When 'use_autoloader' is set to true in an installation profile the
autoloader script is not created automatically and this can result in an
error when the module actually tries to load it.

Fix this by setting up the autoloader script at install time.

When calling syntaxhighlighter_requirements() at install time the
'libraries' module might not have been enabled yet, if that's the case
load it explicitly to be able to call libraries_get_path().

Note that the first check is performed by just using
libraries_get_path() because during the install phase the library has
not been registered yet as the module does that in the
syntaxhighlighter_libraries_info() hook, and so libraries_detect() would
not work.

During the runtime phase it's OK to use libraries_detect() to retrieve
the library version.

The _syntaxhighlighter_setup_autoloader_script() function was called as
a custom form submit handler, but these handlers are being called
_before_ the submitForm() method.

This was a problem because _syntaxhighlighter_setup_autoloader_script()
relies on the module config, but the config was updated in submitForm(),
only _after_ the execution.

That resulted in _syntaxhighlighter_setup_autoloader_script() ignoring
changes to the 'use_autoloader' setting, failing to create or remove the
syntaxhighlighter.autoloader.js file when the setting value changed.

So don't call _syntaxhighlighter_setup_autoloader_script() as a custom
submit handler, call it in submitForm() after the config has been
updated.

By making the libraries module a hard dependency the code can be
simplified: _syntaxhighlighter_get_lib_location() and
_syntaxhighlighter_scan_lib_location() can be removed as they were
merely duplicating the libraries module functionality.

Remove also the custom caching of the library path, the libraries module
already caches this and some other info; if the library location changes
the cache has to be flushed in some way (drush, drupal-console, etc.).

In the code these conventions are used:

  - SyntaxHighlighter with no space refers to the Javascript library.
  - Syntax Highlighter with a space refers to the Drupal module.

It is not necessary because the code only runs in the 'runtime' phase,
and at this point the module has been enabled and loaded already.

Requiring extra code from the module would be needed during the
'install' phase, but currently no code is executed during this phase.

Continuation lines do not need to be indented so much, so indent the
minimum necessary still following the coding standard, as done in other
places in the code.

This is just cosmetics, no functional changes made.

The code now follows the Drupal coding standard.

This fixes the last warnings from phpcs, the code is now following the
Drupal coding standard.

It's more semantically correct to have a proper boolean expression in if
conditions instead of the implicit handling of an arithmetic expression.

And it's more readable to have the increment in the for loop condition
written explicitly when possible.

Fix these phpcs errors:

  Expected one space after the comma, 0 found
  Space found before first semicolon of FOR loop
  Space found before second semicolon of FOR loop
  Space found before semicolon; expected "0;" but found "0 ;"
  Space found before semicolon; expected "$n;" but found "$n ;"
  There should be no white space before a closing ")"
  Use "elseif" in place of "else if"

Fixed automatically with:

   $ phpcbf --sniffs=Drupal.WhiteSpace.Comma,Squiz.ControlStructures.ForLoopDeclaration,Squiz.WhiteSpace.SemicolonSpacing,Drupal.WhiteSpace.CloseBracketSpacing,Drupal.ControlStructures.ElseIf --standard=Drupal .

Fix these phpcs errors:

  A comma should follow the last multiline array item
  Array indentation error
  Closing parenthesis of array declaration must be on a new line
  The first index in a multi-value array must be on a new line

Fixed automatically with:

  $ phpcbf --sniffs=Drupal.Array.Array,Squiz.Arrays.ArrayDeclaration --standard=Drupal .

Plus some manual tweaks.

Fix these phpcs errors:

  Data types in @param tags need to be fully namespaced
  Description for the @return value must be on the next line
  Doc comment is empty
  Doc comment long description must end with a full stop
  Doc comment short description must be on a single line, further text should be a separate paragraph
  Doc comment short description must end with a full stop
  Missing function doc comment
  Parameter comment must start with a capital letter
  There must be exactly one blank line before the tags in a doc comment

Some are fixed automatically by running:

  $  phpcbf --sniffs=Drupal.Commenting.FunctionComment,Drupal.Commenting.DocComment,Drupal.Commenting.DataTypeNamespace --standard=Drupal .

