fix(tsx): Transform top level returns into throws (#1028)

* fix(tsx): Transform top level returns into throws

* fix: logic

* nit: use return elngth

* Create bright-plums-suffer.md

.changeset/bright-plums-suffer.md

@@ -0,0 +1,5 @@
+---
+"@astrojs/compiler": patch
+---
+
+Transform top level returns into throws in the TSX output

internal/js_scanner/js_scanner.go

@@ -12,6 +12,60 @@ import (
 	"github.com/withastro/compiler/internal/loc"
 )
 
+func FindTopLevelReturns(source []byte) []int {
+	l := js.NewLexer(parse.NewInputBytes(source))
+	i := 0
+	returns := make([]int, 0)
+	pairs := make(map[byte]int)
+	inFunction := false
+
+	for {
+		token, value := l.Next()
+
+		if token == js.DivToken || token == js.DivEqToken {
+			lns := bytes.Split(source[i+1:], []byte{'\n'})
+			if bytes.Contains(lns[0], []byte{'/'}) {
+				token, value = l.RegExp()
+			}
+		}
+
+		if token == js.ErrorToken {
+			if l.Err() != io.EOF {
+				return returns
+			}
+			break
+		}
+
+		if js.IsPunctuator(token) {
+			if value[0] == '{' {
+				pairs[value[0]]++
+				i += len(value)
+				continue
+			} else if value[0] == '}' {
+				pairs['{']--
+			}
+		}
+
+		// Track function declarations
+		if token == js.FunctionToken {
+			inFunction = true
+		}
+
+		// Track end of function declarations
+		if inFunction && token == js.CloseBraceToken && pairs['{'] == 1 {
+			inFunction = false
+		}
+
+		if token == js.ReturnToken && !inFunction {
+			returns = append(returns, i)
+		}
+
+		i += len(value)
+	}
+
+	return returns
+}
+
 type HoistedScripts struct {
 	Hoisted     [][]byte
 	HoistedLocs []loc.Loc

internal/printer/print-to-tsx.go

@@ -2,6 +2,7 @@ package printer
 
 import (
 	"fmt"
+	"slices"
 	"strings"
 	"unicode"
 
@@ -366,11 +367,31 @@ declare const Astro: Readonly<import('astro').AstroGlobal<%s, typeof %s`, propsI
 		p.addSourceMapping(loc.Loc{Start: 0})
 		frontmatterStart := len(p.output)
 		for c := n.FirstChild; c != nil; c = c.NextSibling {
+			topLevelReturn := js_scanner.FindTopLevelReturns([]byte(c.Data))
 			if c.Type == TextNode {
 				if len(c.Loc) > 0 {
 					p.addSourceMapping(c.Loc[0])
 				}
-				p.printTextWithSourcemap(c.Data, c.Loc[0])
+				// Remplace all the top level returns with a `throw`
+				if len(topLevelReturn) > 0 {
+					// Loop over the characters and replace the top level returns with a `throw`
+					newString := []byte{}
+
+					i := 0
+					for i < len(c.Data) {
+						if slices.Contains(topLevelReturn, i) {
+							newString = append(newString, []byte("throw ")...)
+							i += len("return")
+						} else {
+							newString = append(newString, c.Data[i])
+							i++
+						}
+					}
+
+					p.printTextWithSourcemap(string(newString), c.Loc[0])
+				} else {
+					p.printTextWithSourcemap(c.Data, c.Loc[0])
+				}
 			} else {
 				renderTsx(p, c, o)
 			}

packages/compiler/test/tsx/top-level-returns.ts

@@ -0,0 +1,44 @@
+import { convertToTSX } from '@astrojs/compiler';
+import { test } from 'uvu';
+import * as assert from 'uvu/assert';
+import { TSXPrefix } from '../utils.js';
+
+test('transforms top-level returns to throw statements', async () => {
+	const input = `---
+if (something) {
+	return Astro.redirect();
+}
+
+function thatDoesSomething() {
+	return "Hey";
+}
+
+class Component {
+	render() {
+		return "wow"!
+	}
+}
+---`;
+	const output = `${TSXPrefix}
+if (something) {
+	throw  Astro.redirect();
+}
+
+function thatDoesSomething() {
+	return "Hey";
+}
+
+class Component {
+	render() {
+		return "wow"!
+	}
+}
+
+
+export default function __AstroComponent_(_props: Record<string, any>): any {}
+`;
+	const { code } = await convertToTSX(input, { sourcemap: 'external' });
+	assert.snapshot(code, output, 'expected code to match snapshot');
+});
+
+test.run();