/
unparser.go
546 lines (503 loc) · 15.3 KB
/
unparser.go
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// Copyright 2019 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 parser
import (
"errors"
"fmt"
"strconv"
"strings"
"github.com/google/cel-go/common/operators"
exprpb "google.golang.org/genproto/googleapis/api/expr/v1alpha1"
)
// Unparse takes an input expression and source position information and generates a human-readable
// expression.
//
// Note, unparsing an AST will often generate the same expression as was originally parsed, but some
// formatting may be lost in translation, notably:
//
// - All quoted literals are doubled quoted.
// - Byte literals are represented as octal escapes (same as Google SQL).
// - Floating point values are converted to the small number of digits needed to represent the value.
// - Spacing around punctuation marks may be lost.
// - Parentheses will only be applied when they affect operator precedence.
//
// This function optionally takes in one or more UnparserFormattingOption to dictate the formatting of the output.
func Unparse(expr *exprpb.Expr, info *exprpb.SourceInfo, opts ...UnparserFormattingOption) (string, error) {
formattingOpts := &formattingOption{
wrapColumn: defaultWrapColumn,
}
var err error
for _, opt := range opts {
formattingOpts, err = opt(formattingOpts)
if err != nil {
return "", err
}
}
un := &unparser{
info: info,
options: formattingOpts,
}
err = un.visit(expr)
if err != nil {
return "", err
}
return un.str.String(), nil
}
// unparser visits an expression to reconstruct a human-readable string from an AST.
type unparser struct {
str strings.Builder
info *exprpb.SourceInfo
options *formattingOption
lastWrappedIndex int
}
func (un *unparser) visit(expr *exprpb.Expr) error {
if expr == nil {
return errors.New("unsupported expression")
}
visited, err := un.visitMaybeMacroCall(expr)
if visited || err != nil {
return err
}
switch expr.ExprKind.(type) {
case *exprpb.Expr_CallExpr:
return un.visitCall(expr)
case *exprpb.Expr_ConstExpr:
return un.visitConst(expr)
case *exprpb.Expr_IdentExpr:
return un.visitIdent(expr)
case *exprpb.Expr_ListExpr:
return un.visitList(expr)
case *exprpb.Expr_SelectExpr:
return un.visitSelect(expr)
case *exprpb.Expr_StructExpr:
return un.visitStruct(expr)
default:
return fmt.Errorf("unsupported expression: %v", expr)
}
}
func (un *unparser) visitCall(expr *exprpb.Expr) error {
c := expr.GetCallExpr()
fun := c.GetFunction()
switch fun {
// ternary operator
case operators.Conditional:
return un.visitCallConditional(expr)
// index operator
case operators.Index:
return un.visitCallIndex(expr)
// unary operators
case operators.LogicalNot, operators.Negate:
return un.visitCallUnary(expr)
// binary operators
case operators.Add,
operators.Divide,
operators.Equals,
operators.Greater,
operators.GreaterEquals,
operators.In,
operators.Less,
operators.LessEquals,
operators.LogicalAnd,
operators.LogicalOr,
operators.Modulo,
operators.Multiply,
operators.NotEquals,
operators.OldIn,
operators.Subtract:
return un.visitCallBinary(expr)
// standard function calls.
default:
return un.visitCallFunc(expr)
}
}
func (un *unparser) visitCallBinary(expr *exprpb.Expr) error {
c := expr.GetCallExpr()
fun := c.GetFunction()
args := c.GetArgs()
lhs := args[0]
// add parens if the current operator is lower precedence than the lhs expr operator.
lhsParen := isComplexOperatorWithRespectTo(fun, lhs)
rhs := args[1]
// add parens if the current operator is lower precedence than the rhs expr operator,
// or the same precedence and the operator is left recursive.
