Resolve tilde expansions in command word.

This causes '~/bin/foo' to highlight as a command, rather than as a file.

Part of issue #201.

highlighters/main/main-highlighter.zsh

@@ -157,7 +157,9 @@ _zsh_highlight_main_highlighter()
       style=$ZSH_HIGHLIGHT_STYLES[precommand]
       sudo=true
      else
-      local res="$(LC_ALL=C builtin type -w ${(Q)arg} 2>/dev/null)"
+      _zsh_highlight_main_highlighter_expand_path $arg
+      local expanded_arg="$REPLY"
+      local res="$(LC_ALL=C builtin type -w ${expanded_arg} 2>/dev/null)"
       case $res in
         *': reserved')  style=$ZSH_HIGHLIGHT_STYLES[reserved-word];;
         *': suffix alias')
@@ -264,8 +266,9 @@ _zsh_highlight_main_highlighter_check_assign()
 # Check if $arg is a path.
 _zsh_highlight_main_highlighter_check_path()
 {
-  setopt localoptions nonomatch
+  _zsh_highlight_main_highlighter_expand_path $arg;
-  local expanded_path; : ${expanded_path:=${(Q)~arg}}
+  local expanded_path="$REPLY"
+
   [[ -z $expanded_path ]] && return 1
   [[ -e $expanded_path ]] && return 0
   # Search the path in CDPATH
@@ -360,3 +363,17 @@ _zsh_highlight_main_highlighter_highlight_dollar_string()
     _zsh_highlight_main_add_region_highlight $j $k $style
   done
 }
+
+# Called with a single positional argument.
+# Perform filename expansion (tilde expansion) on the argument and set $REPLY to the expanded value.
+#
+# Does not perform filename generation (globbing).
+_zsh_highlight_main_highlighter_expand_path()
+{
+  (( $# == 1 )) || echo "zsh-syntax-highlighting: BUG: _zsh_highlight_main_highlighter_expand_path: called without argument" >&2
+
+  # The $~1 syntax normally performs filename generation, but not when it's on the right-hand side of ${x:=y}.
+  setopt localoptions nonomatch
+  unset REPLY
+  : ${REPLY:=${(Q)~1}}
+}

highlighters/main/test-data/tilde-command-word.zsh

@@ -0,0 +1,38 @@
+#!/usr/bin/env zsh
+# -------------------------------------------------------------------------------------------------
+# Copyright (c) 2015 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
+# -------------------------------------------------------------------------------------------------
+
+hash -d D=/usr/bin
+
+BUFFER='~D/env foo'
+
+expected_region_highlight=(
+  "1 6  $ZSH_HIGHLIGHT_STYLES[command]" # ~D/env [= /usr/bin/env]
+  "8 10 $ZSH_HIGHLIGHT_STYLES[default]" # foo
+)