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101 lines
2.6 KiB
Go
101 lines
2.6 KiB
Go
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// Copyright 2023 Google LLC
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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package ext
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import (
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"github.com/google/cel-go/cel"
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"github.com/google/cel-go/common"
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exprpb "google.golang.org/genproto/googleapis/api/expr/v1alpha1"
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)
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// Bindings returns a cel.EnvOption to configure support for local variable
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// bindings in expressions.
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//
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// # Cel.Bind
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//
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// Binds a simple identifier to an initialization expression which may be used
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// in a subsequenct result expression. Bindings may also be nested within each
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// other.
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//
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// cel.bind(<varName>, <initExpr>, <resultExpr>)
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//
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// Examples:
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//
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// cel.bind(a, 'hello',
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// cel.bind(b, 'world', a + b + b + a)) // "helloworldworldhello"
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//
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// // Avoid a list allocation within the exists comprehension.
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// cel.bind(valid_values, [a, b, c],
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// [d, e, f].exists(elem, elem in valid_values))
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//
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// Local bindings are not guaranteed to be evaluated before use.
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func Bindings() cel.EnvOption {
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return cel.Lib(celBindings{})
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}
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const (
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celNamespace = "cel"
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bindMacro = "bind"
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unusedIterVar = "#unused"
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)
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type celBindings struct{}
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func (celBindings) LibraryName() string {
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return "cel.lib.ext.cel.bindings"
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}
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func (celBindings) CompileOptions() []cel.EnvOption {
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return []cel.EnvOption{
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cel.Macros(
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// cel.bind(var, <init>, <expr>)
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cel.NewReceiverMacro(bindMacro, 3, celBind),
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),
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}
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}
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func (celBindings) ProgramOptions() []cel.ProgramOption {
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return []cel.ProgramOption{}
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}
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func celBind(meh cel.MacroExprHelper, target *exprpb.Expr, args []*exprpb.Expr) (*exprpb.Expr, *common.Error) {
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if !macroTargetMatchesNamespace(celNamespace, target) {
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return nil, nil
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}
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varIdent := args[0]
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varName := ""
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switch varIdent.GetExprKind().(type) {
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case *exprpb.Expr_IdentExpr:
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varName = varIdent.GetIdentExpr().GetName()
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default:
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return nil, &common.Error{
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Message: "cel.bind() variable names must be simple identifers",
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Location: meh.OffsetLocation(varIdent.GetId()),
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}
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}
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varInit := args[1]
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resultExpr := args[2]
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return meh.Fold(
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unusedIterVar,
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meh.NewList(),
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varName,
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varInit,
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meh.LiteralBool(false),
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meh.Ident(varName),
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resultExpr,
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), nil
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}
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