main: Allow for "]" in shell aliases

PR #776 fixed an issue with complex aliases and expansion. However, this change
also introduced a problem with aliases which contain `]` (for example, commonly
seen on macOS: `alias ]=open`), due to using an associative array `seen_alias`,
indexed by the alias name. Due to `"$seen_alias[$arg]"`, it would fail when
`$arg` is expanded to anything containing `]`'. Thus, typing `] /` would result
in:

```
> ] /
(anon):unset:3: seen_alias[]]: invalid parameter name
```

This change fixes the issue by ensuring we properly access keys in the
associative array `seen_alias`.

Author: knl

highlighters/main/main-highlighter.zsh

@@ -604,7 +604,7 @@ _zsh_highlight_main_highlighter_highlight_list()
       (){
         local alias_name
         for alias_name in ${(k)seen_alias[(R)<$#in_alias->]}; do
-          unset "seen_alias[$alias_name]"
+          unset "seen_alias[${(q)alias_name}]"
         done
       }
       if (( $#in_alias == 0 )); then
@@ -697,15 +697,15 @@ _zsh_highlight_main_highlighter_highlight_list()
     if [[ $this_word == *':start:'* ]] && ! (( in_redirection )); then
       # Expand aliases.
       # An alias is ineligible for expansion while it's being expanded (see #652/#653).
-      _zsh_highlight_main__type "$arg" "$(( ! ${+seen_alias[$arg]} ))"
+      _zsh_highlight_main__type "$arg" "$(( ! ${+seen_alias[${(q)arg}]} ))"
       local res="$REPLY"
       if [[ $res == "alias" ]]; then
         # Mark insane aliases as unknown-token (cf. #263).
         if [[ $arg == ?*=* ]]; then
           _zsh_highlight_main_add_region_highlight $start_pos $end_pos unknown-token
           continue
         fi
-        seen_alias[$arg]=$#in_alias
+        seen_alias+=(${(q)arg} $#in_alias)
         _zsh_highlight_main__resolve_alias $arg
         local -a alias_args
         # Elision is desired in case alias x=''
@@ -890,7 +890,7 @@ _zsh_highlight_main_highlighter_highlight_list()
         (){
           local alias_name
           for alias_name in ${(k)seen_alias[(R)<$#in_alias->]}; do
-            unset "seen_alias[$alias_name]"
+            unset "seen_alias[${(q)alias_name}]"
           done
         }
         if [[ $arg != '|' && $arg != '|&' ]]; then

highlighters/main/test-data/alias-brackets.zsh

@@ -0,0 +1,38 @@
+#!/usr/bin/env zsh
+# -------------------------------------------------------------------------------------------------
+# Copyright (c) 2021 zsh-syntax-highlighting contributors
+# All rights reserved.
+#
+# Redistribution and use in source and binary forms, with or without modification, are permitted
+# provided that the following conditions are met:
+#
+#  * Redistributions of source code must retain the above copyright notice, this list of conditions
+#    and the following disclaimer.
+#  * Redistributions in binary form must reproduce the above copyright notice, this list of
+#    conditions and the following disclaimer in the documentation and/or other materials provided
+#    with the distribution.
+#  * Neither the name of the zsh-syntax-highlighting contributors nor the names of its contributors
+#    may be used to endorse or promote products derived from this software without specific prior
+#    written permission.
+#
+# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR
+# IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
+# FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR
+# CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+# DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+# DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER
+# IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
+# OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+# -------------------------------------------------------------------------------------------------
+# -*- mode: zsh; sh-indentation: 2; indent-tabs-mode: nil; sh-basic-offset: 2; -*-
+# vim: ft=zsh sw=2 ts=2 et
+# -------------------------------------------------------------------------------------------------
+
+alias ]=open
+
+BUFFER=$'] /'
+
+expected_region_highlight=(
+  '1 1 alias' # ]
+  '3 3 path' # /
+)