org.antlr.analysis

Class DecisionProbe

java.lang.Object

org.antlr.analysis.DecisionProbe

public class DecisionProbe
extends Object

Collection of information about what is wrong with a decision as discovered while building the DFA predictor. The information is collected during NFA->DFA conversion and, while some of this is available elsewhere, it is nice to have it all tracked in one spot so a great error message can be easily had. I also like the fact that this object tracks it all for later perusing to make an excellent error message instead of lots of imprecise on-the-fly warnings (during conversion). A decision normally only has one problem; e.g., some input sequence can be matched by multiple alternatives. Unfortunately, some decisions such as a : ( A | B ) | ( A | B ) | A ; have multiple problems. So in general, you should approach a decision as having multiple flaws each one uniquely identified by a DFAState. For example, statesWithSyntacticallyAmbiguousAltsSet tracks the set of all DFAStates where ANTLR has discovered a problem. Recall that a decision is represented internall with a DFA comprised of multiple states, each of which could potentially have problems. Because of this, you need to iterate over this list of DFA states. You'll note that most of the informational methods like getSampleNonDeterministicInputSequence() require a DFAState. This state will be one of the iterated states from stateToSyntacticallyAmbiguousAltsSet. This class is not thread safe due to shared use of visited maps etc... Only one thread should really need to access one DecisionProbe anyway.

Field Summary

Fields

Modifier and Type	Field and Description
protected Set<Integer>	altsWithProblem The overall list of alts within the decision that have at least one conflicting input sequence.
protected Set<DFAState>	danglingStates The set of states w/o emanating edges and w/o resolving sem preds.
DFA	dfa
protected boolean	nonLLStarDecision If decision with > 1 alt has recursion in > 1 alt, it's nonregular lookahead.
static Integer	REACHABLE_BUSY
static Integer	REACHABLE_NO
static Integer	REACHABLE_YES
protected Map<Integer,Integer>	stateReachable Used to find paths through syntactically ambiguous DFA.
protected Set<DFAState>	statesResolvedWithSemanticPredicatesSet Was a syntactic ambiguity resolved with predicates? Any DFA state that predicts more than one alternative, must be resolved with predicates or it should be reported to the user.
protected Set<String>	statesVisitedAtInputDepth Used while finding a path through an NFA whose edge labels match an input sequence.
protected Set<Integer>	statesVisitedDuringSampleSequence
protected Set<DFAState>	statesWithSyntacticallyAmbiguousAltsSet Track all DFA states with nondeterministic alternatives.
protected Map<DFAState,Map<Integer,SemanticContext>>	stateToAltSetWithSemanticPredicatesMap Track the predicates for each alt per DFA state; more than one DFA state might have syntactically ambig alt prediction.
protected Map<DFAState,Map<Integer,Set<antlr.Token>>>	stateToIncompletelyCoveredAltsMap Tracks alts insufficiently covered.
protected MultiMap<Integer,NFAConfiguration>	stateToRecursionOverflowConfigurationsMap Recursion is limited to a particular depth.
protected Map<DFAState,Set<Integer>>	stateToSyntacticallyAmbiguousTokensRuleAltsMap Track just like stateToSyntacticallyAmbiguousAltsMap, but only for nondeterminisms that arise in the Tokens rule such as keyword vs ID rule.
protected boolean	timedOut Did ANTLR have to terminate early on the analysis of this decision?
static boolean	verbose

Constructor Summary

Constructors

Constructor and Description
DecisionProbe(DFA dfa)

