See comments within for the rationale.

This is a regression test for a regression that was only present in development
versions of PR #764 and was never present in master.

Reported on issue #757 along with other issues.

E.g., on Cygwin /etc/passwd does not necessarily exist.

The bug is as follows:

    % zsh-5.8 -fc 'autoload is-at-least; is-at-least 5.8.0.2 && echo yes || echo no'
    yes
    % zsh-5.8 -fc 'autoload is-at-least; is-at-least 5.8.0.2 $ZSH_VERSION && echo yes || echo no'
    yes

This commit deploys the following workaround:

    % zsh-5.8 -fc 'autoload is-at-least; is-at-least 5.8.0.2 $ZSH_VERSION.0.0 && echo yes || echo no'
    no

Fixes #756.

The parent commit, which merged the feature/redrawhook bug and thereby
closed PR #749, also fixed the following issue:

Fixes #40.

Fixes #90, closes #470. (The latter is a PR for the former.)

Fixes #150, closes #151, closes #160. (The latter two are PR's for the first one.) The related issue #183 appears to have been fixed in master. For #150, a different fix for older versions of zsh was considered but has not been implemented.

Issue #154 was fixed in xsel(1) in 2017. The parent commit probably fixed that issue for pre-2017 xsel(1).

Is #245, #356, and #749. Fixes #245 (redrawhook umbrella issue).

Does not reintroduce #257 (comment).

Does not reintroduce #259 (comment)

Closes #281 as obsolete.

Fixes #295.

Fixes #324.

Fixes #375.

Fixes #377.

Closes #421 as obsolete.

Fixes #520.

Unblocks #536 (already milestoned).

Fixes #632.

Unblocks #635. Milestoned.

Unblocks #688. Milestoned.

Unblocks administrative issue #655 (already milestoned).

(The above is copied from
https://github.com/zsh-users/zsh-syntax-highlighting/pull/749#issuecomment-658407330,
but repeated here for the sake of github's commit-to-issue linking magic.)

* feature/redrawhook:
  docs: Track making the new codepath conditional upon the 'memo=' feature.
  On the feature/redrawhook branch, changelog: Add entries for issues fixed by this branch.
  On the feature/redrawhook branch, change the detection of the 'memo=' feature to avoid a catch-22.
  driver: Make the redrawhook codepath conditional upon the memo= feature.
  On the feature/redrawhook branch, move the changelog entry to the current release's section.
  driver: Fix a bug that prevented subsequent, third-party zle-line-pre-redraw hooks from running.
  driver: Do not pass widget arguments to _zsh_highlight
  driver: Clarify comment.  No functional change.
  driver: Allow for -U in autoloaded function definition
  driver: Use idiomatic module check
  driver: Make the shadowing $WIDGET read only.
  driver: Avoid a fork in the common case.
  test harness: Actually test the new code.
  driver: Rewrite without a state variable
  noop: Make a whitespace-only change to reduce noise in the next commit.
  docs: Rewrap.
  docs: Update FAQ answer per changes on this branch.
  redo _zsh_highlight__function_callable_p
  driver: Use a different way of checking whether add-zle-hook-widget is present.
  changelog: Use a more specific link.
  changelog: Note the effect of fixing #245/#90 and an alternative.
  driver: Pass zle-line-finish arguments on to _zsh_highlight.
  driver: Hook zle-line-finish.
  driver: Reimplement using 'add-zle-hook-widget zle-line-pre-redraw'
  wrappers: Reimplement using Mikachu's zle-line-pre-redraw hook (workers/36650).

The new codepath is used in 5.8.0.2 and newer; see zsh-syntax-highlighting.zsh:417.

This covers issues referenced from #245 or labelled "feature:redrawhook" or "widget-wrapping".  See #749 for details.

* origin/master:
  Post-release version number bump.
  Tag version 0.8.0-alpha1-pre-redrawhook.
  brackets: Optimize the character iteration

Test case: See the first comment of issue #295.

