Support redirects on Markdown pages

src/Application/RedirectSyntax.php

@@ -0,0 +1,96 @@
+<?php
+
+declare( strict_types = 1 );
+
+namespace ProfessionalWiki\NativeMarkdown\Application;
+
+/**
+ * Reads and writes the MediaWiki redirect syntax (`#REDIRECT [[Target]]`) on a
+ * markdown page. The `redirect` magic word is localized, so its synonyms are
+ * injected; the first synonym is the content language's preferred spelling.
+ *
+ * This mirrors how the wikitext content handler treats redirects, so a page
+ * move (which writes this syntax) leaves a working redirect and hand-written
+ * redirects behave the same across content models.
+ */
+final class RedirectSyntax {
+
+	/**
+	 * @param string[] $magicWordSynonyms Redirect magic word spellings, preferred one first
+	 */
+	public function __construct(
+		private readonly array $magicWordSynonyms
+	) {
+	}
+
+	/**
+	 * The raw target text of the redirect, or null when the page is not a
+	 * redirect. Turning that text into a validated title is the caller's job,
+	 * since redirect-target validation is a wiki concern.
+	 */
+	public function extractTargetText( string $pageText ): ?string {
+		if ( $this->magicWordSynonyms === [] ) {
+			return null;
+		}
+
+		$afterMagicWord = preg_replace( $this->magicWordRegex(), '', ltrim( $pageText ), 1, $count );
+
+		if ( $count === 0 || $afterMagicWord === null ) {
+			return null;
+		}
+
+		// Mirrors the first-link extraction of WikitextContentHandler: a leading
+		// colon and a piped label are both allowed and dropped.
+		if ( preg_match( '!^\s*:?\s*\[{2}(.*?)(?:\|.*?)?\]{2}\s*!', $afterMagicWord, $matches ) !== 1 ) {
+			return null;
+		}
+
+		return $this->decodeTarget( $matches[1] );
+	}
+
+	private function decodeTarget( string $target ): string {
+		if ( str_contains( $target, '%' ) ) {
+			return rawurldecode( ltrim( $target, ':' ) );
+		}
+
+		return $target;
+	}
+
+	/**
+	 * Builds the redirect line pointing at the given target text. The caller
+	 * supplies any leading colon needed to escape category or interlanguage
+	 * targets, matching the wikitext handler.
+	 */
+	public function buildRedirectText( string $target ): string {
+		return $this->preferredSynonym() . ' [[' . $target . ']]';
+	}
+
+	/**
+	 * The content language's preferred spelling of the redirect magic word.
+	 * MediaWiki always defines at least the English `#REDIRECT`, the fallback
+	 * used should the injected synonym list ever be empty.
+	 */
+	private function preferredSynonym(): string {
+		return $this->magicWordSynonyms[0] ?? '#REDIRECT';
+	}
+
+	/**
+	 * The redirect magic word is always case-insensitive, so this matches any
+	 * synonym at the very start of the page. Longest synonyms come first, as in
+	 * MediaWiki's own magic word matching, so one is never a prefix of another.
+	 *
+	 * @return non-empty-string
+	 */
+	private function magicWordRegex(): string {
+		$synonyms = $this->magicWordSynonyms;
+		usort( $synonyms, static fn ( string $a, string $b ) => strlen( $b ) <=> strlen( $a ) );
+
+		$alternatives = implode( '|', array_map(
+			static fn ( string $synonym ) => preg_quote( $synonym, '/' ),
+			$synonyms
+		) );
+
+		return '/^(?:' . $alternatives . ')/iu';
+	}
+
+}

src/EntryPoints/MarkdownContent.php

@@ -5,6 +5,7 @@
 namespace ProfessionalWiki\NativeMarkdown\EntryPoints;
 
 use MediaWiki\Content\TextContent;
+use MediaWiki\Title\Title;
 use ProfessionalWiki\NativeMarkdown\NativeMarkdownExtension;
 
