diff --git a/composer.lock b/composer.lock
index 11b5e08089725f3e3ff0d1bc2eb91068c19ce595..648712d1c2bdb38e2f2e1e34e4cefa87785b7170 100644
--- a/composer.lock
+++ b/composer.lock
@@ -486,7 +486,7 @@
"dist": {
"type": "path",
"url": "core",
- "reference": "5bd6798a64831fa08a343a14a0ee47127c4cb99f"
+ "reference": "deeb3ec5ad5b0a9b0aa65505ab74e2bde5255abd"
},
"require": {
"asm89/stack-cors": "^1.1",
diff --git a/core/composer.json b/core/composer.json
index cf64c7800f29937880880b23c90595fba0a6c4b8..513b4b317bbcbf27c720d98fc7821d891a937ba5 100644
--- a/core/composer.json
+++ b/core/composer.json
@@ -85,6 +85,7 @@
"drupal/core-file-cache": "self.version",
"drupal/core-file-security": "self.version",
"drupal/core-filesystem": "self.version",
+ "drupal/core-front-matter": "self.version",
"drupal/core-gettext": "self.version",
"drupal/core-graph": "self.version",
"drupal/core-http-foundation": "self.version",
diff --git a/core/lib/Drupal/Component/FrontMatter/Exception/FrontMatterParseException.php b/core/lib/Drupal/Component/FrontMatter/Exception/FrontMatterParseException.php
new file mode 100644
index 0000000000000000000000000000000000000000..6296f043d45341216713895b744485504471eec6
--- /dev/null
+++ b/core/lib/Drupal/Component/FrontMatter/Exception/FrontMatterParseException.php
@@ -0,0 +1,65 @@
+<?php
+
+namespace Drupal\Component\FrontMatter\Exception;
+
+use Drupal\Component\Serialization\Exception\InvalidDataTypeException;
+
+/**
+ * Defines a class for front matter parsing exceptions.
+ */
+class FrontMatterParseException extends InvalidDataTypeException {
+
+ /**
+ * The line number of where the parse error occurred.
+ *
+ * This line number is in relation to where the parse error occurred in the
+ * source front matter content. It is different from \Exception::getLine()
+ * which is populated with the line number of where this exception was
+ * thrown in PHP.
+ *
+ * @var int
+ */
+ protected $sourceLine;
+
+ /**
+ * Constructs a new FrontMatterParseException instance.
+ *
+ * @param \Drupal\Component\Serialization\Exception\InvalidDataTypeException $exception
+ * The exception thrown when attempting to parse front matter data.
+ */
+ public function __construct(InvalidDataTypeException $exception) {
+ $this->sourceLine = 1;
+
+ // Attempt to extract the line number from the serializer error. This isn't
+ // a very stable way to do this, however it is the only way given that
+ // \Drupal\Component\Serialization\SerializationInterface does not have
+ // methods for accessing this kind of information reliably.
+ $message = 'An error occurred when attempting to parse front matter data';
+ if ($exception) {
+ preg_match('/line:?\s?(\d+)/i', $exception->getMessage(), $matches);
+ if (!empty($matches[1])) {
+ $message .= ' on line %d';
+ // Add any matching line count to the existing source line so it
+ // increases it by 1 to account for the front matter separator (---).
+ $this->sourceLine += (int) $matches[1];
+ }
+ }
+ parent::__construct(sprintf($message, $this->sourceLine), 0, $exception);
+ }
+
+ /**
+ * Retrieves the line number where the parse error occurred.
+ *
+ * This line number is in relation to where the parse error occurred in the
+ * source front matter content. It is different from \Exception::getLine()
+ * which is populated with the line number of where this exception was
+ * thrown in PHP.
+ *
+ * @return int
+ * The source line number.
+ */
+ public function getSourceLine(): int {
+ return $this->sourceLine;
+ }
+
+}
diff --git a/core/lib/Drupal/Component/FrontMatter/FrontMatter.php b/core/lib/Drupal/Component/FrontMatter/FrontMatter.php
new file mode 100644
index 0000000000000000000000000000000000000000..f09396203b8e1bb2a38387f4c2332746546eaf46
--- /dev/null
+++ b/core/lib/Drupal/Component/FrontMatter/FrontMatter.php
@@ -0,0 +1,200 @@
+<?php
+
+namespace Drupal\Component\FrontMatter;
+
+use Drupal\Component\FrontMatter\Exception\FrontMatterParseException;
+use Drupal\Component\Serialization\Exception\InvalidDataTypeException;
+use Drupal\Component\Serialization\SerializationInterface;
+
+/**
+ * Component for parsing front matter from a source.
+ *
+ * This component allows for an easy and convenient way to parse
+ * @link https://jekyllrb.com/docs/front-matter/ front matter @endlink
+ * from a source.
+ *
+ * Front matter is used as a way to provide additional static data associated
+ * with a source without affecting the contents of the source. Typically this
+ * is used in templates to denote special handling or categorization.
+ *
+ * Front matter must be the first thing in the source and must take the form of
+ * valid YAML set in between triple-hyphen lines:
+ *
+ * source.md:
+ * @code
+ * ---
+ * important: true
+ * ---
+ * My content
+ * @endcode
+ *
+ * example.php:
+ * @code
+ * use Drupal\Component\FrontMatter\FrontMatter;
+ *
+ * $frontMatter = FrontMatter::create(file_get_contents('source.md'));
+ * $data = $frontMatter->getData(); // ['important' => TRUE]
+ * $content = $frontMatter->getContent(); // 'My content'
+ * $line => $frontMatter->getLine(); // 4, line where content actually starts.
