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// Copyright 2017-present Strumenta and contributors, licensed under Apache 2.0.
// Copyright 2024-present Strumenta and contributors, licensed under BSD 3-Clause.
package org.antlr.v4.kotlinruntime.atn
import com.strumenta.antlrkotlin.runtime.BitSet
import com.strumenta.antlrkotlin.runtime.System
import com.strumenta.antlrkotlin.runtime.assert
import com.strumenta.antlrkotlin.runtime.synchronized
import org.antlr.v4.kotlinruntime.*
import org.antlr.v4.kotlinruntime.dfa.DFA
import org.antlr.v4.kotlinruntime.dfa.DFAState
import org.antlr.v4.kotlinruntime.misc.DoubleKeyMap
import org.antlr.v4.kotlinruntime.misc.Interval
import org.antlr.v4.kotlinruntime.misc.IntervalSet
/**
* The embodiment of the adaptive LL(*), ALL(*), parsing strategy.
*
* The basic complexity of the adaptive strategy makes it harder to understand.
* We begin with ATN simulation to build paths in a DFA. Subsequent prediction
* requests go through the DFA first. If they reach a state without an edge for
* the current symbol, the algorithm fails over to the ATN simulation to
* complete the DFA path for the current input (until it finds a conflict state
* or uniquely predicting state).
*
* All of that is done without using the outer context because we want to create
* a DFA that is not dependent upon the rule invocation stack when we do a
* prediction. One DFA works in all contexts. We avoid using context not
* necessarily because it's slower, although it can be, but because of the DFA
* caching problem. The closure routine only considers the rule invocation stack
* created during prediction beginning in the decision rule. For example, if
* prediction occurs without invoking another rule's ATN, there are no context
* stacks in the configurations. When lack of context leads to a conflict, we
* don't know if it's an ambiguity or a weakness in the strong LL(*) parsing
* strategy (versus full LL(*)).
*
* When SLL yields a configuration set with conflict, we rewind the input and
* retry the ATN simulation, this time using full outer context without adding
* to the DFA. Configuration context stacks will be the full invocation stacks
* from the start rule. If we get a conflict using full context, then we can
* definitively say we have a true ambiguity for that input sequence. If we
* don't get a conflict, it implies that the decision is sensitive to the outer
* context. (It is not context-sensitive in the sense of context-sensitive
* grammars.)
*
* The next time we reach this DFA state with an SLL conflict, through DFA
* simulation, we will again retry the ATN simulation using full context mode.
* This is slow because we can't save the results and have to "interpret" the
* ATN each time we get that input.
*
* ### CACHING FULL CONTEXT PREDICTIONS
*
* We could cache results from full context to predicted alternative easily and
* that saves a lot of time but doesn't work in presence of predicates. The set
* of visible predicates from the ATN start state changes depending on the
* context, because closure can fall off the end of a rule. I tried to cache
* tuples (stack context, semantic context, predicted alt) but it was slower
* than interpreting and much more complicated. Also required a huge amount of
* memory. The goal is not to create the world's fastest parser anyway. I'd like
* to keep this algorithm simple. By launching multiple threads, we can improve
* the speed of parsing across a large number of files.
*
* There is no strict ordering between the amount of input used by SLL vs LL,
* which makes it really hard to build a cache for full context. Let's say that
* we have input A B C that leads to an SLL conflict with full context X. That
* implies that using X we might only use A B, but we could also use A B C D to
* resolve conflict. Input A B C D could predict alternative 1 in one position
* in the input and A B C E could predict alternative 2 in another position in
* input. The conflicting SLL configurations could still be non-unique in the
* full context prediction, which would lead us to requiring more input than the
* original A B C. To make a prediction cache work, we have to track the exact
* input used during the previous prediction. That amounts to a cache that maps
* X to a specific DFA for that context.
*
* Something should be done for left-recursive expression predictions. They are
* likely LL(1) + pred eval. Easier to do the whole SLL unless error and retry
* with full LL thing Sam does.
*
* ### AVOIDING FULL CONTEXT PREDICTION
*
* We avoid doing full context retry when the outer context is empty, we did not
* dip into the outer context by falling off the end of the decision state rule,
* or when we force SLL mode.
*
* As an example of the not dip into outer context case, consider as super
* constructor calls versus function calls. One grammar might look like
* this:
*
* ```
* ctorBody
* : '{' superCall? stat* '}'
* ;
* ```
*
* Or, you might see something like
*
* ```
* stat
* : superCall ';'
* | expression ';'
* | ...
