accounts/abi/bind: Remove panic in abigen generated code

[royalfork]

This PR fixes a panic which could occur in an abigen'd output file. This is the currently generated code:

// Tuple is a free data retrieval call binding the contract method 0xea8ca604.
//
// Solidity: function tuple(bool reverts) view returns(string a, int256 b, bytes32 c)
func (_Tupler *TuplerCaller) Tuple(opts *bind.CallOpts, reverts bool) (struct {
	A string
	B *big.Int
	C [32]byte
}, error) {
	var out []interface{}
	err := _Tupler.contract.Call(opts, &out, "tuple", reverts)

	outstruct := new(struct {
		A string
		B *big.Int
		C [32]byte
	})

	outstruct.A = out[0].(string)
	outstruct.B = out[1].(*big.Int)
	outstruct.C = out[2].([32]byte)

	return *outstruct, err

}

When _Tupler.contract.Call returns a non-nil err, out will not be populated with result data, and the outstruct.A = out[0].(string) assignment will panic with an "index out of range" runtime error.

This PR adds an if err != nil check to the generated code so that the contract.Call error is properly returned before any outstruct assignments.

// Tuple is a free data retrieval call binding the contract method 0xea8ca604.
//
// Solidity: function tuple(bool reverts) view returns(string a, int256 b, bytes32 c)
func (_Tupler *TuplerCaller) Tuple(opts *bind.CallOpts, reverts bool) (struct {
	A string
	B *big.Int
	C [32]byte
}, error) {
	var out []interface{}
	err := _Tupler.contract.Call(opts, &out, "tuple", reverts)

	outstruct := new(struct {
		A string
		B *big.Int
		C [32]byte
	})
	if err != nil {
		return *outstruct, err
	}

	outstruct.A = out[0].(string)
	outstruct.B = out[1].(*big.Int)
	outstruct.C = out[2].([32]byte)

	return *outstruct, nil

}

[MariusVanDerWijden]

LGTM, thank you for picking this up!

[holiman]

LGTM

[holiman]

Apologies!

I thought this had been merged already, and when #22005 came in, I thought that was handling the same error in a different place, and merged that one. So now although this one was first, the other one got merged instead, and I just now saw that this had been left hanging.

Thanks for the PR, sorry about the screw-up, my bad!

[royalfork]

No worries, just happy a fix has been merged successfully. Thanks!