+ * @endcode
+ *
+ * @ingroup utility
+ */
+class FrontMatter {
+
+ /**
+ * The separator used to indicate front matter data.
+ *
+ * @var string
+ */
+ const SEPARATOR = '---';
+
+ /**
+ * The regular expression used to extract the YAML front matter content.
+ *
+ * @var string
+ */
+ const REGEXP = '/\A(' . self::SEPARATOR . '(.*?)?\R' . self::SEPARATOR . ')(\R.*)?\Z/s';
+
+ /**
+ * The parsed source.
+ *
+ * @var array
+ */
+ protected $parsed;
+
+ /**
+ * A serializer.
+ *
+ * @var string
+ */
+ protected $serializer;
+
+ /**
+ * The source.
+ *
+ * @var string
+ */
+ protected $source;
+
+ /**
+ * FrontMatter constructor.
+ *
+ * @param string $source
+ * A string source.
+ * @param string $serializer
+ * The name of a class that implements
+ * \Drupal\Component\Serialization\SerializationInterface.
+ */
+ public function __construct(string $source, string $serializer = '\Drupal\Component\Serialization\Yaml') {
+ assert(is_subclass_of($serializer, SerializationInterface::class), sprintf('The $serializer parameter must reference a class that implements %s.', SerializationInterface::class));
+ $this->serializer = $serializer;
+ $this->source = $source;
+ }
+
+ /**
+ * Creates a new FrontMatter instance.
+ *
+ * @param string $source
+ * A string source.
+ * @param string $serializer
+ * The name of a class that implements
+ * \Drupal\Component\Serialization\SerializationInterface.
+ *
+ * @return static
+ */
+ public static function create(string $source, string $serializer = '\Drupal\Component\Serialization\Yaml') {
+ return new static($source, $serializer);
+ }
+
+ /**
+ * Parses the source.
+ *
+ * @return array
+ * An associative array containing:
+ * - content: The real content.
+ * - data: The front matter data extracted and decoded.
+ * - line: The line number where the real content starts.
+ *
+ * @throws \Drupal\Component\FrontMatter\Exception\FrontMatterParseException
+ */
+ protected function parse(): array {
+ if (!$this->parsed) {
+ $content = $this->source;
+ $data = [];
+ $line = 1;
+
+ // Parse front matter data.
+ if (preg_match(static::REGEXP, $content, $matches)) {
+ // Extract the source content.
+ $content = !empty($matches[3]) ? trim($matches[3]) : '';
+
+ // Extract the front matter data and typecast to an array to ensure
+ // top level scalars are in an array.
+ $raw = !empty($matches[2]) ? trim($matches[2]) : '';
+ if ($raw) {
+ try {
+ $data = (array) $this->serializer::decode($raw);
+ }
+ catch (InvalidDataTypeException $exception) {
+ // Rethrow a specific front matter parse exception.
+ throw new FrontMatterParseException($exception);
+ }
+ }
+
+ // Determine the real source line by counting all newlines in the first
+ // match (which includes the front matter separators) and append a new
+ // line to denote that the content should start after it.
+ if (!empty($matches[1])) {
+ $line += preg_match_all('/\R/', $matches[1] . "\n");
+ }
+ }
+
+ // Set the parsed data.
+ $this->parsed = [
+ 'content' => $content,
+ 'data' => $data,
+ 'line' => $line,
+ ];
+ }
+
+ return $this->parsed;
+ }
+
+ /**
+ * Retrieves the extracted source content.
+ *
+ * @return string
+ * The extracted source content.
+ *
+ * @throws \Drupal\Component\FrontMatter\Exception\FrontMatterParseException
+ */
+ public function getContent(): string {
+ return $this->parse()['content'];
+ }
+
+ /**
+ * Retrieves the extracted front matter data.
+ *
+ * @return array
+ * The extracted front matter data.
+ *
+ * @throws \Drupal\Component\FrontMatter\Exception\FrontMatterParseException
+ */
+ public function getData(): array {
+ return $this->parse()['data'];
+ }
+
+ /**
+ * Retrieves the line where the source content starts, after any data.
+ *
+ * @return int
+ * The source content line.
+ *
+ * @throws \Drupal\Component\FrontMatter\Exception\FrontMatterParseException
+ */
+ public function getLine(): int {
+ return $this->parse()['line'];
+ }
+
+}
diff --git a/core/lib/Drupal/Component/FrontMatter/LICENSE.txt b/core/lib/Drupal/Component/FrontMatter/LICENSE.txt
new file mode 100644
index 0000000000000000000000000000000000000000..94fb84639c4b6ff359e47a124d8fb4a3aba7a386
--- /dev/null
+++ b/core/lib/Drupal/Component/FrontMatter/LICENSE.txt
@@ -0,0 +1,339 @@
+ GNU GENERAL PUBLIC LICENSE
+ Version 2, June 1991
+
+ Copyright (C) 1989, 1991 Free Software Foundation, Inc.,
+ 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ Everyone is permitted to copy and distribute verbatim copies
+ of this license document, but changing it is not allowed.
+
+ Preamble
+
+ The licenses for most software are designed to take away your
+freedom to share and change it. By contrast, the GNU General Public
+License is intended to guarantee your freedom to share and change free
+software--to make sure the software is free for all its users. This
+General Public License applies to most of the Free Software
+Foundation's software and to any other program whose authors commit to
+using it. (Some other Free Software Foundation software is covered by
+the GNU Lesser General Public License instead.) You can apply it to
+your programs, too.