* ;
* ```
*
* In both cases I believe that no closure operations will dip into the outer
* context. In the first case ctorBody in the worst case will stop at the '}'.
* In the 2nd case it should stop at the ';'. Both cases should stay within the
* entry rule and not dip into the outer context.
*
* ### PREDICATES
*
* Predicates are always evaluated if present in either SLL or LL both. SLL and
* LL simulation deals with predicates differently. SLL collects predicates as
* it performs closure operations like ANTLR v3 did. It delays predicate
* evaluation until it reaches and accept state. This allows us to cache the SLL
* ATN simulation whereas, if we had evaluated predicates on-the-fly during
* closure, the DFA state configuration sets would be different, and we couldn't
* build up a suitable DFA.
*
* When building a DFA accept state during ATN simulation, we evaluate any
* predicates and return the sole semantically valid alternative. If there is
* more than 1 alternative, we report an ambiguity. If there are 0 alternatives,
* we throw an exception. Alternatives without predicates act like they have
* true predicates. The simple way to think about it is to strip away all
* alternatives with false predicates and choose the minimum alternative that
* remains.
*
* When we start in the DFA and reach an accept state that's predicated, we test
* those and return the minimum semantically viable alternative. If no
* alternatives are viable, we throw an exception.
*
* During full LL ATN simulation, closure always evaluates predicates and
* on-the-fly. This is crucial to reducing the configuration set size during
* closure. It hits a landmine when parsing with the Java grammar, for example,
* without this on-the-fly evaluation.
*
* ### SHARING DFA
*
* All instances of the same parser share the same decision DFAs through a
* static field. Each instance gets its own ATN simulator, but they share the
* same [.decisionToDFA] field. They also share a
* [PredictionContextCache] object that makes sure that all
* [PredictionContext] objects are shared among the DFA states. This makes
* a big size difference.
*
* ### THREAD SAFETY
*
* The [ParserATNSimulator] locks on the [decisionToDFA] field when
* it adds a new DFA object to that array. [addDFAEdge]
* locks on the DFA for the current decision when setting the
* [DFAState.edges] field. [addDFAState] locks on
* the DFA for the current decision when looking up a DFA state to see if it
* already exists. We must make sure that all requests to add DFA states that
* are equivalent result in the same shared DFA object. This is because lots of
* threads will be trying to update the DFA at once. The
* [addDFAState] method also locks inside the DFA lock
* but this time on the shared context cache when it rebuilds the
* configurations' [PredictionContext] objects using cached
* sub-graphs/nodes. No other locking occurs, even during DFA simulation. This is
* safe as long as we can guarantee that all threads referencing
* `s.edge[t]` get the same physical target [DFAState], or
* `null`. Once into the DFA, the DFA simulation does not reference the
* [DFA.states] map. It follows the [DFAState.edges] field to new
* targets. The DFA simulator will either find [DFAState.edges] to be
* `null`, to be non-`null` and `dfa.edges[t]` null, or
* `dfa.edges[t]` to be non-null.
* The [addDFAEdge] method could be racing to set the field
* but in either case the DFA simulator works; if `null`, and requests ATN
* simulation. It could also race trying to get `dfa.edges[t]`, but either
* way it will work because it's not doing a test and set operation.
*
* ### Starting with SLL then failing to combined SLL/LL (Two-Stage Parsing)
*
* Sam pointed out that if SLL does not give a syntax error, then there is no
* point in doing full LL, which is slower. We only have to try LL if we get a
* syntax error. For maximum speed, Sam starts the parser set to pure SLL
* mode with the [BailErrorStrategy]:
*
* ```
* parser.interpreter.predictionMode = PredictionMode.SLL
* parser.errorHandler = BailErrorStrategy()
* ```
*
* If it does not get a syntax error, then we're done. If it does get a syntax
* error, we need to retry with the combined SLL/LL strategy.
*
* The reason this works is as follows. If there are no SLL conflicts, then the
* grammar is SLL (at least for that input set). If there is an SLL conflict,
* the full LL analysis must yield a set of viable alternatives which is a
* subset of the alternatives reported by SLL. If the LL set is a singleton,
* then the grammar is LL but not SLL. If the LL set is the same size as the SLL
* set, the decision is SLL. If the LL set has size < 1, then that decision
* is truly ambiguous on the current input. If the LL set is smaller, then the
* SLL conflict resolution might choose an alternative that the full LL would
* rule out as a possibility based upon better context information. If that's
* the case, then the SLL parse will definitely get an error because the full LL
* analysis says it's not viable. If SLL conflict resolution chooses an
* alternative within the LL set, them both SLL and LL would choose the same
* alternative because they both choose the minimum of multiple conflicting
* alternatives.
