driver: Be immune to weird aliases in the calling scope.

Fixes #390.

zsh-syntax-highlighting.zsh

@@ -27,6 +27,9 @@
 # vim: ft=zsh sw=2 ts=2 et
 # -------------------------------------------------------------------------------------------------
 
+# First of all, ensure predictable parsing.
+zsh_highlight__aliases=`alias -L`
+builtin unalias -m '*'
 
 # Set $0 to the expected value, regardless of functionargzero.
 0=${(%):-%N}
@@ -390,4 +393,11 @@ 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) || true
+[[ $#ZSH_HIGHLIGHT_HIGHLIGHTERS -eq 0 ]] && ZSH_HIGHLIGHT_HIGHLIGHTERS=(main)
+
+# Restore the aliases we unned
+eval "$zsh_highlight__aliases"
+builtin unset zsh_highlight__aliases
+
+# Set $?.
+true