workaround for PAT_STATIC bug in zsh

ZSH versions less than 5.3.2 (or 5.4) have a bug that prevents
`history-incremental-pattern-search-backward` for working
correctly (the history stops searching after the first found item).

Closes #407

zsh-syntax-highlighting.zsh

@@ -53,6 +53,15 @@ fi
 # Core highlighting update system
 # -------------------------------------------------------------------------------------------------
 
+# Use workaround for bug in ZSH?
+# zsh-users/zsh@48cadf4 http://www.zsh.org/mla/workers//2017/msg00034.html
+autoload -U is-at-least
+if is-at-least 5.3.2; then
+  zsh_highlight__pat_static_bug=false
+else
+  zsh_highlight__pat_static_bug=true
+fi
+
 # Array declaring active highlighters names.
 typeset -ga ZSH_HIGHLIGHT_HIGHLIGHTERS
 
@@ -67,7 +76,9 @@ _zsh_highlight()
 
   # Remove all highlighting in isearch, so that only the underlining done by zsh itself remains.
   # For details see FAQ entry 'Why does syntax highlighting not work while searching history?'.
-  if [[ $WIDGET == zle-isearch-update ]] && ! (( $+ISEARCHMATCH_ACTIVE )); then
+  # This disables highlighting during isearch (for reasons explained in README.md) unless zsh is new enough
+  # and doesn't have the 5.3.1 bug
+  if [[ $WIDGET == zle-isearch-update ]] && { $zsh_highlight__pat_static_bug || ! (( $+ISEARCHMATCH_ACTIVE )) }; then
     region_highlight=()
     return $ret
   fi
@@ -394,8 +405,6 @@ add-zsh-hook preexec _zsh_highlight_preexec_hook 2>/dev/null || {
 # Load zsh/parameter module if available
 zmodload zsh/parameter 2>/dev/null || true
 
-autoload -U is-at-least
-
 # Initialize the array of active highlighters if needed.
 [[ $#ZSH_HIGHLIGHT_HIGHLIGHTERS -eq 0 ]] && ZSH_HIGHLIGHT_HIGHLIGHTERS=(main)