Merge pull request #55 from gezalore/ensure_unique

README.md

@@ -110,13 +110,19 @@ default values only after having loaded this script into your ZSH session.
   Flags" section in the zshexpn(1) man page to learn about the kinds of
   values you may assign to this variable.
 
-To always receive _unique_ search results, use `setopt HIST_IGNORE_ALL_DUPS`.
+* HISTORY_SUBSTRING_SEARCH_ENSURE_UNIQUE is a global variable that defines
-Alternatively, use `setopt HIST_FIND_NO_DUPS` which makes this plugin skip
+  whether all search results returned are _unique_. If set to a non-empty
-duplicate _adjacent_ search results as you cycle through them---however, this
+  value, then only unique search results are presented. This behaviour is off
-does not guarantee that search results are unique: if your search results were
+  by default. An alternative way to ensure that search results are unique is
-"Dog", "Dog", "HotDog", "Dog", then cycling them gives "Dog", "HotDog", "Dog".
+  to use `setopt HIST_IGNORE_ALL_DUPS`. If this configuration variable is off
-Notice that the "Dog" search result appeared twice as you cycled through them!
+  and `setopt HIST_IGNORE_ALL_DUPS` is unset, then `setopt HIST_FIND_NO_DUPS`
-If you wish to avoid this limitation, then use `setopt HIST_IGNORE_ALL_DUPS`.
+  is still respected and it makes this plugin skip duplicate _adjacent_ search
+  results as you cycle through them, but this does not guarantee that search
+  results are unique: if your search results were "Dog", "Dog", "HotDog",
+  "Dog", then cycling them gives "Dog", "HotDog", "Dog". Notice that the "Dog"
+  search result appeared twice as you cycled through them. If you wish to
+  receive globally unique search results only once, then use this
+  configuration variable, or use `setopt HIST_IGNORE_ALL_DUPS`.
 
 ------------------------------------------------------------------------------
 History

zsh-history-substring-search.zsh

@@ -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
@@ -44,6 +45,7 @@
 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
@@ -180,13 +182,32 @@ _history-substring-search-begin() {
   _history_substring_search_query_highlight=
 
   #
-  # Continue using the previous $_history_substring_search_result by default,
+  # If the buffer is the same as the previously displayed history substring
-  # unless the current query was cleared or a new/different query was entered.
+  # search result, then just keep stepping through the match list. Otherwise
+  # start a new search.
   #
-  if [[ -z $BUFFER || $BUFFER != $_history_substring_search_result ]]; then
+  if [[ -n $BUFFER && $BUFFER == $_history_substring_search_result ]]; then
+    return;
+  fi
+
+  #
+  # Clear the previous result.
+  #
+  _history_substring_search_result=''
+
+  if [[ -z $BUFFER ]]; then
     #
-    # For the purpose of highlighting we will also keep
+    # If the buffer is empty, we will just act like up-history/down-history
-    # a version without doubly-escaped meta characters.
+    # in ZSH, so we do not need to actually search the history. This should
+    # speed things up a little.
+    #
+    _history_substring_search_query=
+    _history_substring_search_raw_matches=()
+
+  else
+    #
+    # For the purpose of highlighting we keep a copy of the original
+    # query string.
     #
     _history_substring_search_query=$BUFFER
 
