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lexer_action_executor.go
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/
lexer_action_executor.go
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// Copyright (c) 2012-2022 The ANTLR Project. All rights reserved.
// Use of this file is governed by the BSD 3-clause license that
// can be found in the LICENSE.txt file in the project root.
package antlr
import "golang.org/x/exp/slices"
// Represents an executor for a sequence of lexer actions which traversed during
// the Matching operation of a lexer rule (token).
//
// <p>The executor tracks position information for position-dependent lexer actions
// efficiently, ensuring that actions appearing only at the end of the rule do
// not cause bloating of the {@link DFA} created for the lexer.</p>
type LexerActionExecutor struct {
lexerActions []LexerAction
cachedHash int
}
func NewLexerActionExecutor(lexerActions []LexerAction) *LexerActionExecutor {
if lexerActions == nil {
lexerActions = make([]LexerAction, 0)
}
l := new(LexerActionExecutor)
l.lexerActions = lexerActions
// Caches the result of {@link //hashCode} since the hash code is an element
// of the performance-critical {@link ATNConfig//hashCode} operation.
l.cachedHash = murmurInit(0)
for _, a := range lexerActions {
l.cachedHash = murmurUpdate(l.cachedHash, a.Hash())
}
l.cachedHash = murmurFinish(l.cachedHash, len(lexerActions))
return l
}
// LexerActionExecutorappend creates a [LexerActionExecutor] which executes the actions for
// the input [LexerActionExecutor] followed by a specified
// [LexerAction].
// TODO: This does not match the Java code
func LexerActionExecutorappend(lexerActionExecutor *LexerActionExecutor, lexerAction LexerAction) *LexerActionExecutor {
if lexerActionExecutor == nil {
return NewLexerActionExecutor([]LexerAction{lexerAction})
}
return NewLexerActionExecutor(append(lexerActionExecutor.lexerActions, lexerAction))
}
// fixOffsetBeforeMatch creates a [LexerActionExecutor] which encodes the current offset
// for position-dependent lexer actions.
//
// Normally, when the executor encounters lexer actions where
// [LexerAction.isPositionDependent] returns true, it calls
// [IntStream.Seek] on the input [CharStream] to set the input
// position to the end of the current token. This behavior provides
// for efficient [DFA] representation of lexer actions which appear at the end
// of a lexer rule, even when the lexer rule Matches a variable number of
// characters.
//
// Prior to traversing a Match transition in the [ATN], the current offset
// from the token start index is assigned to all position-dependent lexer
// actions which have not already been assigned a fixed offset. By storing
// the offsets relative to the token start index, the [DFA] representation of
// lexer actions which appear in the middle of tokens remains efficient due
// to sharing among tokens of the same Length, regardless of their absolute
// position in the input stream.
//
// If the current executor already has offsets assigned to all
// position-dependent lexer actions, the method returns this instance.
//
// The offset is assigned to all position-dependent
// lexer actions which do not already have offsets assigned.
//
// The func returns a [LexerActionExecutor] that stores input stream offsets
// for all position-dependent lexer actions.
func (l *LexerActionExecutor) fixOffsetBeforeMatch(offset int) *LexerActionExecutor {
var updatedLexerActions []LexerAction
for i := 0; i < len(l.lexerActions); i++ {
_, ok := l.lexerActions[i].(*LexerIndexedCustomAction)
if l.lexerActions[i].getIsPositionDependent() && !ok {
if updatedLexerActions == nil {
updatedLexerActions = make([]LexerAction, 0, len(l.lexerActions))
updatedLexerActions = append(updatedLexerActions, l.lexerActions...)
}
updatedLexerActions[i] = NewLexerIndexedCustomAction(offset, l.lexerActions[i])
}
}
if updatedLexerActions == nil {
return l
}
return NewLexerActionExecutor(updatedLexerActions)
}
// Execute the actions encapsulated by l executor within the context of a
// particular {@link Lexer}.
//
// <p>This method calls {@link IntStream//seek} to set the position of the
// {@code input} {@link CharStream} prior to calling
// {@link LexerAction//execute} on a position-dependent action. Before the
// method returns, the input position will be restored to the same position
// it was in when the method was invoked.</p>
//
// @param lexer The lexer instance.
// @param input The input stream which is the source for the current token.
// When l method is called, the current {@link IntStream//index} for
// {@code input} should be the start of the following token, i.e. 1
// character past the end of the current token.
// @param startIndex The token start index. This value may be passed to
// {@link IntStream//seek} to set the {@code input} position to the beginning
// of the token.
// /
func (l *LexerActionExecutor) execute(lexer Lexer, input CharStream, startIndex int) {
requiresSeek := false
stopIndex := input.Index()
defer func() {
if requiresSeek {
input.Seek(stopIndex)
}
}()
for i := 0; i < len(l.lexerActions); i++ {
lexerAction := l.lexerActions[i]
if la, ok := lexerAction.(*LexerIndexedCustomAction); ok {
offset := la.offset
input.Seek(startIndex + offset)
lexerAction = la.lexerAction
requiresSeek = (startIndex + offset) != stopIndex
} else if lexerAction.getIsPositionDependent() {
input.Seek(stopIndex)
requiresSeek = false
}
lexerAction.execute(lexer)
}
}
func (l *LexerActionExecutor) Hash() int {
if l == nil {
// TODO: Why is this here? l should not be nil
return 61
}
// TODO: This is created from the action itself when the struct is created - will this be an issue at some point? Java uses the runtime assign hashcode
return l.cachedHash
}
func (l *LexerActionExecutor) Equals(other interface{}) bool {
if l == other {
return true
}
othert, ok := other.(*LexerActionExecutor)
if !ok {
return false
}
if othert == nil {
return false
}
if l.cachedHash != othert.cachedHash {
return false
}
if len(l.lexerActions) != len(othert.lexerActions) {
return false
}
return slices.EqualFunc(l.lexerActions, othert.lexerActions, func(i, j LexerAction) bool {
return i.Equals(j)
})
}