+
+ When we speak of free software, we are referring to freedom, not
+price. Our General Public Licenses are designed to make sure that you
+have the freedom to distribute copies of free software (and charge for
+this service if you wish), that you receive source code or can get it
+if you want it, that you can change the software or use pieces of it
+in new free programs; and that you know you can do these things.
+
+ To protect your rights, we need to make restrictions that forbid
+anyone to deny you these rights or to ask you to surrender the rights.
+These restrictions translate to certain responsibilities for you if you
+distribute copies of the software, or if you modify it.
+
+ For example, if you distribute copies of such a program, whether
+gratis or for a fee, you must give the recipients all the rights that
+you have. You must make sure that they, too, receive or can get the
+source code. And you must show them these terms so they know their
+rights.
+
+ We protect your rights with two steps: (1) copyright the software, and
+(2) offer you this license which gives you legal permission to copy,
+distribute and/or modify the software.
+
+ Also, for each author's protection and ours, we want to make certain
+that everyone understands that there is no warranty for this free
+software. If the software is modified by someone else and passed on, we
+want its recipients to know that what they have is not the original, so
+that any problems introduced by others will not reflect on the original
+authors' reputations.
+
+ Finally, any free program is threatened constantly by software
+patents. We wish to avoid the danger that redistributors of a free
+program will individually obtain patent licenses, in effect making the
+program proprietary. To prevent this, we have made it clear that any
+patent must be licensed for everyone's free use or not licensed at all.
+
+ The precise terms and conditions for copying, distribution and
+modification follow.
+
+ GNU GENERAL PUBLIC LICENSE
+ TERMS AND CONDITIONS FOR COPYING, DISTRIBUTION AND MODIFICATION
+
+ 0. This License applies to any program or other work which contains
+a notice placed by the copyright holder saying it may be distributed
+under the terms of this General Public License. The "Program", below,
+refers to any such program or work, and a "work based on the Program"
+means either the Program or any derivative work under copyright law:
+that is to say, a work containing the Program or a portion of it,
+either verbatim or with modifications and/or translated into another
+language. (Hereinafter, translation is included without limitation in
+the term "modification".) Each licensee is addressed as "you".
+
+Activities other than copying, distribution and modification are not
+covered by this License; they are outside its scope. The act of
+running the Program is not restricted, and the output from the Program
+is covered only if its contents constitute a work based on the
+Program (independent of having been made by running the Program).
+Whether that is true depends on what the Program does.
+
+ 1. You may copy and distribute verbatim copies of the Program's
+source code as you receive it, in any medium, provided that you
+conspicuously and appropriately publish on each copy an appropriate
+copyright notice and disclaimer of warranty; keep intact all the
+notices that refer to this License and to the absence of any warranty;
+and give any other recipients of the Program a copy of this License
+along with the Program.
+
+You may charge a fee for the physical act of transferring a copy, and
+you may at your option offer warranty protection in exchange for a fee.
+
+ 2. You may modify your copy or copies of the Program or any portion
+of it, thus forming a work based on the Program, and copy and
+distribute such modifications or work under the terms of Section 1
+above, provided that you also meet all of these conditions:
+
+ a) You must cause the modified files to carry prominent notices
+ stating that you changed the files and the date of any change.
+
+ b) You must cause any work that you distribute or publish, that in
+ whole or in part contains or is derived from the Program or any
+ part thereof, to be licensed as a whole at no charge to all third
+ parties under the terms of this License.
+
+ c) If the modified program normally reads commands interactively
+ when run, you must cause it, when started running for such
+ interactive use in the most ordinary way, to print or display an
+ announcement including an appropriate copyright notice and a
+ notice that there is no warranty (or else, saying that you provide
+ a warranty) and that users may redistribute the program under
+ these conditions, and telling the user how to view a copy of this
+ License. (Exception: if the Program itself is interactive but
+ does not normally print such an announcement, your work based on
+ the Program is not required to print an announcement.)
+
+These requirements apply to the modified work as a whole. If
+identifiable sections of that work are not derived from the Program,
+and can be reasonably considered independent and separate works in
+themselves, then this License, and its terms, do not apply to those
+sections when you distribute them as separate works. But when you
+distribute the same sections as part of a whole which is a work based
+on the Program, the distribution of the whole must be on the terms of
+this License, whose permissions for other licensees extend to the
+entire whole, and thus to each and every part regardless of who wrote it.
+
+Thus, it is not the intent of this section to claim rights or contest
+your rights to work written entirely by you; rather, the intent is to
+exercise the right to control the distribution of derivative or
+collective works based on the Program.
+
+In addition, mere aggregation of another work not based on the Program
+with the Program (or with a work based on the Program) on a volume of
+a storage or distribution medium does not bring the other work under
+the scope of this License.
+
+ 3. You may copy and distribute the Program (or a work based on it,
+under Section 2) in object code or executable form under the terms of
+Sections 1 and 2 above provided that you also do one of the following:
+
+ a) Accompany it with the complete corresponding machine-readable
+ source code, which must be distributed under the terms of Sections
+ 1 and 2 above on a medium customarily used for software interchange; or,
+
+ b) Accompany it with a written offer, valid for at least three
+ years, to give any third party, for a charge no more than your
+ cost of physically performing source distribution, a complete
+ machine-readable copy of the corresponding source code, to be
+ distributed under the terms of Sections 1 and 2 above on a medium
+ customarily used for software interchange; or,
+
+ c) Accompany it with the information you received as to the offer
+ to distribute corresponding source code. (This alternative is
+ allowed only for noncommercial distribution and only if you
+ received the program in object code or executable form with such
+ an offer, in accord with Subsection b above.)
