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Rules in plugins

Rules are used to make sure that the API description is in the expected format and aligns with the expected API standards. Before you build any custom rules:

Exhaust the above options first, because they are simpler and more maintainable than building a custom plugin. If you need to build your own rules though, then you're in the right place! Read on ...

Build the custom rule

Each rule is a function that returns an object with methods that Redocly CLI calls to "visit" nodes while traversing the API description document. The object keys are the node types that are encountered in the document. In this simple example, the custom plugin holds a rule that fails if any operationId is set to "test".

To keep the plugin code manageable, each rule can go in its own file. This example is in plugins/rules/opid-not-test.js:

module.exports = OperationIdNotTest;

function OperationIdNotTest() {
  return {
    Operation: {
      enter(operation, ctx) {
        if (operation.operationId === 'test') {
          ctx.report({
            message: `operationId must be not "test"`,
            location: ctx.location.child('operationId'),
          });
        }
      },
    }
  };
}

The ctx object here holds all the context, which can be used to give more situation-aware functionality to the rules you build. This is one of the main use cases for custom rules. The report() method is used to give information to return to the user if the node being visited doesn't comply with the rule. You can read the context and location sections for more information.

Adding this as part of a plugin requires you to add it to the rules part of the plugin object, under the relevant document type. The example rule here is intended to be used with OpenAPI, so the plugin code in plugins/my-rules.js is as follows:

const OperationIdNotTest = require('./rules/opid-not-test.js');

module.exports = {
  id: 'my-rules',
  rules: {
    oas3: {
      'opid-not-test': OperationIdNotTest,
    }
  },
};

To use the example rule, add the following to your redocly.yaml configuration file:

plugins:
  - 'plugins/my-rules.js'

rules:
  my-rules/opid-not-test: warn

Validate your OpenAPI document with redocly lint openapi.yaml. With this rule enabled as shown, any operationId fields that are "test" cause the validation step to emit a warning. You can use the example here as a basis for building your own rules, and many rules can be included in a single plugin.

Object references

The context object

The context object contains additional functionality that is helpful for rules to do their jobs. As the name implies, the context object contains information that is relevant to the context of the rule. The context object has the following properties:

  • location - Current location in the source document. See Location Object.
  • parentLocations - Mapping of the parent node to its location (only for nested visitors).
  • type - Information about the current type from the type tree.
  • parent - Parent object or array.
  • key - Key in the parent object or array.
  • oasVersion - Specific OAS minor version of the current document (can be oas2, oas3 or oas3_1).

The context object also offers some additional functionality to resolve references and to return information about a problem to the user. The methods available are as follows:

  • resolve(node) - Synchronously dereferences $ref node to its value. Works only with $refs from the original document. If you need to resolve a reference from another source, you can use the optional second parameter: resolve(node, from: string).
  • report(descriptor) - Reports a problem in the API description and returns information to the user. See Report rule context for more information.

Report rule context

The main method used is context.report(), which publishes a warning or error (depending on the configuration being used). This method accepts a single argument, which is an object containing the following properties:

  • message - {string} The problem message.
  • location - {Location} (optional) An object specifying the location of the problem. Can be constructed using location object methods.
  • suggest - {string[]} (optional) - "Did you mean" suggestion.
  • from - {Location} (optional) - Referenced by location.

You may use the message alone:

context.report({
  message: "Unexpected identifier"
});

By default, the message is reported at the current node location.

Location object

The Location class has the following fields:

  • source - Current document source.
  • pointer - Pointer within the document to the node.
  • absolutePointer - Absolute pointer to the node (including source document absolute ref).

and the following methods:

  • key() - Returns the new Location pointing to the current node key instead of the value (used to highlight the key in codeframes).
  • child(propName) - Returns the new Location pointing to the propName of the current node. propName can be an array of strings to point deep.

You can use this information for more granular rule definitions.

 
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