If the separator feature is disabled, this makes it possible to
change the main 'path' styles in a running session without the
need to touch the '_pathseparator' styles, too.

Causes such expansions to be highlighted as [unknown-token] rather than as default (absent from $region_highlight).

Fixes #337.

Part of #337.

Fixes #231.
Fixes #330.

Assignments to positional parameters using scalar assignment syntax is
a feature: it is covered by upstream's test suite ("append to positional
parameter" in Test/A06assign.ztst).

This commit is based on the work done by
Jorge Israel Peña (blaenk) in #136.

Changes:
* Adjusted to changes on the latest master branch.
* Use regular path highlighter colors by default.
* Break out early if the separator color is the same to
  improve performance.
* Tests.

Changes the interface of _zsh_highlight_main_highlighter_check_path().

Suggested-by: m0viefreak

If possible, try to use the zsh/parameter module to get
information about a shell words.

This avoids subshells and is a huge speed improvement
on systems such as cygwin.

Note 1:
$commands does not know about PATH_DIRS. So in case
PATH_DIRS is set, 'type -w' is still used if nothing
else matches.

Note 2:
zsh/parameter can't distinguish between 'command' and
'hashed'. Adjusted the test for that case to XFAIL.

The ideal solution would be if whence had an option to
put the result in REPLY instead of printing it to stdout.

The test being extended is highlighters/main/test-data/control-flow2.zsh.

If possible, use zsh/parameter to avoid forks.

Fixes #263.

Found-by: m0viefreak
(in #298)

Consider indexing long buffers (say 300 chars). E.g. following line:
      integer offset=${${buf[start_pos+1,len]}[(i)$needle]}
will gradually go into large indices for first index [a,] and be kept
at large index for second index [,b]. Instead, we can remove already
processed characters from buf:
    proc_buf="${proc_buf[offset + $#arg + 1,-1]}"
$offset and $#arg are small, first index will not be large. $proc_buf
will be smaller and smaller and the second index [,-1] will run shorter
and shorter.

Inspired by #312.

Use correct indexing also for cursor-matchingbracket.

Fixup for 95d82568d8

Without this when bracket_color_size is 0,
    $(( (levelpos[$pos] - 1) % bracket_color_size + 1 ))
errors with division by zero.

Since the _zsh_highlight_add_highlight that the tests use ignores
ZSH_HIGHLIGHT_STYLES, we can test both an injective mapping and an empty
mapping at once.

This removes the need for the typepos array.

zsh arrays start at one, and this will make the next commit easier.

'none' is a valid highlighting type. Since by convention styles are all
lowercase, 'NONE' shouldn't conflict with anything.

Closes #289.

_zsh_highlight_add_highlight appends to region_highlight $1 $2 and the
next non-null parameter. If there is no non-null parameter, do nothing,
This is so that highlighters can add a style with fallbacks if the most
specific style is not defined. If none of the applicable styles are
defined, do the right thing and don't add an invalid entry to
region_highlight.

The pattern highlighter doesn't use this function as it'd need too large
of an API change.

No need to fork every time.

Compute «${#BUFFER}» just once.  I haven't measured the effect of this, but
it might just avoid a strlen() every time around the loop, which could add
up for large ${BUFFER}s.

See issue #295.

zsh older than workers/28418 (zsh revision 23bdfc7fd2)
doesn't support the «${name:offset:length}» syntax.  Therefore, use the older
«$name[start,end]» syntax instead.

Followup to 3cb58fd7d7b9e42067ffcf24892114dc2c9b26e4, "Optimization: -1 is
extra computation of string length internally".

Fixes zsh-users/zsh-syntax-highlighting#279.

While here, also add a test for the '!' reserved word (which is highlighted
since c216242b).

This is a continuation of 451665cb2a which did
the same for the $PS3 prompt.

Reported-by: Sebastian Gniazdowski

./parse.zsh "zplugin.zsh" > out_norm.txt 106,17s user 7,84s system 98% cpu 1:55,85 total

./parse.zsh "zplugin.zsh" > out_opt.txt 51,91s user 7,44s system 99% cpu 59,912 total

% wc -l zplugin.zsh
3188 zplugin.zsh

The input to the $PS3 prompt is not commands, so the 'main' highlighter is
not applicable to it.

Fixes zsh-users/zsh-syntax-highlighting#268.