*
* Let's say we have a set of SLL conflicting alternatives `{1, 2, 3}` and
* a smaller LL set called *s*. If *s* is `{2, 3}`, then SLL
* parsing will get an error because SLL will pursue alternative 1. If
* *s* is `{1, 2}` or `{1, 3}` then both SLL and LL will
* choose the same alternative because alternative one is the minimum of either
* set. If *s* is `{2}` or `{3}` then SLL will get a syntax
* error. If *s* is `{1}` then SLL will succeed.
*
* Of course, if the input is invalid, then we will get an error for sure in
* both SLL and LL parsing. Erroneous input will therefore require 2 passes over
* the input.
*/
@Suppress("MemberVisibilityCanBePrivate", "PropertyName")
public open class ParserATNSimulator(
public val parser: Parser?,
atn: ATN,
public val decisionToDFA: Array,
sharedContextCache: PredictionContextCache,
) : ATNSimulator(atn, sharedContextCache) {
public companion object {
public var debug: Boolean = false
public var trace_atn_sim: Boolean = false
public var dfa_debug: Boolean = false
public var retry_debug: Boolean = false
/**
* Just in case this optimization is bad, add an ENV variable to turn it off.
*/
public val TURN_OFF_LR_LOOP_ENTRY_BRANCH_OPT: Boolean =
getSafeEnv("TURN_OFF_LR_LOOP_ENTRY_BRANCH_OPT", "false").toBoolean()
protected fun getUniqueAlt(configs: ATNConfigSet): Int {
var alt = ATN.INVALID_ALT_NUMBER
for (c in configs) {
if (alt == ATN.INVALID_ALT_NUMBER) {
// Found first alt
alt = c.alt
} else if (c.alt != alt) {
return ATN.INVALID_ALT_NUMBER
}
}
return alt
}
private fun getSafeEnv(envName: String, defaultValue: String? = null): String? =
try {
System.getenv(envName, defaultValue)
} catch (e: Exception) {
System.err.println(e.toString())
null
}
}
/**
* SLL, LL, or LL + exact ambig detection?
*/
public var predictionMode: PredictionMode = PredictionMode.LL
/**
* Each prediction operation uses a cache for merge of prediction contexts.
*
* Don't keep around as it wastes huge amounts of memory. [DoubleKeyMap]
* isn't synchronized, but we're ok since two threads shouldn't reuse same
* parser/atnsim object because it can only handle one input at a time.
*
* This maps graphs a and b to merged result c. (a,b)c. We can avoid
* the merge if we ever see a and b again. Note that (b,a)c should
* also be examined during cache lookup.
*/
protected var mergeCache: DoubleKeyMap? = null
// LAME globals to avoid parameters!!!!! I need these down deep in predTransition
protected var _input: TokenStream? = null
protected var _startIndex: Int = 0
protected var _outerContext: ParserRuleContext? = null
protected var _dfa: DFA? = null
/**
* Testing only!
*/
public constructor(
atn: ATN,
decisionToDFA: Array,
sharedContextCache: PredictionContextCache,
) : this(null, atn, decisionToDFA, sharedContextCache)
override fun reset() {
// Noop
}
override fun clearDFA() {
for (d in decisionToDFA.indices) {
decisionToDFA[d] = DFA(atn.getDecisionState(d)!!, d)
}
}
public open fun adaptivePredict(
input: TokenStream,
decision: Int,
outerContext: ParserRuleContext?,
): Int {
var tempOuterContext = outerContext
if (debug || trace_atn_sim) {
System.out.println(
"adaptivePredict decision $decision" +
" exec LA(1)==${getLookaheadName(input)}" +
" line ${input.LT(1)!!.line}:${input.LT(1)!!.charPositionInLine}"
)
}
_input = input
_startIndex = input.index()
_outerContext = tempOuterContext
val dfa = decisionToDFA[decision]
_dfa = dfa
val m = input.mark()
val index = _startIndex
// Now we are certain to have a specific decision's DFA
// But, do we still need an initial state?
