bug: correct handling of the zero int64 value

[valli0x]

added TypeInt64 in Zero() method

[hashicorp-cla]

All committers have signed the CLA.

[tomhjp]

Thanks for adding this! I left some suggestions for tests, and related non-panic bug, but I'm also happy to add those fixes in a separate PR if you prefer.

[tomhjp]

It would be great to add a test to help catch any future errors like this. I didn't want to overcomplicate by getting into reflection etc, but had a little play and came up with this:

func TestFieldTypeMethods(t *testing.T) {
	unknownFormat := convertType(TypeInvalid).format

	for i := TypeInvalid + 1; i < typeInvalidMax; i++ {
		t.Run(fmt.Sprintf("%d", i), func(t *testing.T) {
			if i.String() == TypeInvalid.String() {
				t.Errorf("unknown type string for %d", i)
			}

			if convertType(i).format == unknownFormat {
				t.Errorf("unknown schema for %d", i)
			}

			_ = i.Zero()
		})
	}
}

You'll notice, that required adding a new (unexported) type to the end of the enum:

	// DO NOT USE. Any new values must be inserted before this value.
	// Used to write tests that ensure type methods handle all possible values.
	typeInvalidMax

That turned up that the String() method is also missing a case for Int64:

	case TypeInt64:
		return "int64"

[valli0x]

@tomhjp looks good, thanks

[tomhjp]

I'll add the test in a separate PR. Thanks for the fix!