ceph-csi/vendor/github.com/google/cel-go/common/containers/container.go

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// Copyright 2018 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 containers defines types and functions for resolving qualified names within a namespace
// or type provided to CEL.
package containers
import (
"fmt"
"strings"
"github.com/google/cel-go/common/ast"
)
var (
// DefaultContainer has an empty container name.
DefaultContainer *Container = nil
// Empty map to search for aliases when needed.
noAliases = make(map[string]string)
)
// NewContainer creates a new Container with the fully-qualified name.
func NewContainer(opts ...ContainerOption) (*Container, error) {
var c *Container
var err error
for _, opt := range opts {
c, err = opt(c)
if err != nil {
return nil, err
}
}
return c, nil
}
// Container holds a reference to an optional qualified container name and set of aliases.
//
// The program container can be used to simplify variable, function, and type specification within
// CEL programs and behaves more or less like a C++ namespace. See ResolveCandidateNames for more
// details.
type Container struct {
name string
aliases map[string]string
}
// Extend creates a new Container with the existing settings and applies a series of
// ContainerOptions to further configure the new container.
func (c *Container) Extend(opts ...ContainerOption) (*Container, error) {
if c == nil {
return NewContainer(opts...)
}
// Copy the name and aliases of the existing container.
ext := &Container{name: c.Name()}
if len(c.aliasSet()) > 0 {
aliasSet := make(map[string]string, len(c.aliasSet()))
for k, v := range c.aliasSet() {
aliasSet[k] = v
}
ext.aliases = aliasSet
}
// Apply the new options to the container.
var err error
for _, opt := range opts {
ext, err = opt(ext)
if err != nil {
return nil, err
}
}
return ext, nil
}
// Name returns the fully-qualified name of the container.
//
// The name may conceptually be a namespace, package, or type.
func (c *Container) Name() string {
if c == nil {
return ""
}
return c.name
}
// ResolveCandidateNames returns the candidates name of namespaced identifiers in C++ resolution
// order.
//
// Names which shadow other names are returned first. If a name includes a leading dot ('.'),
// the name is treated as an absolute identifier which cannot be shadowed.
//
// Given a container name a.b.c.M.N and a type name R.s, this will deliver in order:
//
// a.b.c.M.N.R.s
// a.b.c.M.R.s
// a.b.c.R.s
// a.b.R.s
// a.R.s
// R.s
//
// If aliases or abbreviations are configured for the container, then alias names will take
// precedence over containerized names.
func (c *Container) ResolveCandidateNames(name string) []string {
if strings.HasPrefix(name, ".") {
qn := name[1:]
alias, isAlias := c.findAlias(qn)
if isAlias {
return []string{alias}
}
return []string{qn}
}
alias, isAlias := c.findAlias(name)
if isAlias {
return []string{alias}
}
if c.Name() == "" {
return []string{name}
}
nextCont := c.Name()
candidates := []string{nextCont + "." + name}
for i := strings.LastIndex(nextCont, "."); i >= 0; i = strings.LastIndex(nextCont, ".") {
nextCont = nextCont[:i]
candidates = append(candidates, nextCont+"."+name)
}
return append(candidates, name)
}
// aliasSet returns the alias to fully-qualified name mapping stored in the container.
func (c *Container) aliasSet() map[string]string {
if c == nil || c.aliases == nil {
return noAliases
}
return c.aliases
}
// findAlias takes a name as input and returns an alias expansion if one exists.
//
// If the name is qualified, the first component of the qualified name is checked against known
// aliases. Any alias that is found in a qualified name is expanded in the result:
//
// alias: R -> my.alias.R
// name: R.S.T
// output: my.alias.R.S.T
//
// Note, the name must not have a leading dot.
func (c *Container) findAlias(name string) (string, bool) {
// If an alias exists for the name, ensure it is searched last.
simple := name
qualifier := ""
dot := strings.Index(name, ".")
if dot >= 0 {
simple = name[0:dot]
qualifier = name[dot:]
}
alias, found := c.aliasSet()[simple]
if !found {
return "", false
}
return alias + qualifier, true
}
// ContainerOption specifies a functional configuration option for a Container.
//
// Note, ContainerOption implementations must be able to handle nil container inputs.
type ContainerOption func(*Container) (*Container, error)
// Abbrevs configures a set of simple names as abbreviations for fully-qualified names.
//
// An abbreviation (abbrev for short) is a simple name that expands to a fully-qualified name.
