Override error formatting (#2717)

v2/internal/app/app_dev.go

@@ -213,7 +213,7 @@ func CreateApp(appoptions *options.App) (*App, error) {
 
 	eventHandler := runtime.NewEvents(myLogger)
 	ctx = context.WithValue(ctx, "events", eventHandler)
-	messageDispatcher := dispatcher.NewDispatcher(ctx, myLogger, appBindings, eventHandler)
+	messageDispatcher := dispatcher.NewDispatcher(ctx, myLogger, appBindings, eventHandler, appoptions.ErrorFormatter)
 
 	// Create the frontends and register to event handler
 	desktopFrontend := desktop.NewFrontend(ctx, appoptions, myLogger, appBindings, messageDispatcher)

v2/internal/app/app_production.go

@@ -82,7 +82,7 @@ func CreateApp(appoptions *options.App) (*App, error) {
 		ctx = context.WithValue(ctx, "buildtype", "production")
 	}
 
-	messageDispatcher := dispatcher.NewDispatcher(ctx, myLogger, appBindings, eventHandler)
+	messageDispatcher := dispatcher.NewDispatcher(ctx, myLogger, appBindings, eventHandler, appoptions.ErrorFormatter)
 	appFrontend := desktop.NewFrontend(ctx, appoptions, myLogger, appBindings, messageDispatcher)
 	eventHandler.AddFrontend(appFrontend)
 

v2/internal/frontend/dispatcher/calls.go

@@ -3,8 +3,9 @@ package dispatcher
 import (
 	"encoding/json"
 	"fmt"
-	"github.com/wailsapp/wails/v2/internal/frontend"
 	"strings"
+
+	"github.com/wailsapp/wails/v2/internal/frontend"
 )
 
 type callMessage struct {
@@ -49,7 +50,12 @@ func (d *Dispatcher) processCallMessage(message string, sender frontend.Frontend
 		CallbackID: payload.CallbackID,
 	}
 	if err != nil {
-		callbackMessage.Err = err.Error()
+		// Use the error formatter if one was provided
+		if d.errfmt != nil {
+			callbackMessage.Err = d.errfmt(err)
+		} else {
+			callbackMessage.Err = err.Error()
+		}
 	} else {
 		callbackMessage.Result = result
 	}
@@ -66,7 +72,7 @@ func (d *Dispatcher) processCallMessage(message string, sender frontend.Frontend
 // CallbackMessage defines a message that contains the result of a call
 type CallbackMessage struct {
 	Result     interface{} `json:"result"`
-	Err        string      `json:"error"`
+	Err        any         `json:"error"`
 	CallbackID string      `json:"callbackid"`
 }
 

v2/internal/frontend/dispatcher/dispatcher.go

@@ -7,6 +7,7 @@ import (
 	"github.com/wailsapp/wails/v2/internal/binding"
 	"github.com/wailsapp/wails/v2/internal/frontend"
 	"github.com/wailsapp/wails/v2/internal/logger"
+	"github.com/wailsapp/wails/v2/pkg/options"
 )
 
 type Dispatcher struct {
@@ -15,15 +16,17 @@ type Dispatcher struct {
 	events     frontend.Events
 	bindingsDB *binding.DB
 	ctx        context.Context
+	errfmt     options.ErrorFormatter
 }
 
-func NewDispatcher(ctx context.Context, log *logger.Logger, bindings *binding.Bindings, events frontend.Events) *Dispatcher {
+func NewDispatcher(ctx context.Context, log *logger.Logger, bindings *binding.Bindings, events frontend.Events, errfmt options.ErrorFormatter) *Dispatcher {
 	return &Dispatcher{
 		log:        log,
 		bindings:   bindings,
 		events:     events,
 		bindingsDB: bindings.DB(),
 		ctx:        ctx,
+		errfmt:     errfmt,
 	}
 }
 

v2/pkg/options/options.go

@@ -64,6 +64,9 @@ type App struct {
 	Bind               []interface{}
 	WindowStartState   WindowStartState
 
+	// ErrorFormatter overrides the formatting of errors returned by backend methods
+	ErrorFormatter ErrorFormatter
+
 	// CSS property to test for draggable elements. Default "--wails-draggable"
 	CSSDragProperty string
 
@@ -90,6 +93,8 @@ type App struct {
 	Debug Debug
 }
 
+type ErrorFormatter func(error) any
+
 type RGBA struct {
 	R uint8 `json:"r"`
 	G uint8 `json:"g"`

website/docs/reference/options.mdx

@@ -58,6 +58,7 @@ func main() {
         Bind: []interface{}{
             app,
         },
+        ErrorFormatter: func(err error) any { return err.Error() },
         Windows: &windows.Options{
             WebviewIsTransparent:              false,
             WindowIsTranslucent:               false,
@@ -477,6 +478,14 @@ A slice of struct instances defining methods that need to be bound to the fronte
 Name: Bind<br/>
 Type: `[]interface{}`
 
+### ErrorFormatter
+
+A function that determines how errors are formatted when returned by a JS-to-Go
+method call. The returned value will be marshalled as JSON.
+
+Name: ErrorFormatter<br/>
+Type: `func (error) any`
+
 ### Windows
 
 This defines [Windows specific options](#windows).

website/src/pages/changelog.mdx

@@ -27,6 +27,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Added `-devtools` production build flag. Added by @mmghv in [PR](https://github.com/wailsapp/wails/pull/2725)
 - Added `EnableDefaultContextMenu` option to allow enabling the browser's default context-menu in production . Added by @mmghv in [PR](https://github.com/wailsapp/wails/pull/2733)
 - Added smart functionality for the default context-menu in production with CSS styles to control it. Added by @mmghv in [PR](https://github.com/wailsapp/wails/pull/2748)
+- Added custom error formatting to allow passing structured errors back to the frontend.
 
 ### Changed