7162: add line and column numbers to parse error messages

.changeset/slow-bees-mate.md

@@ -0,0 +1,5 @@
+---
+'@mermaid-js/parser': patch
+---
+
+fix: enhanced parser error messages to include line and column numbers for better debugging experience

packages/mermaid/src/diagrams/info/info.spec.ts

@@ -14,14 +14,14 @@ describe('info', () => {
   it('should throw because of unsupported info grammar', async () => {
     const str = `info unsupported`;
     await expect(parser.parse(str)).rejects.toThrow(
-      'Parsing failed: unexpected character: ->u<- at offset: 5, skipped 11 characters.'
+      'Parsing failed: Lexer error on line 1, column 6: unexpected character: ->u<- at offset: 5, skipped 11 characters.'
     );
   });
 
   it('should throw because of unsupported info grammar', async () => {
     const str = `info unsupported`;
     await expect(parser.parse(str)).rejects.toThrow(
-      'Parsing failed: unexpected character: ->u<- at offset: 5, skipped 11 characters.'
+      'Parsing failed: Lexer error on line 1, column 6: unexpected character: ->u<- at offset: 5, skipped 11 characters.'
     );
   });
 });

packages/parser/src/parse.ts

@@ -72,8 +72,26 @@ export async function parse<T extends DiagramAST>(
 
 export class MermaidParseError extends Error {
   constructor(public result: ParseResult<DiagramAST>) {
-    const lexerErrors: string = result.lexerErrors.map((err) => err.message).join('\n');
-    const parserErrors: string = result.parserErrors.map((err) => err.message).join('\n');
+    const lexerErrors: string = result.lexerErrors
+      .map((err) => {
+        const line = err.line !== undefined && !isNaN(err.line) ? err.line : '?';
+        const column = err.column !== undefined && !isNaN(err.column) ? err.column : '?';
+        return `Lexer error on line ${line}, column ${column}: ${err.message}`;
+      })
+      .join('\n');
+    const parserErrors: string = result.parserErrors
+      .map((err) => {
+        const line =
+          err.token.startLine !== undefined && !isNaN(err.token.startLine)
+            ? err.token.startLine
+            : '?';
+        const column =
+          err.token.startColumn !== undefined && !isNaN(err.token.startColumn)
+            ? err.token.startColumn
+            : '?';
+        return `Parse error on line ${line}, column ${column}: ${err.message}`;
+      })
+      .join('\n');
     super(`Parsing failed: ${lexerErrors} ${parserErrors}`);
   }
 }

packages/parser/tests/radar.test.ts

@@ -2,6 +2,7 @@ import { describe, expect, it } from 'vitest';
 
 import { Radar } from '../src/language/index.js';
 import { expectNoErrorsOrAlternatives, radarParse as parse } from './test-util.js';
+import { parse as parseAsync, MermaidParseError } from '../src/parse.js';
 
 const mutateGlobalSpacing = (context: string) => {
   return [
@@ -340,4 +341,85 @@ describe('radar', () => {
       }
     );
   });
+
+  describe('error messages with line and column numbers', () => {
+    it('should include line and column numbers in parser errors for radar diagrams', async () => {
+      const invalidRadar = `radar-beta
+  title Restaurant Comparison
+  axis food["Food Quality"], service["Service"], price["Price"]
+  axis ambiance["Ambiance"],
+
+  curve a["Restaurant A"]{4, 3, 2, 4}`;
+
+      try {
+        await parseAsync('radar', invalidRadar);
+        expect.fail('Should have thrown MermaidParseError');
+      } catch (error: any) {
+        expect(error).toBeInstanceOf(MermaidParseError);
+        expect(error.message).toMatch(/line \d+/);
+        expect(error.message).toMatch(/column \d+/);
+      }
+    });
+
+    it('should include line and column numbers for missing curve entries', async () => {
+      const invalidRadar = `radar-beta
+  axis my-axis
+  curve my-curve`;
+
+      try {
+        await parseAsync('radar', invalidRadar);
+        expect.fail('Should have thrown MermaidParseError');
+      } catch (error: any) {
+        expect(error).toBeInstanceOf(MermaidParseError);
+        // Line and column may be ? if not available
+        expect(error.message).toMatch(/line (\d+|\?)/);
+        expect(error.message).toMatch(/column (\d+|\?)/);
+      }
+    });
+
+    it('should include line and column numbers for invalid axis syntax', async () => {
+      const invalidRadar = `radar-beta
+  axis my-axis my-axis2`;
+
+      try {
+        await parseAsync('radar', invalidRadar);
+        expect.fail('Should have thrown MermaidParseError');
+      } catch (error: any) {
+        expect(error).toBeInstanceOf(MermaidParseError);
+        expect(error.message).toMatch(/line \d+/);
+        expect(error.message).toMatch(/column \d+/);
+      }
+    });
+
+    it('should handle lexer errors with line and column numbers', async () => {
+      const invalidRadar = `radar-beta
+  axis A
+  curve B{1}
+  invalid@symbol`;
+
+      try {
+        await parseAsync('radar', invalidRadar);
+        expect.fail('Should have thrown MermaidParseError');
+      } catch (error: any) {
+        expect(error).toBeInstanceOf(MermaidParseError);
+        // Should have line and column in the error message
+        expect(error.message).toMatch(/line (\d+|\?)/);
+        expect(error.message).toMatch(/column (\d+|\?)/);
+      }
+    });
+
+    it('should format error message with "Parse error on line X, column Y" prefix', async () => {
+      const invalidRadar = `radar-beta
+  axis`;
+
+      try {
+        await parseAsync('radar', invalidRadar);
+        expect.fail('Should have thrown MermaidParseError');
+      } catch (error: any) {
+        expect(error).toBeInstanceOf(MermaidParseError);
+        // Line and column may be ? if not available
+        expect(error.message).toMatch(/Parse error on line (\d+|\?), column (\d+|\?):/);
+      }
+    });
+  });
 });