fix(core): Resolve escape sequences in fmt / parameterize messages

packages/core/src/utils/parameterize.ts

@@ -12,8 +12,11 @@ import type { ParameterizedString } from '../types/parameterize';
  * @returns A `ParameterizedString` object that can be passed into `captureMessage` or Sentry.logger.X methods.
  */
 export function parameterize(strings: TemplateStringsArray, ...values: unknown[]): ParameterizedString {
-  const formatted = new String(String.raw(strings, ...values)) as ParameterizedString;
-  formatted.__sentry_template_string__ = strings.join('\x00').replace(/%/g, '%%').replace(/\0/g, '%s');
+  // `String.raw` would keep escape sequences such as `\n` as typed, while the template uses the cooked strings.
+  // A string with an invalid escape sequence has no cooked value, so fall back to its raw form.
+  const cooked = strings.map((str, i) => str ?? strings.raw[i]);
+  const formatted = new String(String.raw({ raw: cooked }, ...values)) as ParameterizedString;
+  formatted.__sentry_template_string__ = cooked.join('\x00').replace(/%/g, '%%').replace(/\0/g, '%s');
   formatted.__sentry_template_values__ = values;
   return formatted;
 }

packages/core/test/lib/utils/parameterize.test.ts

@@ -24,4 +24,20 @@ describe('parameterize()', () => {
     expect(formatted.__sentry_template_string__).toEqual(string.__sentry_template_string__);
     expect(formatted.__sentry_template_values__).toEqual(string.__sentry_template_values__);
   });
+
+  test('keeps escape sequences the same in the message and the template', () => {
+    const x = 'first';
+    const formatted = parameterize`Line one\nline two with ${x} → \`done\``;
+
+    expect(String(formatted)).toBe('Line one\nline two with first → `done`');
+    expect(formatted.__sentry_template_string__).toBe('Line one\nline two with %s → `done`');
+  });
+
+  test('keeps the raw text of a string with an invalid escape sequence', () => {
+    const file = 'app.log';
+    const formatted = parameterize`Reading C:\users ${file}`;
+
+    expect(String(formatted)).toBe('Reading C:\\users app.log');
+    expect(formatted.__sentry_template_string__).toBe('Reading C:\\users %s');
+  });
 });