/*
* [The "BSD license"]
* Copyright (c) 2012 Terence Parr
* Copyright (c) 2012 Sam Harwell
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
*
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
* 3. The name of the author may not be used to endorse or promote products
* derived from this software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
* IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
* OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
* IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
* NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
* DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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*/
package org.antlr.v4.runtime;
import org.antlr.v4.runtime.atn.ATN;
import org.antlr.v4.runtime.atn.ATNState;
import org.antlr.v4.runtime.atn.RuleTransition;
import org.antlr.v4.runtime.misc.IntervalSet;
import org.antlr.v4.runtime.misc.NotNull;
import org.antlr.v4.runtime.misc.Nullable;
import org.antlr.v4.runtime.misc.Pair;
/**
* This is the default implementation of {@link ANTLRErrorStrategy} used for
* error reporting and recovery in ANTLR parsers.
*/
public class DefaultErrorStrategy implements ANTLRErrorStrategy {
/**
* Indicates whether the error strategy is currently "recovering from an
* error". This is used to suppress reporting multiple error messages while
* attempting to recover from a detected syntax error.
*
* @see #inErrorRecoveryMode
*/
protected boolean errorRecoveryMode = false;
/** The index into the input stream where the last error occurred.
* This is used to prevent infinite loops where an error is found
* but no token is consumed during recovery...another error is found,
* ad nauseum. This is a failsafe mechanism to guarantee that at least
* one token/tree node is consumed for two errors.
*/
protected int lastErrorIndex = -1;
protected IntervalSet lastErrorStates;
/**
* {@inheritDoc}
*
* <p>The default implementation simply calls {@link #endErrorCondition} to
* ensure that the handler is not in error recovery mode.</p>
*/
@Override
public void reset(Parser recognizer) {
endErrorCondition(recognizer);
}
/**
* This method is called to enter error recovery mode when a recognition
* exception is reported.
*
* @param recognizer the parser instance
*/
protected void beginErrorCondition(@NotNull Parser recognizer) {
errorRecoveryMode = true;
}
/**
* {@inheritDoc}
*/
@Override
public boolean inErrorRecoveryMode(Parser recognizer) {
return errorRecoveryMode;
}
/**
* This method is called to leave error recovery mode after recovering from
* a recognition exception.
*
* @param recognizer
*/
protected void endErrorCondition(@NotNull Parser recognizer) {
errorRecoveryMode = false;
lastErrorStates = null;
lastErrorIndex = -1;
}
/**
* {@inheritDoc}
*
* <p>The default implementation simply calls {@link #endErrorCondition}.</p>
*/
@Override
public void reportMatch(Parser recognizer) {
endErrorCondition(recognizer);
}
/**
* {@inheritDoc}
*
* <p>The default implementation returns immediately if the handler is already
* in error recovery mode. Otherwise, it calls {@link #beginErrorCondition}
* and dispatches the reporting task based on the runtime type of {@code e}
* according to the following table.</p>
*
* <ul>
* <li>{@link NoViableAltException}: Dispatches the call to
* {@link #reportNoViableAlternative}</li>
* <li>{@link InputMismatchException}: Dispatches the call to
* {@link #reportInputMismatch}</li>
* <li>{@link FailedPredicateException}: Dispatches the call to
* {@link #reportFailedPredicate}</li>
* <li>All other types: calls {@link Parser#notifyErrorListeners} to report
* the exception</li>
* </ul>
*/
@Override
public void reportError(Parser recognizer,
RecognitionException e)
{
// if we've already reported an error and have not matched a token
// yet successfully, don't report any errors.
if (inErrorRecoveryMode(recognizer)) {
// System.err.print("[SPURIOUS] ");
return; // don't report spurious errors
}
beginErrorCondition(recognizer);
if ( e instanceof NoViableAltException ) {
reportNoViableAlternative(recognizer, (NoViableAltException) e);
}
else if ( e instanceof InputMismatchException ) {
reportInputMismatch(recognizer, (InputMismatchException)e);
}
else if ( e instanceof FailedPredicateException ) {
reportFailedPredicate(recognizer, (FailedPredicateException)e);
}
else {
System.err.println("unknown recognition error type: "+e.getClass().getName());
recognizer.notifyErrorListeners(e.getOffendingToken(), e.getMessage(), e);
}
}
/**
* {@inheritDoc}
*
* <p>The default implementation resynchronizes the parser by consuming tokens
* until we find one in the resynchronization set--loosely the set of tokens
* that can follow the current rule.</p>
*/
@Override
public void recover(Parser recognizer, RecognitionException e) {
// System.out.println("recover in "+recognizer.getRuleInvocationStack()+
// " index="+recognizer.getInputStream().index()+
// ", lastErrorIndex="+
// lastErrorIndex+
// ", states="+lastErrorStates);
if ( lastErrorIndex==recognizer.getInputStream().index() &&
lastErrorStates != null &&
lastErrorStates.contains(recognizer.getState()) ) {
// uh oh, another error at same token index and previously-visited
// state in ATN; must be a case where LT(1) is in the recovery
// token set so nothing got consumed. Consume a single token
// at least to prevent an infinite loop; this is a failsafe.
