eslint: Uncaught exception when cache file is empty (i.e. invalid JSON)

Tell us about your environment

ESLint Version: 3.10.2
Node Version: 6.9.1

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

Please show your full configuration:

standard 8.6.0

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

Suddenly standard started giving the attached below output. After spending some time searching through my code and reducing it to 0 files I was still getting the same error. Later I’ve found that there is no try/catch trying to parse back the JSON from the cache files found at .standard-cache, so when the file is empty it crashes. The problem seems to be at flat-cache package or its usage, but I thought you may know more about it. I’ll try to take a deeper look, anyway.

What do you think about trying to delete cache files when this kind of error occurs?

Hope I can help in any manner 😃

So, basically the cache file parsing probably needs a try-catch. In case it’s relevant, here’s the place where we set the cache options: https://github.com/Flet/standard-engine/blob/b579ea143c8e64254caebbd276c1d67b16793458/index.js#L35-L36

What did you expect to happen?

No uncaught exceptions.

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

SyntaxError: Unexpected end of JSON input
    at Object.parse (native)
    at Object.parseRecursion [as parse] (.../node_modules/circular-json/build/circular-json.node.js:182:15)
    at module.exports.readJSON (.../node_modules/flat-cache/utils.js:15:25)
    at Object.cache.load (.../node_modules/flat-cache/cache.js:25:23)
    at Object.module.exports.create (.../node_modules/flat-cache/cache.js:158:9)
    at Object.module.exports.load (.../node_modules/flat-cache/cache.js:144:17)
    at Object.module.exports.create (.../node_modules/file-entry-cache/cache.js:13:27)
    at new CLIEngine (.../node_modules/eslint/lib/cli-engine.js:463:38)
    at .../node_modules/standard-engine/index.js:107:16
    at .../node_modules/deglob/index.js:51:12

cc @alvaropinot @VzqzAc

About this issue

Original URL
State: closed
Created 8 years ago
Reactions: 1
Comments: 15 (13 by maintainers)

Commits related to this issue

Chore: add integration tests for cache files (refs #7748) — committed to eslint/eslint by not-an-aardvark 8 years ago
Chore: add integration tests for cache files (refs #7748) — committed to eslint/eslint by not-an-aardvark 8 years ago
Chore: add integration tests for cache files (refs #7748) (#7794) — committed to eslint/eslint by not-an-aardvark 7 years ago

Most upvoted comments

Right now, an uncaught exception is thrown (and the node process terminates) when the cache file is invalid. As a result, the same error occurs the next time ESLint is run, as @not-an-aardvark correctly pointed out.

The issue is in flat-cache on this line. They call a function that can throw exceptions but do not have a try-catch block to handle the case where the string is invalid JSON.

I opened an issue on flat-cache to get the author’s thoughts: https://github.com/royriojas/flat-cache/issues/12

IMO, the correct behavior is to invalidate the cache if it’s unusable.

feross on Dec 17, 2016

Yes, as far as I can tell, it should be safe to publish the changes in https://github.com/royriojas/flat-cache/pull/13 in a new patch version.

not-an-aardvark on Dec 19, 2016

@royriojas I just pushed a commit to the cache-integration-tests branch on the ESLint repo. The commit has tests for a lot of ESLint’s behavior with cache files. Two tests on that commit are currently failing due to this cache-parsing issue.

When I install the commit on your branch:

npm install git://github.com/royriojas/flat-cache/#eaec2239ca1aaf7efb46b95f1b3153f70df8c8d3

…the tests pass. So as far as I can tell, your fix seems to work. 👍

The tests that fail due to the bug can be found here.

To reproduce without running the tests:

echo 'invalid JSON' > .eslintcache
eslint --cache foo.js

not-an-aardvark on Dec 19, 2016

Is there a use case for linting with an invalid cache file?

I wouldn’t call it a use case, but it can definitely happen. I’ve seen multiple issues opened on the standard repo about this issue.

I don’t know for sure what the cause is, but this could easily happen if ESLint throws an uncaught exception or if the user kills the program with Ctrl+C in the middle of execution.

It’s probably a good idea to be robust against invalid cache files.

feross on Dec 14, 2016