add no-unused-expressions with do expressions support

[lyleunderwood]

/cc #13
I haven't really done any work with babel's AST before, so I'm sure I'm missing a ton of cases.

[lyleunderwood]

Also wasn't really sure whether this should be behind an option or not.

[donavon]

any progress on this?

[lyleunderwood]

@donavon thanks for reminding me about this.

I went ahead and added an option to turn support for do expressions off and updated the README. If anything is blocking this from being merged please let me know.

[daniel08s]

I'm trying to test this PR, but I'm not sure how to set it up.

I've fetched the code and then added it to my project by using:
npm install --save-dev <PATH>/eslint-plugin-babel
which was added to my package.json as:
"eslint-plugin-babel": "file:../../eslint-plugin-babel",

My devDependencies:

  "devDependencies": {
    "babel-cli": "^6.26.0",
    "babel-core": "^6.26.0",
    "babel-eslint": "^8.2.1",
    "babel-preset-es2015-node": "^6.1.1",
    "babel-preset-stage-0": "^6.24.1",
    "eslint": "^4.16.0",
    "eslint-config-airbnb": "^16.1.0",
    "eslint-config-airbnb-base": "^12.1.0",
    "eslint-plugin-babel": "file:../../eslint-plugin-babel",
    "eslint-plugin-import": "^2.8.0",
    "eslint-plugin-jsx-a11y": "^6.0.3",
    "eslint-plugin-react": "^7.5.1",
    "supertest": "^3.0.0",
    "tap-spec": "^4.1.1",
    "tape": "^4.8.0"
  }

I then edited my .eslintrc.js file to add the babel plugin and the no-unused-expressions rule, but when I run eslint I still get the error.

My .eslintrc.js file:

module.exports = {
  "parser": "babel-eslint",
  "extends": "airbnb",
  "plugins": [
    "babel"
  ],
  "rules": {
    "object-curly-spacing": ["warn", "never"],
    "func-names": "off",
    "space-before-function-paren": ["error", "never"],
    "max-len": ["error", 120, 4],
    "no-unused-vars": ["error", {"argsIgnorePattern": "next"}],
    "import/prefer-default-export": "off",
    "comma-dangle": ["error", {
      "arrays": "always-multiline",
      "objects": "always-multiline",
      "functions": "ignore"
    }],
    "import/no-extraneous-dependencies": [
    "error", {
       "devDependencies": true, 
       "optionalDependencies": false, 
       "peerDependencies": false, 
       "packageDir": "./"
    }],
    "babel/no-unused-expressions": 1
  }
};

Any help would be very welcome.

[daniel08s]

Ok, so after some validations I'm actually already testing this version of the plugin.
That said, I'm still getting the no-unused-expressions error when using do { ... } expressions.

Code:

level: do {
        if (process.env.NODE_ENV === 'testing') {
          'error'; // eslint-disable-line
        } else if (process.env.NODE_ENV === 'production') {
          'info'; // eslint-disable-line
        } else {
          'debug'; // eslint-disable-line
        }
      }

For each of the comments removed eslint will produce an error:

  11:11  error  Expected an assignment or function call and instead saw an expression  no-unused-expressions
  13:11  error  Expected an assignment or function call and instead saw an expression  no-unused-expressions
  15:11  error  Expected an assignment or function call and instead saw an expression  no-unused-expressions

[lyleunderwood]

@iSkilled make sure you're using the eslint executable from your node_modules and not a globally installed one (run it directly from ./node_modules/.bin/eslint if unsure). Here's all the relevant stuff from my package.json. Your example seems to be working fine when I paste it into a file in my project.

    "eslint": "^3.8.1",
    "eslint-config-airbnb": "^12.0.0",
    "eslint-loader": "^1.7.1",
    "eslint-plugin-babel": "https://github.com/lyleunderwood/eslint-plugin-babel.git#do-expressions",
    "eslint-plugin-flowtype": "^2.21.0",
    "eslint-plugin-fp": "^2.3.0",
    "eslint-plugin-import": "^2.0.1",
    "eslint-plugin-jsx-a11y": "^2.2.3",
    "eslint-plugin-react": "^6.4.1",

  "eslintConfig": {
    "extends": [
      "airbnb",
      "plugin:flowtype/recommended"
    ],
    "parser": "babel-eslint",
    "plugins": [
      "import",
      "flowtype",
      "babel",
      "fp"
    ],
    "env": {
      "browser": true
    },
    "rules": {
      "new-cap": [
        2,
        {
          "capIsNewExceptions": [
            "Map",
            "List"
          ]
        }
      ],
      "no-unused-expressions": 0,
      "babel/no-unused-expressions": 2,
      "import/no-extraneous-dependencies": [
        "error",
        {
          "devDependencies": [
            "**/*.test.js",
            "**/*.test.jsx",
            "**/*.stories.js",
            "**/*.stories.jsx"
          ]
        }
      ],
      "fp/no-mutation": "error",
      "fp/no-arguments": "error",
      "fp/no-delete": "error",
      "fp/no-let": "error",
      "fp/no-loops": "error",
      "fp/no-mutating-assign": "error",
      "fp/no-mutating-methods": "error"
    }
  },

[daniel08s]

I updated the following in my .eslintrc.js:

"babel/no-unused-expressions": 1

to:

"no-unused-expressions": 0,
"babel/no-unused-expressions": 2

and it is now working properly. Thanks!

[Javran]

any news from maintainers?

[lyleunderwood]

Nothing on my end, just waiting.

[mackenzie-orange]

I've been watching this PR for a month now, and no news. Is there a hold up?

I'm pretty excited about this getting merged.

[lyleunderwood]

@mackenzie-orange for want of a better option, you can do what I do. My eslint-plugin-babel record looks like this in my package.json:

"eslint-plugin-babel": "https://github.com/lyleunderwood/eslint-plugin-babel.git#do-expressions",

Of course in this scenario you're sort of beholden to me to not somehow break this repo. If that's a concern then you can just fork it to your own account and reference your own branch.

The other problem with this approach is that the branch won't get updates unless manually rebased.

[existentialism]

@lyleunderwood sorry for the delay, but if you're interested, can you update this now that we've moved to using eslint-plugin-composer?

[lyleunderwood]

@existentialism Done.

I rebased on 5.0.0 and implemented in terms of eslint-rule-composer. I also removed my allowDoExpressions option because I'm not sure how I would even get the option in the context of the composer, and it currently serves essentially the same purpose as just enabling / disabling the plugin-specific rule.

[existentialism]

@lyleunderwood yeah, accessing options inside filterReports won't land until not-an-aardvark/eslint-rule-composer#1, but I agree, I don't think we need an option here.

[existentialism]

@lyleunderwood this was released in 5.1.0! thanks again!

[lyleunderwood]

Cool, thanks.