rhsParen := isComplexOperatorWithRespectTo(fun, rhs)
if !rhsParen && isLeftRecursive(fun) {
rhsParen = isSamePrecedence(fun, rhs)
}
err := un.visitMaybeNested(lhs, lhsParen)
if err != nil {
return err
}
unmangled, found := operators.FindReverseBinaryOperator(fun)
if !found {
return fmt.Errorf("cannot unmangle operator: %s", fun)
}
un.str.WriteString(" ")
un.str.WriteString(unmangled)
if !un.wrapForOperator(fun) {
un.str.WriteString(" ")
}
return un.visitMaybeNested(rhs, rhsParen)
}
func (un *unparser) visitCallConditional(expr *exprpb.Expr) error {
c := expr.GetCallExpr()
args := c.GetArgs()
// add parens if operand is a conditional itself.
nested := isSamePrecedence(operators.Conditional, args[0]) ||
isComplexOperator(args[0])
err := un.visitMaybeNested(args[0], nested)
if err != nil {
return err
}
un.str.WriteString(" ?")
if !un.wrapForOperator(operators.Conditional) {
un.str.WriteString(" ")
}
// add parens if operand is a conditional itself.
nested = isSamePrecedence(operators.Conditional, args[1]) ||
isComplexOperator(args[1])
err = un.visitMaybeNested(args[1], nested)
if err != nil {
return err
}
un.str.WriteString(" : ")
// add parens if operand is a conditional itself.
nested = isSamePrecedence(operators.Conditional, args[2]) ||
isComplexOperator(args[2])
return un.visitMaybeNested(args[2], nested)
}
func (un *unparser) visitCallFunc(expr *exprpb.Expr) error {
c := expr.GetCallExpr()
fun := c.GetFunction()
args := c.GetArgs()
if c.GetTarget() != nil {
nested := isBinaryOrTernaryOperator(c.GetTarget())
err := un.visitMaybeNested(c.GetTarget(), nested)
if err != nil {
return err
}
un.str.WriteString(".")
}
un.str.WriteString(fun)
un.str.WriteString("(")
for i, arg := range args {
err := un.visit(arg)
if err != nil {
return err
}
if i < len(args)-1 {
un.str.WriteString(", ")
}
}
un.str.WriteString(")")
return nil
}
func (un *unparser) visitCallIndex(expr *exprpb.Expr) error {
c := expr.GetCallExpr()
args := c.GetArgs()
nested := isBinaryOrTernaryOperator(args[0])
err := un.visitMaybeNested(args[0], nested)
if err != nil {
return err
}
un.str.WriteString("[")
err = un.visit(args[1])
if err != nil {
return err
}
un.str.WriteString("]")
return nil
}
func (un *unparser) visitCallUnary(expr *exprpb.Expr) error {
c := expr.GetCallExpr()
fun := c.GetFunction()
args := c.GetArgs()
unmangled, found := operators.FindReverse(fun)
if !found {
return fmt.Errorf("cannot unmangle operator: %s", fun)
}
un.str.WriteString(unmangled)
nested := isComplexOperator(args[0])
return un.visitMaybeNested(args[0], nested)
}
func (un *unparser) visitConst(expr *exprpb.Expr) error {
c := expr.GetConstExpr()
switch c.ConstantKind.(type) {
case *exprpb.Constant_BoolValue:
un.str.WriteString(strconv.FormatBool(c.GetBoolValue()))
case *exprpb.Constant_BytesValue:
// bytes constants are surrounded with b"<bytes>"
b := c.GetBytesValue()
un.str.WriteString(`b"`)
un.str.WriteString(bytesToOctets(b))
un.str.WriteString(`"`)
case *exprpb.Constant_DoubleValue:
// represent the float using the minimum required digits
d := strconv.FormatFloat(c.GetDoubleValue(), 'g', -1, 64)
un.str.WriteString(d)
case *exprpb.Constant_Int64Value:
i := strconv.FormatInt(c.GetInt64Value(), 10)
un.str.WriteString(i)
case *exprpb.Constant_NullValue:
un.str.WriteString("null")
case *exprpb.Constant_StringValue:
// strings will be double quoted with quotes escaped.
un.str.WriteString(strconv.Quote(c.GetStringValue()))
case *exprpb.Constant_Uint64Value:
// uint literals have a 'u' suffix.
