feat(rules): add no-prerender-export-outside-pages rule (#550)

* feat: add no-prerender-export-outside-pages rule

* feat: add docs for no-prerender-export-outside-pages

* chore: add changeset

Author: jp-knj

.changeset/funny-chicken-ring.md

@@ -0,0 +1,5 @@
+---
+"eslint-plugin-astro": minor
+---
+
+add `astro/no-prerender-export-outside-pages` rule that disallow `prerender` export outside of pages/ directory

docs/rules/no-prerender-export-outside-pages.md

@@ -0,0 +1,51 @@
+---
+title: "astro/no-prerender-export-outside-pages"
+description: "disallow `prerender` export outside of pages/ directory"
+---
+
+# astro/no-prerender-export-outside-pages
+
+> disallow `prerender` export outside of pages/ directory
+
+## 📖 Rule Details
+
+This rule reports `prerender` exports from Astro files that are not inside a `pages/` directory.
+
+The `prerender` directive only has an effect on page files (files under `src/pages/`). Exporting it from components or layouts has no effect.
+
+<ESLintCodeBlock>
+
+<!--eslint-skip-->
+
+```astro
+---
+/* eslint astro/no-prerender-export-outside-pages: "error" */
+
+/* ✓ GOOD — in src/pages/index.astro */
+export const prerender = true
+
+/* ✗ BAD — in src/components/MyComponent.astro */
+export const prerender = true
+---
+```
+
+</ESLintCodeBlock>
+
+## 🔧 Options
+
+Nothing.
+
+## 🔇 When Not To Use It
+
+If your project doesn't use hybrid rendering or if all files under `src/pages/` don't need prerender exports, you may disable this rule.
+
+## 📚 Further Reading
+
+- [Astro Docs: On-demand Rendering](https://docs.astro.build/en/guides/on-demand-rendering/)
+- [Astro Docs: `prerender` export](https://docs.astro.build/en/reference/routing-reference/#prerender)
+
+## 🔍 Implementation
+
+- [Rule source](https://github.com/ota-meshi/eslint-plugin-astro/blob/main/src/rules/no-prerender-export-outside-pages.ts)
+- [Test source](https://github.com/ota-meshi/eslint-plugin-astro/blob/main/tests/src/rules/no-prerender-export-outside-pages.ts)
+- [Test fixture sources](https://github.com/ota-meshi/eslint-plugin-astro/tree/main/tests/fixtures/rules/no-prerender-export-outside-pages)

src/rules/index.ts

@@ -8,6 +8,7 @@ import noDeprecatedAstroFetchcontent from "./no-deprecated-astro-fetchcontent.ts
 import noDeprecatedAstroResolve from "./no-deprecated-astro-resolve.ts"
 import noDeprecatedGetentrybyslug from "./no-deprecated-getentrybyslug.ts"
 import noExportsFromComponents from "./no-exports-from-components.ts"
+import noPrerenderExportOutsidePages from "./no-prerender-export-outside-pages.ts"
 import noSetHtmlDirective from "./no-set-html-directive.ts"
 import noSetTextDirective from "./no-set-text-directive.ts"
 import noUnsafeInlineScripts from "./no-unsafe-inline-scripts.ts"
@@ -30,6 +31,7 @@ export const originalRules: RuleModule[] = [
   noDeprecatedAstroResolve,
   noDeprecatedGetentrybyslug,
   noExportsFromComponents,
+  noPrerenderExportOutsidePages,
   noSetHtmlDirective,
   noSetTextDirective,
   noUnsafeInlineScripts,

src/rules/no-prerender-export-outside-pages.ts

@@ -0,0 +1,75 @@
+import type { TSESTree } from "@typescript-eslint/types"
+import type { RuleModule } from "../types.ts"
+import { createRule } from "../utils/index.ts"
+import { getSourceCode, getFilename } from "../utils/compat.ts"
+
+const PAGES_DIR_PATTERN = /(?:^|[/\\])pages[/\\]/
+
+const rule: RuleModule = createRule("no-prerender-export-outside-pages", {
+  meta: {
+    docs: {
+      description: "disallow `prerender` export outside of pages/ directory",
+      category: "Possible Errors",
+      recommended: false,
+    },
+    schema: [],
+    messages: {
+      disallowPrerenderOutsidePages:
+        "'prerender' export is only valid inside a pages/ directory.",
+    },
+    type: "problem",
+  },
+  create(context) {
+    const sourceCode = getSourceCode(context)
+    if (!sourceCode.parserServices?.isAstro) {
+      return {}
+    }
+
+    const filename = getFilename(context)
+    if (PAGES_DIR_PATTERN.test(filename)) {
+      return {}
+    }
+
+    /**
+     * Verify for export declarations
+     */
+    function verifyDeclaration(
+      node: TSESTree.ExportNamedDeclaration["declaration"],
+    ) {
+      if (!node) return
+      if (
+        node.type === "VariableDeclaration" &&
+        node.declarations.some(
+          (decl) =>
+            decl.id.type === "Identifier" && decl.id.name === "prerender",
+        )
+      ) {
+        context.report({
+          node,
+          messageId: "disallowPrerenderOutsidePages",
+        })
+      }
+    }
+
+    return {
+      ExportNamedDeclaration(node) {
+        if (node.exportKind === "type") return
+        verifyDeclaration(node.declaration)
+        for (const spec of node.specifiers) {
+          if (spec.exportKind === "type") continue
+          if (
+            spec.exported.type === "Identifier" &&
+            spec.exported.name === "prerender"
+          ) {
+            context.report({
+              node: spec,
+              messageId: "disallowPrerenderOutsidePages",
+            })
+          }
+        }
+      },
+    }
+  },
+})
+
+export default rule

tests/fixtures/rules/no-prerender-export-outside-pages/invalid/export-const-prerender-errors.json

@@ -0,0 +1,7 @@
+[
+  {
+    "message": "'prerender' export is only valid inside a pages/ directory.",
+    "line": 2,
+    "column": 8
+  }
+]

tests/fixtures/rules/no-prerender-export-outside-pages/invalid/export-const-prerender-input.astro

@@ -0,0 +1,4 @@
+---
+export const prerender = true
+---
+<div>Component</div>

tests/fixtures/rules/no-prerender-export-outside-pages/valid/no-prerender-input.astro

@@ -0,0 +1,4 @@
+---
+const foo = "bar"
+---
+<div>Component</div>

tests/fixtures/rules/no-prerender-export-outside-pages/valid/pages/export-const-prerender-input.astro

@@ -0,0 +1,4 @@
+---
+export const prerender = true
+---
+<div>Page</div>

tests/src/rules/no-prerender-export-outside-pages.ts

@@ -0,0 +1,16 @@
+import { RuleTester } from "../../utils/eslint-compat.ts"
+import rule from "../../../src/rules/no-prerender-export-outside-pages.ts"
+import { loadTestCases } from "../../utils/utils.ts"
+
+const tester = new RuleTester({
+  languageOptions: {
+    ecmaVersion: 2020,
+    sourceType: "module",
+  },
+})
+
+tester.run(
+  "no-prerender-export-outside-pages",
+  rule as any,
+  loadTestCases("no-prerender-export-outside-pages"),
+)