Improve error recovery (#705)

* feat: improve error recovery

* fix: only coerce to error if not nil

* refactor: move ErrorToJSError to wasm_utils

* refactor: do not transform stacktraces

* Update spicy-ways-sing.md

* Update utils.go

* chore: remove unused imports

Co-authored-by: Nate Moore <[email protected]>

.changeset/spicy-ways-sing.md

@@ -0,0 +1,5 @@
+---
+'@astrojs/compiler': minor
+---
+
+Improve error recovery when using the `transform` function. The compiler will now properly reject the promise with a useful message and stacktrace rather than print internal errors to stdout.

cmd/astro-wasm/astro-wasm.go

@@ -260,15 +260,23 @@ func Transform() any {
 		h := handler.NewHandler(source, transformOptions.Filename)
 
 		styleError := []string{}
-		handler := js.FuncOf(func(this js.Value, args []js.Value) any {
+		promiseHandle := js.FuncOf(func(this js.Value, args []js.Value) any {
 			resolve := args[0]
+			reject := args[1]
 
 			go func() {
 				var doc *astro.Node
+				defer func() {
+					if err := recover(); err != nil {
+						reject.Invoke(wasm_utils.ErrorToJSError(h, err.(error)))
+						return
+					}
+				}()
 
 				doc, err := astro.ParseWithOptions(strings.NewReader(source), astro.ParseOptionWithHandler(h))
 				if err != nil {
-					fmt.Println(err)
+					reject.Invoke(wasm_utils.ErrorToJSError(h, err))
+					return
 				}
 
 				// Hoist styles and scripts to the top-level
@@ -403,11 +411,11 @@ func Transform() any {
 
 			return nil
 		})
-		defer handler.Release()
+		defer promiseHandle.Release()
 
 		// Create and return the Promise object
 		promiseConstructor := js.Global().Get("Promise")
-		return promiseConstructor.New(handler)
+		return promiseConstructor.New(promiseHandle)
 	})
 }
 

internal_wasm/utils/utils.go

@@ -1,9 +1,13 @@
 package wasm_utils
 
 import (
+	"runtime/debug"
+	"strings"
 	"syscall/js"
 
+	"github.com/norunners/vert"
 	astro "github.com/withastro/compiler/internal"
+	"github.com/withastro/compiler/internal/handler"
 )
 
 // See https://stackoverflow.com/questions/68426700/how-to-wait-a-js-async-function-from-golang-wasm
@@ -50,3 +54,22 @@ func GetAttrs(n *astro.Node) js.Value {
 	}
 	return attrs
 }
+
+type JSError struct {
+	Message string `js:"message"`
+	Stack   string `js:"stack"`
+}
+
+func (err *JSError) Value() js.Value {
+	return vert.ValueOf(err).Value
+}
+
+func ErrorToJSError(h *handler.Handler, err error) js.Value {
+	stack := string(debug.Stack())
+	message := strings.TrimSpace(err.Error())
+	jsError := JSError{
+		Message: message,
+		Stack:   stack,
+	}
+	return jsError.Value()
+}