try {
var s0 = if (dfa.isPrecedenceDfa) {
// the start state for a precedence DFA depends on the current
// parser precedence, and is provided by a DFA method.
dfa.getPrecedenceStartState(parser!!.precedence)
} else {
// the start state for a "regular" DFA is just s0
dfa.s0
}
if (s0 == null) {
if (tempOuterContext == null) {
tempOuterContext = ParserRuleContext.EMPTY
}
val fullCtx = false
var s0Closure = computeStartState(dfa.atnStartState, ParserRuleContext.EMPTY, fullCtx)
if (dfa.isPrecedenceDfa) {
// If this is a precedence DFA, we use applyPrecedenceFilter
// to convert the computed start state to a precedence start
// state. We then use DFA.setPrecedenceStartState to set the
// appropriate start state for the precedence level rather
// than simply setting DFA.s0.
// Not used for prediction but useful to know start configs anyway
dfa.s0!!.configs = s0Closure
s0Closure = applyPrecedenceFilter(s0Closure)
s0 = addDFAState(dfa, DFAState(s0Closure))
dfa.setPrecedenceStartState(parser!!.precedence, s0)
} else {
s0 = addDFAState(dfa, DFAState(s0Closure))
dfa.s0 = s0
}
}
val alt = execATN(dfa, s0, input, index, tempOuterContext!!)
if (debug) {
System.out.println("DFA after predictATN: ${dfa.toString(parser!!.vocabulary)}")
}
return alt
} finally {
// Wack cache after each prediction
mergeCache = null
_dfa = null
input.seek(index)
input.release(m)
}
}
/**
* Performs ATN simulation to compute a predicted alternative based
* upon the remaining input, but also updates the DFA cache to avoid
* having to traverse the ATN again for the same input sequence.
*
* There are some key conditions we're looking for after computing a new
* set of ATN configs (proposed DFA state):
*
* - if the set is empty, there is no viable alternative for current symbol
* - does the state uniquely predict an alternative?
* - does the state have a conflict that would prevent us from
* putting it on the work list?
*
* We also have some key operations to do:
*
* - add an edge from previous DFA state to potentially new DFA state, D,
* upon current symbol but only if adding to work list, which means in all
* cases except no viable alternative (and possibly non-greedy decisions?)
* - collecting predicates and adding semantic context to DFA accept states
* - adding rule context to context-sensitive DFA accept states
* - consuming an input symbol
* - reporting a conflict
* - reporting an ambiguity
* - reporting a context sensitivity
* - reporting insufficient predicates
*
* Cover these cases:
*
* - dead end
* - single alt
* - single alt + preds
* - conflict
* - conflict + preds
*/
protected open fun execATN(
dfa: DFA,
s0: DFAState,
input: TokenStream,
startIndex: Int,
outerContext: ParserRuleContext,
): Int {
if (debug || trace_atn_sim) {
System.out.println(
"execATN decision ${dfa.decision}" +
", DFA state $s0" +
", LA(1)==${getLookaheadName(input)}" +
", line ${input.LT(1)!!.line}:${input.LT(1)!!.charPositionInLine}"
)
}
var previousD = s0
var t = input.LA(1)
while (true) {
@Suppress("LocalVariableName")
val D = getExistingTargetState(previousD, t) ?: computeTargetState(dfa, previousD, t)
if (D === ERROR) {
// If any configs in previous dipped into outer context, that
// means that input up to t actually finished entry rule
// at least for SLL decision. Full LL doesn't dip into outer
// so don't need special case.
// We will get an error no matter what so delay until after
// decision; better error message. Also, no reachable target
// ATN states in SLL implies LL will also get nowhere.
// If conflict in states that dip out, choose min since we
// will get error no matter what.