Before:
num  calls                time                       self            name
-----------------------------------------------------------------------------------
 1)   14         284.67    20.33   82.84%    284.67    20.33   82.84%  _zsh_highlight_highlighter_brackets_paint
 2)   15         313.72    20.91   91.30%     26.62     1.77    7.75%  _zsh_highlight
 3)   14         318.68    22.76   92.74%      7.41     0.53    2.16%  _zsh_highlight_call_widget

After:
num  calls                time                       self            name
-----------------------------------------------------------------------------------
 1)   15          57.25     3.82   45.33%     28.30     1.89   22.41%  _zsh_highlight
 2)   14          81.96     5.85   64.90%     27.02     1.93   21.40%  _zsh_highlight_call_widget
 3)   14          26.31     1.88   20.84%     26.31     1.88   20.84%  _zsh_highlight_highlighter_brackets_paint
 4)    2          10.66     5.33    8.44%      8.97     4.49    7.10%  VCS_INFO_formats
 5)    2          25.92    12.96   20.52%      7.72     3.86    6.11%  VCS_INFO_get_data_git

(That's not in my everyday configuration but in my minimal testing
setup, which runs vcs_info with the default settings.)

* origin/master:
  Revert "driver: Move the initialization of $zsh_highlight__memo_feature out of the entry point function."

This reverts commit 8a1bd7c8b6.

The detection only works correctly from a widget function, so the change
was wrong: it caused zsh_highlight__memo_feature to be set to false
every time.

Fixes #579 (zsh-autosuggestions interoperability).
Fixes #735 (ditto).

See https://github.com/zsh-users/zsh-syntax-highlighting/issues/579#issuecomment-650126055
See https://github.com/zsh-users/zsh-autosuggestions/issues/529#issuecomment-650481227

* origin/master:
  driver: Move the initialization of $zsh_highlight__memo_feature out of the entry point function.

This is needed for feature/redrawhook to be able to use it.

