Add a custom eslint rule to check the constructors

.eslintrc.js

@@ -10,10 +10,11 @@ module.exports = {
     tsconfigRootDir: __dirname,
     project: ["./tsconfig.eslint.json"],
   },
-  plugins: ["@typescript-eslint"],
+  plugins: ["@typescript-eslint", "custom-rules"],
   rules: {
     "@typescript-eslint/no-inferrable-types": 0,
     "import/no-namespace": 2,
+    "custom-rules/valid-constructors": 2,
   },
   root: true,
   ignorePatterns: ["**/*.js", "node_modules"],

eslint/README.md

@@ -0,0 +1,7 @@
+# Custom ESLint Rules
+
+This directory defines any custom rules to be checked against the @guardian/cdk library.
+
+These rules should all have a corresponding [ADR](../docs/architecture-design-records).
+
+More information on building custom rules can be found on the [eslint site](https://eslint.org/docs/developer-guide/working-with-rules).

eslint/index.js

@@ -0,0 +1,5 @@
+module.exports = {
+  rules: {
+    "valid-constructors": require("./rules/valid-constructors"),
+  },
+};

eslint/package.json

@@ -0,0 +1,5 @@
+{
+  "name": "eslint-plugin-custom-rules",
+  "version": "1.0.0",
+  "main": "index.js"
+}

eslint/rules/valid-constructors.js

@@ -0,0 +1,141 @@
+// Rules
+// 1. Must be at least 2 parameters
+// 2. Can't be more than 3 parameters
+// 3. First parameter must be called scope
+// 4. First parameter must be of type GuStack
+// 5. Second parameter must be called id
+// 6. Second parameter must be of type string
+// 7. Third parameter (if exists) must called props
+// 8. If third parameter is present and non-optional then the second parameter should not be initialised
+// TODO: 9. If all values in third type are optional then parameter should be optional
+// 10. Third parameter type should be custom
+
+module.exports = {
+  meta: {
+    type: "suggestion",
+    docs: {
+      description: "ensure constructors conform with agreed pattern",
+      category: "Best Practices",
+      url: "https://github.com/guardian/cdk/blob/main/docs/architecture-decision-records/002-component-constuctors.md",
+    },
+    schema: [],
+  },
+
+  create(context) {
+    return {
+      MethodDefinition(node) {
+        if (node.kind !== "constructor") return null;
+
+        const params = node.value.params;
+
+        // 1. Must be at least 2 parameters
+        if (!Array.isArray(params) || params.length < 2) {
+          return context.report(
+            node,
+            params.loc,
+            "Construct or pattern constructors must take at least a scope and an id parameter"
+          );
+        }
+
+        // 2. Can't be more than 3 parameters
+        if (params.length > 3) {
+          return context.report(
+            node,
+            params.loc,
+            "Construct or pattern constructors can only take scope, id and props parameters"
+          );
+        }
+
+        const scope = params[0];
+
+        // 3. First parameter must be called scope
+        if (scope.name !== "scope") {
+          return context.report(
+            node,
+            scope.loc,
+            `The first parameter in a construct or pattern contructor must be called scope`
+          );
+        }
+
+        // 4. First parameter must be of type GuStack
+        if (scope.typeAnnotation.typeAnnotation.typeName.name !== "GuStack") {
+          return context.report(
+            node,
+            scope.typeAnnotation.typeAnnotation.typeName.loc,
+            `The first parameter in a construct or pattern contructor must be of type GuStack`
+          );
+        }
+
+        const id = params[1];
+
+        // 5. Second parameter must be called id
+        if (
+          (id.type === "Identifier" && id.name !== "id") ||
+          (id.type === "AssignmentPattern" && id.left.name !== "id")
+        ) {
+          return context.report(
+            node,
+            id.loc,
+            `The second parameter in a construct or pattern contructor must be called id`
+          );
+        }
+
+        // 6. Second parameter must be of type string
+        if (
+          (id.type === "Identifier" && id.typeAnnotation.typeAnnotation.type !== "TSStringKeyword") ||
+          (id.type === "AssignmentPattern" && id.left.typeAnnotation.typeAnnotation.type !== "TSStringKeyword")
+        ) {
+          return context.report(
+            node,
+            id.typeAnnotation.typeAnnotation.typeName.loc,
+            `The second parameter in a construct or pattern contructor must be of type string`
+          );
+        }
+
+        if (params.length === 3) {
+          const props = params[2];
+
+          // 7. Third parameter (if exists) must called props
+          if (
+            (props.type === "Identifier" && props.name !== "props") ||
+            (props.type === "AssignmentPattern" && props.left.name !== "props")
+          ) {
+            return context.report(
+              node,
+              props.loc,
+              `The third parameter in a construct or pattern contructor must be called props`
+            );
+          }
+
+          // 10. Third parameter type should be custom
+          if (
+            (props.type === "Identifier" && props.typeAnnotation.typeAnnotation.type !== "TSTypeReference") ||
+            (props.type === "AssignmentPattern" && props.left.typeAnnotation.typeAnnotation.type !== "TSTypeReference")
+          ) {
+            return context.report(
+              node,
+              props.loc,
+              `The third parameter in a construct or pattern contructor must be a custom type`
+            );
+          }
+        }
+
+        // 8. If third parameter is present and non-optional then the second parameter should not be initialised
+        if (
+          params.length === 3 &&
+          params[2].type !== "AssignmentPattern" &&
+          !params[2].optional &&
+          id.type === "AssignmentPattern"
+        ) {
+          return context.report(
+            node,
+            id.loc,
+            `The second parameter cannot be initialised if there is a non-optional third parameter`
+          );
+        }
+
+        return null;
+      },
+    };
+  },
+};

package.json

@@ -24,6 +24,7 @@
     "eslint-plugin-eslint-comments": "^3.2.0",
     "eslint-plugin-import": "^2.22.1",
     "eslint-plugin-prettier": "^3.3.0",
+    "eslint-plugin-custom-rules": "file:eslint",
     "jest": "^26.4.2",
     "np": "^7.0.0",
     "prettier": "^2.2.1",