// System.err.println("seen error condition before index="+
// lastErrorIndex+", states="+lastErrorStates);
// System.err.println("FAILSAFE consumes "+recognizer.getTokenNames()[recognizer.getInputStream().LA(1)]);
recognizer.consume();
}
lastErrorIndex = recognizer.getInputStream().index();
if ( lastErrorStates==null ) lastErrorStates = new IntervalSet();
lastErrorStates.add(recognizer.getState());
IntervalSet followSet = getErrorRecoverySet(recognizer);
consumeUntil(recognizer, followSet);
}
/**
* The default implementation of {@link ANTLRErrorStrategy#sync} makes sure
* that the current lookahead symbol is consistent with what were expecting
* at this point in the ATN. You can call this anytime but ANTLR only
* generates code to check before subrules/loops and each iteration.
*
* <p>Implements Jim Idle's magic sync mechanism in closures and optional
* subrules. E.g.,</p>
*
* <pre>
* a : sync ( stuff sync )* ;
* sync : {consume to what can follow sync} ;
* </pre>
*
* At the start of a sub rule upon error, {@link #sync} performs single
* token deletion, if possible. If it can't do that, it bails on the current
* rule and uses the default error recovery, which consumes until the
* resynchronization set of the current rule.
*
* <p>If the sub rule is optional ({@code (...)?}, {@code (...)*}, or block
* with an empty alternative), then the expected set includes what follows
* the subrule.</p>
*
* <p>During loop iteration, it consumes until it sees a token that can start a
* sub rule or what follows loop. Yes, that is pretty aggressive. We opt to
* stay in the loop as long as possible.</p>
*
* <p><strong>ORIGINS</strong></p>
*
* <p>Previous versions of ANTLR did a poor job of their recovery within loops.
* A single mismatch token or missing token would force the parser to bail
* out of the entire rules surrounding the loop. So, for rule</p>
*
* <pre>
* classDef : 'class' ID '{' member* '}'
* </pre>
*
* input with an extra token between members would force the parser to
* consume until it found the next class definition rather than the next
* member definition of the current class.
*
* <p>This functionality cost a little bit of effort because the parser has to
* compare token set at the start of the loop and at each iteration. If for
* some reason speed is suffering for you, you can turn off this
* functionality by simply overriding this method as a blank { }.</p>
*/
@Override
public void sync(Parser recognizer) throws RecognitionException {
ATNState s = recognizer.getInterpreter().atn.states.get(recognizer.getState());
// System.err.println("sync @ "+s.stateNumber+"="+s.getClass().getSimpleName());
// If already recovering, don't try to sync
if (inErrorRecoveryMode(recognizer)) {
return;
}
TokenStream tokens = recognizer.getInputStream();
int la = tokens.LA(1);
// try cheaper subset first; might get lucky. seems to shave a wee bit off
if ( recognizer.getATN().nextTokens(s).contains(la) || la==Token.EOF ) return;
// Return but don't end recovery. only do that upon valid token match
if (recognizer.isExpectedToken(la)) {
return;
}
switch (s.getStateType()) {
case ATNState.BLOCK_START:
case ATNState.STAR_BLOCK_START:
case ATNState.PLUS_BLOCK_START:
case ATNState.STAR_LOOP_ENTRY:
// report error and recover if possible
if ( singleTokenDeletion(recognizer)!=null ) {
return;
}
throw new InputMismatchException(recognizer);
case ATNState.PLUS_LOOP_BACK:
case ATNState.STAR_LOOP_BACK:
// System.err.println("at loop back: "+s.getClass().getSimpleName());
reportUnwantedToken(recognizer);
IntervalSet expecting = recognizer.getExpectedTokens();
IntervalSet whatFollowsLoopIterationOrRule =
expecting.or(getErrorRecoverySet(recognizer));
consumeUntil(recognizer, whatFollowsLoopIterationOrRule);
break;
default:
// do nothing if we can't identify the exact kind of ATN state
break;
}
}
/**
* This is called by {@link #reportError} when the exception is a
* {@link NoViableAltException}.
