'main': Introduce style fallback for the command word.

Fixes #316.

* danielsh/i316-v2:
  'main': Enable fallback to the 'arg0' style.
  'main': Set fallback style for the 'arg0' style.

docs/highlighters/main.md

@@ -44,6 +44,7 @@ This highlighter defines the following styles:
 * `assign` - parameter assignments
 * `redirection` - redirection operators (`<`, `>`, etc)
 * `comment` - comments, when `setopt INTERACTIVE_COMMENTS` is in effect (`echo # foo`)
+* `arg0` - a command word other than one of those enumrated above (other than a command, precommand, alias, function, or shell builtin command).
 * `default` - everything else
 
 To override one of those styles, change its entry in `ZSH_HIGHLIGHT_STYLES`,
@@ -65,4 +66,26 @@ The syntax for values is the same as the syntax of "types of highlighting" of
 the zsh builtin `$zle_highlight` array, which is documented in [the `zshzle(1)`
 manual page][zshzle-Character-Highlighting].
 
+### Useless trivia
+
+#### Forward compatibility.
+
+zsh-syntax-highlighting attempts to be forward-compatible with zsh.
+Specifically, we attempt to facilitate highlighting _command word_ types that
+had not yet been invented when this version of zsh-syntax-highlighting was
+released.
+
+A _command word_ is something like a function name, external command name, et
+cetera.  (See
+[Simple Commands & Pipelines in `zshmisc(1)`][zshmisc-Simple-Commands-And-Pipelines]
+for a formal definition.)
+
+If a new _kind_ of command word is ever added to zsh — something conceptually
+different than "function" and "alias" and "external command" — then command words
+of that (new) kind will be highlighted by the style `arg0_$kind`,
+where `$kind` is the output of `type -w` on the new kind of command word.  If that
+style is not defined, then the style `arg0` will be used instead.
+
+[zshmisc-Simple-Commands-And-Pipelines]: http://zsh.sourceforge.net/Doc/Release/Shell-Grammar.html#Simple-Commands-_0026-Pipelines
+
 [zshzle-Character-Highlighting]: http://zsh.sourceforge.net/Doc/Release/Zsh-Line-Editor.html#Character-Highlighting

highlighters/main/main-highlighter.zsh

@@ -32,17 +32,11 @@
 : ${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_pathseparator]:=}
-: ${ZSH_HIGHLIGHT_STYLES[path_prefix]:=underline}
 : ${ZSH_HIGHLIGHT_STYLES[path_prefix_pathseparator]:=}
 : ${ZSH_HIGHLIGHT_STYLES[globbing]:=fg=blue}
 : ${ZSH_HIGHLIGHT_STYLES[history-expansion]:=fg=blue}
@@ -58,6 +52,7 @@
 : ${ZSH_HIGHLIGHT_STYLES[assign]:=none}
 : ${ZSH_HIGHLIGHT_STYLES[redirection]:=none}
 : ${ZSH_HIGHLIGHT_STYLES[comment]:=fg=black,bold}
+: ${ZSH_HIGHLIGHT_STYLES[arg0]:=fg=green}
 
 # Whether the highlighter should be called or not.
 _zsh_highlight_highlighter_main_predicate()
@@ -71,6 +66,33 @@ _zsh_highlight_main_add_region_highlight() {
   integer start=$1 end=$2
   shift 2
 
+  if (( $+argv[2] )); then
+    # Caller specified inheritance explicitly.
+  else
+    # Automate inheritance.
+    typeset -A fallback_of; fallback_of=(
+        alias arg0
+        suffix-alias arg0
+        builtin arg0
+        function arg0
+        command arg0
+        precommand arg0
+        hashed-command arg0
+        
+        path_prefix path
+        # The path separator fallback won't ever be used, due to the optimisation
+        # in _zsh_highlight_main_highlighter_highlight_path_separators().
+        path_pathseparator path
+        path_prefix_pathseparator path_prefix
+    )
+    local needle=$1 value
+    while [[ -n ${value::=$fallback_of[$needle]} ]]; do
+      unset "fallback_of[$needle]" # paranoia against infinite loops
+      argv+=($value)
+      needle=$value
+    done
+  fi
+
   # The calculation was relative to $PREBUFFER$BUFFER, but region_highlight is
   # relative to $BUFFER.
   (( start -= $#PREBUFFER ))
@@ -581,7 +603,7 @@ _zsh_highlight_highlighter_main_paint()
                           fi
                         fi
                         ;;
-        *)              _zsh_highlight_main_add_region_highlight $start_pos $end_pos commandtypefromthefuture-$res
+        *)              _zsh_highlight_main_add_region_highlight $start_pos $end_pos arg0_$res arg0
                         already_added=1
                         ;;
       esac

highlighters/main/test-data/inheritance.zsh

@@ -0,0 +1,40 @@
+#!/usr/bin/env zsh
+# -------------------------------------------------------------------------------------------------
+# Copyright (c) 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
+# -------------------------------------------------------------------------------------------------
+
+_zsh_highlight_add_highlight()
+{
+  region_highlight+=("$1 $2 ${(j.,.)argv[3,-1]}")
+}
+
+BUFFER='type'
+
+expected_region_highlight=(
+  '1 4 builtin,arg0' # type
+)