Update: Flag a violation when rule options are used but an empty sche…

…ma is present in `require-meta-schema` rule (#138)

This new check is similar to how:
* `require-meta-fixable` checks that `fixable: true` is specified when an autofixer is found
* `require-meta-has-suggestions` checks that `hasSuggestions: true` is specified when suggestions are provided

Note: this is *not* a breaking change, since ESLint itself already prevents rules from using options when an empty rule schema is specified, so it's not possible that this new violation could be flagged on existing rules.

docs/rules/require-meta-schema.md

@@ -22,6 +22,13 @@ module.exports = {
   meta: { schema: null },
   create (context) {/* ... */},
 };
+
+module.exports = {
+  meta: { schema: [] },
+  create (context) {
+    const options = context.options; /* using options when schema is empty */
+  },
+};
 ```
 
 Examples of **correct** code for this rule:

lib/rules/require-meta-schema.js

@@ -28,6 +28,7 @@ module.exports = {
       },
     ],
     messages: {
+      foundOptionsUsage: 'Found usage of rule options but no options are defined in `meta.schema`.',
       missing: '`meta.schema` is required (use [] if rule has no schema).',
       wrongType: '`meta.schema` should be an array or object (use [] if rule has no schema).',
     },
@@ -37,15 +38,20 @@ module.exports = {
     const sourceCode = context.getSourceCode();
     const { scopeManager } = sourceCode;
     const info = utils.getRuleInfo(sourceCode);
+    if (info === null || info.meta === null) {
+      return {};
+    }
+
+    let contextIdentifiers;
+    let hasEmptySchema = false;
+    let schemaNode;
 
     return {
-      Program () {
-        if (info === null || info.meta === null) {
-          return;
-        }
+      Program (ast) {
+        contextIdentifiers = utils.getContextIdentifiers(context, ast);
 
         const metaNode = info.meta;
-        const schemaNode =
+        schemaNode =
           metaNode &&
           metaNode.properties &&
           metaNode.properties.find(p => p.type === 'Property' && utils.getKeyName(p) === 'schema');
@@ -83,10 +89,31 @@ module.exports = {
           value = variable.defs[0].node.init;
         }
 
+        if (
+          (value.type === 'ArrayExpression' && value.elements.length === 0) ||
+          (value.type === 'ObjectExpression' && value.properties.length === 0)
+        ) {
+          // Schema is explicitly defined as having no options.
+          hasEmptySchema = true;
+        }
+
         if (!['ArrayExpression', 'ObjectExpression'].includes(value.type)) {
           context.report({ node: value, messageId: 'wrongType' });
         }
       },
+
+      MemberExpression (node) {
+        // Check if `context.options` was used when no options were defined in `meta.schema`.
+        if (
+          hasEmptySchema &&
+          node.object.type === 'Identifier' &&
+          contextIdentifiers.has(node.object) &&
+          node.property.type === 'Identifier' &&
+          node.property.name === 'options'
+        ) {
+          context.report({ node: schemaNode, messageId: 'foundOptionsUsage' });
+        }
+      },
     };
   },
 };

tests/lib/rules/require-meta-schema.js

@@ -32,6 +32,27 @@ ruleTester.run('require-meta-schema', rule, {
         create(context) {}
       };
     `,
+    // Schema with options and using `context.options`.
+    `
+      module.exports = {
+        meta: { schema: { "enum": ["always", "never"] } },
+        create(context) { const options = context.options; }
+      };
+    `,
+    // Empty schema, using arbitrary property of `context`.
+    `
+      module.exports = {
+        meta: { schema: [] },
+        create(context) { const foo = context.foo; }
+      };
+    `,
+    // Empty schema, using arbitrary `options` property.
+    `
+      module.exports = {
+        meta: { schema: [] },
+        create(context) { const options = foo.options; }
+      };
+    `,
     `
       const schema = [];
       module.exports = {
@@ -119,5 +140,27 @@ schema: [] },
       output: null,
       errors: [{ messageId: 'wrongType', type: 'Literal' }],
     },
+    {
+      // Empty schema (array), but using rule options.
+      code: `
+        module.exports = {
+          meta: { schema: [] },
+          create(context) { const options = context.options; }
+        };
+      `,
+      output: null,
+      errors: [{ messageId: 'foundOptionsUsage', type: 'Property' }],
+    },
+    {
+      // Empty schema (object), but using rule options.
+      code: `
+        module.exports = {
+          meta: { schema: {} },
+          create(context) { const options = context.options; }
+        };
+      `,
+      output: null,
+      errors: [{ messageId: 'foundOptionsUsage', type: 'Property' }],
+    },
   ],
 });