Method Summary

Methods

Modifier and Type	Method and Description
boolean	analysisOverflowed() Took too long to analyze a DFA
boolean	analysisTimedOut() Did the analysis complete it's work?
Set	getDanglingStates() return set of states w/o emanating edges and w/o resolving sem preds.
String	getDescription() Return a string like "3:22: ( A {;} | B )" that describes this decision.
protected Set	getDFAPathStatesToTarget(DFAState targetState)
Set	getDFAStatesWithSyntacticallyAmbiguousAlts() Return all DFA states in this DFA that have NFA configurations that conflict.
Set	getDisabledAlternatives(DFAState d) Which alts were specifically turned off to resolve nondeterminisms? This is different than the unreachable alts.
Map<Integer,Set<antlr.Token>>	getIncompletelyCoveredAlts(DFAState d) Return a list of alts whose predicate context was insufficient to resolve a nondeterminism for state d.
String	getInputSequenceDisplay(List labels) Given List, return a String with a useful representation of the associated input string.
protected boolean	getNFAPath(NFAState s, int labelIndex, List labels, List path) Given a sample input sequence, you usually would like to know the path taken through the NFA.
List	getNFAPathStatesForAlt(int firstAlt, int alt, List labels) Given an alternative associated with a nondeterministic DFA state, find the path of NFA states associated with the labels sequence.
Set	getNonDeterministicAlts()
List	getNonDeterministicAltsForState(DFAState targetState) Return the sorted list of alts that conflict within a single state.
Set	getNondeterministicStatesResolvedWithSemanticPredicate()
int	getNumberOfStates() How many states does the DFA predictor have?
protected void	getSampleInputSequenceUsingStateSet(State startState, State targetState, Set states, List<Label> labels) Given a start state and a final state, find a list of edge labels between the two ignoring epsilon.
List<Label>	getSampleNonDeterministicInputSequence(DFAState targetState) Return a List indicating an input sequence that can be matched from the start state of the DFA to the targetState (which is known to have a problem).
SemanticContext	getSemanticContextForAlt(DFAState d, int alt) Each state in the DFA represents a different input sequence for an alt of the decision.
protected String	getStateLabelIndexKey(int s, int i)
String	getTokenNameForTokensRuleAlt(int alt) From an alt number associated with artificial Tokens rule, return the name of the token that is associated with that alt.
List<Integer>	getUnreachableAlts() Get a list of all unreachable alternatives for this decision.
boolean	hasPredicate() At least one alt refs a sem or syn pred
boolean	isCyclic()
boolean	isDeterministic() If no states are dead-ends, no alts are unreachable, there are no nondeterminisms unresolved by syn preds, all is ok with decision.
boolean	isNonLLStarDecision() Found recursion in > 1 alt
boolean	isReduced()
protected void	issueRecursionWarnings()
void	issueWarnings()
protected boolean	reachesState(DFAState startState, DFAState targetState, Set states) Given a start state and a target state, return true if start can reach target state.
void	removeRecursiveOverflowState(DFAState d) If a recursion overflow is resolve with predicates, then we need to shut off the warning that would be generated.
void	reportAltPredicateContext(DFAState d, Map altPredicateContext) Report the list of predicates found for each alternative; copy the list because this set gets altered later by the method tryToResolveWithSemanticPredicates() while flagging NFA configurations in d as resolved.
void	reportAnalysisTimeout()
void	reportDanglingState(DFAState d) Report the fact that DFA state d is not a state resolved with predicates and yet it has no emanating edges.
void	reportIncompletelyCoveredAlts(DFAState d, Map<Integer,Set<antlr.Token>> altToLocationsReachableWithoutPredicate)
void	reportLexerRuleNondeterminism(DFAState d, Set<Integer> nondeterministicAlts) Currently the analysis reports issues between token definitions, but we don't print out warnings in favor of just picking the first token definition found in the grammar ala lex/flex.
void	reportNondeterminism(DFAState d, Set<Integer> nondeterministicAlts)
void	reportNondeterminismResolvedWithSemanticPredicate(DFAState d)
void	reportNonLLStarDecision(DFA dfa) Report that at least 2 alts have recursive constructs.
void	reportRecursionOverflow(DFAState d, NFAConfiguration recursionNFAConfiguration)
void	reset()
protected void	stripWildCardAlts(Set disabledAlts) Get the last disabled alt number and check in the grammar to see if that alt is a simple wildcard.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

