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commands.go
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commands.go
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// Copyright 2022 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
//
// https://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 repl
import (
"errors"
"fmt"
"strings"
antlr "github.com/antlr4-go/antlr/v4"
"github.com/google/cel-go/repl/parser"
exprpb "google.golang.org/genproto/googleapis/api/expr/v1alpha1"
)
var (
compileUsage = `Compile emits a textproto representation of the compiled expression.
%compile <expr>`
parseUsage = `Parse emits a textproto representation of the parsed expression.
%parse <expr>`
declareUsage = `Declare introduces a variable or function for type checking, but
doesn't define a value for it:
%declare <identifier> : <type>
%declare <identifier> (<param_identifier> : <param_type>, ...) : <result-type>`
deleteUsage = `Delete removes a variable or function declaration from the evaluation context.
%delete <identifier>`
letUsage = `Let introduces a variable or function defined by a sub-CEL expression.
%let <identifier> (: <type>)? = <expr>
%let <identifier> (<param_identifier> : <param_type>, ...) : <result-type> -> <expr>`
optionUsage = `Option enables a CEL environment option which enables configuration and
optional language features.
%option --container 'google.protobuf'
%option --extension 'all'`
loadDescriptorsUsage = `LoadDescriptors loads a protobuf descriptor file (google.protobuf.FileDescriptorSet)
from disk or from a predefined package. Supported packages are "cel-spec-test-types"
(TestAllTypes) and "google-rpc" (AttributeContext).
%load_descriptors 'path/to/descriptor_set.binarypb'
%load_descriptors --pkg 'cel-spec-test-types'`
exitUsage = `Exit terminates the REPL.
%exit`
helpUsage = `Help prints usage information for the commands supported by the REPL.
%help`
)
type letVarCmd struct {
identifier string
typeHint *exprpb.Type
src string
}
type letFnCmd struct {
identifier string
resultType *exprpb.Type
params []letFunctionParam
src string
}
type delCmd struct {
identifier string
}
type simpleCmd struct {
cmd string
args []string
}
type compileCmd struct {
expr string
}
type parseCmd struct {
expr string
}
type evalCmd struct {
expr string
}
// Cmder interface provides normalized command name from a repl command.
// Command specifics are available via checked type casting to the specific
// command type.
type Cmder interface {
// Cmd returns the normalized name for the command.
Cmd() string
}
func (c *letVarCmd) Cmd() string {
if c.src == "" {
return "declare"
}
return "let"
}
func (c *letFnCmd) Cmd() string {
if c.src == "" {
return "declare"
}
return "let"
}
func (c *delCmd) Cmd() string {
return "delete"
}
func (c *simpleCmd) Cmd() string {
return c.cmd
}
func (c *compileCmd) Cmd() string {
return "compile"
}
func (c *parseCmd) Cmd() string {
return "parse"
}
func (c *evalCmd) Cmd() string {
return "eval"
}
type commandParseListener struct {
antlr.DefaultErrorListener
parser.BaseCommandsListener
errs []error
cmd Cmder
usage string
}
func (c *commandParseListener) reportIssue(e error) {
c.errs = append(c.errs, e)
}
// extractSourceText extracts original text from a parse rule match.
// Preserves original whitespace if possible.
func extractSourceText(ctx antlr.ParserRuleContext) string {
if ctx.GetStart() == nil || ctx.GetStop() == nil ||
ctx.GetStart().GetStart() < 0 || ctx.GetStop().GetStop() < 0 {
// fallback to the normalized parse
return ctx.GetText()
}
s, e := ctx.GetStart().GetStart(), ctx.GetStop().GetStop()
return ctx.GetStart().GetInputStream().GetText(s, e)
}
// Parse parses a repl command line into a command object. This provides
// the normalized command name plus any parsed parameters (e.g. variable names
// in let statements).
//
// An error is returned if the statement isn't well formed. See the parser
// pacakage for details on the antlr grammar.
func Parse(line string) (Cmder, error) {
line = strings.TrimSpace(line)
listener := &commandParseListener{}
is := antlr.NewInputStream(line)
lexer := parser.NewCommandsLexer(is)
lexer.RemoveErrorListeners()
lexer.AddErrorListener(listener)
p := parser.NewCommandsParser(antlr.NewCommonTokenStream(lexer, antlr.TokenDefaultChannel))
p.RemoveErrorListeners()
p.AddErrorListener(listener)
antlr.ParseTreeWalkerDefault.Walk(listener, p.StartCommand())
if len(listener.errs) > 0 {
errFmt := make([]string, len(listener.errs))
for i, err := range listener.errs {
errFmt[i] = err.Error()
}
if listener.usage != "" {
errFmt = append(errFmt, "", "Usage:", listener.usage)
}
return nil, fmt.Errorf("invalid command: %v", strings.Join(errFmt, "\n"))
}
if listener.cmd.Cmd() == "help" {
return nil, errors.New(strings.Join([]string{
compileUsage,
parseUsage,
declareUsage,
deleteUsage,
letUsage,
optionUsage,
loadDescriptorsUsage,
helpUsage,
exitUsage,
}, "\n\n"))
}
return listener.cmd, nil
}
// ANTLR interface implementations
// Implement antlr ErrorListener interface for syntax errors.
func (c *commandParseListener) SyntaxError(recognizer antlr.Recognizer, offendingSymbol any, line, column int, msg string, e antlr.RecognitionException) {
c.errs = append(c.errs, fmt.Errorf("(%d:%d) %s", line, column, msg))
}
// Implement ANTLR interface for commands listener.
