zsh-syntax-highlighting/highlighters/main/main-highlighter.zsh

# -------------------------------------------------------------------------------------------------
# Copyright (c) 2010-2016 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
# -------------------------------------------------------------------------------------------------


# Define default styles.
: ${ZSH_HIGHLIGHT_STYLES[default]:=none}
: ${ZSH_HIGHLIGHT_STYLES[unknown-token]:=fg=red,bold}
: ${ZSH_HIGHLIGHT_STYLES[reserved-word]:=fg=yellow}
: ${ZSH_HIGHLIGHT_STYLES[alias]:=fg=green}
: ${ZSH_HIGHLIGHT_STYLES[suffix-alias]:=fg=green,underline}
: ${ZSH_HIGHLIGHT_STYLES[builtin]:=fg=green}
: ${ZSH_HIGHLIGHT_STYLES[function]:=fg=green}
: ${ZSH_HIGHLIGHT_STYLES[command]:=fg=green}
: ${ZSH_HIGHLIGHT_STYLES[precommand]:=fg=green,underline}
: ${ZSH_HIGHLIGHT_STYLES[commandseparator]:=none}
: ${ZSH_HIGHLIGHT_STYLES[hashed-command]:=fg=green}
: ${ZSH_HIGHLIGHT_STYLES[path]:=underline}
: ${ZSH_HIGHLIGHT_STYLES[path_prefix]:=underline}
: ${ZSH_HIGHLIGHT_STYLES[globbing]:=fg=blue}
: ${ZSH_HIGHLIGHT_STYLES[history-expansion]:=fg=blue}
: ${ZSH_HIGHLIGHT_STYLES[single-hyphen-option]:=none}
: ${ZSH_HIGHLIGHT_STYLES[double-hyphen-option]:=none}
: ${ZSH_HIGHLIGHT_STYLES[back-quoted-argument]:=none}
: ${ZSH_HIGHLIGHT_STYLES[single-quoted-argument]:=fg=yellow}
: ${ZSH_HIGHLIGHT_STYLES[double-quoted-argument]:=fg=yellow}
: ${ZSH_HIGHLIGHT_STYLES[dollar-quoted-argument]:=fg=yellow}
: ${ZSH_HIGHLIGHT_STYLES[dollar-double-quoted-argument]:=fg=cyan}
: ${ZSH_HIGHLIGHT_STYLES[back-double-quoted-argument]:=fg=cyan}
: ${ZSH_HIGHLIGHT_STYLES[back-dollar-quoted-argument]:=fg=cyan}
: ${ZSH_HIGHLIGHT_STYLES[assign]:=none}
: ${ZSH_HIGHLIGHT_STYLES[redirection]:=none}
: ${ZSH_HIGHLIGHT_STYLES[comment]:=fg=black,bold}

# Whether the highlighter should be called or not.
_zsh_highlight_main_highlighter_predicate()
{
  # accept-* may trigger removal of path_prefix highlighting
  [[ $WIDGET == accept-* ]] ||
    _zsh_highlight_buffer_modified
}

# Helper to deal with tokens crossing line boundaries.
_zsh_highlight_main_add_region_highlight() {
  integer start=$1 end=$2
  shift 2

  # The calculation was relative to $PREBUFFER$BUFFER, but region_highlight is
  # relative to $BUFFER.
  (( start -= $#PREBUFFER ))
  (( end -= $#PREBUFFER ))

  (( end < 0 )) && return # having end<0 would be a bug
  (( start < 0 )) && start=0 # having start<0 is normal with e.g. multiline strings
  _zsh_highlight_add_highlight $start $end "$@"
}

