New: Add generic-type-naming (typescript-eslint#111) (typescript-esli…

…nt#113)

packages/eslint-plugin-typescript/README.md

@@ -55,6 +55,7 @@ Then configure the rules you want to use under the rules section.
 * [`typescript/class-name-casing`](./docs/rules/class-name-casing.md) — Require PascalCased class and interface names (`class-name` from TSLint)
 * [`typescript/explicit-function-return-type`](./docs/rules/explicit-function-return-type.md) — Require explicit return types on functions and class methods
 * [`typescript/explicit-member-accessibility`](./docs/rules/explicit-member-accessibility.md) — Require explicit accessibility modifiers on class properties and methods (`member-access` from TSLint)
+* [`typescript/generic-type-naming`](./docs/rules/generic-type-naming.md) — Enforces naming of generic type variables
 * [`typescript/interface-name-prefix`](./docs/rules/interface-name-prefix.md) — Require that interface names be prefixed with `I` (`interface-name` from TSLint)
 * [`typescript/member-delimiter-style`](./docs/rules/member-delimiter-style.md) — Require a specific member delimiter style for interfaces and type literals
 * [`typescript/member-naming`](./docs/rules/member-naming.md) — Enforces naming conventions for class members by visibility.

packages/eslint-plugin-typescript/docs/rules/generic-type-naming.md

@@ -0,0 +1,42 @@
+# Enforces naming of generic type variables (generic-type-naming)
+
+It can be helpful to enforce a consistent naming style for generic type variables used within a type.
+For example, prefixing them with `T` and ensuring a somewhat descriptive name, or enforcing Hungarian notation.
+
+## Rule Details
+
+This rule allows you to enforce conventions over type variables. By default, it does nothing.
+
+## Options
+
+The rule takes a single string option, which is a regular expression that type variables should match.
+
+Examples of **correct** code with a configuration of `'^T[A-Z][a-zA-Z]+$'`:
+
+```typescript
+type ReadOnly<TType extends object> = {
+  readonly [TKey in keyof TType]: TType[TKey];
+}
+
+interface SimpleMap<TValue> {
+  [key: string]: TValue;
+}
+```
+
+Examples of **incorrect** code with a configuration of `'^T[A-Z][a-zA-Z]+$'`:
+
+```typescript
+type ReadOnly<T extends object> = {
+  readonly [Key in keyof T]: T[Key];
+}
+
+interface SimpleMap<T> {
+  [key: string]: T;
+}
+```
+
+## When Not To Use It
+If you do not want to enforce a naming convention for type variables.
+
+## Further Reading
+- [TypeScript Generics](https://www.typescriptlang.org/docs/handbook/generics.html)

packages/eslint-plugin-typescript/lib/rules/generic-type-naming.js

@@ -0,0 +1,71 @@
+/**
+ * @fileoverview Enforces naming of generic type variables.
+ */
+"use strict";
+
+/**
+ *
+ * @param {any} context ESLint context
+ * @param {string} rule Option
+ * @returns {Function} Node's visitor function
+ */
+function createTypeParameterChecker(context, rule) {
+    const regex = new RegExp(rule);
+
+    return function checkTypeParameters(pnode) {
+        const params = pnode.typeParameters && pnode.typeParameters.params;
+
+        if (!Array.isArray(params) || params.length === 0) {
+            return;
+        }
+        params.forEach(node => {
+            const type = node.type;
+
+            if (type === "TSTypeParameter" || type === "TypeParameter") {
+                const name = node.name;
+
+                if (name && !regex.test(name)) {
+                    const data = { name, rule };
+
+                    context.report({
+                        node,
+                        message:
+                            "Type parameter {{name}} does not match rule {{rule}}",
+                        data
+                    });
+                }
+            }
+        });
+    };
+}
+
+module.exports = {
+    meta: {
+        docs: {
+            description: "Enforces naming of generic type variables",
+            category: "TypeScript",
+            url:
+                "https://github.com/nzakas/eslint-plugin-typescript/blob/master/docs/rules/generic-type-naming.md"
+        }
+    },
+
+    create(context) {
+        const rule = context.options[0];
+
+        if (!rule) {
+            return {};
+        }
+
+        const checkTypeParameters = createTypeParameterChecker(context, rule);
+
+        return {
+            VariableDeclarator: checkTypeParameters,
+            ClassDeclaration: checkTypeParameters,
+            InterfaceDeclaration: checkTypeParameters,
+            TSInterfaceDeclaration: checkTypeParameters,
+            FunctionDeclaration: checkTypeParameters,
+            TSCallSignature: checkTypeParameters,
+            CallSignature: checkTypeParameters
+        };
+    }
+};

packages/eslint-plugin-typescript/tests/lib/rules/generic-type-naming.js

@@ -0,0 +1,74 @@
+"use strict";
+
+//------------------------------------------------------------------------------
+// Requirements
+//------------------------------------------------------------------------------
+
+const rule = require("../../../lib/rules/generic-type-naming"),
+    RuleTester = require("eslint").RuleTester;
+
+//------------------------------------------------------------------------------
+// Tests
+//------------------------------------------------------------------------------
+
+const ruleTester = new RuleTester({
+    parser: "typescript-eslint-parser"
+});
+
+const messagePattern = "Type parameter {{name}} does not match rule {{rule}}";
+
+/**
+ * Creates error object
+ * @param {Object} data Data
+ * @returns {Object} Object with message property
+ */
+function error(data) {
+    let message = messagePattern;
+
+    Object.keys(data).forEach(key => {
+        message = message.replace(new RegExp(`{{${key}}}`, "g"), data[key]);
+    });
+    return { message };
+}
+
+ruleTester.run("generic-type-naming", rule, {
+    valid: [
+        { code: "class<T,U,V> { }", options: [] },
+        { code: "type ReadOnly<T extends object> = {}", options: [] },
+        { code: "interface SimpleMap<V> { }", options: [] },
+        { code: "function get<T>() {}", options: [] },
+        { code: "interface GenericIdentityFn { <T>(arg: T): T }", options: [] },
+        { code: "class<x> { }", options: ["^x+$"] },
+        {
+            code: "class CounterContainer extends Container<Counter> { }",
+            options: ["^T$"]
+        }
+    ],
+    invalid: [
+        {
+            code: "class<x> { }",
+            options: ["^[A-Z]+$"],
+            errors: [error({ name: "x", rule: "^[A-Z]+$" })]
+        },
+        {
+            code: "interface SimpleMap<x> { }",
+            options: ["^[A-Z]+$"],
+            errors: [error({ name: "x", rule: "^[A-Z]+$" })]
+        },
+        {
+            code: "type R<x> = {}",
+            options: ["^[A-Z]+$"],
+            errors: [error({ name: "x", rule: "^[A-Z]+$" })]
+        },
+        {
+            code: "function get<x>() {}",
+            options: ["^[A-Z]+$"],
+            errors: [error({ name: "x", rule: "^[A-Z]+$" })]
+        },
+        {
+            code: "interface GenericIdentityFn { <x>(arg: x): x }",
+            options: ["^[A-Z]+$"],
+            errors: [error({ name: "x", rule: "^[A-Z]+$" })]
+        }
+    ]
+});