accounts/abi: fix method constant flag for solidity 6.0 (#20482)

accounts/abi/abi.go

@@ -108,12 +108,13 @@ func (abi ABI) UnpackIntoMap(v map[string]interface{}, name string, data []byte)
 // UnmarshalJSON implements json.Unmarshaler interface
 func (abi *ABI) UnmarshalJSON(data []byte) error {
 	var fields []struct {
-		Type      string
-		Name      string
-		Constant  bool
-		Anonymous bool
-		Inputs    []Argument
-		Outputs   []Argument
+		Type            string
+		Name            string
+		Constant        bool
+		StateMutability string
+		Anonymous       bool
+		Inputs          []Argument
+		Outputs         []Argument
 	}
 	if err := json.Unmarshal(data, &fields); err != nil {
 		return err
@@ -134,10 +135,11 @@ func (abi *ABI) UnmarshalJSON(data []byte) error {
 				name = fmt.Sprintf("%s%d", field.Name, idx)
 				_, ok = abi.Methods[name]
 			}
+			isConst := field.Constant || field.StateMutability == "pure" || field.StateMutability == "view"
 			abi.Methods[name] = Method{
 				Name:    name,
 				RawName: field.Name,
-				Const:   field.Constant,
+				Const:   isConst,
 				Inputs:  field.Inputs,
 				Outputs: field.Outputs,
 			}

accounts/abi/bind/bind_test.go

@@ -1530,6 +1530,61 @@ var bindTests = []struct {
 		nil,
 		[]string{"ContractOne", "ContractTwo", "ExternalLib"},
 	},
+	// Test the existence of the free retrieval calls
+	{
+		`PureAndView`,
+		`pragma solidity >=0.6.0;
+		contract PureAndView {
+			function PureFunc() public pure returns (uint) {
+				return 42;
+			}
+			function ViewFunc() public view returns (uint) {
+				return block.number;
+			}
+		}
+		`,
+		[]string{`608060405234801561001057600080fd5b5060b68061001f6000396000f3fe6080604052348015600f57600080fd5b506004361060325760003560e01c806376b5686a146037578063bb38c66c146053575b600080fd5b603d606f565b6040518082815260200191505060405180910390f35b60596077565b6040518082815260200191505060405180910390f35b600043905090565b6000602a90509056fea2646970667358221220d158c2ab7fdfce366a7998ec79ab84edd43b9815630bbaede2c760ea77f29f7f64736f6c63430006000033`},
+		[]string{`[{"inputs": [],"name": "PureFunc","outputs": [{"internalType": "uint256","name": "","type": "uint256"}],"stateMutability": "pure","type": "function"},{"inputs": [],"name": "ViewFunc","outputs": [{"internalType": "uint256","name": "","type": "uint256"}],"stateMutability": "view","type": "function"}]`},
+		`
+			"math/big"
+
+			"github.com/ethereum/go-ethereum/accounts/abi/bind"
+			"github.com/ethereum/go-ethereum/accounts/abi/bind/backends"
+			"github.com/ethereum/go-ethereum/core"
+			"github.com/ethereum/go-ethereum/crypto"
+		`,
+		`
+			// Generate a new random account and a funded simulator
+			key, _ := crypto.GenerateKey()
+			auth := bind.NewKeyedTransactor(key)
+
+			sim := backends.NewSimulatedBackend(core.GenesisAlloc{auth.From: {Balance: big.NewInt(10000000000)}}, 10000000)
+			defer sim.Close()
+
+			// Deploy a tester contract and execute a structured call on it
+			_, _, pav, err := DeployPureAndView(auth, sim)
+			if err != nil {
+				t.Fatalf("Failed to deploy PureAndView contract: %v", err)
+			}
+			sim.Commit()
+
+			// This test the existence of the free retreiver call for view and pure functions
+			if num, err := pav.PureFunc(nil); err != nil {
+				t.Fatalf("Failed to call anonymous field retriever: %v", err)
+			} else if num.Cmp(big.NewInt(42)) != 0 {
+				t.Fatalf("Retrieved value mismatch: have %v, want %v", num, 42)
+			}
+			if num, err := pav.ViewFunc(nil); err != nil {
+				t.Fatalf("Failed to call anonymous field retriever: %v", err)
+			} else if num.Cmp(big.NewInt(1)) != 0 {
+				t.Fatalf("Retrieved value mismatch: have %v, want %v", num, 1)
+			}
+		`,
+		nil,
+		nil,
+		nil,
+		nil,
+	},
 }
 
 // Tests that packages generated by the binder can be successfully compiled and