# Get the type of a command.
#
# Uses the zsh/parameter module if available to avoid forks, and a
# wrapper around 'type -w' as fallback.
#
# Takes a single argument.
#
# The result will be stored in REPLY.
_zsh_highlight_main__type() {
  if (( $+_zsh_highlight_main__command_type_cache )); then
    REPLY=$_zsh_highlight_main__command_type_cache[(e)$1]
    if [[ -n "$REPLY" ]]; then
      return
    fi
  fi
  if (( $#options_to_set )); then
    setopt localoptions $options_to_set;
  fi
  unset REPLY
  if zmodload -e zsh/parameter; then
    if (( $+aliases[(e)$1] )); then
      REPLY=alias
    elif (( $+saliases[(e)${1##*.}] )); then
      REPLY='suffix alias'
    elif (( $reswords[(Ie)$1] )); then
      REPLY=reserved
    elif (( $+functions[(e)$1] )); then
      REPLY=function
    elif (( $+builtins[(e)$1] )); then
      REPLY=builtin
    elif (( $+commands[(e)$1] )); then
      REPLY=command
    elif ! builtin type -w -- $1 >/dev/null 2>&1; then
      REPLY=none
    fi
  fi
  if ! (( $+REPLY )); then
    REPLY="${$(LC_ALL=C builtin type -w -- $1 2>/dev/null)#*: }"
  fi
  if (( $+_zsh_highlight_main__command_type_cache )); then
    _zsh_highlight_main__command_type_cache[(e)$1]=$REPLY
  fi
}

# Check whether the first argument is a redirection operator token.
# Report result via the exit code.
_zsh_highlight_main__is_redirection() {
  # A redirection operator token:
  # - starts with an optional single-digit number;
  # - then, has a '<' or '>' character;
  # - is not a process substitution [<(...) or >(...)].
  [[ $1 == (<0-9>|)(\<|\>)* ]] && [[ $1 != (\<|\>)$'\x28'* ]]
}

# Resolve alias.
#
# Takes a single argument.
#
# The result will be stored in REPLY.
_zsh_highlight_main__resolve_alias() {
  if zmodload -e zsh/parameter; then
    REPLY=${aliases[$arg]}
  else
    REPLY="${"$(alias -- $arg)"#*=}"
  fi
}

# Main syntax highlighting function.
_zsh_highlight_main_highlighter()
{
  ## Before we even 'emulate -L', we must test a few options that would reset.
  if [[ -o interactive_comments ]]; then
    local interactive_comments= # set to empty
  fi
  if [[ -o path_dirs ]]; then
    integer path_dirs_was_set=1
  else
    integer path_dirs_was_set=0
  fi
  emulate -L zsh
  setopt localoptions extendedglob bareglobqual

  # At the PS3 prompt and in vared, highlight nothing.
  #
  # (We can't check this in _zsh_highlight_main_highlighter_predicate because
  # if the predicate returns false, the previous value of region_highlight
  # would be reused.)
  if [[ $CONTEXT == (select|vared) ]]; then
    return
  fi

  ## Variable declarations and initializations
  local start_pos=0 end_pos highlight_glob=true arg style
  local in_array_assignment=false # true between 'a=(' and the matching ')'
  typeset -a ZSH_HIGHLIGHT_TOKENS_COMMANDSEPARATOR
  typeset -a ZSH_HIGHLIGHT_TOKENS_PRECOMMANDS
  typeset -a ZSH_HIGHLIGHT_TOKENS_CONTROL_FLOW
  local -a options_to_set # used in callees
  local buf="$PREBUFFER$BUFFER"
  integer len="${#buf}"

  if (( path_dirs_was_set )); then
    options_to_set+=( PATH_DIRS )
  fi
  unset path_dirs_was_set

  ZSH_HIGHLIGHT_TOKENS_COMMANDSEPARATOR=(
    '|' '||' ';' '&' '&&'
    '|&'
    '&!' '&|'
    # ### 'case' syntax, but followed by a pattern, not by a command
    # ';;' ';&' ';|'
  )
  ZSH_HIGHLIGHT_TOKENS_PRECOMMANDS=(
    'builtin' 'command' 'exec' 'nocorrect' 'noglob'
    'pkexec' # immune to #121 because it's usually not passed --option flags
  )