dfa

public DFA dfa

statesWithSyntacticallyAmbiguousAltsSet

protected Set<DFAState> statesWithSyntacticallyAmbiguousAltsSet

Track all DFA states with nondeterministic alternatives. By reaching the same DFA state, a path through the NFA for some input is able to reach the same NFA state by starting at more than one alternative's left edge. Though, later, we may find that predicates resolve the issue, but track info anyway. Note that from the DFA state, you can ask for which alts are nondeterministic.

stateToSyntacticallyAmbiguousTokensRuleAltsMap

protected Map<DFAState,Set<Integer>> stateToSyntacticallyAmbiguousTokensRuleAltsMap

Track just like stateToSyntacticallyAmbiguousAltsMap, but only for nondeterminisms that arise in the Tokens rule such as keyword vs ID rule. The state maps to the list of Tokens rule alts that are in conflict.

statesResolvedWithSemanticPredicatesSet

protected Set<DFAState> statesResolvedWithSemanticPredicatesSet

Was a syntactic ambiguity resolved with predicates? Any DFA state that predicts more than one alternative, must be resolved with predicates or it should be reported to the user.

stateToAltSetWithSemanticPredicatesMap

protected Map<DFAState,Map<Integer,SemanticContext>> stateToAltSetWithSemanticPredicatesMap

Track the predicates for each alt per DFA state; more than one DFA state might have syntactically ambig alt prediction. Maps DFA state to another map, mapping alt number to a SemanticContext (pred(s) to execute to resolve syntactic ambiguity).

stateToIncompletelyCoveredAltsMap

protected Map<DFAState,Map<Integer,Set<antlr.Token>>> stateToIncompletelyCoveredAltsMap

Tracks alts insufficiently covered. For example, p1||true gets reduced to true and so leaves whole alt uncovered. This maps DFA state to the set of alts

danglingStates

protected Set<DFAState> danglingStates

The set of states w/o emanating edges and w/o resolving sem preds.

altsWithProblem

protected Set<Integer> altsWithProblem

The overall list of alts within the decision that have at least one conflicting input sequence.

nonLLStarDecision

protected boolean nonLLStarDecision

If decision with > 1 alt has recursion in > 1 alt, it's nonregular lookahead. The decision cannot be made with a DFA. the alts are stored in altsWithProblem.

stateToRecursionOverflowConfigurationsMap

protected MultiMap<Integer,NFAConfiguration> stateToRecursionOverflowConfigurationsMap

Recursion is limited to a particular depth. If that limit is exceeded the proposed new NFAConfiguration is recorded for the associated DFA state.

timedOut

protected boolean timedOut

Did ANTLR have to terminate early on the analysis of this decision?

stateReachable

protected Map<Integer,Integer> stateReachable

Used to find paths through syntactically ambiguous DFA. If we've seen statement number before, what did we learn?

REACHABLE_BUSY

public static final Integer REACHABLE_BUSY

REACHABLE_NO

public static final Integer REACHABLE_NO

REACHABLE_YES

public static final Integer REACHABLE_YES

statesVisitedAtInputDepth

protected Set<String> statesVisitedAtInputDepth

Used while finding a path through an NFA whose edge labels match an input sequence. Tracks the input position we were at the last time at this node. If same input position, then we'd have reached same state without consuming input...probably an infinite loop. Stop. Set. The strings look like stateNumber_labelIndex.

statesVisitedDuringSampleSequence

protected Set<Integer> statesVisitedDuringSampleSequence

verbose

public static boolean verbose

Constructor Detail

DecisionProbe

public DecisionProbe(DFA dfa)

Method Detail

getDescription

public String getDescription()

Return a string like "3:22: ( A {;} | B )" that describes this decision.

