Method combine

policy/composer.go:533–580

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

(step compositionStep)

// The last combination case indicates that an optional value in one case should be resolved
// to a non-optional value as
func (s optionalCompositionStep) combine(step compositionStep) compositionStep {
	if step == nil {
		// This is likely unreachable for an optional step, but worth adding as a safeguard
		return s
	}
	ctx := s.ctx
	trueCondition := ctx.NewLiteral(types.True)
	if step.isOptional() {
		// Introduce a ternary to capture the conditional return when combining a
		// conditional optional with another optional.
		if s.isConditional() {
			return newOptionalCompositionStep(ctx,
				trueCondition,
				ctx.NewCall(operators.Conditional,
					s.condition(),
					s.expr(),
					step.expr()),
			)
		}
		// When an optional is unconditionally combined with another optional, rely
		// on the optional 'or' to fall-through from one optional to another.
		if !isOptionalNone(step.expr()) {
			return newOptionalCompositionStep(ctx,
				trueCondition,
				ctx.NewMemberCall("or", s.expr(), step.expr()))
		}
		// Otherwise, the current step 's' is unconditional and effectively prunes away
		// the other input 'step'.
		return s
	}
	if s.isConditional() {
		// Introduce a ternary to capture the conditional return while wrapping the
		// non-optional result from a lower step into an optional value.
		return newOptionalCompositionStep(ctx,
			trueCondition,
			ctx.NewCall(operators.Conditional,
				s.condition(),
				s.expr(),
				ctx.NewCall("optional.of", step.expr())))
	}
	// If the current step is unconditional and the step is non-optional, attempt
	// to convert to the optional step 's' to a non-optional value using `orValue`
	// with the 'step' expression value.
	return newNonOptionalCompositionStep(ctx,
		trueCondition,
		ctx.NewMemberCall("orValue", s.expr(), step.expr()),
	)
}

func isOptionalNone(e ast.Expr) bool {
	return e.Kind() == ast.CallKind &&