@@ -195,47 +216,59 @@ _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) returns the "keys" (history index numbers) instead of the values
-    # (Oa) reverses the order, because (R) returns results reversed.
+    # (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=(${(kOa)history[(R)(#$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
+  # In order to stay as responsive as possible, we will process the raw
-    # can take: [0, $_history_substring_search_matches_count_plus].
+  # matches lazily (when the user requests the next match) to choose items
-    #
+  # that need to be displayed to the user.
-    _history_substring_search_matches_count=$#_history_substring_search_matches
+  # _history_substring_search_raw_match_index holds the index of the last
-    _history_substring_search_matches_count_plus=$(( _history_substring_search_matches_count + 1 ))
+  # unprocessed entry in _history_substring_search_raw_matches. Any items
-    _history_substring_search_matches_count_sans=$(( _history_substring_search_matches_count - 1 ))
+  # 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
+  # If $_history_substring_search_match_index is equal to
-    # $_history_substring_search_matches_count_plus, this indicates that we
+  # $#_history_substring_search_matches + 1, this indicates that we
-    # are beyond the beginning of $_history_substring_search_matches.
+  # are beyond the end of $_history_substring_search_matches and that we
-    #
+  # have also processed all entries in
-    # If $_history_substring_search_match_index is equal to 0, this indicates
+  # _history_substring_search_raw_matches.
-    # that we are beyond the end of $_history_substring_search_matches.
+  #
-    #
+  # If $#_history_substring_search_match_index is equal to 0, this indicates
-    # If we have initially pressed "up" we have to initialize
+  # that we are beyond the beginning of $_history_substring_search_matches.
-    # $_history_substring_search_match_index to
+  #
-    # $_history_substring_search_matches_count_plus so that it will be
+  # If we have initially pressed "up" we have to initialize
-    # decreased to $_history_substring_search_matches_count.
+  # $_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
+  # If we have initially pressed "down" we have to initialize
-    # $_history_substring_search_matches_count so that it will be increased to
+  # $_history_substring_search_match_index to 1 so that it will be
-    # $_history_substring_search_matches_count_plus.
+  # decremented to 0.
-    #
+  #
-    if [[ $WIDGET == history-substring-search-down ]]; then
+  if [[ $WIDGET == history-substring-search-down ]]; then
-       _history_substring_search_match_index=$_history_substring_search_matches_count
+     _history_substring_search_match_index=1
-    else
+  else
-      _history_substring_search_match_index=$_history_substring_search_matches_count_plus
+    _history_substring_search_match_index=0
-    fi
   fi
 }
 
@@ -244,7 +277,7 @@ _history-substring-search-end() {
 
   _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=()
@@ -259,7 +292,7 @@ _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 ))
@@ -378,12 +411,143 @@ _history-substring-search-down-history() {
   return 1
 }
 
+_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() {
+  #
+  # 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() {
   #
-  # Nothing matched the search query, so put it back into the $BUFFER while
+  # No more matches are available.
-  # highlighting it accordingly so the user can revise it and search again.
+  #
+  # 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
 }
@@ -392,91 +556,84 @@ _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 is the current list of matches that
-  # $_history_substring_search_matches_count is the current number of matches
+  # need to be displayed to the user.
-  # $_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_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
+  # is: [0, $#_history_substring_search_matches + 1].  A value of 0
-  # indicates that we are beyond the end of
+  # 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
+  # $#_history_substring_search_matches + 1 indicates that we are beyond
-  # the beginning of $_history_substring_search_matches.
+  # 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_match_index is 0. This value is set in
-  # $_history_substring_search_matches_count_plus.  This value is set in
+  # _history-substring-search-begin(). _history-substring-search-up-search()
-  # _history-substring-search-begin().  _history-substring-search-up-search()
+  # will initially increment it to 1.
-  # will initially decrease it to $_history_substring_search_matches_count.
   #
-  if [[ $_history_substring_search_match_index -ge 2 ]]; then
-    #
-    # Highlight the next match:
-    #
-    # 1. Decrease the value of $_history_substring_search_match_index.
-    #
-    # 2. Use $HISTORY_SUBSTRING_SEARCH_HIGHLIGHT_FOUND
-    #    to highlight the current buffer.
-    #
-    (( _history_substring_search_match_index-- ))
-    BUFFER=$history[$_history_substring_search_matches[$_history_substring_search_match_index]]
-    _history_substring_search_query_highlight=$HISTORY_SUBSTRING_SEARCH_HIGHLIGHT_FOUND
 
-  elif [[ $_history_substring_search_match_index -eq 1 ]]; then
+  if [[ $_history_substring_search_match_index -gt $#_history_substring_search_matches ]]; then
     #
-    # We will move beyond the end of $_history_substring_search_matches:
+    # 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.
     #
-    # 1. Decrease the value of $_history_substring_search_match_index.
+    # 1. Update display to indicate search not 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.
-    #
-    # 3. Make $BUFFER equal to $_history_substring_search_query.
-    #
-    # 4. Use $HISTORY_SUBSTRING_SEARCH_HIGHLIGHT_NOT_FOUND
-    #    to highlight the current buffer.
-    #
-    (( _history_substring_search_match_index-- ))
-    _history-substring-search-not-found
-
-  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
-
-  else
-    #
-    # We are at the beginning of history and there are no further matches.
     #
     _history-substring-search-not-found
     return
   fi
 
