feat: Initial clean release of CHM

packages/editor/CodeMirror/extensions/markdownFrontMatterExtension.ts

@@ -0,0 +1,126 @@
+// Extension for parsing and highlighting YAML FrontMatter blocks at the start of a document.
+//
+// A FrontMatter block is delimited by --- at the very start of the document:
+// ---
+// title: My Document
+// date: 2024-01-01
+// ---
+
+import { Tag } from '@lezer/highlight';
+import { parseMixed, SyntaxNodeRef, Input, NestedParse, ParseWrapper } from '@lezer/common';
+import { MarkdownConfig, BlockContext, Line, LeafBlock, MarkdownExtension } from '@lezer/markdown';
+import { StreamLanguage } from '@codemirror/language';
+import { yaml } from '@codemirror/legacy-modes/mode/yaml';
+
+export const frontMatterTagName = 'FrontMatter';
+export const frontMatterContentTagName = 'FrontMatterContent';
+export const frontMatterMarkerTagName = 'FrontMatterMarker';
+
+export const frontMatterTag = Tag.define();
+
+// Create the YAML language parser using the legacy mode
+const yamlLanguage = StreamLanguage.define(yaml);
+
+// Wraps a YAML parser for the FrontMatter content.
+// This replaces [nodeTag] from the syntax tree with a region handled by the YAML parser.
+const wrappedYamlParser = (nodeTag: string): ParseWrapper => {
+	return parseMixed((node: SyntaxNodeRef, _input: Input): NestedParse => {
+		if (node.name !== nodeTag) {
+			return null;
+		}
+
+		return {
+			parser: yamlLanguage.parser,
+		};
+	});
+};
+
+// Regex to match the FrontMatter delimiter (--- at start of line)
+const frontMatterDelimiterRegex = /^---\s*$/;
+
+const frontMatterConfig: MarkdownConfig = {
+	defineNodes: [
+		{
+			name: frontMatterTagName,
+			style: frontMatterTag,
+		},
+		{
+			name: frontMatterContentTagName,
+		},
+		{
+			name: frontMatterMarkerTagName,
+			style: frontMatterTag,
+		},
+	],
+	parseBlock: [{
+		name: frontMatterTagName,
+		before: 'HorizontalRule',
+		parse(cx: BlockContext, line: Line): boolean {
+			// FrontMatter must be at the very start of the document
+			if (cx.lineStart !== 0) {
+				return false;
+			}
+
+			// Check if the first line is ---
+			if (!frontMatterDelimiterRegex.test(line.text)) {
+				return false;
+			}
+
+			// If the document starts with --- always claim it as a frontmatter block,
+			// even when the closing delimiter is absent.
+			const openingMarkerStart = cx.lineStart;
+			const openingMarkerEnd = cx.lineStart + line.text.length;
+			const contentStart = openingMarkerEnd + 1;
+
+			let foundEnd = false;
+
+			// Consume lines until we find the closing --- or reach end of document.
+			while (cx.nextLine()) {
+				if (frontMatterDelimiterRegex.test(line.text)) {
+					foundEnd = true;
+					break;
+				}
+			}
+
+			// cx.lineStart now points to the closing --- (if found) or end of document (if not).
+			const contentEnd = cx.lineStart;
+
+			const openingMarkerElem = cx.elt(frontMatterMarkerTagName, openingMarkerStart, openingMarkerEnd);
+			const contentElem = cx.elt(frontMatterContentTagName, contentStart, contentEnd);
+
+			if (foundEnd) {
+				const closingMarkerStart = cx.lineStart;
+				const closingMarkerEnd = cx.lineStart + line.text.length;
+				const closingMarkerElem = cx.elt(frontMatterMarkerTagName, closingMarkerStart, closingMarkerEnd);
+
+				const containerElement = cx.elt(
+					frontMatterTagName,
+					0,
+					closingMarkerEnd,
+					[openingMarkerElem, contentElem, closingMarkerElem],
+				);
+				cx.addElement(containerElement);
+				cx.nextLine();
+			} else {
+				const containerElement = cx.elt(
+					frontMatterTagName,
+					0,
+					contentEnd,
+					[openingMarkerElem, contentElem],
+				);
+				cx.addElement(containerElement);
+			}
+
+			return true;
+		},
+		// FrontMatter blocks can end leaf blocks like paragraphs
+		endLeaf(_cx: BlockContext, line: Line, _leaf: LeafBlock): boolean {
+			return frontMatterDelimiterRegex.test(line.text);
+		},
+	}],
+	wrap: wrappedYamlParser(frontMatterContentTagName),
+};
+
+const markdownFrontMatterExtension: MarkdownExtension = [frontMatterConfig];
+
+export default markdownFrontMatterExtension;