isReduced

public boolean isReduced()

isCyclic

public boolean isCyclic()

isDeterministic

public boolean isDeterministic()

If no states are dead-ends, no alts are unreachable, there are no nondeterminisms unresolved by syn preds, all is ok with decision.

analysisTimedOut

public boolean analysisTimedOut()

Did the analysis complete it's work?

analysisOverflowed

public boolean analysisOverflowed()

Took too long to analyze a DFA

isNonLLStarDecision

public boolean isNonLLStarDecision()

Found recursion in > 1 alt

getNumberOfStates

public int getNumberOfStates()

How many states does the DFA predictor have?

getUnreachableAlts

public List<Integer> getUnreachableAlts()

Get a list of all unreachable alternatives for this decision. There may be multiple alternatives with ambiguous input sequences, but this is the overall list of unreachable alternatives (either due to conflict resolution or alts w/o accept states).

getDanglingStates

public Set getDanglingStates()

return set of states w/o emanating edges and w/o resolving sem preds. These states come about because the analysis algorithm had to terminate early to avoid infinite recursion for example (due to left recursion perhaps).

getNonDeterministicAlts

public Set getNonDeterministicAlts()

getNonDeterministicAltsForState

public List getNonDeterministicAltsForState(DFAState targetState)

Return the sorted list of alts that conflict within a single state. Note that predicates may resolve the conflict.

getDFAStatesWithSyntacticallyAmbiguousAlts

public Set getDFAStatesWithSyntacticallyAmbiguousAlts()

Return all DFA states in this DFA that have NFA configurations that conflict. You must report a problem for each state in this set because each state represents a different input sequence.

getDisabledAlternatives

public Set getDisabledAlternatives(DFAState d)

Which alts were specifically turned off to resolve nondeterminisms? This is different than the unreachable alts. Disabled doesn't mean that the alternative is totally unreachable necessarily, it just means that for this DFA state, that alt is disabled. There may be other accept states for that alt that make an alt reachable.

removeRecursiveOverflowState

public void removeRecursiveOverflowState(DFAState d)

If a recursion overflow is resolve with predicates, then we need to shut off the warning that would be generated.

getSampleNonDeterministicInputSequence

public List<Label> getSampleNonDeterministicInputSequence(DFAState targetState)

Return a List indicating an input sequence that can be matched from the start state of the DFA to the targetState (which is known to have a problem).

getInputSequenceDisplay

public String getInputSequenceDisplay(List labels)

Given List, return a String with a useful representation of the associated input string. One could show something different for lexers and parsers, for example.

getNFAPathStatesForAlt

public List getNFAPathStatesForAlt(int firstAlt,
                          int alt,
                          List labels)

Given an alternative associated with a nondeterministic DFA state, find the path of NFA states associated with the labels sequence. Useful tracing where in the NFA, a single input sequence can be matched. For different alts, you should get different NFA paths. The first NFA state for all NFA paths will be the same: the starting NFA state of the first nondeterministic alt. Imagine (A|B|A|A): 5->9-A->o | 6->10-B->o | 7->11-A->o | 8->12-A->o There are 3 nondeterministic alts. The paths should be: 5 9 ... 5 6 7 11 ... 5 6 7 8 12 ... The NFA path matching the sample input sequence (labels) is computed using states 9, 11, and 12 rather than 5, 7, 8 because state 5, for example can get to all ambig paths. Must isolate for each alt (hence, the extra state beginning each alt in my NFA structures). Here, firstAlt=1.

getSemanticContextForAlt

public SemanticContext getSemanticContextForAlt(DFAState d,
                                       int alt)

Each state in the DFA represents a different input sequence for an alt of the decision. Given a DFA state, what is the semantic predicate context for a particular alt.

hasPredicate

public boolean hasPredicate()