+
+The source code for a work means the preferred form of the work for
+making modifications to it. For an executable work, complete source
+code means all the source code for all modules it contains, plus any
+associated interface definition files, plus the scripts used to
+control compilation and installation of the executable. However, as a
+special exception, the source code distributed need not include
+anything that is normally distributed (in either source or binary
+form) with the major components (compiler, kernel, and so on) of the
+operating system on which the executable runs, unless that component
+itself accompanies the executable.
+
+If distribution of executable or object code is made by offering
+access to copy from a designated place, then offering equivalent
+access to copy the source code from the same place counts as
+distribution of the source code, even though third parties are not
+compelled to copy the source along with the object code.
+
+ 4. You may not copy, modify, sublicense, or distribute the Program
+except as expressly provided under this License. Any attempt
+otherwise to copy, modify, sublicense or distribute the Program is
+void, and will automatically terminate your rights under this License.
+However, parties who have received copies, or rights, from you under
+this License will not have their licenses terminated so long as such
+parties remain in full compliance.
+
+ 5. You are not required to accept this License, since you have not
+signed it. However, nothing else grants you permission to modify or
+distribute the Program or its derivative works. These actions are
+prohibited by law if you do not accept this License. Therefore, by
+modifying or distributing the Program (or any work based on the
+Program), you indicate your acceptance of this License to do so, and
+all its terms and conditions for copying, distributing or modifying
+the Program or works based on it.
+
+ 6. Each time you redistribute the Program (or any work based on the
+Program), the recipient automatically receives a license from the
+original licensor to copy, distribute or modify the Program subject to
+these terms and conditions. You may not impose any further
+restrictions on the recipients' exercise of the rights granted herein.
+You are not responsible for enforcing compliance by third parties to
+this License.
+
+ 7. If, as a consequence of a court judgment or allegation of patent
+infringement or for any other reason (not limited to patent issues),
+conditions are imposed on you (whether by court order, agreement or
+otherwise) that contradict the conditions of this License, they do not
+excuse you from the conditions of this License. If you cannot
+distribute so as to satisfy simultaneously your obligations under this
+License and any other pertinent obligations, then as a consequence you
+may not distribute the Program at all. For example, if a patent
+license would not permit royalty-free redistribution of the Program by
+all those who receive copies directly or indirectly through you, then
+the only way you could satisfy both it and this License would be to
+refrain entirely from distribution of the Program.
+
+If any portion of this section is held invalid or unenforceable under
+any particular circumstance, the balance of the section is intended to
+apply and the section as a whole is intended to apply in other
+circumstances.
+
+It is not the purpose of this section to induce you to infringe any
+patents or other property right claims or to contest validity of any
+such claims; this section has the sole purpose of protecting the
+integrity of the free software distribution system, which is
+implemented by public license practices. Many people have made
+generous contributions to the wide range of software distributed
+through that system in reliance on consistent application of that
+system; it is up to the author/donor to decide if he or she is willing
+to distribute software through any other system and a licensee cannot
+impose that choice.
+
+This section is intended to make thoroughly clear what is believed to
+be a consequence of the rest of this License.
+
+ 8. If the distribution and/or use of the Program is restricted in
+certain countries either by patents or by copyrighted interfaces, the
+original copyright holder who places the Program under this License
+may add an explicit geographical distribution limitation excluding
+those countries, so that distribution is permitted only in or among
+countries not thus excluded. In such case, this License incorporates
+the limitation as if written in the body of this License.
+
+ 9. The Free Software Foundation may publish revised and/or new versions
+of the General Public License from time to time. Such new versions will
+be similar in spirit to the present version, but may differ in detail to
+address new problems or concerns.
+
+Each version is given a distinguishing version number. If the Program
+specifies a version number of this License which applies to it and "any
+later version", you have the option of following the terms and conditions
+either of that version or of any later version published by the Free
+Software Foundation. If the Program does not specify a version number of
+this License, you may choose any version ever published by the Free Software
+Foundation.
+
+ 10. If you wish to incorporate parts of the Program into other free
+programs whose distribution conditions are different, write to the author
+to ask for permission. For software which is copyrighted by the Free
+Software Foundation, write to the Free Software Foundation; we sometimes
+make exceptions for this. Our decision will be guided by the two goals
+of preserving the free status of all derivatives of our free software and
+of promoting the sharing and reuse of software generally.
+
+ NO WARRANTY
+
+ 11. BECAUSE THE PROGRAM IS LICENSED FREE OF CHARGE, THERE IS NO WARRANTY
+FOR THE PROGRAM, TO THE EXTENT PERMITTED BY APPLICABLE LAW. EXCEPT WHEN
+OTHERWISE STATED IN WRITING THE COPYRIGHT HOLDERS AND/OR OTHER PARTIES
+PROVIDE THE PROGRAM "AS IS" WITHOUT WARRANTY OF ANY KIND, EITHER EXPRESSED
+OR IMPLIED, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
+MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. THE ENTIRE RISK AS
+TO THE QUALITY AND PERFORMANCE OF THE PROGRAM IS WITH YOU. SHOULD THE
+PROGRAM PROVE DEFECTIVE, YOU ASSUME THE COST OF ALL NECESSARY SERVICING,
+REPAIR OR CORRECTION.