func (c *commandParseListener) EnterSimple(ctx *parser.SimpleContext) {
cmd := "undefined"
if ctx.GetCmd() != nil {
cmd = ctx.GetCmd().GetText()[1:]
}
var args []string
for _, arg := range ctx.GetArgs() {
a := arg.GetText()
if strings.HasPrefix(a, "-") {
a = "--" + strings.ToLower(strings.TrimLeft(a, "-"))
} else {
a = strings.Trim(a, "\"'")
}
args = append(args, a)
}
c.cmd = &simpleCmd{cmd: cmd, args: args}
}
func (c *commandParseListener) EnterHelp(ctx *parser.HelpContext) {
c.cmd = &simpleCmd{cmd: "help"}
}
func (c *commandParseListener) EnterEmpty(ctx *parser.EmptyContext) {
c.cmd = &simpleCmd{cmd: "null"}
}
func (c *commandParseListener) EnterLet(ctx *parser.LetContext) {
c.usage = letUsage
if ctx.GetFn() != nil {
c.cmd = &letFnCmd{}
} else if ctx.GetVar_() != nil {
c.cmd = &letVarCmd{}
} else {
c.errs = append(c.errs, fmt.Errorf("missing declaration in let"))
}
}
func (c *commandParseListener) EnterDeclare(ctx *parser.DeclareContext) {
c.usage = declareUsage
if ctx.GetFn() != nil {
c.cmd = &letFnCmd{}
} else if ctx.GetVar_() != nil {
c.cmd = &letVarCmd{}
} else {
c.errs = append(c.errs, fmt.Errorf("missing declaration in declare"))
}
}
func (c *commandParseListener) ExitDeclare(ctx *parser.DeclareContext) {
var typeHint *exprpb.Type
switch cmd := c.cmd.(type) {
case *letVarCmd:
typeHint = cmd.typeHint
case *letFnCmd:
typeHint = cmd.resultType
}
if typeHint == nil {
c.reportIssue(errors.New("result type required for declare"))
}
}
func (c *commandParseListener) EnterDelete(ctx *parser.DeleteContext) {
c.usage = deleteUsage
if ctx.GetVar_() == nil && ctx.GetFn() == nil {
c.reportIssue(errors.New("missing identifier in delete"))
return
}
c.cmd = &delCmd{}
}
func (c *commandParseListener) EnterCompile(ctx *parser.CompileContext) {
c.cmd = &compileCmd{}
}
func (c *commandParseListener) EnterParse(ctx *parser.ParseContext) {
c.cmd = &parseCmd{}
}
func (c *commandParseListener) EnterExprCmd(ctx *parser.ExprCmdContext) {
c.cmd = &evalCmd{}
}
func (c *commandParseListener) ExitFnDecl(ctx *parser.FnDeclContext) {
switch cmd := c.cmd.(type) {
case *letFnCmd:
if ctx.GetId() == nil {
c.reportIssue(errors.New("missing identifier in function declaration"))
return
}
if ctx.GetRType() == nil {
c.reportIssue(errors.New("missing result type in function declaration"))
return
}
cmd.identifier = ctx.GetId().GetText()
ty, err := ParseType(ctx.GetRType().GetText())
if err != nil {
c.reportIssue(err)
}
for _, p := range ctx.GetParams() {
if p.GetT() == nil {
c.reportIssue(errors.New("missing type in function param declaration"))
continue
}
if p.GetPid() == nil {
c.reportIssue(errors.New("missing identifier in function param declaration"))
}
ty, err := ParseType(p.GetT().GetText())
if err != nil {
c.reportIssue(err)
}
cmd.params = append(cmd.params, letFunctionParam{
identifier: p.GetPid().GetText(),
typeHint: ty,
})
}
cmd.resultType = ty
case *delCmd:
if ctx.GetId() == nil {
c.reportIssue(errors.New("missing identifier in delete"))
}
cmd.identifier = ctx.GetId().GetText()
default:
c.reportIssue(errors.New("unexepected function declaration"))
}
}
func (c *commandParseListener) ExitQualId(ctx *parser.QualIdContext) {
if ctx.GetRid() == nil {
c.reportIssue(errors.New("missing root identifier"))
}
}
func (c *commandParseListener) ExitVarDecl(ctx *parser.VarDeclContext) {
switch cmd := c.cmd.(type) {
case *letVarCmd:
if ctx.GetId() == nil {
c.reportIssue(errors.New("no identifier in variable declaration"))
return
}
cmd.identifier = ctx.GetId().GetText()
if ctx.GetT() != nil {
ty, err := ParseType(ctx.GetT().GetText())
if err != nil {
c.reportIssue(err)
}
cmd.typeHint = ty
}
case *delCmd:
if ctx.GetId() == nil {
c.reportIssue(errors.New("missing identifier in delete"))
}
cmd.identifier = ctx.GetId().GetText()
default:
c.reportIssue(errors.New("unexpected var declaration"))
}
}
func (c *commandParseListener) ExitExpr(ctx *parser.ExprContext) {
expr := extractSourceText(ctx)
switch cmd := c.cmd.(type) {
case *compileCmd:
cmd.expr = expr
case *parseCmd:
cmd.expr = expr
case *evalCmd:
cmd.expr = expr
case *letFnCmd:
cmd.src = expr
case *letVarCmd:
cmd.src = expr
default:
c.reportIssue(errors.New("unexpected CEL expression"))
}
}