Added the require-event-dispatcher-types rule (#354)

Co-authored-by: Yosuke Ota <otameshiyo23@gmail.com>

.changeset/witty-donuts-jog.md

@@ -0,0 +1,5 @@
+---
+"eslint-plugin-svelte": minor
+---
+
+Added the require-event-dispatcher-types rule

README.md

@@ -336,6 +336,7 @@ These rules relate to better ways of doing things to help you avoid problems:
 | [svelte/no-unused-svelte-ignore](https://ota-meshi.github.io/eslint-plugin-svelte/rules/no-unused-svelte-ignore/) | disallow unused svelte-ignore comments | :star: |
 | [svelte/no-useless-mustaches](https://ota-meshi.github.io/eslint-plugin-svelte/rules/no-useless-mustaches/) | disallow unnecessary mustache interpolations | :wrench: |
 | [svelte/prefer-destructured-store-props](https://ota-meshi.github.io/eslint-plugin-svelte/rules/prefer-destructured-store-props/) | destructure values from object stores for better change tracking & fewer redraws | :bulb: |
+| [svelte/require-event-dispatcher-types](https://ota-meshi.github.io/eslint-plugin-svelte/rules/require-event-dispatcher-types/) | require type parameters for createEventDispatcher |  |
 | [svelte/require-optimized-style-attribute](https://ota-meshi.github.io/eslint-plugin-svelte/rules/require-optimized-style-attribute/) | require style attributes that can be optimized |  |
 | [svelte/require-stores-init](https://ota-meshi.github.io/eslint-plugin-svelte/rules/require-stores-init/) | require initial value in store |  |
 

docs/rules.md

@@ -55,6 +55,7 @@ These rules relate to better ways of doing things to help you avoid problems:
 | [svelte/no-unused-svelte-ignore](./rules/no-unused-svelte-ignore.md) | disallow unused svelte-ignore comments | :star: |
 | [svelte/no-useless-mustaches](./rules/no-useless-mustaches.md) | disallow unnecessary mustache interpolations | :wrench: |
 | [svelte/prefer-destructured-store-props](./rules/prefer-destructured-store-props.md) | destructure values from object stores for better change tracking & fewer redraws | :bulb: |
+| [svelte/require-event-dispatcher-types](./rules/require-event-dispatcher-types.md) | require type parameters for createEventDispatcher |  |
 | [svelte/require-optimized-style-attribute](./rules/require-optimized-style-attribute.md) | require style attributes that can be optimized |  |
 | [svelte/require-stores-init](./rules/require-stores-init.md) | require initial value in store |  |
 

docs/rules/require-event-dispatcher-types.md

@@ -0,0 +1,50 @@
+---
+pageClass: "rule-details"
+sidebarDepth: 0
+title: "svelte/require-event-dispatcher-types"
+description: "require type parameters for createEventDispatcher"
+---
+
+# svelte/require-event-dispatcher-types
+
+> require type parameters for createEventDispatcher
+
+## :book: Rule Details
+
+This rule is aimed to enforce type parameters when calling `createEventDispatcher`. Adding types makes all `dispatch` calls as well as all event listeners typechecked. For more information, see the [svelte docs](https://github.com/sveltejs/language-tools/blob/master/docs/preprocessors/typescript.md#typing-component-events). 
+
+<ESLintCodeBlock language="javascript">
+
+<!--eslint-skip-->
+
+```svelte
+<script lang="ts">
+  /* eslint svelte/require-event-dispatcher-types: "error" */
+
+  import { createEventDispatcher } from "svelte"
+
+  /* ✓ GOOD */
+  const dispatch1 = createEventDispatcher<{ one: never; two: number }>()
+  const dispatch2 = createEventDispatcher<Record<string, never>>()
+  const dispatch3 = createEventDispatcher<any>()
+  const dispatch4 = createEventDispatcher<unknown>()
+
+  /* ✗ BAD */
+  const dispatch5 = createEventDispatcher()
+</script>
+```
+
+</ESLintCodeBlock>
+
+## :wrench: Options
+
+Nothing.
+
+## :rocket: Version
+
+This rule was introduced in eslint-plugin-svelte v2.16.0
+
+## :mag: Implementation
+
+- [Rule source](https://github.com/ota-meshi/eslint-plugin-svelte/blob/main/src/rules/require-event-dispatcher-types.ts)
+- [Test source](https://github.com/ota-meshi/eslint-plugin-svelte/blob/main/tests/src/rules/require-event-dispatcher-types.ts)

src/rules/reference-helpers/svelte-createEventDispatcher.ts

@@ -0,0 +1,20 @@
+import type { TSESTree } from "@typescript-eslint/types"
+import { ReferenceTracker } from "eslint-utils"
+import type { RuleContext } from "../../types"
+
+/** Extract 'svelte createEventDispatcher' references */
+export function* extractCreateEventDispatcherReferences(
+  context: RuleContext,
+): Generator<TSESTree.CallExpression, void> {
+  const referenceTracker = new ReferenceTracker(context.getScope())
+  for (const { node } of referenceTracker.iterateEsmReferences({
+    svelte: {
+      [ReferenceTracker.ESM]: true,
+      createEventDispatcher: {
+        [ReferenceTracker.CALL]: true,
+      },
+    },
+  })) {
+    yield node as TSESTree.CallExpression
+  }
+}