+
+ 12. IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN WRITING
+WILL ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MAY MODIFY AND/OR
+REDISTRIBUTE THE PROGRAM AS PERMITTED ABOVE, BE LIABLE TO YOU FOR DAMAGES,
+INCLUDING ANY GENERAL, SPECIAL, INCIDENTAL OR CONSEQUENTIAL DAMAGES ARISING
+OUT OF THE USE OR INABILITY TO USE THE PROGRAM (INCLUDING BUT NOT LIMITED
+TO LOSS OF DATA OR DATA BEING RENDERED INACCURATE OR LOSSES SUSTAINED BY
+YOU OR THIRD PARTIES OR A FAILURE OF THE PROGRAM TO OPERATE WITH ANY OTHER
+PROGRAMS), EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN ADVISED OF THE
+POSSIBILITY OF SUCH DAMAGES.
+
+ END OF TERMS AND CONDITIONS
+
+ How to Apply These Terms to Your New Programs
+
+ If you develop a new program, and you want it to be of the greatest
+possible use to the public, the best way to achieve this is to make it
+free software which everyone can redistribute and change under these terms.
+
+ To do so, attach the following notices to the program. It is safest
+to attach them to the start of each source file to most effectively
+convey the exclusion of warranty; and each file should have at least
+the "copyright" line and a pointer to where the full notice is found.
+
+ <one line to give the program's name and a brief idea of what it does.>
+ Copyright (C) <year> <name of author>
+
+ This program is free software; you can redistribute it and/or modify
+ it under the terms of the GNU General Public License as published by
+ the Free Software Foundation; either version 2 of the License, or
+ (at your option) any later version.
+
+ This program is distributed in the hope that it will be useful,
+ but WITHOUT ANY WARRANTY; without even the implied warranty of
+ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ GNU General Public License for more details.
+
+ You should have received a copy of the GNU General Public License along
+ with this program; if not, write to the Free Software Foundation, Inc.,
+ 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+
+Also add information on how to contact you by electronic and paper mail.
+
+If the program is interactive, make it output a short notice like this
+when it starts in an interactive mode:
+
+ Gnomovision version 69, Copyright (C) year name of author
+ Gnomovision comes with ABSOLUTELY NO WARRANTY; for details type `show w'.
+ This is free software, and you are welcome to redistribute it
+ under certain conditions; type `show c' for details.
+
+The hypothetical commands `show w' and `show c' should show the appropriate
+parts of the General Public License. Of course, the commands you use may
+be called something other than `show w' and `show c'; they could even be
+mouse-clicks or menu items--whatever suits your program.
+
+You should also get your employer (if you work as a programmer) or your
+school, if any, to sign a "copyright disclaimer" for the program, if
+necessary. Here is a sample; alter the names:
+
+ Yoyodyne, Inc., hereby disclaims all copyright interest in the program
+ `Gnomovision' (which makes passes at compilers) written by James Hacker.
+
+ <signature of Ty Coon>, 1 April 1989
+ Ty Coon, President of Vice
+
+This General Public License does not permit incorporating your program into
+proprietary programs. If your program is a subroutine library, you may
+consider it more useful to permit linking proprietary applications with the
+library. If this is what you want to do, use the GNU Lesser General
+Public License instead of this License.
diff --git a/core/lib/Drupal/Component/FrontMatter/README.txt b/core/lib/Drupal/Component/FrontMatter/README.txt
new file mode 100644
index 0000000000000000000000000000000000000000..aad859e6d1b5d4cc224002f9cd5d5c339dc35535
--- /dev/null
+++ b/core/lib/Drupal/Component/FrontMatter/README.txt
@@ -0,0 +1,12 @@
+The Drupal FrontMatter Component
+
+Thanks for using this Drupal component.
+
+You can participate in its development on Drupal.org, through our issue system:
+https://www.drupal.org/project/issues/drupal
+
+You can get the full Drupal repo here:
+https://www.drupal.org/project/drupal/git-instructions
+
+You can browse the full Drupal repo here:
+https://git.drupalcode.org/project/drupal
diff --git a/core/lib/Drupal/Component/FrontMatter/TESTING.txt b/core/lib/Drupal/Component/FrontMatter/TESTING.txt
new file mode 100644
index 0000000000000000000000000000000000000000..36229d13df90703939124def89d54f93bf27bd13
--- /dev/null
+++ b/core/lib/Drupal/Component/FrontMatter/TESTING.txt
@@ -0,0 +1,18 @@
+HOW-TO: Test this Drupal component
+
+In order to test this component, you'll need to get the entire Drupal repo and
+run the tests there.
+
+You'll find the tests under core/tests/Drupal/Tests/Component.