 /**
@@ -19,6 +20,19 @@ public function __construct( string $text ) {
 		parent::__construct( $text, NativeMarkdownExtension::CONTENT_MODEL );
 	}
 
+	/**
+	 * Redirect resolution lives on the handler, which has the services to turn
+	 * the redirect syntax into a validated title. This drives redirect detection
+	 * for the whole wiki: page moves, WhatLinksHere and the redirect table.
+	 */
+	public function getRedirectTarget(): ?Title {
+		$handler = $this->getContentHandler();
+
+		return $handler instanceof MarkdownContentHandler
+			? $handler->getRedirectTargetForContent( $this )
+			: null;
+	}
+
 	/**
 	 * The search index gets the rendered words rather than the raw markdown, so
 	 * result snippets do not show markup characters or hidden front matter.

src/EntryPoints/MarkdownContentHandler.php

@@ -7,8 +7,11 @@
 use MediaWiki\Content\Content;
 use MediaWiki\Content\Renderer\ContentParseParams;
 use MediaWiki\Content\TextContentHandler;
+use MediaWiki\Languages\LanguageNameUtils;
+use MediaWiki\MediaWikiServices;
 use MediaWiki\Parser\ParserOutput;
 use MediaWiki\Parser\ParserOutputFlags;
+use MediaWiki\Title\Title;
 use MediaWiki\Title\TitleValue;
 use ProfessionalWiki\NativeMarkdown\Application\RenderedMarkdown;
 use ProfessionalWiki\NativeMarkdown\Application\Section;
@@ -44,9 +47,81 @@ public function isParserCacheSupported() {
 		return true;
 	}
 
+	public function supportsRedirects(): bool {
+		return true;
+	}
+
+	public function makeRedirectContent( Title $destination, $text = '' ): Content {
+		$redirectText = NativeMarkdownExtension::getInstance()->newRedirectSyntax()->buildRedirectText(
+			$this->redirectTargetText( $destination )
+		);
+
+		if ( $text !== '' ) {
+			$redirectText .= "\n" . $text;
+		}
+
+		return new MarkdownContent( $redirectText );
+	}
+
+	private function redirectTargetText( Title $destination ): string {
+		$colon = $this->redirectTargetNeedsColon( $destination ) ? ':' : '';
+
+		return $colon . $destination->getFullText();
+	}
+
+	/**
+	 * A redirect to a category or an interlanguage link needs a leading colon,
+	 * otherwise the target reads as a category assignment or a language link
+	 * rather than a redirect. Mirrors WikitextContentHandler.
+	 */
+	private function redirectTargetNeedsColon( Title $destination ): bool {
+		// NS_CATEGORY is a MediaWiki global constant psalm cannot resolve from scanned core files.
+		/** @psalm-suppress UndefinedConstant */
+		if ( $destination->getNamespace() === NS_CATEGORY ) {
+			return true;
+		}
+
+		$interwiki = $destination->getInterwiki();
+
+		return $interwiki !== '' && MediaWikiServices::getInstance()->getLanguageNameUtils()->getLanguageName(
+			$interwiki,
+			LanguageNameUtils::AUTONYMS,
+			LanguageNameUtils::DEFINED
+		) !== '';
+	}
+
+	public function getRedirectTargetForContent( MarkdownContent $content ): ?Title {
+		return $this->resolveRedirectTarget( $content->getText() );
+	}
+
+	private function resolveRedirectTarget( string $text ): ?Title {
+		$targetText = NativeMarkdownExtension::getInstance()->newRedirectSyntax()->extractTargetText( $text );
+
+		if ( $targetText === null ) {
+			return null;
+		}
+
+		$target = MediaWikiServices::getInstance()->getTitleFactory()->newFromText( $targetText );
+
+		if ( !$target instanceof Title || !$target->isValidRedirectTarget() ) {
+			return null;
+		}
+
+		return $target;
+	}
+
 	protected function fillParserOutput( Content $content, ContentParseParams $cpoParams, ParserOutput &$output ): void {
+		$text = $content instanceof MarkdownContent ? $content->getText() : '';
+
+		$redirectTarget = $this->resolveRedirectTarget( $text );
+
+		if ( $redirectTarget !== null ) {
+			$this->fillRedirectParserOutput( $output, $cpoParams, $redirectTarget );
+			return;
+		}
+
 		$rendered = NativeMarkdownExtension::getInstance()->getMarkdownRenderer()->render(
-			$content instanceof MarkdownContent ? $content->getText() : '',
+			$text,
 			$cpoParams->getGenerateHtml()
 		);
 
