feat: enforce to use function declaration on top-level

packages/eslint-plugin-antfu/src/rules/top-level-function.ts

@@ -0,0 +1,81 @@
+import { createEslintRule } from '../utils'
+
+export const RULE_NAME = 'top-level-function'
+export type MessageIds = 'topLevelFunctionDeclaration'
+export type Options = []
+
+export default createEslintRule<Options, MessageIds>({
+  name: RULE_NAME,
+  meta: {
+    type: 'problem',
+    docs: {
+      description: 'Enforce top-level functions to be declared with function keyword',
+      recommended: 'error',
+    },
+    fixable: 'code',
+    schema: [],
+    messages: {
+      topLevelFunctionDeclaration: 'Top-level functions should be declared with function keyword',
+    },
+  },
+  defaultOptions: [],
+  create: (context) => {
+    return {
+      VariableDeclaration(node) {
+        if (node.parent.type !== 'Program' && node.parent.type !== 'ExportNamedDeclaration')
+          return
+
+        if (node.declarations.length !== 1)
+          return
+        if (node.kind !== 'const')
+          return
+        if (node.declare)
+          return
+
+        const declaration = node.declarations[0]
+
+        if (declaration.init?.type !== 'ArrowFunctionExpression')
+          return
+        if (declaration.id?.type !== 'Identifier')
+          return
+        if (declaration.id.typeAnnotation)
+          return
+
+        const arrowFn = declaration.init
+        const body = declaration.init.body
+        const id = declaration.id
+
+        context.report({
+          node,
+          loc: {
+            start: node.loc.start,
+            end: node.loc.end,
+          },
+          messageId: 'topLevelFunctionDeclaration',
+          fix(fixer) {
+            const code = context.getSourceCode().text
+            const textName = code.slice(id.range[0], id.range[1])
+            const textArgs = arrowFn.params.length
+              ? code.slice(arrowFn.params[0].range[0], arrowFn.params[arrowFn.params.length - 1].range[1])
+              : ''
+            const textBody = body.type === 'BlockStatement'
+              ? code.slice(body.range[0], body.range[1])
+              : `{ return ${code.slice(body.range[0], body.range[1])} }`
+            const textGeneric = arrowFn.typeParameters
+              ? code.slice(arrowFn.typeParameters.range[0], arrowFn.typeParameters.range[1])
+              : ''
+            const textTypeReturn = arrowFn.returnType
+              ? code.slice(arrowFn.returnType.range[0], arrowFn.returnType.range[1])
+              : ''
+            const text = `function ${textName} ${textGeneric}(${textArgs})${textTypeReturn} ${textBody}`
+            // console.log({
+            //   input: code.slice(node.range[0], node.range[1]),
+            //   output: text,
+            // })
+            return fixer.replaceTextRange([node.range[0], node.range[1]], text)
+          },
+        })
+      },
+    }
+  },
+})