At least one alt refs a sem or syn pred

getNondeterministicStatesResolvedWithSemanticPredicate

public Set getNondeterministicStatesResolvedWithSemanticPredicate()

getIncompletelyCoveredAlts

public Map<Integer,Set<antlr.Token>> getIncompletelyCoveredAlts(DFAState d)

Return a list of alts whose predicate context was insufficient to resolve a nondeterminism for state d.

issueWarnings

public void issueWarnings()

stripWildCardAlts

protected void stripWildCardAlts(Set disabledAlts)

Get the last disabled alt number and check in the grammar to see if that alt is a simple wildcard. If so, treat like an else clause and don't emit the error. Strip out the last alt if it's wildcard.

issueRecursionWarnings

protected void issueRecursionWarnings()

reportDanglingState

public void reportDanglingState(DFAState d)

Report the fact that DFA state d is not a state resolved with predicates and yet it has no emanating edges. Usually this is a result of the closure/reach operations being unable to proceed

reportAnalysisTimeout

public void reportAnalysisTimeout()

reportNonLLStarDecision

public void reportNonLLStarDecision(DFA dfa)

Report that at least 2 alts have recursive constructs. There is no way to build a DFA so we terminated.

reportRecursionOverflow

public void reportRecursionOverflow(DFAState d,
                           NFAConfiguration recursionNFAConfiguration)

reportNondeterminism

public void reportNondeterminism(DFAState d,
                        Set<Integer> nondeterministicAlts)

reportLexerRuleNondeterminism

public void reportLexerRuleNondeterminism(DFAState d,
                                 Set<Integer> nondeterministicAlts)

Currently the analysis reports issues between token definitions, but we don't print out warnings in favor of just picking the first token definition found in the grammar ala lex/flex.

reportNondeterminismResolvedWithSemanticPredicate

public void reportNondeterminismResolvedWithSemanticPredicate(DFAState d)

reportAltPredicateContext

public void reportAltPredicateContext(DFAState d,
                             Map altPredicateContext)

Report the list of predicates found for each alternative; copy the list because this set gets altered later by the method tryToResolveWithSemanticPredicates() while flagging NFA configurations in d as resolved.

reportIncompletelyCoveredAlts

public void reportIncompletelyCoveredAlts(DFAState d,
                                 Map<Integer,Set<antlr.Token>> altToLocationsReachableWithoutPredicate)

reachesState

protected boolean reachesState(DFAState startState,
                   DFAState targetState,
                   Set states)

Given a start state and a target state, return true if start can reach target state. Also, compute the set of DFA states that are on a path from start to target; return in states parameter.

getDFAPathStatesToTarget

protected Set getDFAPathStatesToTarget(DFAState targetState)

getSampleInputSequenceUsingStateSet

protected void getSampleInputSequenceUsingStateSet(State startState,
                                       State targetState,
                                       Set states,
                                       List<Label> labels)

Given a start state and a final state, find a list of edge labels between the two ignoring epsilon. Limit your scan to a set of states passed in. This is used to show a sample input sequence that is nondeterministic with respect to this decision. Return List as a parameter. The incoming states set must be all states that lead from startState to targetState and no others so this algorithm doesn't take a path that eventually leads to a state other than targetState. Don't follow loops, leading to short (possibly shortest) path.

getNFAPath

protected boolean getNFAPath(NFAState s,
                 int labelIndex,
                 List labels,
                 List path)

Given a sample input sequence, you usually would like to know the path taken through the NFA. Return the list of NFA states visited while matching a list of labels. This cannot use the usual interpreter, which does a deterministic walk. We need to be able to take paths that are turned off during nondeterminism resolution. So, just do a depth-first walk traversing edges labeled with the current label. Return true if a path was found emanating from state s.

getStateLabelIndexKey

protected String getStateLabelIndexKey(int s,
                           int i)

getTokenNameForTokensRuleAlt

public String getTokenNameForTokensRuleAlt(int alt)

From an alt number associated with artificial Tokens rule, return the name of the token that is associated with that alt.

reset

public void reset()