  # Tokens that, at (naively-determined) "command position", are followed by
  # a de jure command position.  All of these are reserved words.
  ZSH_HIGHLIGHT_TOKENS_CONTROL_FLOW=(
    $'\x7b' # block
    $'\x28' # subshell
    '()' # anonymous function
    'while'
    'until'
    'if'
    'then'
    'elif'
    'else'
    'do'
    'time'
    'coproc'
    '!' # reserved word; unrelated to $histchars[1]
  )

  # State machine
  #
  # The states are:
  # - :start:      Command word
  # - :sudo_opt:   A leading-dash option to sudo (such as "-u" or "-i")
  # - :sudo_arg:   The argument to a sudo leading-dash option that takes one,
  #                when given as a separate word; i.e., "foo" in "-u foo" (two
  #                words) but not in "-ufoo" (one word).
  # - :regular:    "Not a command word", and command delimiters are permitted.
  #                Mainly used to detect premature termination of commands.
  #
  # When the kind of a word is not yet known, $this_word / $next_word may contain
  # multiple states.  For example, after "sudo -i", the next word may be either
  # another --flag or a command name, hence the state would include both :start:
  # and :sudo_opt:.
  #
  # The tokens are always added with both leading and trailing colons to serve as
  # word delimiters (an improvised array); [[ $x == *:foo:* ]] and x=${x//:foo:/} 
  # will DTRT regardless of how many elements or repetitions $x has..
  #
  # Handling of redirections: upon seeing a redirection token, we must stall
  # the current state --- that is, the value of $this_word --- for two iterations
  # (one for the redirection operator, one for the word following it representing
  # the redirection target).  Therefore, we set $in_redirection to 2 upon seeing a
  # redirection operator, decrement it each iteration, and stall the current state
  # when it is non-zero.  Thus, upon reaching the next word (the one that follows
  # the redirection operator and target), $this_word will still contain values
  # appropriate for the word immediately following the word that preceded the
  # redirection operator.
  #
  # The "the previous word was a redirection operator" state is not communicated
  # to the next iteration via $next_word/$this_word as usual, but via
  # $in_redirection.  The value of $next_word from the iteration that processed
  # the operator is discarded.
  #
  local this_word=':start:' next_word
  integer in_redirection
  # Processing buffer
  local proc_buf="$buf"
  for arg in ${interactive_comments-${(z)buf}} \
             ${interactive_comments+${(zZ+c+)buf}}; do
    if (( in_redirection )); then
      (( --in_redirection ))
    fi
    if (( in_redirection == 0 )); then
      # Initialize $next_word to its default value.
      next_word=':regular:'
    else
      # Stall $next_word.
    fi
    # $already_added is set to 1 to disable adding an entry to region_highlight
    # for this iteration.  Currently, that is done for "" and $'' strings,
    # which add the entry early so escape sequences within the string override
    # the string's color.
    integer already_added=0
    if [[ $this_word == *':start:'* ]]; then
      in_array_assignment=false
      if [[ $arg == 'noglob' ]]; then
        highlight_glob=false
      fi
    fi

    # advance $start_pos, skipping over whitespace in $buf.
    if [[ $arg == ';' ]] ; then
      # We're looking for either a semicolon or a newline, whichever comes
      # first.  Both of these are rendered as a ";" (SEPER) by the ${(z)..}
      # flag.
      #
      # We can't use the (Z+n+) flag because that elides the end-of-command
      # token altogether, so 'echo foo\necho bar' (two commands) becomes
      # indistinguishable from 'echo foo echo bar' (one command with three
      # words for arguments).
      local needle=$'[;\n]'
      integer offset=$(( ${proc_buf[(i)$needle]} - 1 ))
      (( start_pos += offset ))
      (( end_pos = start_pos + $#arg ))
    else
      integer offset=$(((len-start_pos)-${#${proc_buf##([[:space:]]|\\[[:space:]])#}}))
      ((start_pos+=offset))
      ((end_pos=$start_pos+${#arg}))
    fi

