no such overload: !_

[davenewza]

With v0.21.0, I'm using NewCustomEnv with custom declarations for just the basic boolean operators ||, && and !. However, evaluation fails when I use ! in an expression (e.g. !value):

no such overload: !_

|| and && work just fine.

env, err := cel.NewCustomEnv(
	cel.Declarations(
		decls.NewFunction(operators.LogicalAnd, decls.NewOverload(
			overloads.LogicalAnd,
			[]*expr.Type{decls.Bool, decls.Bool},
			decls.Bool,
		)),
		decls.NewFunction(operators.LogicalOr, decls.NewOverload(
			overloads.LogicalOr,
			[]*expr.Type{decls.Bool, decls.Bool},
			decls.Bool,
		)),
		decls.NewFunction(operators.LogicalNot, decls.NewOverload(
			overloads.LogicalNot,
			[]*expr.Type{decls.Bool},
			decls.Bool,
		))),
	cel.Variable("value", cel.BoolType),
)
if err != nil {
	log.Fatalf("program setup err: %s", err)
}

ast, issues := env.Compile("!value")
if issues != nil && issues.Err() != nil {
	log.Fatalf("type-check error: %s", issues.Err())
}

prg, err := env.Program(ast)
if err != nil {
	log.Fatalf("program construction error: %s", err)
}

out, _, err := prg.Eval(map[string]interface{}{
	"value": true,
})
if err != nil {
	log.Fatalf("eval error: %s", err) // <--- fails here
}

fmt.Println(out) // <- expecting 'false'

Can someone please point out what I am doing wrong.

[TristonianJones]

Hi @davenewza,

You need to provide the implementation of your version of !. Since || and && are so integral to CEL and have very special semantics we don't allow overloads of these functions (which means they magically exist without further configuration). If you want to provide your own logical not, you'd need to look at how we do this in the common/stdlib package:

cel-go/common/stdlib/standard.go

Lines 69 to 77 in f9db1d6

	function(operators.LogicalNot,
	decls.Overload(overloads.LogicalNot, argTypes(types.BoolType), types.BoolType),
	decls.SingletonUnaryBinding(func(val ref.Val) ref.Val {
	b, ok := val.(types.Bool)
	if !ok {
	return types.MaybeNoSuchOverloadErr(val)
	}
	return b.Negate()
	})),

[davenewza]

Thanks @TristonianJones. I discovered so upon further experimenting. I had assumed ! to have "native" support.