Some fixes required manual intervention.

While at it also improve the grammar here and there.

Fix these phpcs errors:

  Inline comments must start with a capital letter
  Inline comments must end in full-stops, exclamation marks, colons, question marks, or closing parentheses

Fixed automatically with:

  $ phpcbf --sniffs=Drupal.Commenting.InlineComment --standard=Drupal .

Fix phpcs error:

  "require_once" is a statement not a function; no parentheses are required

Fixed automatically with:

  $ phpcbf --sniffs=PEAR.Files.IncludingFile --standard=Drupal .

Fix these phpcs errors:

  Expected 1 blank line after function; 2 found
  Expected 1 newline at end of file; 2 found

Fixed automatically by running:

  $ phpcbf --sniffs=Squiz.WhiteSpace.FunctionSpacing,Drupal.Files.EndFileNewline --standard=Drupal .

This fixes the very same errors reported by phpcs.

Fixed automaticaly by running:

  $ phpcbf --sniffs=Drupal.Array.DisallowLongArraySyntax --standard=Drupal .

Also remove the correspondent entry from the TODO file.

This fixes the "Whitespace found at end of line" errors from phpcs.

In _syntaxhighlighter_validate_input() the checks and the corresponding
error messages are not very accurate, a case like the following:

  <pre>
  </pre>
  <pre>

will report both unbalanced and nested elements, even if there is no
nesting.

A case like this:

  <pre>
  </pre>
  </pre>
  <pre>

will tell that there are nested elements, which is not technically
correct either, the tags are not nested but unbalanced.

So check for the order of elements only if the number of opening and
closing tags is equal, and make the error message about nesting more
generic to apply to the case when the opening and closing tags are in
equal number but still unbalanced.

While at it also set the error message right after the check, as the
errors do not accumulate anymore.

Remove the TODO entry about the issue.

There is no need to use 'define()' because the constants are declared
unconditionally and their names are literals.

Remove the correspondent TODO entry.

The constant is supposed to use the module name as a prefix but the
current prefix lacks an 'I', fix it.

This also fixes an actual warning message from phpcs, although the fix
proposed by phpcs is not correct:

  38 | WARNING | [ ] All constants defined by a module must be
     |         |     prefixed with the module's name, expected
     |         |     "SYNTAXHIGHLIGHTER_SYNTAXHIGHLGHTER_TAG_STRING"
     |         |     but found "SYNTAXHIGHLGHTER_TAG_STRING"

And remove the correspondent TODO entry.

The module is still compatible with the 'PHP Filter' plugin.

The latter is now a contrib module, installable with:

  composer require drupal/php

So remove the corresponding entry in the TODO file and also mention that
the PHP mechanism for matching pages could go away if the Javascript
library is attached only when the input filter gets applied.

The module is still compatible with the development version of the
libraries, but it may not be with a future stable release, add a note
about that in the code.

Also fix the 'download url' field in syntaxhighlighter_libraries_info()
because the previous value is not valid anymore, and remove the
'download' field which is not documented anywhere for
hook_libraries_info().

Now that the compatibility status has been verified, drop the TODO
entries about it.

List of changes:
  - add syntaxhighlighter_form_node_form_alter() to re-enable validation
    for nodes, since hook_node_validate() is not available anymore in
    Drupal 8;
  - update _syntaxhighlighter_comment_validate() and
    _syntaxhighlighter_node_validate() to use $form_state; the latter is
    now a callback local to the module, before it was a global hook;
  - update _syntaxhighlighter_format_has_syntaxhighlighter_filter() to
    use a Drupal 8 API, namely FilterFormat, because
    filter_list_format() is not available anymore;
  - pass the $form_state object to _syntaxhighlighter_validate_input()
    so it can use $form_state->setErrorByName() to set the error
    messages.

Placeholders using exclamation marks do not exist anymore in Drupal 8,
replace them and user Markup to show the HTML entities unescaped.

Changes:
  - update the info about the location of the Javascript library;
  - update the URL of the Javascript library;
  - update the examples about the text formats;
  - use an impersonal form;
  - formatting fixes.