches + 1 indicates that we are beyond
+  # the end of $_history_substring_search_matches and that we have also
+  # processed all entries in _history_substring_search_raw_matches.
+  #
+  # If $_history_substring_search_match_index equals
+  # $#_history_substring_search_matches and
+  # $_history_substring_search_raw_match_index is not greater than
+  # $#_history_substring_search_raw_matches, then we need to further process
+  # $_history_substring_search_raw_matches to see if there are any more
+  # entries that need to be displayed to the user.
   #
   # In _history-substring-search-up-search() the initial value of
-  # $_history_substring_search_match_index is
-  # $_history_substring_search_matches_count_plus.  This value is set in
-  # _history-substring-search-begin().  _history-substring-search-up-search()
-  # will initially decrease it to $_history_substring_search_matches_count.
+  # $_history_substring_search_match_index is 0. This value is set in
+  # _history-substring-search-begin(). _history-substring-search-up-search()
+  # will initially increment it to 1.
   #
-  if [[ $_history_substring_search_match_index -ge 2 ]]; then
-    #
-    # Highlight the next match:
+
+  if [[ $_history_substring_search_match_index -gt $#_history_substring_search_matches ]]; then
     #
-    # 1. Decrease the value of $_history_substring_search_match_index.
+    # We are beyond the end of $_history_substring_search_matches. This
+    # can only happen if we have also exhausted the unprocessed matches in
+    # _history_substring_search_raw_matches.
     #
-    # 2. Use $HISTORY_SUBSTRING_SEARCH_HIGHLIGHT_FOUND
-    #    to highlight the current buffer.
+    # 1. Update display to indicate search not found.
     #
-    (( _history_substring_search_match_index-- ))
-    BUFFER=$history[$_history_substring_search_matches[$_history_substring_search_match_index]]
-    _history_substring_search_query_highlight=$HISTORY_SUBSTRING_SEARCH_HIGHLIGHT_FOUND
+    _history-substring-search-not-found
+    return
+  fi
 
-  elif [[ $_history_substring_search_match_index -eq 1 ]]; then
+  if _history-substring-search-has-next; then
     #
-    # We will move beyond the end of $_history_substring_search_matches:
+    # We do have older matches.
     #
-    # 1. Decrease the value of $_history_substring_search_match_index.
+    # 1. Move index to point to the next match.
+    # 2. Update display to indicate search found.
     #
-    # 2. Save the current buffer in $_history_substring_search_old_buffer,
-    #    so that it can be retrieved by
-    #    _history-substring-search-down-search() later.
+    (( _history_substring_search_match_index++ ))
+    _history-substring-search-found
+
+  else
     #
-    # 3. Make $BUFFER equal to $_history_substring_search_query.
+    # We do not have older matches.
     #
-    # 4. Use $HISTORY_SUBSTRING_SEARCH_HIGHLIGHT_NOT_FOUND
-    #    to highlight the current buffer.
+    # 1. Move the index beyond the end of
+    #    _history_substring_search_matches.
+    # 2. Update display to indicate search not found.
     #
-    (( _history_substring_search_match_index-- ))
+    (( _history_substring_search_match_index++ ))
     _history-substring-search-not-found
+  fi
 
-  elif [[ $_history_substring_search_match_index -eq $_history_substring_search_matches_count_plus ]]; then
-    #
-    # We were beyond the beginning of $_history_substring_search_matches but
-    # UP makes us move back to $_history_substring_search_matches:
-    #
-    # 1. Decrease the value of $_history_substring_search_match_index.
-    #
-    # 2. Restore $BUFFER from $_history_substring_search_old_buffer.
-    #
-    # 3. Use $HISTORY_SUBSTRING_SEARCH_HIGHLIGHT_FOUND
-    #    to highlight the current buffer.
-    #
-    (( _history_substring_search_match_index-- ))
-    BUFFER=$_history_substring_search_old_buffer
-    _history_substring_search_query_highlight=$HISTORY_SUBSTRING_SEARCH_HIGHLIGHT_FOUND
+  #
+  # When HIST_FIND_NO_DUPS is set, meaning that only unique command lines from
+  # history should be matched, make sure the new and old results are different.
+  #
+  # However, if the HIST_IGNORE_ALL_DUPS shell option, or
+  # HISTORY_SUBSTRING_SEARCH_ENSURE_UNIQUE is set, then we already have a
+  # unique history, so in this case we do not need to do anything.
+  #
+  if [[ -o HIST_IGNORE_ALL_DUPS || -n $HISTORY_SUBSTRING_SEARCH_ENSURE_UNIQUE ]]; then
+    return
+  fi
 
-  else
+  if [[ -o HIST_FIND_NO_DUPS && $BUFFER == $_history_substring_search_result ]]; then
     #
-    # We are at the beginning of history and there are no further matches.
+    # Repeat the current search so that a different (unique) match is found.
     #
-    _history-substring-search-not-found
+    _history-substring-search-up-search
   fi
 }
 
-function _history-substring-search-down-search() {
+_history-substring-search-down-search() {
   _history_substring_search_refresh_display=1
 