*
* @see #reportError
*
* @param recognizer the parser instance
* @param e the recognition exception
*/
protected void reportNoViableAlternative(@NotNull Parser recognizer,
@NotNull NoViableAltException e)
{
TokenStream tokens = recognizer.getInputStream();
String input;
if ( tokens!=null ) {
if ( e.getStartToken().getType()==Token.EOF ) input = "<EOF>";
else input = tokens.getText(e.getStartToken(), e.getOffendingToken());
}
else {
input = "<unknown input>";
}
String msg = "no viable alternative at input "+escapeWSAndQuote(input);
recognizer.notifyErrorListeners(e.getOffendingToken(), msg, e);
}
/**
* This is called by {@link #reportError} when the exception is an
* {@link InputMismatchException}.
*
* @see #reportError
*
* @param recognizer the parser instance
* @param e the recognition exception
*/
protected void reportInputMismatch(@NotNull Parser recognizer,
@NotNull InputMismatchException e)
{
String msg = "mismatched input "+getTokenErrorDisplay(e.getOffendingToken())+
" expecting "+e.getExpectedTokens().toString(recognizer.getVocabulary());
recognizer.notifyErrorListeners(e.getOffendingToken(), msg, e);
}
/**
* This is called by {@link #reportError} when the exception is a
* {@link FailedPredicateException}.
*
* @see #reportError
*
* @param recognizer the parser instance
* @param e the recognition exception
*/
protected void reportFailedPredicate(@NotNull Parser recognizer,
@NotNull FailedPredicateException e)
{
String ruleName = recognizer.getRuleNames()[recognizer._ctx.getRuleIndex()];
String msg = "rule "+ruleName+" "+e.getMessage();
recognizer.notifyErrorListeners(e.getOffendingToken(), msg, e);
}
/**
* This method is called to report a syntax error which requires the removal
* of a token from the input stream. At the time this method is called, the
* erroneous symbol is current {@code LT(1)} symbol and has not yet been
* removed from the input stream. When this method returns,
* {@code recognizer} is in error recovery mode.
*
* <p>This method is called when {@link #singleTokenDeletion} identifies
* single-token deletion as a viable recovery strategy for a mismatched
* input error.</p>
*
* <p>The default implementation simply returns if the handler is already in
* error recovery mode. Otherwise, it calls {@link #beginErrorCondition} to
* enter error recovery mode, followed by calling
* {@link Parser#notifyErrorListeners}.</p>
*
* @param recognizer the parser instance
*/
protected void reportUnwantedToken(@NotNull Parser recognizer) {
if (inErrorRecoveryMode(recognizer)) {
return;
}
beginErrorCondition(recognizer);
Token t = recognizer.getCurrentToken();
String tokenName = getTokenErrorDisplay(t);
IntervalSet expecting = getExpectedTokens(recognizer);
String msg = "extraneous input "+tokenName+" expecting "+
expecting.toString(recognizer.getVocabulary());
recognizer.notifyErrorListeners(t, msg, null);
}
/**
* This method is called to report a syntax error which requires the
* insertion of a missing token into the input stream. At the time this
* method is called, the missing token has not yet been inserted. When this
* method returns, {@code recognizer} is in error recovery mode.