* origin/master: (297 commits)
  driver: Follow-up to grandparent: Have all test suite entry points declare the mock $region_highlight.
  Use the new, unreleased zsh 'memo=' feature to remove only our own entries from $region_highlight.
  driver: Stop re-declaring $region_highlight.  It's unneeded.
  docs: regexp highlighter: Fix a wrong associative array name in the example.
  docs: Fix obs-repository link
  tests: Fix a wrong value of $PREBUFFER in a test, and add checks to prevent this from recurring.
  test harness: Fix use of an undefined variable in an error message.
  'main': Don't progress the $in_redirection staller while $in_param.
  tests: Add an XFail test for issue #712.
  'main': Highlight the parentheses of array assignments as reserved words.
  CI += zsh-5.8
  main: Add tests for arithmetic expansion
  main: Add arithmetic substitution highlighting
  changelog.md: Restore vertical whitespace before section headers.
  'main': Fix issue #677, concerning multiline aliases.
  changelog: Update through HEAD.
  'main': Further optimize argument parsing.
  'main': Optimize a hot path.
  tests: Add a performance testing script, for measuring the performance of the 'main' highlighter on a large file.
  changelog: Update through HEAD.
  test harness: Print the expected-v.-actual on every failure, not just upon cardinality failures.
  Document ZSH_HIGHLIGHT_MAXLENGTH.
  'main': Fix the last commit's bug concerning parameter elision not happening in redirects in command position.
  'main': Add a test for parameter elision not happening in redirects in command position.
  'main': Fix regression in zsh 5.3.1 and older: all precmd hooks later than z-sy-h would be aborted.
  changelog += WARN_NESTED_VAR fixes (#727, #731)
  'main': Fix a regression caused by the great-grandparent commit's WARN_NESTED_VAR fix.
  'main': Don't run `_zsh_highlight_main__type` on every non-command word.
  'make perf': Show only a cumulative datum per highligher, rather than per test file.
  'main': Don't trip WARN_NESTED_VAR.
  'main': Follow-up to previous: Document the version number, and deduplicate some option letters.
  'main': precommands += strace
  editorconfig: Fix Makefile settings
  Fix typo
  Bump copyright years.
  driver: Fix "_zsh_highlight:3: read-only variable: ret" warnings when POSIX_BUILTINS is set.
  tests: Add a test for the infinite loop fixed by each of the last two commits.
  'main': Fix expansion of positional parameters in `_zsh_highlight_main_highlighter__try_expand_parameter`.
  'main': Fix an infinite loop.
  'main': precommands += ionice(1) (from util-linux)
  driver: Simplify initialization of $zsyh_user_options in the fallback codepath.
  driver: Make sure we don't change the return value in a called function.
  'main': Make logic more robust.  No functional change.
  'main': Break out an anonymous function into a named function.
  Fix typos in comments.
  main: Add test for issue #713
  'main': Support the 'env' precommand.
  test harness: Fix the pretty-printer's padding implementation.
  Revert "test harness: Rewrite the columnar pretty-printer without external tools." and "travis: Remove bsdmainutils since column(1) has been removed, three commits ago."
  changelog: Update through HEAD.
  'main': Correctly highlight '&&' and '||' inside '[[ … ]]' conditions.
  'main': Highlight reserved words following assignments as errors.
  tests: Add tests for issue #461.
  test harness: Output the time information to the same place the test name was printed to.
  test harness: Stringify values in a more readable manner.
  tests: Add a unit test for a path specified with mixed quoting.
  tests: Add a test for issue #498, which has already been fixed.
  tests: Test that global qualifiers and command substitutions aren't evaluated.
  'main': Don't consider path_prefix in alias expansions.
  'main': Add a test for aliases to AUTO_CD directories.
  'main': Let AUTO_CD directories be highlighted with their own style.
  'main': Add an auxiliary variable for readability.
  'main': In command position, do not highlight directories (unless AUTO_CD is set) and non-executable files.
  'main': Extend tests to capture the current behaviour.
  'main': Add an XFail test for issue #202.
  'main': Highlight errors from the EQUALS option.
  'main': Let the type determination ignore global aliases when it ignores regular ones.
  'main': Add a regression test for parameters that expand to global aliases.
  'main': Enable the zsh/parameter codepath of global aliases highlighting.
  changelog: Update through HEAD.
  travis: Remove bsdmainutils since column(1) has been removed, three commits ago.
  'main': Highlight global aliases
  tests: Record current behaviour on global aliases.
  test harness: Rewrite the columnar pretty-printer without external tools.
  test harness: Fix an issue with the pretty-printed $expected_region_highlight/$region_highlight diffing.
  'main': Support the "close file descriptor" and "coproc" redirection syntaxes
  tests: Add a test for the "close file descriptor" and "coproc" redirection syntaxes
  tests: Fix the test added in the last commit.
  tests: Add a test for issue #705, concerning continuation lines.
  test harness: Let tests fail early by exiting non-zero or by setting a flag.
  test harness: Print the test name when $skip_test is set.
  test harness: Remove a bogus check.
  test harness: Fix $skip_test support, broken yesterday.
  travis: Install bsdmainutils to provide column(1).
  test harness: When the cardinality check fails, pretty-print \$expected_region_highlight and \$region_highlight.
  test harness: Don't leak options from test files to the test harness.
  test harness: Fix test failures under zsh 5.0.8 and older.
  'main': Fix a bug manifesting under zsh 5.2 and older.
  'main': Don't highlight arithmetic expansions as command substitutions.
  tests: Add a test documenting the current state, prior to introducing #704.
  test harness: Change cardinality check semantics
  test harness: No-op change to minimize the next diff.
  'main': Document additional meanings of the 'S' $braces_stack flag.
  'main': When the redirection operator '>&' or '<&' is followed by a positive integer, do not consider that as a filename; it's always a file descriptor.
  'main': Add $last_arg for "lookbehind".
  noop: Clarify comment.
  'main': Honour the MULTIOS option when applying the 'globbing' style.
  'main': Document what $in_redirection is currently used for.
  'main': The optimized cmdsubst input syntax doesn't glob.
  changelog: Fix markup.
  ...

tests/generate.zsh already does this.

Fixes #418 (interoperability issue with other plugins).

Factored out from #747.

Discussed: https://github.com/zsh-users/zsh-syntax-highlighting/pull/706#issuecomment-642072978

The error message uses «$1», but it is always unset at that point.
Furthermore, the NO_UNSET (-u) option is in effect.  Therefore, when the
error message was to be printed, zsh's NO_UNSET error message was
printed instead:
.
    (anon):20: 1: parameter not set

That error message was printed to stderr, and was caught by the caller
within the test harness:
.
    Bail out! On './highlighters/main/test-data/path_prefix3.zsh': output on stderr

Thus, the bug being fixed would not caused false positive or false
negative test results, but only wrong error messages.

Follow-up to 0.7.1-71-ge6eea1f, "test harness: Don't leak options from
test files to the test harness".