@@ -62,6 +137,30 @@ protected function fillParserOutput( Content $content, ContentParseParams $cpoPa
 		$output->setRawText( $cpoParams->getGenerateHtml() ? $rendered->html : null );
 	}
 
+	/**
+	 * A redirect page shows MediaWiki's redirect view (the arrow to the target)
+	 * in place of its markdown body, and records the target as a link so page
+	 * moves, WhatLinksHere and the redirect table all see it.
+	 */
+	private function fillRedirectParserOutput( ParserOutput $output, ContentParseParams $cpoParams, Title $target ): void {
+		$output->setFromParserOptions( $cpoParams->getParserOptions() );
+		$output->addLink( $target );
+
+		if ( !$cpoParams->getGenerateHtml() ) {
+			$output->setRawText( null );
+			return;
+		}
+
+		$services = MediaWikiServices::getInstance();
+		$page = $services->getTitleFactory()->newFromPageReference( $cpoParams->getPage() );
+
+		$output->setRedirectHeader(
+			$services->getLinkRenderer()->makeRedirectHeader( $page->getPageLanguage(), $target )
+		);
+		$output->addModuleStyles( [ 'mediawiki.action.view.redirectPage' ] );
+		$output->setRawText( '' );
+	}
+
 	private function registerLinks( ParserOutput $output, RenderedMarkdown $rendered ): void {
 		foreach ( $rendered->links as $link ) {
 			// addLink() routes interwiki targets to the interwiki table itself.

src/NativeMarkdownExtension.php

@@ -8,6 +8,7 @@
 use MediaWiki\Parser\Parser;
 use ProfessionalWiki\NativeMarkdown\Application\MarkdownDefaultPolicy;
 use ProfessionalWiki\NativeMarkdown\Application\MarkdownRenderer;
+use ProfessionalWiki\NativeMarkdown\Application\RedirectSyntax;
 use ProfessionalWiki\NativeMarkdown\Persistence\MediaWikiFileEmbedRenderer;
 use ProfessionalWiki\NativeMarkdown\Persistence\MediaWikiPageLinkRenderer;
 use ProfessionalWiki\NativeMarkdown\Persistence\MediaWikiTitleParser;
@@ -68,6 +69,15 @@ private function newMarkdownRenderer(): MarkdownRenderer {
 		);
 	}
 
+	public function newRedirectSyntax(): RedirectSyntax {
+		return new RedirectSyntax(
+			magicWordSynonyms: MediaWikiServices::getInstance()
+				->getMagicWordFactory()
+				->get( 'redirect' )
+				->getSynonyms()
+		);
+	}
+
 	public function newMarkdownDefaultPolicy(): MarkdownDefaultPolicy {
 		$config = MediaWikiServices::getInstance()->getMainConfig();
 

