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// Copyright 2023 Google LLC
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package ext
import (
"github.com/google/cel-go/cel"
"github.com/google/cel-go/common/ast"
"github.com/google/cel-go/common/types"
)
// Bindings returns a cel.EnvOption to configure support for local variable
// bindings in expressions.
//
// # Cel.Bind
//
// Binds a simple identifier to an initialization expression which may be used
// in a subsequenct result expression. Bindings may also be nested within each
// other.
//
// cel.bind(<varName>, <initExpr>, <resultExpr>)
//
// Examples:
//
// cel.bind(a, 'hello',
// cel.bind(b, 'world', a + b + b + a)) // "helloworldworldhello"
//
// // Avoid a list allocation within the exists comprehension.
// cel.bind(valid_values, [a, b, c],
// [d, e, f].exists(elem, elem in valid_values))
//
// Local bindings are not guaranteed to be evaluated before use.
func Bindings() cel.EnvOption {
return cel.Lib(celBindings{})
}
const (
celNamespace = "cel"
bindMacro = "bind"
unusedIterVar = "#unused"
)
type celBindings struct{}
func (celBindings) LibraryName() string {
return "cel.lib.ext.cel.bindings"
}
func (celBindings) CompileOptions() []cel.EnvOption {
return []cel.EnvOption{
cel.Macros(
// cel.bind(var, <init>, <expr>)
cel.ReceiverMacro(bindMacro, 3, celBind),
),
}
}
func (celBindings) ProgramOptions() []cel.ProgramOption {
return []cel.ProgramOption{}
}
func celBind(mef cel.MacroExprFactory, target ast.Expr, args []ast.Expr) (ast.Expr, *cel.Error) {
if !macroTargetMatchesNamespace(celNamespace, target) {
return nil, nil
}
varIdent := args[0]
varName := ""
switch varIdent.Kind() {
case ast.IdentKind:
varName = varIdent.AsIdent()
default:
return nil, mef.NewError(varIdent.ID(), "cel.bind() variable names must be simple identifiers")
}
varInit := args[1]
resultExpr := args[2]
return mef.NewComprehension(
mef.NewList(),
unusedIterVar,
varName,
varInit,
mef.NewLiteral(types.False),
mef.NewIdent(varName),
resultExpr,
), nil
}
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