[binding] TS returns Promise<void> when go returns error (#2247)

v2/internal/binding/binding_test/binding_returned_promises_test.go

@@ -0,0 +1,59 @@
+package binding_test
+
+import (
+	"io/fs"
+	"os"
+	"testing"
+
+	"github.com/wailsapp/wails/v2/internal/binding"
+	"github.com/wailsapp/wails/v2/internal/logger"
+)
+
+const expectedPromiseBindings = `// Cynhyrchwyd y ffeil hon yn awtomatig. PEIDIWCH Â MODIWL
+// This file is automatically generated. DO NOT EDIT
+
+export function ErrorReturn(arg1:number):Promise<void>;
+
+export function NoReturn(arg1:string):Promise<void>;
+
+export function SingleReturn(arg1:any):Promise<number>;
+
+export function SingleReturnWithError(arg1:number):Promise<string>;
+
+export function TwoReturn(arg1:any):Promise<string|number>;
+`
+
+type PromisesTest struct{}
+
+func (h *PromisesTest) NoReturn(_ string)                           {}
+func (h *PromisesTest) ErrorReturn(_ int) error                     { return nil }
+func (h *PromisesTest) SingleReturn(_ interface{}) int              { return 0 }
+func (h *PromisesTest) SingleReturnWithError(_ int) (string, error) { return "", nil }
+func (h *PromisesTest) TwoReturn(_ interface{}) (string, int)       { return "", 0 }
+
+func TestPromises(t *testing.T) {
+	// given
+	generationDir := t.TempDir()
+
+	// setup
+	testLogger := &logger.Logger{}
+	b := binding.NewBindings(testLogger, []interface{}{&PromisesTest{}}, []interface{}{}, false)
+
+	// then
+	err := b.GenerateGoBindings(generationDir)
+	if err != nil {
+		t.Fatalf("could not generate the Go bindings: %v", err)
+	}
+
+	// then
+	rawGeneratedBindings, err := fs.ReadFile(os.DirFS(generationDir), "binding_test/PromisesTest.d.ts")
+	if err != nil {
+		t.Fatalf("could not read the generated bindings: %v", err)
+	}
+
+	// then
+	generatedBindings := string(rawGeneratedBindings)
+	if generatedBindings != expectedPromiseBindings {
+		t.Fatalf("the generated bindings does not match the expected ones.\nWanted:\n%s\n\nGot:\n%s", expectedPromiseBindings, generatedBindings)
+	}
+}

v2/internal/binding/generate.go

@@ -77,21 +77,27 @@ func (b *Bindings) GenerateGoBindings(baseDir string) error {
 					args.Add(arg + ":" + goTypeToTypescriptType(input.TypeName, &importNamespaces))
 				}
 				tsBody.WriteString(args.Join(",") + "):")
-				returnType := "Promise"
+				// now build Typescript return types
-				if methodDetails.OutputCount() > 0 {
+				// If there is no return value or only returning error, TS returns Promise<void>
+				// If returning single value, TS returns Promise<type>
+				// If returning single value or error, TS returns Promise<type>
+				// If returning two values, TS returns Promise<type1|type2>
+				// Otherwise, TS returns Promise<type1> (instead of throwing Go error?)
+				var returnType string
+				if methodDetails.OutputCount() == 0 {
+					returnType = "Promise<void>"
+				} else if methodDetails.OutputCount() == 1 && methodDetails.Outputs[0].TypeName == "error" {
+					returnType = "Promise<void>"
+				} else {
 					outputTypeName := entityFullReturnType(methodDetails.Outputs[0].TypeName, b.tsPrefix, b.tsSuffix, &importNamespaces)
 					firstType := goTypeToTypescriptType(outputTypeName, &importNamespaces)
-					returnType += "<" + firstType
+					returnType = "Promise<" + firstType
-					if methodDetails.OutputCount() == 2 {
+					if methodDetails.OutputCount() == 2 && methodDetails.Outputs[1].TypeName != "error" {
-						if methodDetails.Outputs[1].TypeName != "error" {
+						outputTypeName = entityFullReturnType(methodDetails.Outputs[1].TypeName, b.tsPrefix, b.tsSuffix, &importNamespaces)
-							outputTypeName = entityFullReturnType(methodDetails.Outputs[1].TypeName, b.tsPrefix, b.tsSuffix, &importNamespaces)
+						secondType := goTypeToTypescriptType(outputTypeName, &importNamespaces)
-							secondType := goTypeToTypescriptType(outputTypeName, &importNamespaces)
+						returnType += "|" + secondType
-							returnType += "|" + secondType
-						}
 					}
 					returnType += ">"
-				} else {
-					returnType = "Promise<void>"
 				}
 				tsBody.WriteString(returnType + ";\n")
 			}