accounts/abi/bind/backends: return errors instead of panic (ethereum#…

…24242)

accounts/abi/bind/backends/simulated.go

@@ -639,25 +639,24 @@ func (b *SimulatedBackend) callContract(ctx context.Context, call ethereum.CallM
 }
 
 // SendTransaction updates the pending block to include the given transaction.
-// It panics if the transaction is invalid.
 func (b *SimulatedBackend) SendTransaction(ctx context.Context, tx *types.Transaction) error {
 	b.mu.Lock()
 	defer b.mu.Unlock()
 
 	// Get the last block
 	block, err := b.blockByHash(ctx, b.pendingBlock.ParentHash())
 	if err != nil {
-		panic("could not fetch parent")
+		return fmt.Errorf("could not fetch parent")
 	}
 	// Check transaction validity
 	signer := types.MakeSigner(b.blockchain.Config(), block.Number())
 	sender, err := types.Sender(signer, tx)
 	if err != nil {
-		panic(fmt.Errorf("invalid transaction: %v", err))
+		return fmt.Errorf("invalid transaction: %v", err)
 	}
 	nonce := b.pendingState.GetNonce(sender)
 	if tx.Nonce() != nonce {
-		panic(fmt.Errorf("invalid transaction nonce: got %d, want %d", tx.Nonce(), nonce))
+		return fmt.Errorf("invalid transaction nonce: got %d, want %d", tx.Nonce(), nonce)
 	}
 	// Include tx in chain
 	blocks, _ := core.GenerateChain(b.config, block, ethash.NewFaker(), b.database, 1, func(number int, block *core.BlockGen) {