feat: override langium TokenBuilder for custom terminal rules

packages/mermaid-parser/src/language/index.ts

@@ -1,3 +1,4 @@
 export * from './generated/ast';
 export * from './generated/grammar';
 export * from './generated/module';
+export * from './mermaid-token-builder';

packages/mermaid-parser/src/language/mermaid-token-builder.ts

@@ -0,0 +1,73 @@
+import { CustomPatternMatcherFunc, EOF, TokenType } from 'chevrotain';
+import { DefaultTokenBuilder } from 'langium';
+import { TerminalRule } from 'langium/lib/grammar/generated/ast';
+
+const titleRegex = /(?:^|[ \t]+)title(?:[ \t]+([^\n]*)|$)/;
+const matchTitle: CustomPatternMatcherFunc = (str: string) => {
+    const match = titleRegex.exec(str);
+    if (match) {
+        // single line title
+        if (match[1] !== undefined) {
+            return [match[1].trim()];
+        }
+    }
+    return null;
+};
+
+/**
+ * Matches a single accessible title
+ */
+const accTitleRegex = /(?:^|[ \t]+)accTitle[ \t]*:[ \t]*([^\n]*)?/;
+const matchAccTitle: CustomPatternMatcherFunc = (str: string) => {
+    const match = accTitleRegex.exec(str);
+    if (match) {
+        // single line title
+        if (match[1] !== undefined) {
+            return [match[1].trim()];
+        }
+    }
+    return null;
+};
+
+/**
+ * Matches single and multiline accessible description
+ */
+const accDescrRegex =
+    /(?:^|[ \t]+)accDescr(?:[ \t]*:[ \t]*([^\n]*)?|\s*{([^}]*)?})/;
+const matchAccDescr: CustomPatternMatcherFunc = (str: string) => {
+    const match = accDescrRegex.exec(str);
+    if (match) {
+        // single line description
+        if (match[1] !== undefined) {
+            return [match[1].trim()];
+        }
+
+        // multi line description
+        if (match[2] !== undefined) {
+            return [match[2].replace(/^(\n+|[ \t]+)|\s+$/gm, '')];
+        }
+    }
+    return null;
+};
+
+export class MermiadTokenBuilder extends DefaultTokenBuilder {
+    override buildTerminalToken(terminal: TerminalRule): TokenType {
+        let tokenType = super.buildTerminalToken(terminal);
+        if (tokenType.name === 'EOF') {
+            tokenType = EOF;
+        } else if (tokenType.name === 'TITLE') {
+            tokenType.LINE_BREAKS = false;
+            tokenType.PATTERN = matchTitle;
+            tokenType.START_CHARS_HINT = ['title'];
+        } else if (tokenType.name === 'ACC_TITLE') {
+            tokenType.LINE_BREAKS = false;
+            tokenType.PATTERN = matchAccTitle;
+            tokenType.START_CHARS_HINT = ['accTitle'];
+        } else if (tokenType.name === 'ACC_DESCR') {
+            tokenType.LINE_BREAKS = true;
+            tokenType.PATTERN = matchAccDescr;
+            tokenType.START_CHARS_HINT = ['accDescr'];
+        }
+        return tokenType;
+    }
+}