Method combine

policy/composer.go:475–503

combine assembles a new compositionStep from the target output step an an input output step. non-optional.combine(non-optional) // non-optional (non-optional && conditional).combine(optional) // optional (non-optional && unconditional).combine(optional) // non-optional The last combination case is

(step compositionStep)

// The last combination case is unusual, but effectively it means that the non-optional value prunes away
// the potential optional output.
func (s nonOptionalCompositionStep) combine(step compositionStep) compositionStep {
	if step == nil {
		// The input `step` may be nil if this is the first compositionStep
		return s
	}
	ctx := s.ctx
	trueCondition := ctx.NewLiteral(types.True)
	if step.isOptional() {
		// If the step is optional, convert the non-optional value to an optional one and return a ternary
		if s.isConditional() {
			return newOptionalCompositionStep(ctx,
				trueCondition,
				ctx.NewCall(operators.Conditional,
					s.condition(),
					ctx.NewCall("optional.of", s.expr()),
					step.expr()),
			)
		}
		// The `step` is pruned away by a unconditional non-optional step `s`.
		// Likely a candidate for dead-code warnings.
		return s
	}
	return newNonOptionalCompositionStep(ctx,
		trueCondition,
		ctx.NewCall(operators.Conditional,
			s.condition(),
			s.expr(),
			step.expr()))
}

// newOptionalCompositionStep returns an output step with an optional policy output.
func newOptionalCompositionStep(ctx *cel.OptimizerContext, cond, out ast.Expr) optionalCompositionStep {