Add no-inner-literal rule (#84)

* - Add inner literal rule; fixes #17

* Support `return` statement; avoid BigInt in ESLint < 6

README.md

@@ -36,6 +36,7 @@ Enable the rules that you would like to use:
 {
   "rules": {
     "chai-expect/no-inner-compare": 2,
+    "chai-expect/no-inner-literal": 2,
     "chai-expect/missing-assertion": 2,
     "chai-expect/terminating-properties": 2
   }
@@ -54,8 +55,13 @@ and just extend the config:
 ## Rules
 
 - `no-inner-compare` - Prevent using comparisons in the `expect()` argument
-- `missing-assertion` - Prevent calling `expect(...)` without an assertion like `.to.be.ok`
-- `terminating-properties` - Prevent calling `to.be.ok` and other assertion properties as functions
+- `no-inner-literal` - Prevent using literals in the `expect()` argument
+  (`undefined`, `null`, `NaN`, `(+|-)Infinity`, `this`, booleans, numbers,
+  strings, and BigInt or regex literals)
+- `missing-assertion` - Prevent calling `expect(...)` without an assertion
+  like `.to.be.ok`
+- `terminating-properties` - Prevent calling `to.be.ok` and other assertion
+  properties as functions
 
 
 ### Additional configuration
@@ -83,6 +89,7 @@ The terminating-properties rule can be configured to ensure these (or other) add
 }
 ```
 
+
 ## License
 
 eslint-plugin-chai-expect is licensed under the [MIT License](http://www.opensource.org/licenses/mit-license.php).

index.js

@@ -6,13 +6,15 @@ module.exports = {
       plugins: ['chai-expect'],
       rules: {
         'chai-expect/no-inner-compare': 'error',
+        'chai-expect/no-inner-literal': 'error',
         'chai-expect/missing-assertion': 'error',
         'chai-expect/terminating-properties': 'error'
       }
     }
   },
   rules: {
     'no-inner-compare': require('./lib/rules/no-inner-compare'),
+    'no-inner-literal': require('./lib/rules/no-inner-literal'),
     'missing-assertion': require('./lib/rules/missing-assertion'),
     'terminating-properties': require('./lib/rules/terminating-properties')
   }

lib/rules/no-inner-literal.js

@@ -0,0 +1,59 @@
+'use strict';
+
+const findExpectCall = require('../util/find-expect-call');
+
+module.exports = function(context) {
+  function checkMemberOrCallExpression (expression) {
+    if (expression.type !== 'MemberExpression' && expression.type !== 'CallExpression')
+      return;
+
+    let expect = findExpectCall(expression);
+    if (!expect)
+      return;
+
+    let args = expect.arguments;
+    let [firstArgument] = args;
+    if (!firstArgument)
+      return;
+
+    let value;
+    if (firstArgument.type === 'Literal' || firstArgument.type === 'BigIntLiteral') {
+      value = firstArgument.raw;
+    } else if (firstArgument.type === 'Identifier' && [
+      'undefined', 'NaN', 'Infinity'
+    ].includes(firstArgument.name)) {
+      value = firstArgument.name;
+    } else if (firstArgument.type === 'ThisExpression') {
+      value = 'this';
+    } else if (
+      firstArgument.type === 'UnaryExpression' &&
+      firstArgument.argument.type === 'Identifier' &&
+      firstArgument.argument.name === 'Infinity'
+    ) {
+      value = `${firstArgument.operator}Infinity`;
+    } else {
+      return;
+    }
+
+    context.report({
+      node: firstArgument,
+      message: `\`${value}\` used in expect()`
+    });
+  }
+  return {
+    ReturnStatement(node) {
+      if (
+        node.argument && node.argument.type === 'CallExpression' &&
+        node.argument.callee
+      ) {
+        checkMemberOrCallExpression(node.argument);
+      } else if (node.argument && node.argument.type === 'MemberExpression') {
+        checkMemberOrCallExpression(node.argument);
+      }
+    },
+    ExpressionStatement(node) {
+      let {expression} = node;
+      checkMemberOrCallExpression(expression);
+    }
+  };
+};

tests/lib/rules/no-inner-literal.js

@@ -0,0 +1,127 @@
+'use strict';
+
+const rule = require('../../../lib/rules/no-inner-literal');
+const {RuleTester} = require('eslint');
+
+let ruleTester = new RuleTester();
+ruleTester.run('no-inner-literal', rule, {
+  valid: [{
+    code: 'expect(a).to.be.ok;'
+  }, {
+    code: 'expect(a && b).to.be.ok;'
+  }, {
+    code: 'expect(a || b).to.be.ok;'
+  }, {
+    code: 'expect(a).to.equal(5);'
+  }, {
+    code: 'expect(`template literal`).to.equal(5);',
+    parserOptions: {
+      ecmaVersion: 2015
+    }
+  }, {
+    code: 'expect(tagged`template literal`).to.equal(5);',
+    parserOptions: {
+      ecmaVersion: 2015
+    }
+  }, {
+    code: `
+      it('should have no problems', function () {
+        return expect(a).to.be.ok();
+      });
+    `
+  }, {
+    code: `
+      it('should have no problems', function () {
+        return expect(a).to.be.true;
+      });
+    `
+  }],
+
+  invalid: [{
+    code: 'expect(undefined).to.be.ok;',
+    errors: [{
+      message: '`undefined` used in expect()'
+    }]
+  }, {
+    code: 'expect(null).to.be.ok;',
+    errors: [{
+      message: '`null` used in expect()'
+    }]
+  }, {
+    code: 'expect(true).to.be.ok;',
+    errors: [{
+      message: '`true` used in expect()'
+    }]
+  }, {
+    code: 'expect(52).to.be.ok;',
+    errors: [{
+      message: '`52` used in expect()'
+    }]
+  }, {
+    code: 'expect("string").to.be.ok;',
+    errors: [{
+      message: '`"string"` used in expect()'
+    }]
+  }, {
+    code: 'expect(/regex/).to.be.ok;',
+    errors: [{
+      message: '`/regex/` used in expect()'
+    }]
+  }, {
+    code: 'expect(NaN).to.be.ok;',
+    errors: [{
+      message: '`NaN` used in expect()'
+    }]
+  }, {
+    code: 'expect(Infinity).to.be.ok;',
+    errors: [{
+      message: '`Infinity` used in expect()'
+    }]
+  }, {
+    code: 'expect(+Infinity).to.be.ok;',
+    errors: [{
+      message: '`+Infinity` used in expect()'
+    }]
+  }, {
+    code: 'expect(-Infinity).to.be.ok;',
+    errors: [{
+      message: '`-Infinity` used in expect()'
+    }]
+  }, {
+    code: 'expect(this).to.be.ok;',
+    errors: [{
+      message: '`this` used in expect()'
+    }]
+  }, {
+    code: 'expect(false).to.equal(true);',
+    errors: [{
+      message: '`false` used in expect()'
+    }]
+  }, {
+    code: `
+      it('should have no problems but does', function () {
+        return expect(false).to.equal(true);
+      });
+    `,
+    errors: [{
+      message: '`false` used in expect()'
+    }]
+  }, {
+    code: `
+      it('should have no problems but does', function () {
+        return expect(false).to.be.true;
+      });
+    `,
+    errors: [{
+      message: '`false` used in expect()'
+    }]
+  }, ...require('eslint/package.json').version.match(/^[1-5]\./) ? [] : [{
+    code: 'expect(132n).to.be.ok;',
+    errors: [{
+      message: '`132n` used in expect()'
+    }],
+    parserOptions: {
+      ecmaVersion: 2020
+    }
+  }]]
+});