tests/phpunit/Application/RedirectSyntaxTest.php

@@ -0,0 +1,75 @@
+<?php
+
+declare( strict_types = 1 );
+
+namespace ProfessionalWiki\NativeMarkdown\Tests\Application;
+
+use PHPUnit\Framework\TestCase;
+use ProfessionalWiki\NativeMarkdown\Application\RedirectSyntax;
+
+/**
+ * @covers \ProfessionalWiki\NativeMarkdown\Application\RedirectSyntax
+ */
+class RedirectSyntaxTest extends TestCase {
+
+	private function englishSyntax(): RedirectSyntax {
+		return new RedirectSyntax( magicWordSynonyms: [ '#REDIRECT' ] );
+	}
+
+	public function testExtractsTargetFollowingMagicWord(): void {
+		$this->assertSame( 'Target Page', $this->englishSyntax()->extractTargetText( '#REDIRECT [[Target Page]]' ) );
+	}
+
+	public function testHasNoTargetWithoutMagicWord(): void {
+		$this->assertNull( $this->englishSyntax()->extractTargetText( '[[Target Page]]' ) );
+	}
+
+	public function testHasNoTargetInPlainText(): void {
+		$this->assertNull( $this->englishSyntax()->extractTargetText( 'Just some prose with a [link](https://example.com).' ) );
+	}
+
+	public function testMatchesMagicWordCaseInsensitively(): void {
+		$this->assertSame( 'Target Page', $this->englishSyntax()->extractTargetText( '#redirect [[Target Page]]' ) );
+	}
+
+	public function testIgnoresLeadingWhitespaceBeforeMagicWord(): void {
+		$this->assertSame( 'Target Page', $this->englishSyntax()->extractTargetText( "\n\n   #REDIRECT [[Target Page]]" ) );
+	}
+
+	public function testRecognizesAnyLocalizedSynonym(): void {
+		$syntax = new RedirectSyntax( magicWordSynonyms: [ '#REDIRECT', '#WEITERLEITUNG' ] );
+
+		$this->assertSame( 'Ziel', $syntax->extractTargetText( '#WEITERLEITUNG [[Ziel]]' ) );
+	}
+
+	public function testDropsPipedLabelFromTarget(): void {
+		$this->assertSame( 'Target Page', $this->englishSyntax()->extractTargetText( '#REDIRECT [[Target Page|see over here]]' ) );
+	}
+
+	public function testKeepsLeadingColonEscapeInTarget(): void {
+		$this->assertSame( ':Category:Guides', $this->englishSyntax()->extractTargetText( '#REDIRECT [[:Category:Guides]]' ) );
+	}
+
+	public function testUrlDecodesPercentEncodedTarget(): void {
+		$this->assertSame( 'Foo Bar', $this->englishSyntax()->extractTargetText( '#REDIRECT [[Foo%20Bar]]' ) );
+	}
+
+	public function testKeepsSectionFragmentInTarget(): void {
+		$this->assertSame( 'Target Page#History', $this->englishSyntax()->extractTargetText( '#REDIRECT [[Target Page#History]]' ) );
+	}
+
+	public function testHasNoTargetWhenNoLinkFollowsMagicWord(): void {
+		$this->assertNull( $this->englishSyntax()->extractTargetText( '#REDIRECT nowhere in particular' ) );
+	}
+
+	public function testBuildsRedirectUsingPreferredSynonym(): void {
+		$syntax = new RedirectSyntax( magicWordSynonyms: [ '#WEITERLEITUNG', '#REDIRECT' ] );
+
+		$this->assertSame( '#WEITERLEITUNG [[Target Page]]', $syntax->buildRedirectText( 'Target Page' ) );
+	}
+
+	public function testBuildsRedirectWithColonEscapedTarget(): void {
+		$this->assertSame( '#REDIRECT [[:Category:Guides]]', $this->englishSyntax()->buildRedirectText( ':Category:Guides' ) );
+	}
+
+}

tests/phpunit/EntryPoints/MarkdownEditingBehaviorTest.php

@@ -77,8 +77,8 @@ public function testDiffShowsAddedAndRemovedLines(): void {
 		$this->assertStringContainsString( 'diff-addedline', $diff );
 	}
 
-	public function testMarkdownContentModelDoesNotSupportRedirects(): void {
-		$this->assertFalse( $this->handler()->supportsRedirects() );
+	public function testMarkdownContentModelSupportsRedirects(): void {
+		$this->assertTrue( $this->handler()->supportsRedirects() );
 	}
 
 }