*
* <p>This method is called when {@link #singleTokenInsertion} identifies
* single-token insertion as a viable recovery strategy for a mismatched
* input error.</p>
*
* <p>The default implementation simply returns if the handler is already in
* error recovery mode. Otherwise, it calls {@link #beginErrorCondition} to
* enter error recovery mode, followed by calling
* {@link Parser#notifyErrorListeners}.</p>
*
* @param recognizer the parser instance
*/
protected void reportMissingToken(@NotNull Parser recognizer) {
if (inErrorRecoveryMode(recognizer)) {
return;
}
beginErrorCondition(recognizer);
Token t = recognizer.getCurrentToken();
IntervalSet expecting = getExpectedTokens(recognizer);
String msg = "missing "+expecting.toString(recognizer.getVocabulary())+
" at "+getTokenErrorDisplay(t);
recognizer.notifyErrorListeners(t, msg, null);
}
/**
* {@inheritDoc}
*
* <p>The default implementation attempts to recover from the mismatched input
* by using single token insertion and deletion as described below. If the
* recovery attempt fails, this method throws an
* {@link InputMismatchException}.</p>
*
* <p><strong>EXTRA TOKEN</strong> (single token deletion)</p>
*
* <p>{@code LA(1)} is not what we are looking for. If {@code LA(2)} has the
* right token, however, then assume {@code LA(1)} is some extra spurious
* token and delete it. Then consume and return the next token (which was
* the {@code LA(2)} token) as the successful result of the match operation.</p>
*
* <p>This recovery strategy is implemented by {@link #singleTokenDeletion}.</p>
*
* <p><strong>MISSING TOKEN</strong> (single token insertion)</p>
*
* <p>If current token (at {@code LA(1)}) is consistent with what could come
* after the expected {@code LA(1)} token, then assume the token is missing
* and use the parser's {@link TokenFactory} to create it on the fly. The
* "insertion" is performed by returning the created token as the successful
* result of the match operation.</p>
*
* <p>This recovery strategy is implemented by {@link #singleTokenInsertion}.</p>
*
* <p><strong>EXAMPLE</strong></p>
*
* <p>For example, Input {@code i=(3;} is clearly missing the {@code ')'}. When
* the parser returns from the nested call to {@code expr}, it will have
* call chain:</p>
*
* <pre>
* stat → expr → atom
* </pre>
*
* and it will be trying to match the {@code ')'} at this point in the
* derivation:
*
* <pre>
* => ID '=' '(' INT ')' ('+' atom)* ';'
* ^
* </pre>
*
* The attempt to match {@code ')'} will fail when it sees {@code ';'} and
* call {@link #recoverInline}. To recover, it sees that {@code LA(1)==';'}
* is in the set of tokens that can follow the {@code ')'} token reference
* in rule {@code atom}. It can assume that you forgot the {@code ')'}.
*/
@Override
public Token recoverInline(Parser recognizer)
throws RecognitionException
{
// SINGLE TOKEN DELETION
Token matchedSymbol = singleTokenDeletion(recognizer);
if ( matchedSymbol!=null ) {
// we have deleted the extra token.
// now, move past ttype token as if all were ok
recognizer.consume();
return matchedSymbol;
}
// SINGLE TOKEN INSERTION
if ( singleTokenInsertion(recognizer) ) {
return getMissingSymbol(recognizer);
}
// even that didn't work; must throw the exception
throw new InputMismatchException(recognizer);
}
/**
* This method implements the single-token insertion inline error recovery
* strategy. It is called by {@link #recoverInline} if the single-token
* deletion strategy fails to recover from the mismatched input. If this
* method returns {@code true}, {@code recognizer} will be in error recovery
* mode.
*
* <p>This method determines whether or not single-token insertion is viable by
* checking if the {@code LA(1)} input symbol could be successfully matched
* if it were instead the {@code LA(2)} symbol. If this method returns
* {@code true}, the caller is responsible for creating and inserting a
* token with the correct type to produce this behavior.</p>
*
* @param recognizer the parser instance
* @return {@code true} if single-token insertion is a viable recovery
* strategy for the current mismatched input, otherwise {@code false}
*/
protected boolean singleTokenInsertion(@NotNull Parser recognizer) {
int currentSymbolType = recognizer.getInputStream().LA(1);
// if current token is consistent with what could come after current
// ATN state, then we know we're missing a token; error recovery
// is free to conjure up and insert the missing token
ATNState currentState = recognizer.getInterpreter().atn.states.get(recognizer.getState());
ATNState next = currentState.transition(0).target;
ATN atn = recognizer.getInterpreter().atn;
IntervalSet expectingAtLL2 = atn.nextTokens(next, recognizer._ctx);
// System.out.println("LT(2) set="+expectingAtLL2.toString(recognizer.getTokenNames()));
if ( expectingAtLL2.contains(currentSymbolType) ) {
reportMissingToken(recognizer);
return true;
}
return false;
}
/**
* This method implements the single-token deletion inline error recovery
* strategy. It is called by {@link #recoverInline} to attempt to recover
* from mismatched input. If this method returns null, the parser and error
* handler state will not have changed. If this method returns non-null,
* {@code recognizer} will <em>not</em> be in error recovery mode since the
* returned token was a successful match.