// Abbreviations can be useful when working with variables, functions, and especially types from
// multiple namespaces:
//
// // CEL object construction
// qual.pkg.version.ObjTypeName{
// field: alt.container.ver.FieldTypeName{value: ...}
// }
//
// Only one the qualified names above may be used as the CEL container, so at least one of these
// references must be a long qualified name within an otherwise short CEL program. Using the
// following abbreviations, the program becomes much simpler:
//
// // CEL Go option
// Abbrevs("qual.pkg.version.ObjTypeName", "alt.container.ver.FieldTypeName")
// // Simplified Object construction
// ObjTypeName{field: FieldTypeName{value: ...}}
//
// There are a few rules for the qualified names and the simple abbreviations generated from them:
// - Qualified names must be dot-delimited, e.g. `package.subpkg.name`.
// - The last element in the qualified name is the abbreviation.
// - Abbreviations must not collide with each other.
// - The abbreviation must not collide with unqualified names in use.
//
// Abbreviations are distinct from container-based references in the following important ways:
// - Abbreviations must expand to a fully-qualified name.
// - Expanded abbreviations do not participate in namespace resolution.
// - Abbreviation expansion is done instead of the container search for a matching identifier.
// - Containers follow C++ namespace resolution rules with searches from the most qualified name
// to the least qualified name.
// - Container references within the CEL program may be relative, and are resolved to fully
// qualified names at either type-check time or program plan time, whichever comes first.
//
// If there is ever a case where an identifier could be in both the container and as an
// abbreviation, the abbreviation wins as this will ensure that the meaning of a program is
// preserved between compilations even as the container evolves.
func Abbrevs(qualifiedNames ...string) ContainerOption {
return func(c *Container) (*Container, error) {
for _, qn := range qualifiedNames {
ind := strings.LastIndex(qn, ".")
if ind <= 0 || ind >= len(qn)-1 {
return nil, fmt.Errorf(
"invalid qualified name: %s, wanted name of the form 'qualified.name'", qn)
}
alias := qn[ind+1:]
var err error
c, err = aliasAs("abbreviation", qn, alias)(c)
if err != nil {
return nil, err
}
}
return c, nil
}
}
// Alias associates a fully-qualified name with a user-defined alias.
//
// In general, Abbrevs is preferred to Alias since the names generated from the Abbrevs option
// are more easily traced back to source code. The Alias option is useful for propagating alias
// configuration from one Container instance to another, and may also be useful for remapping
// poorly chosen protobuf message / package names.
//
// Note: all of the rules that apply to Abbrevs also apply to Alias.
func Alias(qualifiedName, alias string) ContainerOption {
return aliasAs("alias", qualifiedName, alias)
}
func aliasAs(kind, qualifiedName, alias string) ContainerOption {
return func(c *Container) (*Container, error) {
if len(alias) == 0 || strings.Contains(alias, ".") {
return nil, fmt.Errorf(
"%s must be non-empty and simple (not qualified): %s=%s", kind, kind, alias)
}
if qualifiedName[0:1] == "." {
return nil, fmt.Errorf("qualified name must not begin with a leading '.': %s",
qualifiedName)
}
ind := strings.LastIndex(qualifiedName, ".")
if ind <= 0 || ind == len(qualifiedName)-1 {
return nil, fmt.Errorf("%s must refer to a valid qualified name: %s",
kind, qualifiedName)
}
aliasRef, found := c.aliasSet()[alias]
if found {
return nil, fmt.Errorf(
"%s collides with existing reference: name=%s, %s=%s, existing=%s",
kind, qualifiedName, kind, alias, aliasRef)
}
if strings.HasPrefix(c.Name(), alias+".") || c.Name() == alias {
return nil, fmt.Errorf(
"%s collides with container name: name=%s, %s=%s, container=%s",
kind, qualifiedName, kind, alias, c.Name())
}
if c == nil {
c = &Container{}
}
if c.aliases == nil {
c.aliases = make(map[string]string)
}
c.aliases[alias] = qualifiedName
return c, nil
}
}
// Name sets the fully-qualified name of the Container.
func Name(name string) ContainerOption {
return func(c *Container) (*Container, error) {
if len(name) > 0 && name[0:1] == "." {
return nil, fmt.Errorf("container name must not contain a leading '.': %s", name)
}
if c.Name() == name {
return c, nil
}
if c == nil {
return &Container{name: name}, nil
}
c.name = name
return c, nil
}
}
// ToQualifiedName converts an expression AST into a qualified name if possible, with a boolean
// 'found' value that indicates if the conversion is successful.
func ToQualifiedName(e ast.Expr) (string, bool) {
switch e.Kind() {
case ast.IdentKind:
id := e.AsIdent()
return id, true
case ast.SelectKind:
sel := e.AsSelect()
// Test only expressions are not valid as qualified names.
if sel.IsTestOnly() {
return "", false
}
if qual, found := ToQualifiedName(sel.Operand()); found {
return qual + "." + sel.FieldName(), true
}
}
return "", false
}