+  if _history-substring-search-has-next; then
+    #
+    # We do have older matches.
+    #
+    # 1. Move index to point to the next match.
+    # 2. Update display to indicate search found.
+    #
+    (( _history_substring_search_match_index++ ))
+    _history-substring-search-found
+
+  else
+    #
+    # We do not have older matches.
+    #
+    # 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-not-found
+  fi
+
   #
   # 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.
-  # But when HIST_IGNORE_ALL_DUPS is set, ZSH already ensures a unique history.
   #
-  if [[ ! -o HIST_IGNORE_ALL_DUPS && -o HIST_FIND_NO_DUPS && $BUFFER == $_history_substring_search_result ]]; then
+  # 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
+
+  if [[ -o HIST_FIND_NO_DUPS && $BUFFER == $_history_substring_search_result ]]; then
     #
     # Repeat the current search so that a different (unique) match is found.
     #
@@ -488,92 +645,75 @@ _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 is the current list of matches that
-  # $_history_substring_search_matches_count is the current number of matches
+  # need to be displayed to the user.
-  # $_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_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
+  # is: [0, $#_history_substring_search_matches + 1].  A value of 0
-  # indicates that we are beyond the end of
+  # 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
+  # $#_history_substring_search_matches + 1 indicates that we are beyond
-  # the beginning of $_history_substring_search_matches.
+  # 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_match_index is 1. This value is set in
-  # $_history_substring_search_matches_count.  This value is set in
+  # _history-substring-search-begin(). _history-substring-search-down-search()
-  # _history-substring-search-begin().
+  # will initially decrement it to 0.
-  # _history-substring-search-down-search() will initially increase it to
-  # $_history_substring_search_matches_count_plus.
   #
-  if [[ $_history_substring_search_match_index -le $_history_substring_search_matches_count_sans ]]; then
-    #
-    # Highlight the next match:
-    #
-    # 1. Increase $_history_substring_search_match_index by 1.
-    #
-    # 2. Use $HISTORY_SUBSTRING_SEARCH_HIGHLIGHT_FOUND
-    #    to highlight the current buffer.
-    #
-    (( _history_substring_search_match_index++ ))
-    BUFFER=$history[$_history_substring_search_matches[$_history_substring_search_match_index]]
-    _history_substring_search_query_highlight=$HISTORY_SUBSTRING_SEARCH_HIGHLIGHT_FOUND
 
-  elif [[ $_history_substring_search_match_index -eq $_history_substring_search_matches_count ]]; then
+  if [[ $_history_substring_search_match_index -lt 1 ]]; then
     #
-    # We will move beyond the beginning of $_history_substring_search_matches:
+    # We are beyond the beginning of $_history_substring_search_matches.
     #
-    # 1. Increase $_history_substring_search_match_index by 1.
+    # 1. Update display to indicate search not 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.
-    #
-    # 3. Make $BUFFER equal to $_history_substring_search_query.
-    #
-    # 4. Use $HISTORY_SUBSTRING_SEARCH_HIGHLIGHT_NOT_FOUND
-    #    to highlight the current buffer.
-    #
-    (( _history_substring_search_match_index++ ))
-    _history-substring-search-not-found
-
-  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
-
-  else
-    #
-    # We are at the end of history and there are no further matches.
     #
     _history-substring-search-not-found
     return
   fi
 
+  if _history-substring-search-has-prev; then
+    #
+    # We do have younger matches.
+    #
+    # 1. Move index to point to the previous match.
+    # 2. Update display to indicate search found.
+    #
+    (( _history_substring_search_match_index-- ))
+    _history-substring-search-found
+
+  else
+    #
+    # We do not have younger matches.
+    #
+    # 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-not-found
+  fi
+
   #
   # 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.
-  # But when HIST_IGNORE_ALL_DUPS is set, ZSH already ensures a unique history.
   #
-  if [[ ! -o HIST_IGNORE_ALL_DUPS && -o HIST_FIND_NO_DUPS && $BUFFER == $_history_substring_search_result ]]; then
+  # 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
+
+  if [[ -o HIST_FIND_NO_DUPS && $BUFFER == $_history_substring_search_result ]]; then
     #
     # Repeat the current search so that a different (unique) match is found.
     #