*
* <p>If the single-token deletion is successful, this method calls
* {@link #reportUnwantedToken} to report the error, followed by
* {@link Parser#consume} to actually "delete" the extraneous token. Then,
* before returning {@link #reportMatch} is called to signal a successful
* match.</p>
*
* @param recognizer the parser instance
* @return the successfully matched {@link Token} instance if single-token
* deletion successfully recovers from the mismatched input, otherwise
* {@code null}
*/
@Nullable
protected Token singleTokenDeletion(@NotNull Parser recognizer) {
int nextTokenType = recognizer.getInputStream().LA(2);
IntervalSet expecting = getExpectedTokens(recognizer);
if ( expecting.contains(nextTokenType) ) {
reportUnwantedToken(recognizer);
/*
System.err.println("recoverFromMismatchedToken deleting "+
((TokenStream)recognizer.getInputStream()).LT(1)+
" since "+((TokenStream)recognizer.getInputStream()).LT(2)+
" is what we want");
*/
recognizer.consume(); // simply delete extra token
// we want to return the token we're actually matching
Token matchedSymbol = recognizer.getCurrentToken();
reportMatch(recognizer); // we know current token is correct
return matchedSymbol;
}
return null;
}
/** Conjure up a missing token during error recovery.
*
* The recognizer attempts to recover from single missing
* symbols. But, actions might refer to that missing symbol.
* For example, x=ID {f($x);}. The action clearly assumes
* that there has been an identifier matched previously and that
* $x points at that token. If that token is missing, but
* the next token in the stream is what we want we assume that
* this token is missing and we keep going. Because we
* have to return some token to replace the missing token,
* we have to conjure one up. This method gives the user control
* over the tokens returned for missing tokens. Mostly,
* you will want to create something special for identifier
* tokens. For literals such as '{' and ',', the default
* action in the parser or tree parser works. It simply creates
* a CommonToken of the appropriate type. The text will be the token.
* If you change what tokens must be created by the lexer,
* override this method to create the appropriate tokens.
*/
@NotNull
protected Token getMissingSymbol(@NotNull Parser recognizer) {
Token currentSymbol = recognizer.getCurrentToken();
IntervalSet expecting = getExpectedTokens(recognizer);
int expectedTokenType = expecting.getMinElement(); // get any element
String tokenText;
if ( expectedTokenType== Token.EOF ) tokenText = "<missing EOF>";
else tokenText = "<missing "+recognizer.getVocabulary().getDisplayName(expectedTokenType)+">";
Token current = currentSymbol;
Token lookback = recognizer.getInputStream().LT(-1);
if ( current.getType() == Token.EOF && lookback!=null ) {
current = lookback;
}
return
recognizer.getTokenFactory().create(new Pair<TokenSource, CharStream>(current.getTokenSource(), current.getTokenSource().getInputStream()), expectedTokenType, tokenText,
Token.DEFAULT_CHANNEL,
-1, -1,
current.getLine(), current.getCharPositionInLine());
}
@NotNull
protected IntervalSet getExpectedTokens(@NotNull Parser recognizer) {
return recognizer.getExpectedTokens();
}
/** How should a token be displayed in an error message? The default
* is to display just the text, but during development you might
* want to have a lot of information spit out. Override in that case
* to use t.toString() (which, for CommonToken, dumps everything about
* the token). This is better than forcing you to override a method in
* your token objects because you don't have to go modify your lexer
* so that it creates a new Java type.
*/
protected String getTokenErrorDisplay(Token t) {
if ( t==null ) return "<no token>";
String s = getSymbolText(t);
if ( s==null ) {
if ( getSymbolType(t)==Token.EOF ) {
s = "<EOF>";
}
else {
s = "<"+getSymbolType(t)+">";
}
}
return escapeWSAndQuote(s);
}
protected String getSymbolText(@NotNull Token symbol) {
return symbol.getText();
}
protected int getSymbolType(@NotNull Token symbol) {
return symbol.getType();
}
@NotNull
protected String escapeWSAndQuote(@NotNull String s) {
// if ( s==null ) return s;
s = s.replace("\n","\\n");
s = s.replace("\r","\\r");
s = s.replace("\t","\\t");
return "'"+s+"'";
}
/* Compute the error recovery set for the current rule. During
* rule invocation, the parser pushes the set of tokens that can
* follow that rule reference on the stack; this amounts to
* computing FIRST of what follows the rule reference in the
* enclosing rule. See LinearApproximator.FIRST().
