Some error messages are missing in v4.3.0

[not-an-aardvark]

Tell us about your environment

• ESLint Version: 4.3.0
• Node Version: 8.2.1
• npm Version: 5.3.0

What parser (default, Babel-ESLint, etc.) are you using?

default

Please show your full configuration:

Configuration

# intentionally invalid YML

rules:
  semi: error
yoda: error
  quotes: error

What did you do? Please include the actual source code causing the issue.

a

What did you expect to happen?

I expected to receive a useful error message indicating that the configuration was invalid.

What actually happened? Please include the actual, raw output from ESLint.

Error
    at generateError (/path/to/eslint/node_modules/js-yaml/lib/js-yaml/loader.js:165:10)
    at throwError (/path/to/eslint/node_modules/js-yaml/lib/js-yaml/loader.js:171:9)
    at readBlockMapping (/path/to/eslint/node_modules/js-yaml/lib/js-yaml/loader.js:1080:7)
    at composeNode (/path/to/eslint/node_modules/js-yaml/lib/js-yaml/loader.js:1332:12)
    at readDocument (/path/to/eslint/node_modules/js-yaml/lib/js-yaml/loader.js:1492:3)
    at loadDocuments (/path/to/eslint/node_modules/js-yaml/lib/js-yaml/loader.js:1548:5)
    at load (/path/to/eslint/node_modules/js-yaml/lib/js-yaml/loader.js:1569:19)
    at Object.safeLoad (/path/to/eslint/node_modules/js-yaml/lib/js-yaml/loader.js:1591:10)
    at loadYAMLConfigFile (/path/to/eslint/lib/config/config-file.js:97:21)
    at loadConfigFile (/path/to/eslint/lib/config/config-file.js:233:22)

In 4.2.0, the error also included a message:

Cannot read config file: /path/to/sandbox/.eslintrc.yml
Error: bad indentation of a mapping entry at line 6, column 9:
      quotes: error
            ^
Error
    at generateError (/path/to/eslint/node_modules/js-yaml/lib/js-yaml/loader.js:165:10)
    at throwError (/path/to/eslint/node_modules/js-yaml/lib/js-yaml/loader.js:171:9)
    at readBlockMapping (/path/to/eslint/node_modules/js-yaml/lib/js-yaml/loader.js:1080:7)
    at composeNode (/path/to/eslint/node_modules/js-yaml/lib/js-yaml/loader.js:1332:12)
    at readDocument (/path/to/eslint/node_modules/js-yaml/lib/js-yaml/loader.js:1492:3)
    at loadDocuments (/path/to/eslint/node_modules/js-yaml/lib/js-yaml/loader.js:1548:5)
    at load (/path/to/eslint/node_modules/js-yaml/lib/js-yaml/loader.js:1569:19)
    at Object.safeLoad (/path/to/eslint/node_modules/js-yaml/lib/js-yaml/loader.js:1591:10)
    at loadYAMLConfigFile (/path/to/eslint/lib/config/config-file.js:97:21)
    at loadConfigFile (/path/to/eslint/lib/config/config-file.js:233:22)

This is a regression caused by a5fd101. To avoid duplicated error messages, we stopped printing error.message for uncaught exceptions since the message is usually already contained in error.stack. However, there are several places where we mutate error.message after creating an error in order to add additional information, so the information is now getting lost.

[VictorHom]

@not-an-aardvark

I am getting the same error as you indicated from 4.2.0. My configuration is the following:

eslint: v4.3.0
node: v6.9.4
npm: 3.10.10

However, I do see the same(lack of) error when I switched to node 8.2.1

[not-an-aardvark]

Hmm, this is more complicated than I thought. It seems like Node has a strange behavior with error stacks -- modifying the message will also modify the stack, but only if the stack has never been previously accessed.

const err = new Error('original message');
err.message = 'updated message';
console.log(err.stack);

// => Error: updated message
//           (followed by stack trace)

const err = new Error('original message');

// access the stack property
err.stack;

err.message = 'updated message';
console.log(err.stack);

// => Error: original message
//           (followed by stack trace)

There doesn't appear to be a getter on err.stack, so it's probably some magical internal behavior in V8.

This applies in both Node 8.2.1 and Node 6.11.1. However, the difference in behavior between the two Node versions is probably related to nodeca/js-yaml#351, which might also be caused by weird Error.stack behavior.

[not-an-aardvark]

I made a partial fix upstream in nodeca/js-yaml#360. This will make sure at least some error message is present, rather than having the stack be empty. However, the stack still won't update after the message property is reassigned, so the stack will only contain the error message from js-yaml as a result of that fix, and not the additional information from ESLint.

The root cause of the issue is this commit in V8, which was first introduced in Node 7. Stack traces are evaluated lazily in Node (they are only created the first time the stack property is accessed on an error object). As a result, modifying the message property of an error sometimes causes the stack to change, but only if the stack property has never been accessed. js-yaml uses Error.captureStackTrace internally, and starting in Node 7 Error.captureStackTrace will eagerly compute the stack trace.

The commit in V8 was reverted a few weeks ago here, but it might take awhile before that lands in a Node release. Also, I'm not sure we should rely on this behavior, since it seems risky to rely on whether the stack property of an error is accessed anywhere.