'main': Support parameter elision in command position.

highlighters/main/main-highlighter.zsh

@@ -656,6 +656,7 @@ _zsh_highlight_main_highlighter_highlight_list()
       local MATCH; integer MBEGIN MEND
       local parameter_name
       local -a words
+      integer elision_is_happening
       if [[ $arg[1] == '$' ]] && [[ ${arg[2]} == '{' ]] && [[ ${arg[-1]} == '}' ]]; then
         parameter_name=${${arg:2}%?}
       elif [[ $arg[1] == '$' ]]; then
@@ -663,24 +664,37 @@ _zsh_highlight_main_highlighter_highlight_list()
       fi
       if [[ $res == none ]] && zmodload -e zsh/parameter &&
          [[ ${parameter_name} =~ ^${~parameter_name_pattern}$ ]] &&
-         (( ${+parameters[(e)${MATCH}]} )) && [[ ${parameters[(e)$MATCH]} != *special* ]]
+         [[ ${parameters[(e)$MATCH]} != *special* ]]
          then
         # Set $arg and update $res.
         case ${(tP)MATCH} in
           (*array*|*assoc*)
             words=( ${(P)MATCH} )
+            elision_is_happening=$(( $#words == 0 ))
+            ;;
+          ("")
+            # not set
+            words=( )
+            elision_is_happening=1
             ;;
           (*)
             # scalar, presumably
             words=( ${(P)MATCH} )
+            elision_is_happening=$(( $#words == 0 ))
             ;;
         esac
+        if (( elision_is_happening )); then
+          (( ++in_redirection ))
+          _zsh_highlight_main_add_region_highlight $start_pos $end_pos comment
+          continue
+        else
           (( in_param = 1 + $#words ))
           args=( $words $args )
           arg=$args[1]
           _zsh_highlight_main__type "$arg" 0
           res=$REPLY
         fi
+      fi
     }
 
     # Parse the sudo command line

highlighters/main/test-data/parameter-elision-command-word.zsh

@@ -0,0 +1,36 @@
+#!/usr/bin/env zsh
+# -------------------------------------------------------------------------------------------------
+# Copyright (c) 2020 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
+# -------------------------------------------------------------------------------------------------
+
+BUFFER='$x ls'
+
+expected_region_highlight=(
+  '1 2 comment' # $x
+  '4 5 command' # ls
+)