+
+You can get the full Drupal repo here:
+https://www.drupal.org/project/drupal/git-instructions
+
+You can find more information about running PHPUnit tests with Drupal here:
+https://www.drupal.org/node/2116263
+
+Each component in the Drupal\Component namespace has its own annotated test
+group. You can use this group to run only the tests for this component. Like
+this:
+
+$ ./vendor/bin/phpunit -c core --group FrontMatter
diff --git a/core/lib/Drupal/Component/FrontMatter/composer.json b/core/lib/Drupal/Component/FrontMatter/composer.json
new file mode 100644
index 0000000000000000000000000000000000000000..15a0b081eca144f172fcac43a20a97a145b91c3e
--- /dev/null
+++ b/core/lib/Drupal/Component/FrontMatter/composer.json
@@ -0,0 +1,16 @@
+{
+ "name": "drupal/core-front-matter",
+ "description": "Component for parsing front matter from a source.",
+ "keywords": ["drupal"],
+ "homepage": "https://www.drupal.org/project/drupal",
+ "license": "GPL-2.0-or-later",
+ "require": {
+ "php": ">=7.3.0",
+ "drupal/core-serialization": "^8.8"
+ },
+ "autoload": {
+ "psr-4": {
+ "Drupal\\Component\\FrontMatter\\": ""
+ }
+ }
+}
diff --git a/core/lib/Drupal/Core/Render/theme.api.php b/core/lib/Drupal/Core/Render/theme.api.php
index 082f139f3c92d95790f68c685b77c2e647618c3b..12f485394c51dc5dc438e70b5525c48b7dace0c0 100644
--- a/core/lib/Drupal/Core/Render/theme.api.php
+++ b/core/lib/Drupal/Core/Render/theme.api.php
@@ -200,6 +200,15 @@
* }
* @endcode
*
+ * @section front_matter Front Matter
+ * Twig has been extended in Drupal to provide an easy way to parse front
+ * matter from template files. See \Drupal\Component\FrontMatter\FrontMatter
+ * for more information:
+ * @code
+ * $metadata = \Drupal::service('twig')->getTemplateMetadata('/path/to/template.html.twig');
+ * @endcode
+ * Note: all front matter is stripped from templates prior to rendering.
+ *
* @see hooks
* @see callbacks
* @see theme_render
diff --git a/core/lib/Drupal/Core/Template/TwigEnvironment.php b/core/lib/Drupal/Core/Template/TwigEnvironment.php
index 61dd220e0a39945f2bfd7a10fa6e274a54037e32..34df39f099cd8be608eee5a69a826e0f3ffe5c41 100644
--- a/core/lib/Drupal/Core/Template/TwigEnvironment.php
+++ b/core/lib/Drupal/Core/Template/TwigEnvironment.php
@@ -2,13 +2,18 @@
namespace Drupal\Core\Template;
+use Drupal\Component\FrontMatter\Exception\FrontMatterParseException;
+use Drupal\Component\FrontMatter\FrontMatter;
use Drupal\Core\Cache\CacheBackendInterface;
use Drupal\Core\PhpStorage\PhpStorageFactory;
use Drupal\Core\Render\Markup;
+use Drupal\Core\Serialization\Yaml;
use Drupal\Core\State\StateInterface;
use Twig\Environment;
+use Twig\Error\SyntaxError;
use Twig\Extension\SandboxExtension;
use Twig\Loader\LoaderInterface;
+use Twig\Source;
/**
* A class that defines a Twig environment for Drupal.
@@ -97,6 +102,36 @@ public function __construct($root, CacheBackendInterface $cache, $twig_extension
$this->addExtension($sandbox);
}
+ /**
+ * {@inheritdoc}
+ */
+ public function compileSource(Source $source) {
+ // Note: always use \Drupal\Core\Serialization\Yaml here instead of the
+ // "serializer.yaml" service. This allows the core serializer to utilize
+ // core related functionality which isn't available as the standalone
+ // component based serializer.
+ $frontMatter = FrontMatter::create($source->getCode(), Yaml::class);
+
+ // Reconstruct the source if there is front matter data detected. Prepend
+ // the source with {% line \d+ %} to inform Twig that the source code
+ // actually starts on a different line past the front matter data. This is
+ // particularly useful when used in error reporting.
+ try {
+ if (($line = $frontMatter->getLine()) > 1) {
+ $content = "{% line $line %}" . $frontMatter->getContent();
+ $source = new Source($content, $source->getName(), $source->getPath());
+ }
+ }
+ catch (FrontMatterParseException $exception) {
+ // Convert parse exception into a syntax exception for Twig and append
+ // the path/name of the source to help further identify where it occurred.
+ $message = sprintf($exception->getMessage() . ' in %s', $source->getPath() ?: $source->getName());
+ throw new SyntaxError($message, $exception->getSourceLine(), $source, $exception);
+ }
+
+ return parent::compileSource($source);
+ }
+
/**
* Invalidates all compiled Twig templates.
*
@@ -118,6 +153,37 @@ public function getTwigCachePrefix() {
return $this->twigCachePrefix;
}
+ /**
+ * Retrieves metadata associated with a template.
+ *
+ * @param string $name
+ * The name for which to calculate the template class name.
+ *
+ * @return array
+ * The template metadata, if any.
+ *
+ * @throws \Twig\Error\LoaderError
+ * @throws \Twig\Error\SyntaxError
+ */
+ public function getTemplateMetadata(string $name): array {
+ $loader = $this->getLoader();
+ $source = $loader->getSourceContext($name);
+
+ // Note: always use \Drupal\Core\Serialization\Yaml here instead of the
+ // "serializer.yaml" service. This allows the core serializer to utilize
+ // core related functionality which isn't available as the standalone
+ // component based serializer.
+ try {
+ return FrontMatter::create($source->getCode(), Yaml::class)->getData();
+ }
+ catch (FrontMatterParseException $exception) {
+ // Convert parse exception into a syntax exception for Twig and append
+ // the path/name of the source to help further identify where it occurred.
+ $message = sprintf($exception->getMessage() . ' in %s', $source->getPath() ?: $source->getName());
+ throw new SyntaxError($message, $exception->getSourceLine(), $source, $exception);
+ }
+ }
+
/**
* Gets the template class associated with the given string.