    # Above `if` computes new start_pos and end_pos.
    # Here we compute new proc_buf. We advance it
    # (chop off characters from the beginning)
    # beyond what end_pos points to, by skipping
    # as many characters as end_pos was advanced.
    #
    # end_pos was advanced by $offset (via start_pos)
    # and by $#arg. Note the `start_pos=$end_pos`
    # below.
    #
    # As for the [,len]. We could use [,len-start_pos+offset]
    # here, but to make it easier on eyes, we use len and
    # rely on the fact that Zsh simply handles that. The
    # length of proc_buf is len-start_pos+offset because
    # we're chopping it to match current start_pos, so its
    # length matches the previous value of start_pos.
    #
    # Why [,-1] is slower than [,length] isn't clear.
    proc_buf="${proc_buf[offset + $#arg + 1,len]}"

    if [[ -n ${interactive_comments+'set'} && $arg[1] == $histchars[3] ]]; then
      if [[ $this_word == *(':regular:'|':start:')* ]]; then
        style=comment
      else
        style=unknown-token # prematurely terminated
      fi
      _zsh_highlight_main_add_region_highlight $start_pos $end_pos $style
      already_added=1
      continue
    fi

    # Parse the sudo command line
    if (( ! in_redirection )); then
      if [[ $this_word == *':sudo_opt:'* ]]; then
        case "$arg" in
          # Flag that requires an argument
          '-'[Cgprtu]) this_word=${this_word//:start:/};
                       next_word=':sudo_arg:';;
          # This prevents misbehavior with sudo -u -otherargument
          '-'*)        this_word=${this_word//:start:/};
                       next_word+=':start:';
                       next_word+=':sudo_opt:';;
          *)           ;;
        esac
      elif [[ $this_word == *':sudo_arg:'* ]]; then
        next_word+=':sudo_opt:'
        next_word+=':start:'
      fi
    fi