* This local follow set only includes tokens
* from within the rule; i.e., the FIRST computation done by
* ANTLR stops at the end of a rule.
*
* EXAMPLE
*
* When you find a "no viable alt exception", the input is not
* consistent with any of the alternatives for rule r. The best
* thing to do is to consume tokens until you see something that
* can legally follow a call to r *or* any rule that called r.
* You don't want the exact set of viable next tokens because the
* input might just be missing a token--you might consume the
* rest of the input looking for one of the missing tokens.
*
* Consider grammar:
*
* a : '[' b ']'
* | '(' b ')'
* ;
* b : c '^' INT ;
* c : ID
* | INT
* ;
*
* At each rule invocation, the set of tokens that could follow
* that rule is pushed on a stack. Here are the various
* context-sensitive follow sets:
*
* FOLLOW(b1_in_a) = FIRST(']') = ']'
* FOLLOW(b2_in_a) = FIRST(')') = ')'
* FOLLOW(c_in_b) = FIRST('^') = '^'
*
* Upon erroneous input "[]", the call chain is
*
* a -> b -> c
*
* and, hence, the follow context stack is:
*
* depth follow set start of rule execution
* 0 <EOF> a (from main())
* 1 ']' b
* 2 '^' c
*
* Notice that ')' is not included, because b would have to have
* been called from a different context in rule a for ')' to be
* included.
*
* For error recovery, we cannot consider FOLLOW(c)
* (context-sensitive or otherwise). We need the combined set of
* all context-sensitive FOLLOW sets--the set of all tokens that
* could follow any reference in the call chain. We need to
* resync to one of those tokens. Note that FOLLOW(c)='^' and if
* we resync'd to that token, we'd consume until EOF. We need to
* sync to context-sensitive FOLLOWs for a, b, and c: {']','^'}.
* In this case, for input "[]", LA(1) is ']' and in the set, so we would
* not consume anything. After printing an error, rule c would
* return normally. Rule b would not find the required '^' though.
* At this point, it gets a mismatched token error and throws an
* exception (since LA(1) is not in the viable following token
* set). The rule exception handler tries to recover, but finds
* the same recovery set and doesn't consume anything. Rule b
* exits normally returning to rule a. Now it finds the ']' (and
* with the successful match exits errorRecovery mode).
*
* So, you can see that the parser walks up the call chain looking
* for the token that was a member of the recovery set.
*
* Errors are not generated in errorRecovery mode.
*
* ANTLR's error recovery mechanism is based upon original ideas:
*
* "Algorithms + Data Structures = Programs" by Niklaus Wirth
*
* and
*
* "A note on error recovery in recursive descent parsers":
* http://portal.acm.org/citation.cfm?id=947902.947905
*
* Later, Josef Grosch had some good ideas:
*
* "Efficient and Comfortable Error Recovery in Recursive Descent
* Parsers":
* ftp://www.cocolab.com/products/cocktail/doca4.ps/ell.ps.zip
*
* Like Grosch I implement context-sensitive FOLLOW sets that are combined
* at run-time upon error to avoid overhead during parsing.
*/
@NotNull
protected IntervalSet getErrorRecoverySet(@NotNull Parser recognizer) {
ATN atn = recognizer.getInterpreter().atn;
RuleContext ctx = recognizer._ctx;
IntervalSet recoverSet = new IntervalSet();
while ( ctx!=null && ctx.invokingState>=0 ) {
// compute what follows who invoked us
ATNState invokingState = atn.states.get(ctx.invokingState);
RuleTransition rt = (RuleTransition)invokingState.transition(0);
IntervalSet follow = atn.nextTokens(rt.followState);
recoverSet.addAll(follow);
ctx = ctx.parent;
}
recoverSet.remove(Token.EPSILON);
// System.out.println("recover set "+recoverSet.toString(recognizer.getTokenNames()));
return recoverSet;
}
/** Consume tokens until one matches the given token set. */
protected void consumeUntil(@NotNull Parser recognizer, @NotNull IntervalSet set) {
// System.err.println("consumeUntil("+set.toString(recognizer.getTokenNames())+")");
int ttype = recognizer.getInputStream().LA(1);
while (ttype != Token.EOF && !set.contains(ttype) ) {
//System.out.println("consume during recover LA(1)="+getTokenNames()[input.LA(1)]);
// recognizer.getInputStream().consume();
recognizer.consume();
ttype = recognizer.getInputStream().LA(1);
}
}
}