*
diff --git a/core/tests/Drupal/KernelTests/Core/Theme/FrontMatterTest.php b/core/tests/Drupal/KernelTests/Core/Theme/FrontMatterTest.php
new file mode 100644
index 0000000000000000000000000000000000000000..f902547dceb2168d9984ff7c7808d8c60dbae119
--- /dev/null
+++ b/core/tests/Drupal/KernelTests/Core/Theme/FrontMatterTest.php
@@ -0,0 +1,130 @@
+<?php
+
+namespace Drupal\KernelTests\Core\Theme;
+
+use Drupal\Core\DependencyInjection\ContainerBuilder;
+use Drupal\KernelTests\KernelTestBase;
+use Drupal\Tests\Component\FrontMatter\FrontMatterTest as ComponentFrontMatterTest;
+use Symfony\Component\DependencyInjection\Definition;
+use Twig\Error\Error;
+use Twig\Error\SyntaxError;
+
+/**
+ * Tests Twig front matter support.
+ *
+ * @covers \Drupal\Core\Template\Loader\FrontMatterLoaderDecorator
+ * @covers \Drupal\Core\Template\FrontMatterSourceDecorator
+ * @group Twig
+ */
+class FrontMatterTest extends KernelTestBase {
+
+ /**
+ * A broken source.
+ */
+ const BROKEN_SOURCE = '<div>Hello {{ world</div>';
+
+ /**
+ * Twig service.
+ *
+ * @var \Drupal\Core\Template\TwigEnvironment
+ */
+ protected $twig;
+
+ /**
+ * {@inheritdoc}
+ */
+ protected function setUp(): void {
+ parent::setUp();
+ $this->twig = \Drupal::service('twig');
+ }
+
+ /**
+ * {@inheritdoc}
+ */
+ public function register(ContainerBuilder $container) {
+ parent::register($container);
+
+ $container->setDefinition('twig_loader__file_system', new Definition('Twig_Loader_Filesystem', [[sys_get_temp_dir()]]))
+ ->addTag('twig.loader');
+ }
+
+ /**
+ * Creates a new temporary Twig file.
+ *
+ * @param string $content
+ * The contents of the Twig file to save.
+ *
+ * @return string
+ * The absolute path to the temporary file.
+ */
+ protected function createTwigTemplate(string $content = ''): string {
+ $file = tempnam(sys_get_temp_dir(), 'twig') . ".html.twig";
+ file_put_contents($file, $content);
+ return $file;
+ }
+
+ /**
+ * Tests broken front matter.
+ *
+ * @covers \Drupal\Core\Template\TwigEnvironment::getTemplateMetadata
+ * @covers \Drupal\Component\FrontMatter\Exception\FrontMatterParseException
+ */
+ public function testFrontMatterBroken() {
+ $source = "---\ncollection:\n- key: foo\n foo: bar\n---\n" . ComponentFrontMatterTest::SOURCE;
+ $file = $this->createTwigTemplate($source);
+ $this->expectException(SyntaxError::class);
+ $this->expectExceptionMessage('An error occurred when attempting to parse front matter data on line 4 in ' . $file);
+ $this->twig->getTemplateMetadata(basename($file));
+ }
+
+ /**
+ * Test Twig template front matter.
+ *
+ * @param array|null $yaml
+ * The YAML used for metadata in a Twig template.
+ * @param int $line
+ * The expected line number where the source code starts.
+ * @param string $content
+ * The content to use for testing purposes.
+ *
+ * @covers \Drupal\Core\Template\TwigEnvironment::compileSource
+ * @covers \Drupal\Core\Template\TwigEnvironment::getTemplateMetadata
+ *
+ * @dataProvider \Drupal\Tests\Component\FrontMatter\FrontMatterTest::providerFrontMatterData
+ */
+ public function testFrontMatter($yaml, $line, $content = ComponentFrontMatterTest::SOURCE) {
+ // Create a temporary Twig template.
+ $source = ComponentFrontMatterTest::createFrontMatterSource($yaml, $content);
+ $file = $this->createTwigTemplate($source);
+ $name = basename($file);
+
+ // Ensure the proper metadata is returned.
+ $metadata = $this->twig->getTemplateMetadata($name);
+ $this->assertEquals($yaml === NULL ? [] : $yaml, $metadata);
+
+ // Ensure the metadata is never rendered.
+ $output = $this->twig->load($name)->render();
+ $this->assertEquals($content, $output);
+
+ // Create a temporary Twig template.
+ $source = ComponentFrontMatterTest::createFrontMatterSource($yaml, static::BROKEN_SOURCE);
+ $file = $this->createTwigTemplate($source);
+ $name = basename($file);
+
+ try {
+ $this->twig->load($name);
+ }
+ catch (Error $error) {
+ $this->assertEquals($line, $error->getTemplateLine());
+ }
+
+ // Ensure string based templates work too.