ui := strconv.FormatUint(c.GetUint64Value(), 10)
un.str.WriteString(ui)
un.str.WriteString("u")
default:
return fmt.Errorf("unsupported constant: %v", expr)
}
return nil
}
func (un *unparser) visitIdent(expr *exprpb.Expr) error {
un.str.WriteString(expr.GetIdentExpr().GetName())
return nil
}
func (un *unparser) visitList(expr *exprpb.Expr) error {
l := expr.GetListExpr()
elems := l.GetElements()
un.str.WriteString("[")
for i, elem := range elems {
err := un.visit(elem)
if err != nil {
return err
}
if i < len(elems)-1 {
un.str.WriteString(", ")
}
}
un.str.WriteString("]")
return nil
}
func (un *unparser) visitSelect(expr *exprpb.Expr) error {
sel := expr.GetSelectExpr()
// handle the case when the select expression was generated by the has() macro.
if sel.GetTestOnly() {
un.str.WriteString("has(")
}
nested := !sel.GetTestOnly() && isBinaryOrTernaryOperator(sel.GetOperand())
err := un.visitMaybeNested(sel.GetOperand(), nested)
if err != nil {
return err
}
un.str.WriteString(".")
un.str.WriteString(sel.GetField())
if sel.GetTestOnly() {
un.str.WriteString(")")
}
return nil
}
func (un *unparser) visitStruct(expr *exprpb.Expr) error {
s := expr.GetStructExpr()
// If the message name is non-empty, then this should be treated as message construction.
if s.GetMessageName() != "" {
return un.visitStructMsg(expr)
}
// Otherwise, build a map.
return un.visitStructMap(expr)
}
func (un *unparser) visitStructMsg(expr *exprpb.Expr) error {
m := expr.GetStructExpr()
entries := m.GetEntries()
un.str.WriteString(m.GetMessageName())
un.str.WriteString("{")
for i, entry := range entries {
f := entry.GetFieldKey()
un.str.WriteString(f)
un.str.WriteString(": ")
v := entry.GetValue()
err := un.visit(v)
if err != nil {
return err
}
if i < len(entries)-1 {
un.str.WriteString(", ")
}
}
un.str.WriteString("}")
return nil
}
func (un *unparser) visitStructMap(expr *exprpb.Expr) error {
m := expr.GetStructExpr()
entries := m.GetEntries()
un.str.WriteString("{")
for i, entry := range entries {
k := entry.GetMapKey()
err := un.visit(k)
if err != nil {
return err
}
un.str.WriteString(": ")
v := entry.GetValue()
err = un.visit(v)
if err != nil {
return err
}
if i < len(entries)-1 {
un.str.WriteString(", ")
}
}
un.str.WriteString("}")
return nil
}
func (un *unparser) visitMaybeMacroCall(expr *exprpb.Expr) (bool, error) {
macroCalls := un.info.GetMacroCalls()
call, found := macroCalls[expr.GetId()]
if !found {
return false, nil
}
return true, un.visit(call)
}
func (un *unparser) visitMaybeNested(expr *exprpb.Expr, nested bool) error {
if nested {
un.str.WriteString("(")
}
err := un.visit(expr)
if err != nil {
return err
}
if nested {
un.str.WriteString(")")
}
return nil
}
// isLeftRecursive indicates whether the parser resolves the call in a left-recursive manner as
// this can have an effect of how parentheses affect the order of operations in the AST.
func isLeftRecursive(op string) bool {
return op != operators.LogicalAnd && op != operators.LogicalOr
}
// isSamePrecedence indicates whether the precedence of the input operator is the same as the
// precedence of the (possible) operation represented in the input Expr.
//
// If the expr is not a Call, the result is false.
func isSamePrecedence(op string, expr *exprpb.Expr) bool {
if expr.GetCallExpr() == nil {
return false
}
c := expr.GetCallExpr()
other := c.GetFunction()
return operators.Precedence(op) == operators.Precedence(other)
}
// isLowerPrecedence indicates whether the precedence of the input operator is lower precedence
// than the (possible) operation represented in the input Expr.