    if [[ $this_word == *':start:'* ]] && (( in_redirection == 0 )); then # $arg is the command word
     if [[ -n ${(M)ZSH_HIGHLIGHT_TOKENS_PRECOMMANDS:#"$arg"} ]]; then
      style=precommand
     elif [[ "$arg" = "sudo" ]]; then
      style=precommand
      next_word=${next_word//:regular:/}
      next_word+=':sudo_opt:'
      next_word+=':start:'
     else
      _zsh_highlight_main_highlighter_expand_path $arg
      local expanded_arg="$REPLY"
      _zsh_highlight_main__type ${expanded_arg}
      local res="$REPLY"
      () {
        # Special-case: command word is '$foo', like that, without braces or anything.
        #
        # That's not entirely correct --- if the parameter's value happens to be a reserved
        # word, the parameter expansion will be highlighted as a reserved word --- but that
        # incorrectness is outweighed by the usability improvement of permitting the use of
        # parameters that refer to commands, functions, and builtins.
        local -a match mbegin mend
        local MATCH; integer MBEGIN MEND
        if [[ $res == none ]] && (( ${+parameters} )) &&
           [[ ${arg[1]} == \$ ]] && [[ ${arg:1} =~ ^([A-Za-z_][A-Za-z0-9_]*|[0-9]+)$ ]]; then
          _zsh_highlight_main__type ${(P)MATCH}
          res=$REPLY
        fi
      }
      case $res in
        reserved)       style=reserved-word;;
        'suffix alias') style=suffix-alias;;
        alias)          () {
                          integer insane_alias
                          case $arg in 
                            # Issue #263: aliases with '=' on their LHS.
                            #
                            # There are three cases:
                            #
                            # - Unsupported, breaks 'alias -L' output, but invokable:
                            ('='*) :;;
                            # - Unsupported, not invokable:
                            (*'='*) insane_alias=1;;
                            # - The common case:
                            (*) :;;
                          esac
                          if (( insane_alias )); then
                            style=unknown-token
                          else
                            style=alias
                            _zsh_highlight_main__resolve_alias $arg
                            local alias_target="$REPLY"
                            [[ -n ${(M)ZSH_HIGHLIGHT_TOKENS_PRECOMMANDS:#"$alias_target"} && -z ${(M)ZSH_HIGHLIGHT_TOKENS_PRECOMMANDS:#"$arg"} ]] && ZSH_HIGHLIGHT_TOKENS_PRECOMMANDS+=($arg)
                          fi
                        }
                        ;;
        builtin)        style=builtin;;
        function)       style=function;;
        command)        style=command;;
        hashed)         style=hashed-command;;
        none)           if _zsh_highlight_main_highlighter_check_assign; then
                          style=assign
                          if [[ $arg[-1] == '(' ]]; then
                            in_array_assignment=true
                          else
                            # assignment to a scalar parameter.
                            # (For array assignments, the command doesn't start until the ")" token.)
                            next_word+=':start:'
                          fi
                        elif [[ $arg[0,1] = $histchars[0,1] ]] && (( $#arg[0,2] == 2 )); then
                          style=history-expansion
                        elif [[ $arg[0,1] == $histchars[2,2] ]]; then
                          style=history-expansion
                        elif [[ -n ${(M)ZSH_HIGHLIGHT_TOKENS_COMMANDSEPARATOR:#"$arg"} ]]; then
                          if [[ $this_word == *':regular:'* ]]; then
                            # This highlights empty commands (semicolon follows nothing) as an error.
                            # Zsh accepts them, though.
                            style=commandseparator
                          else
                            style=unknown-token
                          fi
                        elif _zsh_highlight_main__is_redirection $arg; then
                          # A '<' or '>', possibly followed by a digit
                          style=redirection
                          (( in_redirection=2 ))
                        elif [[ $arg[1,2] == '((' ]]; then
                          # Arithmetic evaluation.
                          #
                          # Note: prior to zsh-5.1.1-52-g4bed2cf (workers/36669), the ${(z)...}
                          # splitter would only output the '((' token if the matching '))' had
                          # been typed.  Therefore, under those versions of zsh, BUFFER="(( 42"
                          # would be highlighted as an error until the matching "))" are typed.
                          #
                          # We highlight just the opening parentheses, as a reserved word; this
                          # is how [[ ... ]] is highlighted, too.
                          style=reserved-word
                          _zsh_highlight_main_add_region_highlight $start_pos $((start_pos + 2)) $style
                          already_added=1
                          if [[ $arg[-2,-1] == '))' ]]; then
                            _zsh_highlight_main_add_region_highlight $((end_pos - 2)) $end_pos $style
                            already_added=1
                          fi
                        elif [[ $arg == '()' || $arg == $'\x28' ]]; then
                          # anonymous function
                          # subshell
                          style=reserved-word
                        else
                          if _zsh_highlight_main_highlighter_check_path; then
                            style=$REPLY
                          else
                            style=unknown-token
                          fi
                        fi
                        ;;
        *)              _zsh_highlight_main_add_region_highlight commandtypefromthefuture-$res
                        already_added=1
                        ;;
      esac
     fi
    else # $arg is a non-command word
      case $arg in
        $'\x29') # subshell or end of array assignment
                 if $in_array_assignment; then
                   style=assign
                   in_array_assignment=false
                 else
                   style=reserved-word
                 fi;;
        $'\x7d') style=reserved-word;; # block
        '--'*)   style=double-hyphen-option;;
        '-'*)    style=single-hyphen-option;;
        "'"*)    style=single-quoted-argument;;
        '"'*)    style=double-quoted-argument
                 _zsh_highlight_main_add_region_highlight $start_pos $end_pos $style
                 _zsh_highlight_main_highlighter_highlight_string
                 already_added=1
                 ;;
        \$\'*)   style=dollar-quoted-argument
                 _zsh_highlight_main_add_region_highlight $start_pos $end_pos $style
                 _zsh_highlight_main_highlighter_highlight_dollar_string
                 already_added=1
                 ;;
        '`'*)    style=back-quoted-argument;;
        [*?]*|*[^\\][*?]*)
                 $highlight_glob && style=globbing || style=default;;
        *)       if false; then
                 elif [[ $arg[0,1] = $histchars[0,1] ]] && (( $#arg[0,2] == 2 )); then
                   style=history-expansion
                 elif [[ -n ${(M)ZSH_HIGHLIGHT_TOKENS_COMMANDSEPARATOR:#"$arg"} ]]; then
                   if [[ $this_word == *':regular:'* ]]; then
                     style=commandseparator
                   else
                     style=unknown-token
                   fi
                 elif _zsh_highlight_main__is_redirection $arg; then
                   style=redirection
                   (( in_redirection=2 ))
                 else
                   if _zsh_highlight_main_highlighter_check_path; then
                     style=$REPLY
                   else
                     style=default
                   fi
                 fi
                 ;;
      esac
    fi
    (( already_added )) || _zsh_highlight_main_add_region_highlight $start_pos $end_pos $style
    if [[ -n ${(M)ZSH_HIGHLIGHT_TOKENS_COMMANDSEPARATOR:#"$arg"} ]]; then
      next_word=':start:'
      highlight_glob=true
    elif
       [[ -n ${(M)ZSH_HIGHLIGHT_TOKENS_CONTROL_FLOW:#"$arg"} && $this_word == *':start:'* ]] ||
       [[ -n ${(M)ZSH_HIGHLIGHT_TOKENS_PRECOMMANDS:#"$arg"} && $this_word == *':start:'* ]]; then
      next_word=':start:'
    elif [[ $arg == "repeat" && $this_word == *':start:'* ]]; then
      # skip the repeat-count word
      in_redirection=2
      # The redirection mechanism assumes $this_word describes the word
      # following the redirection.  Make it so.
      #
      # The repeat-count word will be handled like a redirection target.
      this_word=':start:'
    fi
    start_pos=$end_pos
    (( in_redirection == 0 )) && this_word=$next_word
  done
}

