TypeError: Cannot read property 'some' of undefined when `ast.comments` is missing on the AST

[sompylasar]

https://github.com/benmosher/eslint-plugin-import/blob/1377f55bc3d003519a74a89b048e11b20d53990e/src/ExportMap.js#L333

ExportMap.parse = function (path, content, context) {
  // ...

  // attempt to collect module doc
  ast.comments.some(c => {

[ljharb]

What code generates this error?

[sompylasar]

@ljharb I'm still investigating, but for some reason typescript-eslint-parser which I'm experimenting with returned me an AST without .comments on it.

[ljharb]

If that's a guarantee that other tools provide, then it might be a bug with typescript-eslint-parser.

[sompylasar]

@ljharb OK, let's keep it as is then, no change required.

I have accidentally fed up JavaScript code to typescript-eslint-parser instead of babel-eslint, and for some reason the comments weren't extracted.

All that because while waiting for #839 to be merged and published I'm trying to detect TypeScript code by file contents, and my naive detection failed.

[ljharb]

I'd recommend using the extension, since the sole purpose of file extensions is to tell you how to parse a file :-)

[sompylasar]

@ljharb Definitely! But I have no filePath where I need it yet to get the file extension from (this #839 solves it, but it's not released yet so I cannot install it as a dependency).

[samhh]

I just hit this same issue with typescript-eslint-parser. Am I to follow #839 for updates on a fix?

[sompylasar]

@samhh Depends on what you're trying to do. The #839 makes it possible for me to provide ESLint with a custom parser which can parse both TypeScript and JavaScript while Babel/Babylon is lagging behind:

// ./webpack/parserForEslint.js

function shouldUseTypeScriptParser(text, parserOptions) {
  return isTypeScriptFilePath(parserOptions.filePath);
}

// ...

module.exports = {
  parse: function (text, parserOptions) {
    if (shouldUseTypeScriptParser(text, parserOptions)) {
      return parseTypeScript(text, parserOptions);
    }

    return parseJavaScript(text, parserOptions);
  },
};

// .eslintrc.js
  // ...
  "parser": "./webpack/parserForEslint.js",
  // ...

[mattdell]

I had this issue when accidentally trying to import a JS file in a TS file.

[sompylasar]

@mattdell Yes, looks like typescript-eslint-parser cannot parse JS (only TS), and that's fine.

You'll have to do the same as I did for a JS+TS project: a conditional parser that decides which real parser to use.

This conditional parser requires filePath in parserOptions to reliably guess the type if the code it's been given for parsing.

But eslint-plugin-import doesn't provide this yet, hence #839.

[piecyk]

hmm got the same error, using eslint-plugin-import@2.3.0 and typescript-eslint-parser@3.0.0
working on JS+TS project, why we need conditional parser @sompylasar ?

i was thinking that import/parsers will do that job ?

'import/parsers': {
  'typescript-eslint-parser': ['.ts', '.tsx']
},

[sompylasar]

@piecyk Because either I missed this import/parsers option, or it wasn't there at the time I was setting this up. Thanks for the pointer.

[piecyk]

@sompylasar 👍

Was looking on this issue because after upgrading to typescript-eslint-parser@3.0.0 the ast.comments for ts, tsx files is undefined and got the same error...

[piecyk]

oki problem was that i didn't set comment in parserOptions in .eslintrc
as typescript-eslint-parser requires
https://github.com/eslint/typescript-eslint-parser/blob/master/parser.js#L30

that option is passed to eslint-plugin-import and we got ast.comments