//
// If the expr is not a Call, the result is false.
func isLowerPrecedence(op string, expr *exprpb.Expr) bool {
c := expr.GetCallExpr()
other := c.GetFunction()
return operators.Precedence(op) < operators.Precedence(other)
}
// Indicates whether the expr is a complex operator, i.e., a call expression
// with 2 or more arguments.
func isComplexOperator(expr *exprpb.Expr) bool {
if expr.GetCallExpr() != nil && len(expr.GetCallExpr().GetArgs()) >= 2 {
return true
}
return false
}
// Indicates whether it is a complex operation compared to another.
// expr is *not* considered complex if it is not a call expression or has
// less than two arguments, or if it has a higher precedence than op.
func isComplexOperatorWithRespectTo(op string, expr *exprpb.Expr) bool {
if expr.GetCallExpr() == nil || len(expr.GetCallExpr().GetArgs()) < 2 {
return false
}
return isLowerPrecedence(op, expr)
}
// Indicate whether this is a binary or ternary operator.
func isBinaryOrTernaryOperator(expr *exprpb.Expr) bool {
if expr.GetCallExpr() == nil || len(expr.GetCallExpr().GetArgs()) < 2 {
return false
}
_, isBinaryOp := operators.FindReverseBinaryOperator(expr.GetCallExpr().GetFunction())
return isBinaryOp || isSamePrecedence(operators.Conditional, expr)
}
// bytesToOctets converts byte sequences to a string using a three digit octal encoded value
// per byte.
func bytesToOctets(byteVal []byte) string {
var b strings.Builder
for _, c := range byteVal {
fmt.Fprintf(&b, "\\%03o", c)
}
return b.String()
}
// Takes in a function then inserts a newline based on the rules provided in formatting options
func (un *unparser) wrapForOperator(fun string) bool {
_, wrapOperatorExists := un.options.operatorsToWrapOn[fun]
lineLength := un.str.Len() - un.lastWrappedIndex
if wrapOperatorExists && lineLength >= un.options.wrapColumn {
un.lastWrappedIndex = un.str.Len()
un.str.WriteString("\n")
return true
}
return false
}
// Defined defaults for the formatting options
var (
defaultWrapColumn = 80
)
// UnparserFormattingOption is a funcitonal option for configuring the output formatting
// of the Unparse function.
type UnparserFormattingOption func(*formattingOption) (*formattingOption, error)
// Internal representation of the UnparserFormattingOption type
type formattingOption struct {
wrapColumn int // Defaults to 80
operatorsToWrapOn map[string]bool
}
// WrapOnColumn returns an UnparserFormattingOption with the column limit set.
// Word wrapping will be performed when a line's length exceeds the limit
// for operators set by WrapOnOperators function.
//
// Example usage:
//
// Unparse(expr, sourceInfo, WrapColumn(3), WrapOnOperators(Operators.LogicalAnd))
//
// This will insert a newline immediately after the logical AND operator for the below example input:
//
// Input: a && b
// Output: a &&\nb
func WrapColumn(col int) UnparserFormattingOption {
return func(opt *formattingOption) (*formattingOption, error) {
if col < 1 {
return nil, fmt.Errorf("Invalid formatting option. Wrap column value must be greater than or equal to 1. Got %v instead", col)
}
opt.wrapColumn = col
return opt, nil
}
}
// WrapOnOperators returns an UnparserFormattedOption with operators to perform word wrapping on.
// Word wrapping is supported on non-unary symbolic operators. Refer to operators.go for the full list
//
// This will replace any previously supplied operators instead of merging them.
func WrapOnOperators(symbols ...string) UnparserFormattingOption {
return func(fmtOpt *formattingOption) (*formattingOption, error) {
fmtOpt.operatorsToWrapOn = make(map[string]bool)
for _, symbol := range symbols {
_, found := operators.FindReverse(symbol)
if !found {
return nil, fmt.Errorf("Invalid formatting option. Unsupported operator: %s", symbol)
}
arity := operators.Arity(symbol)
if arity < 2 {
return nil, fmt.Errorf("Invalid formatting option. Unary operators are unsupported: %s", symbol)
}
fmtOpt.operatorsToWrapOn[symbol] = true
}
return fmtOpt, nil
}
}