# Check if $arg is variable assignment
_zsh_highlight_main_highlighter_check_assign()
{
    setopt localoptions extended_glob
    [[ $arg == [[:alpha:]_][[:alnum:]_]#(|\[*\])(|[+])=* ]]
}

# Check if $arg is a path.
# If yes, return 0 and in $REPLY the style to use.
# Else, return non-zero (and the contents of $REPLY is undefined).
_zsh_highlight_main_highlighter_check_path()
{
  _zsh_highlight_main_highlighter_expand_path $arg;
  local expanded_path="$REPLY"

  REPLY=path

  [[ -z $expanded_path ]] && return 1
  [[ -e $expanded_path ]] && return 0

  # Search the path in CDPATH
  local cdpath_dir
  for cdpath_dir in $cdpath ; do
    [[ -e "$cdpath_dir/$expanded_path" ]] && return 0
  done

  # If dirname($arg) doesn't exist, neither does $arg.
  [[ ! -e ${expanded_path:h} ]] && return 1

  # If this word ends the buffer, check if it's the prefix of a valid path.
  if [[ ${BUFFER[1]} != "-" && ${#BUFFER} == $end_pos ]] &&
     [[ $WIDGET != accept-* ]]; then
    local -a tmp
    tmp=( ${expanded_path}*(N) )
    (( $#tmp > 0 )) && REPLY=path_prefix && return 0
  fi

