Fix regex for code block end detection in wikiparser (#9739)

* Fix regex for code block end detection in wikiparser

* Anchor the codeblock end fence to its own line

Close an empty code block without consuming the tiddler, while a fence
only counts when it stands alone on its line.

* Match the end fence with (^|\r?\n) so the empty block case closes at
  the line start and a code line ending in ``` stays inside the block
* Add test-codeblock-parser.js covering empty blocks with language and
  CRLF, delimiter newline handling, mid-line fences and a missing fence

core/modules/parsers/wikiparser/rules/codeblock.js

@@ -25,7 +25,7 @@ exports.init = function(parser) {
 };
 
 exports.parse = function() {
-	var reEnd = /(\r?\n```$)/mg;
+	var reEnd = /(^|\r?\n)```$/mg;
 	var languageStart = this.parser.pos + 3,
 		languageEnd = languageStart + this.match[1].length;
 	// Move past the match

editions/test/tiddlers/tests/test-codeblock-parser.js

@@ -0,0 +1,69 @@
+/*\
+title: test-codeblock-parser.js
+type: application/javascript
+tags: [[$:/tags/test-spec]]
+
+Tests the codeblock wikitext rule (#9047): an empty code block must parse
+cleanly, and a closing fence only counts when it stands alone on its line.
+
+\*/
+"use strict";
+
+describe("codeblock parser tests (#9047)", function() {
+
+	var wiki = new $tw.Wiki();
+
+	function parse(text) {
+		return wiki.parseText("text/vnd.tiddlywiki",text).tree;
+	}
+
+	it("parses an empty code block with a language", function() {
+		// Browser console: $tw.wiki.parseText("text/vnd.tiddlywiki","```bash\n```").tree
+		// Expected: one codeblock node, code "", language "bash".
+		var tree = parse("```bash\n```");
+		expect(tree.length).toBe(1);
+		expect(tree[0].type).toBe("codeblock");
+		expect(tree[0].attributes.code.value).toBe("");
+		expect(tree[0].attributes.language.value).toBe("bash");
+	});
+
+	it("handles CRLF line endings around both fences", function() {
+		// Browser console: $tw.wiki.parseText("text/vnd.tiddlywiki","```bash\r\nfoo\r\n```").tree
+		// Expected: one codeblock node with code "foo"; neither the CRLF after the
+		// opening fence nor the one before the closing fence is part of the code.
+		var tree = parse("```bash\r\nfoo\r\n```");
+		expect(tree.length).toBe(1);
+		expect(tree[0].type).toBe("codeblock");
+		expect(tree[0].attributes.code.value).toBe("foo");
+	});
+
+	it("keeps the content of a block and drops the delimiting newlines", function() {
+		// Browser console: $tw.wiki.parseText("text/vnd.tiddlywiki","```\nfoo\n```").tree
+		// Expected: one codeblock node with code "foo"; the newlines around the
+		// delimiter lines are not part of the code.
+		var tree = parse("```\nfoo\n```");
+		expect(tree.length).toBe(1);
+		expect(tree[0].type).toBe("codeblock");
+		expect(tree[0].attributes.code.value).toBe("foo");
+	});
+
+	it("only closes the block when the fence stands alone on its line", function() {
+		// A content line ending in ``` is code, not a closing fence, e.g. nested
+		// markdown fences or template literals quoted inside a code block.
+		// Browser console: $tw.wiki.parseText("text/vnd.tiddlywiki","```\nabc```\ndef\n```").tree
+		// Expected: one codeblock containing "abc```\ndef"; nothing leaks out as wikitext.
+		var tree = parse("```\nabc```\ndef\n```");
+		expect(tree.length).toBe(1);
+		expect(tree[0].type).toBe("codeblock");
+		expect(tree[0].attributes.code.value).toBe("abc```\ndef");
+	});
+
+	it("swallows the rest of the tiddler when no closing fence exists", function() {
+		// Browser console: $tw.wiki.parseText("text/vnd.tiddlywiki","```bash\nfoo").tree
+		// Expected: one codeblock node with code "foo", extending to the end of the text.
+		var tree = parse("```bash\nfoo");
+		expect(tree.length).toBe(1);
+		expect(tree[0].type).toBe("codeblock");
+		expect(tree[0].attributes.code.value).toBe("foo");
+	});
+});

editions/tw5.com/tiddlers/releasenotes/5.5.0/#9739-empty-codeblock.tid

@@ -0,0 +1,13 @@
+change-category: hackability
+change-type: bugfix
+created: 20260711181412000
+description: Empty code blocks parse cleanly; a closing fence only counts alone on its line
+github-contributors: pmario
+github-links: https://github.com/TiddlyWiki/TiddlyWiki5/pull/9739
+release: 5.5.0
+tags: $:/tags/ChangeNote
+title: $:/changenotes/5.5.0/#9739
+type: text/vnd.tiddlywiki
+
+* An empty code block such as ```` ```bash ```` directly followed by the closing fence parses as an empty codeblock instead of swallowing the rest of the tiddler (fixes [[Issue #9047|https://github.com/TiddlyWiki/TiddlyWiki5/issues/9047]])
+* A closing fence only ends the block when it stands alone on its line, so code lines ending in three backticks stay inside the block