Method Optimize

policy/composer.go:159–181

Optimize implements an AST optimizer for CEL which composes an expression graph into a single expression value.

(ctx *cel.OptimizerContext, a *ast.AST)

// Optimize implements an AST optimizer for CEL which composes an expression graph into a single
// expression value.
func (opt *ruleComposerImpl) Optimize(ctx *cel.OptimizerContext, a *ast.AST) *ast.AST {
	// The input to optimize is a dummy expression which is completely replaced according
	// to the configuration of the rule composition graph.
	ruleExpr := opt.optimizeRule(ctx, opt.rule)

	// If there were no variables, return the expression.
	if len(opt.varIndices) == 0 {
		return ctx.NewAST(ruleExpr)
	}

	// Otherwise populate the cel.@block with the variable declarations and wrap the expression
	// in the block.
	varExprs := make([]ast.Expr, len(opt.varIndices))
	for i, vi := range opt.varIndices {
		varExprs[i] = vi.expr
		err := ctx.ExtendEnv(cel.Variable(vi.indexVar, vi.celType))
		if err != nil {
			ctx.ReportErrorAtID(ruleExpr.ID(), "%s", err.Error())
		}
	}
	blockExpr := ctx.NewCall("cel.@block", ctx.NewList(varExprs, []int32{}), ruleExpr)
	return ctx.NewAST(blockExpr)
}

func (opt *ruleComposerImpl) optimizeRule(ctx *cel.OptimizerContext, r *CompiledRule) ast.Expr {
	// Visitor to rewrite variables-prefixed identifiers with index names.