Add svelte/require-stores-init rule (#211)

* Add `svelte/require-stores-init` rule

* Update doc

* revert tests/utils.ts

* fix lint errors

* fix test case

Author: ota-meshi

README.md

@@ -287,6 +287,7 @@ 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/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 |  |
 
 ## Stylistic Issues
 

docs-svelte-kit/src/lib/components/ESLintCodeBlock.svelte

@@ -12,9 +12,10 @@
   let code = ""
   export let rules = {}
   export let fix = false
+  export let language = "html"
   let time = ""
-  let options = {
-    filename: "example.svelte",
+  $: options = {
+    filename: language === "html" ? "example.svelte" : "example.js",
     preprocess,
     postprocess,
   }
@@ -43,7 +44,7 @@
     {linter}
     bind:code
     config={{
-      parser: "svelte-eslint-parser",
+      parser: language === "html" ? "svelte-eslint-parser" : undefined,
       parserOptions: {
         ecmaVersion: 2020,
         sourceType: "module",
@@ -54,6 +55,7 @@
         es2021: true,
       },
     }}
+    {language}
     {options}
     on:result={onLintedResult}
     showDiff={showDiff && fix}

docs-svelte-kit/src/lib/eslint/ESLintEditor.svelte

@@ -11,6 +11,7 @@
   export let options = {}
   export let fix = true
   export let showDiff = true
+  export let language = "html"
 
   let fixedValue = code
   let leftMarkers = []
@@ -221,7 +222,7 @@
     bind:this={editor}
     bind:code
     bind:rightCode={fixedValue}
-    language="html"
+    {language}
     diffEditor={fix && showDiff}
     markers={leftMarkers}
     {rightMarkers}

docs/rules.md

@@ -47,6 +47,7 @@ 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/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 |  |
 
 ## Stylistic Issues
 

docs/rules/require-stores-init.md

@@ -0,0 +1,54 @@
+---
+pageClass: "rule-details"
+sidebarDepth: 0
+title: "svelte/require-stores-init"
+description: "require initial value in store"
+---
+
+# svelte/require-stores-init
+
+> require initial value in store
+
+- :exclamation: <badge text="This rule has not been released yet." vertical="middle" type="error"> **_This rule has not been released yet._** </badge>
+
+## :book: Rule Details
+
+This rule is aimed to enforce initial values when initializing the Svelte stores.
+
+<ESLintCodeBlock language="javascript">
+
+<!--eslint-skip-->
+
+```js
+/* eslint svelte/require-stores-init: "error" */
+
+import { writable, readable, derived } from "svelte/store"
+
+/* ✓ GOOD */
+export const w1 = writable(false)
+export const r1 = readable({})
+export const d1 = derived([a, b], () => {}, false)
+
+/* ✗ BAD */
+export const w2 = writable()
+export const r2 = readable()
+export const d2 = derived([a, b], () => {})
+```
+
+</ESLintCodeBlock>
+
+## :wrench: Options
+
+Nothing.
+
+## :heart: Compatibility
+
+This rule was taken from [@tivac/eslint-plugin-svelte].  
+This rule is compatible with `@tivac/svelte/stores-initial-value` rule.
+
+[@tivac/eslint-plugin-svelte]: https://github.com/tivac/eslint-plugin-svelte/
+
+## :mag: Implementation
+
+- [Rule source](https://github.com/ota-meshi/eslint-plugin-svelte/blob/main/src/rules/require-stores-init.ts)
+- [Test source](https://github.com/ota-meshi/eslint-plugin-svelte/blob/main/tests/src/rules/require-stores-init.ts)

package.json

@@ -83,6 +83,7 @@
     "@types/escape-html": "^1.0.2",
     "@types/eslint": "^8.0.0",
     "@types/eslint-scope": "^3.7.0",
+    "@types/eslint-utils": "^3.0.1",
     "@types/eslint-visitor-keys": "^1.0.0",
     "@types/estree": "^1.0.0",
     "@types/less": "^3.0.3",

src/rules/require-stores-init.ts

@@ -0,0 +1,67 @@
+import { createRule } from "../utils"
+import type * as ESTree from "estree"
+import { ReferenceTracker } from "eslint-utils"
+
+export default createRule("require-stores-init", {
+  meta: {
+    docs: {
+      description: "require initial value in store",
+      category: "Best Practices",
+      recommended: false,
+    },
+    schema: [],
+    messages: {
+      storeDefaultValue: `Always set a default value for svelte stores.`,
+    },
+    type: "suggestion",
+  },
+  create(context) {
+    /** Extract 'svelte/store' references */
+    function* extractStoreReferences() {
+      const referenceTracker = new ReferenceTracker(context.getScope())
+      for (const { node, path } of referenceTracker.iterateEsmReferences({
+        "svelte/store": {
+          [ReferenceTracker.ESM]: true,
+          writable: {
+            [ReferenceTracker.CALL]: true,
+          },
+          readable: {
+            [ReferenceTracker.CALL]: true,
+          },
+          derived: {
+            [ReferenceTracker.CALL]: true,
+          },
+        },
+      })) {
+        yield {
+          node: node as ESTree.CallExpression,
+          name: path[path.length - 1],
+        }
+      }
+    }
+
+    return {
+      Program() {
+        for (const { node, name } of extractStoreReferences()) {
+          const minArgs =
+            name === "writable" || name === "readable"
+              ? 1
+              : name === "derived"
+              ? 3
+              : 0
+
+          if (
+            node.arguments.length >= minArgs ||
+            node.arguments.some((arg) => arg.type === "SpreadElement")
+          ) {
+            continue
+          }
+          context.report({
+            node,
+            messageId: "storeDefaultValue",
+          })
+        }
+      },
+    }
+  },
+})

src/utils/rules.ts

@@ -28,6 +28,7 @@ import noUselessMustaches from "../rules/no-useless-mustaches"
 import preferClassDirective from "../rules/prefer-class-directive"
 import preferStyleDirective from "../rules/prefer-style-directive"
 import requireOptimizedStyleAttribute from "../rules/require-optimized-style-attribute"
+import requireStoresInit from "../rules/require-stores-init"
 import shorthandAttribute from "../rules/shorthand-attribute"
 import shorthandDirective from "../rules/shorthand-directive"
 import sortAttributes from "../rules/sort-attributes"
@@ -65,6 +66,7 @@ export const rules = [
   preferClassDirective,
   preferStyleDirective,
   requireOptimizedStyleAttribute,
+  requireStoresInit,
   shorthandAttribute,
   shorthandDirective,
   sortAttributes,

tests/fixtures/rules/.eslintrc.js

@@ -1,6 +1,7 @@
-"use strict"
-
 module.exports = {
+  parserOptions: {
+    sourceType: "module",
+  },
   overrides: [
     {
       files: ["*output.svelte"],
@@ -17,5 +18,6 @@ module.exports = {
     "no-empty-function": "off",
     "one-var": "off",
     "func-style": "off",
+    "node/no-unsupported-features/es-syntax": "off",
   },
 }

tests/fixtures/rules/indent/invalid/.eslintrc.js

@@ -1,5 +1,3 @@
-"use strict"
-
 module.exports = {
   rules: {
     "no-sparse-arrays": "off",