feat: new if-newline rule

packages/eslint-plugin-antfu/src/rules/if-newline.ts

@@ -0,0 +1,45 @@
+import { createEslintRule } from '../utils'
+
+export const RULE_NAME = 'if-newline'
+export type MessageIds = 'missingIfNewline'
+export type Options = []
+
+export default createEslintRule<Options, MessageIds>({
+  name: RULE_NAME,
+  meta: {
+    type: 'problem',
+    docs: {
+      description: 'Newline after if',
+      recommended: 'error',
+    },
+    fixable: 'code',
+    schema: [],
+    messages: {
+      missingIfNewline: 'Expect newline after if',
+    },
+  },
+  defaultOptions: [],
+  create: (context) => {
+    return {
+      IfStatement(node) {
+        if (!node.consequent)
+          return
+        if (node.consequent.type === 'BlockStatement')
+          return
+        if (node.test.loc.end.line === node.consequent.loc.start.line) {
+          context.report({
+            node,
+            loc: {
+              start: node.test.loc.end,
+              end: node.consequent.loc.start,
+            },
+            messageId: 'missingIfNewline',
+            fix(fixer) {
+              return fixer.replaceTextRange([node.consequent.range[0], node.consequent.range[0]], '\n')
+            },
+          })
+        }
+      },
+    }
+  },
+})