From 38c1d592b7121f26dc661c1bc2bf0e32eba9d888 Mon Sep 17 00:00:00 2001
From: Connor Stein <connor.stein@mail.mcgill.ca>
Date: Sat, 12 Dec 2020 04:16:34 -0500
Subject: [PATCH] abi/bind: fix error-handling in generated wrappers for
 functions returning structs (#22005)

Fixes the template used when generating code, which in some scenarios would lead to panic instead of returning an error.
---
 accounts/abi/bind/bind_test.go | 39 ++++++++++++++++++++++++++++++++++
 accounts/abi/bind/template.go  |  3 +++
 2 files changed, 42 insertions(+)

diff --git a/accounts/abi/bind/bind_test.go b/accounts/abi/bind/bind_test.go
index 1a8a17e45e..4a504516bb 100644
--- a/accounts/abi/bind/bind_test.go
+++ b/accounts/abi/bind/bind_test.go
@@ -569,6 +569,45 @@ var bindTests = []struct {
 		nil,
 		nil,
 	},
+	{
+		`NonExistentStruct`,
+		`
+			contract NonExistentStruct {
+				function Struct() public view returns(uint256 a, uint256 b) {
+					return (10, 10);
+				}
+			}
+		`,
+		[]string{`6080604052348015600f57600080fd5b5060888061001e6000396000f3fe6080604052348015600f57600080fd5b506004361060285760003560e01c8063d5f6622514602d575b600080fd5b6033604c565b6040805192835260208301919091528051918290030190f35b600a809156fea264697066735822beefbeefbeefbeefbeefbeefbeefbeefbeefbeefbeefbeefbeefbeefbeefbeefbeef64736f6c6343decafe0033`},
+		[]string{`[{"inputs":[],"name":"Struct","outputs":[{"internalType":"uint256","name":"a","type":"uint256"},{"internalType":"uint256","name":"b","type":"uint256"}],"stateMutability":"pure","type":"function"}]`},
+		`
+			"github.com/ethereum/go-ethereum/accounts/abi/bind"
+			"github.com/ethereum/go-ethereum/accounts/abi/bind/backends"
+			"github.com/ethereum/go-ethereum/common"
+			"github.com/ethereum/go-ethereum/core"
+		`,
+		`
+			// Create a simulator and wrap a non-deployed contract
+
+			sim := backends.NewSimulatedBackend(core.GenesisAlloc{}, uint64(10000000000))
+			defer sim.Close()
+
+			nonexistent, err := NewNonExistentStruct(common.Address{}, sim)
+			if err != nil {
+				t.Fatalf("Failed to access non-existent contract: %v", err)
+			}
+			// Ensure that contract calls fail with the appropriate error
+			if res, err := nonexistent.Struct(nil); err == nil {
+				t.Fatalf("Call succeeded on non-existent contract: %v", res)
+			} else if (err != bind.ErrNoCode) {
+				t.Fatalf("Error mismatch: have %v, want %v", err, bind.ErrNoCode)
+			}
+		`,
+		nil,
+		nil,
+		nil,
+		nil,
+	},
 	// Tests that gas estimation works for contracts with weird gas mechanics too.
 	{
 		`FunkyGasPattern`,
diff --git a/accounts/abi/bind/template.go b/accounts/abi/bind/template.go
index 8dac11f79f..351eabd258 100644
--- a/accounts/abi/bind/template.go
+++ b/accounts/abi/bind/template.go
@@ -304,6 +304,9 @@ var (
 			err := _{{$contract.Type}}.contract.Call(opts, &out, "{{.Original.Name}}" {{range .Normalized.Inputs}}, {{.Name}}{{end}})
 			{{if .Structured}}
 			outstruct := new(struct{ {{range .Normalized.Outputs}} {{.Name}} {{bindtype .Type $structs}}; {{end}} })
+			if err != nil {
+				return *outstruct, err
+			}
 			{{range $i, $t := .Normalized.Outputs}} 
 			outstruct.{{.Name}} = out[{{$i}}].({{bindtype .Type $structs}}){{end}}