+ try {
+ $this->twig->createTemplate($source)->render();
+ }
+ catch (Error $error) {
+ $this->assertEquals($line, $error->getTemplateLine());
+ }
+ }
+
+}
diff --git a/core/tests/Drupal/Tests/Component/FrontMatter/FrontMatterTest.php b/core/tests/Drupal/Tests/Component/FrontMatter/FrontMatterTest.php
new file mode 100644
index 0000000000000000000000000000000000000000..3e6a27aabf1dd113853abe65269ae8741ed521cc
--- /dev/null
+++ b/core/tests/Drupal/Tests/Component/FrontMatter/FrontMatterTest.php
@@ -0,0 +1,172 @@
+<?php
+
+namespace Drupal\Tests\Component\FrontMatter;
+
+use Drupal\Component\FrontMatter\Exception\FrontMatterParseException;
+use Drupal\Component\FrontMatter\FrontMatter;
+use Drupal\Component\Serialization\Yaml;
+use PHPUnit\Framework\TestCase;
+
+/**
+ * Tests front matter parsing helper methods.
+ *
+ * @group FrontMatter
+ *
+ * @coversDefaultClass \Drupal\Component\FrontMatter\FrontMatter
+ */
+class FrontMatterTest extends TestCase {
+
+ /**
+ * A basic source string.
+ */
+ const SOURCE = '<div>Hello world</div>';
+
+ /**
+ * Creates a front matter source string.
+ *
+ * @param array|null $yaml
+ * The YAML array to prepend as a front matter block.
+ * @param string $content
+ * The source contents.
+ *
+ * @return string
+ * The new source.
+ */
+ public static function createFrontMatterSource(?array $yaml, string $content = self::SOURCE): string {
+ // Encode YAML and wrap in a front matter block.
+ $frontMatter = '';
+ if (is_array($yaml)) {
+ $yaml = $yaml ? trim(Yaml::encode($yaml)) . "\n" : '';
+ $frontMatter = FrontMatter::SEPARATOR . "\n$yaml" . FrontMatter::SEPARATOR . "\n";
+ }
+ return $frontMatter . $content;
+ }
+
+ /**
+ * Tests when a passed serializer doesn't implement the proper interface.
+ *
+ * @covers ::__construct
+ * @covers ::create
+ */
+ public function testFrontMatterSerializerException() {
+ $this->expectException(\AssertionError::class);
+ $this->expectExceptionMessage('The $serializer parameter must reference a class that implements Drupal\Component\Serialization\SerializationInterface.');
+ FrontMatter::create('', '');
+ }
+
+ /**
+ * Tests broken front matter.
+ *
+ * @covers ::__construct
+ * @covers ::create
+ * @covers ::parse
+ * @covers \Drupal\Component\FrontMatter\Exception\FrontMatterParseException
+ */
+ public function testFrontMatterBroken() {
+ $this->expectException(FrontMatterParseException::class);
+ $this->expectExceptionMessage('An error occurred when attempting to parse front matter data on line 4');
+ $source = "---\ncollection:\n- key: foo\n foo: bar\n---\n";
+ FrontMatter::create($source)->getData();
+ }
+
+ /**
+ * Tests the parsed data from front matter.
+ *
+ * @param array|null $yaml
+ * The YAML used as front matter data to prepend the source.
+ * @param int $line
+ * The expected line number where the source code starts.
+ * @param string $content
+ * The content to use for testing purposes.
+ *
+ * @covers ::__construct
+ * @covers ::getContent
+ * @covers ::getData
+ * @covers ::getLine
+ * @covers ::create
+ * @covers ::parse
+ *
+ * @dataProvider providerFrontMatterData
+ */
+ public function testFrontMatterData($yaml, $line, $content = self::SOURCE) {
+ $source = static::createFrontMatterSource($yaml, $content);
+ $frontMatter = FrontMatter::create($source);
+ $this->assertEquals($content, $frontMatter->getContent());
+ $this->assertEquals($yaml === NULL ? [] : $yaml, $frontMatter->getData());
+ $this->assertEquals($line, $frontMatter->getLine());
+ }
+
+ /**
+ * Provides the front matter data to test.
+ *
+ * @return array
+ * Array of front matter data.
+ */
+ public static function providerFrontMatterData() {
+ $data['none'] = [
+ 'yaml' => NULL,
+ 'line' => 1,
+ ];
+ $data['scalar'] = [
+ 'yaml' => [
+ 'string' => 'value',
+ 'number' => 42,
+ 'bool' => TRUE,
+ 'null' => NULL,
+ ],
+ 'line' => 7,
+ ];
+ $data['indexed_arrays'] = [
+ 'yaml' => [
+ 'brackets' => [1, 2, 3],
+ 'items' => [
+ 'item1',
+ 'item2',
+ 'item3',
+ ],
+ ],
+ 'line' => 11,
+ ];
+ $data['associative_arrays'] = [
+ 'yaml' => [
+ 'brackets' => [
+ 'a' => 1,
+ 'b' => 2,
+ 'c' => 3,
+ ],
+ 'items' => [
+ 'a' => 'item1',
+ 'b' => 'item2',
+ 'c' => 'item3',
+ ],
+ ],
+ 'line' => 11,
+ ];
+ $data['empty_data'] = [
+ 'yaml' => [],
+ 'line' => 3,
+ ];
+ $data['empty_content'] = [
+ 'yaml' => ['key' => 'value'],
+ 'line' => 4,
+ 'content' => '',
+ ];
+ $data['empty_data_and_content'] = [
+ 'yaml' => [],
+ 'line' => 3,
+ 'content' => '',
+ ];
+ $data['empty_string'] = [
+ 'yaml' => NULL,
+ 'line' => 1,
+ 'content' => '',
+ ];
+ $data['multiple_separators'] = [
+ 'yaml' => ['key' => '---'],
+ 'line' => 4,
+ 'content' => "Something\n---\nSomething more",
+ ];
+ return $data;
+ }
+
+}