   #
-  # Highlight matches during history-substring-up-search:
+  # Select history entry during history-substring-down-search:
   #
-  # The following constants have been initialized in
+  # The following variables have been initialized in
   # _history-substring-search-up/down-search():
   #
-  # $_history_substring_search_matches is the current list of matches
-  # $_history_substring_search_matches_count is the current number of matches
-  # $_history_substring_search_matches_count_plus is the current number of matches + 1
-  # $_history_substring_search_matches_count_sans is the current number of matches - 1
+  # $_history_substring_search_matches is the current list of matches that
+  # need to be displayed to the user.
   # $_history_substring_search_match_index is the index of the current match
+  # that is being displayed to the user.
   #
   # The range of values that $_history_substring_search_match_index can take
-  # is: [0, $_history_substring_search_matches_count_plus].  A value of 0
-  # indicates that we are beyond the end of
+  # is: [0, $#_history_substring_search_matches + 1].  A value of 0
+  # indicates that we are beyond the beginning of
   # $_history_substring_search_matches. A value of
-  # $_history_substring_search_matches_count_plus indicates that we are beyond
-  # the beginning of $_history_substring_search_matches.
+  # $#_history_substring_search_matches + 1 indicates that we are beyond
+  # the end of $_history_substring_search_matches and that we have also
+  # processed all entries in _history_substring_search_raw_matches.
   #
   # In _history-substring-search-down-search() the initial value of
-  # $_history_substring_search_match_index is
-  # $_history_substring_search_matches_count.  This value is set in
-  # _history-substring-search-begin().
-  # _history-substring-search-down-search() will initially increase it to
-  # $_history_substring_search_matches_count_plus.
+  # $_history_substring_search_match_index is 1. This value is set in
+  # _history-substring-search-begin(). _history-substring-search-down-search()
+  # will initially decrement it to 0.
   #
-  if [[ $_history_substring_search_match_index -le $_history_substring_search_matches_count_sans ]]; then
-    #
-    # Highlight the next match:
+
+  if [[ $_history_substring_search_match_index -lt 1 ]]; then
     #
-    # 1. Increase $_history_substring_search_match_index by 1.
+    # We are beyond the beginning of $_history_substring_search_matches.
     #
-    # 2. Use $HISTORY_SUBSTRING_SEARCH_HIGHLIGHT_FOUND
-    #    to highlight the current buffer.
+    # 1. Update display to indicate search not found.
     #
-    (( _history_substring_search_match_index++ ))
-    BUFFER=$history[$_history_substring_search_matches[$_history_substring_search_match_index]]
-    _history_substring_search_query_highlight=$HISTORY_SUBSTRING_SEARCH_HIGHLIGHT_FOUND
+    _history-substring-search-not-found
+    return
+  fi
 
-  elif [[ $_history_substring_search_match_index -eq $_history_substring_search_matches_count ]]; then
+  if _history-substring-search-has-prev; then
     #
-    # We will move beyond the beginning of $_history_substring_search_matches:
+    # We do have younger matches.
     #
-    # 1. Increase $_history_substring_search_match_index by 1.
+    # 1. Move index to point to the previous match.
+    # 2. Update display to indicate search found.
     #
-    # 2. Save the current buffer in $_history_substring_search_old_buffer, so
-    #    that it can be retrieved by _history-substring-search-up-search()
-    #    later.
+    (( _history_substring_search_match_index-- ))
+    _history-substring-search-found
+
+  else
     #
-    # 3. Make $BUFFER equal to $_history_substring_search_query.
+    # We do not have younger matches.
     #
-    # 4. Use $HISTORY_SUBSTRING_SEARCH_HIGHLIGHT_NOT_FOUND
-    #    to highlight the current buffer.
+    # 1. Move the index beyond the beginning of
+    #    _history_substring_search_matches.
+    # 2. Update display to indicate search not found.
     #
-    (( _history_substring_search_match_index++ ))
+    (( _history_substring_search_match_index-- ))
     _history-substring-search-not-found
+  fi
 
-  elif [[ $_history_substring_search_match_index -eq 0 ]]; then
-    #
-    # We were beyond the end of $_history_substring_search_matches but DOWN
-    # makes us move back to the $_history_substring_search_matches:
-    #
-    # 1. Increase $_history_substring_search_match_index by 1.
-    #
-    # 2. Restore $BUFFER from $_history_substring_search_old_buffer.
-    #
-    # 3. Use $HISTORY_SUBSTRING_SEARCH_HIGHLIGHT_FOUND
-    #    to highlight the current buffer.
-    #
-    (( _history_substring_search_match_index++ ))
-    BUFFER=$_history_substring_search_old_buffer
-    _history_substring_search_query_highlight=$HISTORY_SUBSTRING_SEARCH_HIGHLIGHT_FOUND
+  #
+  # When HIST_FIND_NO_DUPS is set, meaning that only unique command lines from
+  # history should be matched, make sure the new and old results are different.
+  #
+  # However, if the HIST_IGNORE_ALL_DUPS shell option, or
+  # HISTORY_SUBSTRING_SEARCH_ENSURE_UNIQUE is set, then we already have a
+  # unique history, so in this case we do not need to do anything.
+  #
+  if [[ -o HIST_IGNORE_ALL_DUPS || -n $HISTORY_SUBSTRING_SEARCH_ENSURE_UNIQUE ]]; then
+    return
+  fi
 
-  else
+  if [[ -o HIST_FIND_NO_DUPS && $BUFFER == $_history_substring_search_result ]]; then
     #
-    # We are at the end of history and there are no further matches.
+    # Repeat the current search so that a different (unique) match is found.
     #
-    _history-substring-search-not-found
+    _history-substring-search-down-search
   fi
 }