fix vikstrous#15 add a default panic handler

Author: vikstrous

dataloadgen.go

@@ -273,7 +273,7 @@ func (l *Loader[KeyT, ValueT]) startBatch(ctx context.Context) {
 				}
 			}
 
-			batch.results, batch.errors = l.fetch(batch.firstContext, batch.keys)
+			batch.results, batch.errors = l.safeFetch(batch.firstContext, batch.keys)
 
 			if l.tracer != nil {
 				for _, span := range spans {
@@ -286,6 +286,16 @@ func (l *Loader[KeyT, ValueT]) startBatch(ctx context.Context) {
 	}
 }
 
+func (l *Loader[KeyT, ValueT]) safeFetch(ctx context.Context, keys []KeyT) (values []ValueT, errs []error) {
+	defer func() {
+		panicValue := recover()
+		if panicValue != nil {
+			errs = []error{fmt.Errorf("panic during fetch: %v", panicValue)}
+		}
+	}()
+	return l.fetch(ctx, keys)
+}
+
 // addKeyToBatch will return the location of the key in the batch, if its not found
 // it will add the key to the batch
 func (l *Loader[KeyT, ValueT]) addKeyToBatch(b *loaderBatch[KeyT, ValueT], key KeyT) int {
@@ -305,7 +315,7 @@ func (l *Loader[KeyT, ValueT]) addKeyToBatch(b *loaderBatch[KeyT, ValueT], key K
 				}
 			}
 
-			b.results, b.errors = l.fetch(b.firstContext, b.keys)
+			b.results, b.errors = l.safeFetch(b.firstContext, b.keys)
 
 			if l.tracer != nil {
 				for _, span := range spans {

dataloadgen_test.go

@@ -108,3 +108,16 @@ func TestErrors(t *testing.T) {
 		t.Fatalf("wrong error: %s", errs[2].Error())
 	}
 }
+
+func TestPanic(t *testing.T) {
+	ctx := context.Background()
+	dl := dataloadgen.NewLoader(func(_ context.Context, keys []int) ([]string, []error) {
+		panic("fetch panic")
+	},
+		dataloadgen.WithBatchCapacity(1),
+	)
+	_, err := dl.Load(ctx, 1)
+	if err.Error() != "panic during fetch: fetch panic" {
+		t.Fatalf("wrong error: %s", err.Error())
+	}
+}