src/rules/require-event-dispatcher-types.ts

@@ -0,0 +1,39 @@
+import { createRule } from "../utils"
+import { getLangValue } from "../utils/ast-utils"
+import { extractCreateEventDispatcherReferences } from "./reference-helpers/svelte-createEventDispatcher"
+
+export default createRule("require-event-dispatcher-types", {
+  meta: {
+    docs: {
+      description: "require type parameters for createEventDispatcher",
+      category: "Best Practices",
+      recommended: false,
+    },
+    schema: [],
+    messages: {
+      missingTypeParameter: `Type parameters missing for the createEventDispatcher function call.`,
+    },
+    type: "suggestion",
+  },
+  create(context) {
+    let isTs = false
+    return {
+      SvelteScriptElement(node) {
+        const lang = getLangValue(node)?.toLowerCase()
+        if (lang === "ts" || lang === "typescript") {
+          isTs = true
+        }
+      },
+      "Program:exit"() {
+        if (!isTs) {
+          return
+        }
+        for (const node of extractCreateEventDispatcherReferences(context)) {
+          if (node.typeParameters === undefined) {
+            context.report({ node, messageId: "missingTypeParameter" })
+          }
+        }
+      },
+    }
+  },
+})

src/utils/rules.ts

@@ -36,6 +36,7 @@ import noUselessMustaches from "../rules/no-useless-mustaches"
 import preferClassDirective from "../rules/prefer-class-directive"
 import preferDestructuredStoreProps from "../rules/prefer-destructured-store-props"
 import preferStyleDirective from "../rules/prefer-style-directive"
+import requireEventDispatcherTypes from "../rules/require-event-dispatcher-types"
 import requireOptimizedStyleAttribute from "../rules/require-optimized-style-attribute"
 import requireStoreCallbacksUseSetParam from "../rules/require-store-callbacks-use-set-param"
 import requireStoreReactiveAccess from "../rules/require-store-reactive-access"
@@ -86,6 +87,7 @@ export const rules = [
   preferClassDirective,
   preferDestructuredStoreProps,
   preferStyleDirective,
+  requireEventDispatcherTypes,
   requireOptimizedStyleAttribute,
   requireStoreCallbacksUseSetParam,
   requireStoreReactiveAccess,

tests/fixtures/rules/require-event-dispatcher-types/invalid/import-alias01-errors.yaml

@@ -0,0 +1,4 @@
+- message: Type parameters missing for the createEventDispatcher function call.
+  line: 4
+  column: 20
+  suggestions: null

tests/fixtures/rules/require-event-dispatcher-types/invalid/import-alias01-input.svelte

@@ -0,0 +1,5 @@
+<script lang="ts">
+  import { createEventDispatcher as ced } from "svelte"
+
+  const dispatch = ced()
+</script>

tests/fixtures/rules/require-event-dispatcher-types/invalid/no-types01-errors.yaml

@@ -0,0 +1,4 @@
+- message: Type parameters missing for the createEventDispatcher function call.
+  line: 4
+  column: 20
+  suggestions: null

tests/fixtures/rules/require-event-dispatcher-types/invalid/no-types01-input.svelte

@@ -0,0 +1,5 @@
+<script lang="ts">
+  import { createEventDispatcher } from "svelte"
+
+  const dispatch = createEventDispatcher()
+</script>

tests/fixtures/rules/require-event-dispatcher-types/valid/has-types01-input.svelte

@@ -0,0 +1,8 @@
+<script lang="ts">
+  import { createEventDispatcher } from "svelte"
+
+  const dispatch1 = createEventDispatcher<{ one: never; two: number }>()
+  const dispatch2 = createEventDispatcher<Record<string, never>>()
+  const dispatch3 = createEventDispatcher<any>()
+  const dispatch4 = createEventDispatcher<unknown>()
+</script>

tests/fixtures/rules/require-event-dispatcher-types/valid/no-typescript01-input.svelte

@@ -0,0 +1,5 @@
+<script>
+  import { createEventDispatcher } from "svelte"
+
+  const dispatch = createEventDispatcher()
+</script>

tests/fixtures/rules/require-event-dispatcher-types/valid/non-svelte-dispatcher01-input.svelte

@@ -0,0 +1,5 @@
+<script lang="ts">
+  import { createEventDispatcher } from "./unknown"
+
+  const dispatch = createEventDispatcher()
+</script>

tests/src/rules/require-event-dispatcher-types.ts

@@ -0,0 +1,16 @@
+import { RuleTester } from "eslint"
+import rule from "../../../src/rules/require-event-dispatcher-types"
+import { loadTestCases } from "../../utils/utils"
+
+const tester = new RuleTester({
+  parserOptions: {
+    ecmaVersion: 2020,
+    sourceType: "module",
+  },
+})
+
+tester.run(
+  "require-event-dispatcher-types",
+  rule as any,
+  loadTestCases("require-event-dispatcher-types"),
+)