  # It's not a path.
  return 1
}

# Highlight special chars inside double-quoted strings
_zsh_highlight_main_highlighter_highlight_string()
{
  setopt localoptions noksharrays
  local -a match mbegin mend
  local MATCH; integer MBEGIN MEND
  local i j k style
  # Starting quote is at 1, so start parsing at offset 2 in the string.
  for (( i = 2 ; i < end_pos - start_pos ; i += 1 )) ; do
    (( j = i + start_pos - 1 ))
    (( k = j + 1 ))
    case "$arg[$i]" in
      '$' ) style=dollar-double-quoted-argument
            # Look for an alphanumeric parameter name.
            if [[ ${arg:$i} =~ ^([A-Za-z_][A-Za-z0-9_]*|[0-9]+) ]] ; then
              (( k += $#MATCH )) # highlight the parameter name
              (( i += $#MATCH )) # skip past it
            elif [[ ${arg:$i} =~ ^[{]([A-Za-z_][A-Za-z0-9_]*|[0-9]+)[}] ]] ; then
              (( k += $#MATCH )) # highlight the parameter name and braces
              (( i += $#MATCH )) # skip past it
            else
              continue
            fi
            ;;
      "\\") style=back-double-quoted-argument
            if [[ \\\`\"\$ == *$arg[$i+1]* ]]; then
              (( k += 1 )) # Color following char too.
              (( i += 1 )) # Skip parsing the escaped char.
            else
              continue
            fi
            ;;
      *) continue ;;

    esac
    _zsh_highlight_main_add_region_highlight $j $k $style
  done
}

# Highlight special chars inside dollar-quoted strings
_zsh_highlight_main_highlighter_highlight_dollar_string()
{
  setopt localoptions noksharrays
  local -a match mbegin mend
  local MATCH; integer MBEGIN MEND
  local i j k style
  local AA
  integer c
  # Starting dollar-quote is at 1:2, so start parsing at offset 3 in the string.
  for (( i = 3 ; i < end_pos - start_pos ; i += 1 )) ; do
    (( j = i + start_pos - 1 ))
    (( k = j + 1 ))
    case "$arg[$i]" in
      "\\") style=back-dollar-quoted-argument
            for (( c = i + 1 ; c <= end_pos - start_pos ; c += 1 )); do
              [[ "$arg[$c]" != ([0-9xXuUa-fA-F]) ]] && break
            done
            AA=$arg[$i+1,$c-1]
            # Matching for HEX and OCT values like \0xA6, \xA6 or \012
            if [[    "$AA" =~ "^(x|X)[0-9a-fA-F]{1,2}"
                  || "$AA" =~ "^[0-7]{1,3}"
                  || "$AA" =~ "^u[0-9a-fA-F]{1,4}"
                  || "$AA" =~ "^U[0-9a-fA-F]{1,8}"
               ]]; then
              (( k += $#MATCH ))
              (( i += $#MATCH ))
            else
              if (( $#arg > $i+1 )) && [[ $arg[$i+1] == [xXuU] ]]; then
                # \x not followed by hex digits is probably an error
                style=unknown-token
              fi
              (( k += 1 )) # Color following char too.
              (( i += 1 )) # Skip parsing the escaped char.
            fi
            ;;
      *) continue ;;

    esac
    _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}}
}

# -------------------------------------------------------------------------------------------------
# Main highlighter initialization
# -------------------------------------------------------------------------------------------------

_zsh_highlight_main__precmd_hook() {
  _zsh_highlight_main__command_type_cache=()
}

autoload -U add-zsh-hook
if add-zsh-hook precmd _zsh_highlight_main__precmd_hook 2>/dev/null; then
  # Initialize command type cache
  typeset -gA _zsh_highlight_main__command_type_cache
else
  echo 'zsh-syntax-highlighting: Failed to load add-zsh-hook. Some speed optimizations will not be used.' >&2
  # Make sure the cache is unset
  unset _zsh_highlight_main__command_type_cache
fi