val e = noViableAlt(input, outerContext, previousD.configs, startIndex)
input.seek(startIndex)
val alt = getSynValidOrSemInvalidAltThatFinishedDecisionEntryRule(previousD.configs, outerContext)
if (alt != ATN.INVALID_ALT_NUMBER) {
return alt
}
throw e
}
if (D!!.requiresFullContext && predictionMode != PredictionMode.SLL) {
// IF PREDS, MIGHT RESOLVE TO SINGLE ALT => SLL (or syntax error)
var conflictingAlts = D.configs.conflictingAlts
if (D.predicates != null) {
if (debug) {
System.out.println("DFA state has preds in DFA sim LL failover")
}
val conflictIndex = input.index()
if (conflictIndex != startIndex) {
input.seek(startIndex)
}
conflictingAlts = evalSemanticContext(D.predicates!!, outerContext, true)
if (conflictingAlts.cardinality() == 1) {
if (debug) {
System.out.println("Full LL avoided")
}
return conflictingAlts.nextSetBit(0)
}
if (conflictIndex != startIndex) {
// restore the index so reporting the fallback to full
// context occurs with the index at the correct spot
input.seek(conflictIndex)
}
}
if (dfa_debug) {
System.out.println("ctx sensitive state $outerContext in $D")
}
val fullCtx = true
val s0Closure = computeStartState(dfa.atnStartState, outerContext, fullCtx)
reportAttemptingFullContext(dfa, conflictingAlts!!, D.configs, startIndex, input.index())
return execATNWithFullContext(
dfa = dfa,
D = D,
s0 = s0Closure,
input = input,
startIndex = startIndex,
outerContext = outerContext,
)
}
if (D.isAcceptState) {
if (D.predicates == null) {
return D.prediction
}
val stopIndex = input.index()
input.seek(startIndex)
val alts = evalSemanticContext(D.predicates!!, outerContext, true)
when (alts.cardinality()) {
0 -> throw noViableAlt(input, outerContext, D.configs, startIndex)
1 -> return alts.nextSetBit(0)
else -> {
// Report ambiguity after predicate evaluation to make sure the correct
// set of ambig alts is reported.
reportAmbiguity(dfa, D, startIndex, stopIndex, false, alts, D.configs)
return alts.nextSetBit(0)
}
}
}
previousD = D
if (t != IntStream.EOF) {
input.consume()
t = input.LA(1)
}
}
}
/**
* Get an existing target state for an edge in the DFA.
*
* If the target state for the edge has not yet been computed
* or is otherwise not available, this method returns `null`.
*
* @param previousD The current DFA state
* @param t The next input symbol
* @return The existing target DFA state for the given input symbol
* [t], or `null` if the target state for this edge is not already cached
*/
protected open fun getExistingTargetState(previousD: DFAState, t: Int): DFAState? {
val edges = previousD.edges
if (edges == null || t + 1 < 0 || t + 1 >= edges.size) {
return null
}
return edges[t + 1]
}
/**
* Compute a target state for an edge in the DFA, and attempt to add the
* computed state and corresponding edge to the DFA.
*
* @param dfa The DFA
* @param previousD The current DFA state
* @param t The next input symbol
* @return The computed target DFA state for the given input symbol [t].
* If [t] does not lead to a valid DFA state, this method returns [ATNSimulator.ERROR]
*/
protected open fun computeTargetState(dfa: DFA, previousD: DFAState, t: Int): DFAState? {
val reach = computeReachSet(previousD.configs, t, false)
if (reach == null) {
addDFAEdge(dfa, previousD, t, ERROR)
return ERROR
}
// Create new target state, we'll add to DFA after it's complete
@Suppress("LocalVariableName")
val D = DFAState(reach)
val predictedAlt = getUniqueAlt(reach)
if (debug) {
val altSubSets = PredictionMode.getConflictingAltSubsets(reach)
System.out.println(
"SLL altSubSets=$altSubSets" +
", configs=$reach" +
", predict=$predictedAlt" +
", allSubsetsConflict=${PredictionMode.allSubsetsConflict(altSubSets)}" +
", conflictingAlts=${getConflictingAlts(reach)}"
)
}
if (predictedAlt != ATN.INVALID_ALT_NUMBER) {
// NO CONFLICT, UNIQUELY PREDICTED ALT
D.isAcceptState = true
D.configs.uniqueAlt = predictedAlt
D.prediction = predictedAlt
} else if (PredictionMode.hasSLLConflictTerminatingPrediction(predictionMode, reach)) {
// MORE THAN ONE VIABLE ALTERNATIVE
D.configs.conflictingAlts = getConflictingAlts(reach)
D.requiresFullContext = true
// In SLL-only mode, we will stop at this state and return the minimum alt
D.isAcceptState = true
D.prediction = D.configs.conflictingAlts!!.nextSetBit(0)
}
if (D.isAcceptState && D.configs.hasSemanticContext) {
predicateDFAState(D, atn.getDecisionState(dfa.decision)!!)
if (D.predicates != null) {
D.prediction = ATN.INVALID_ALT_NUMBER
}
}
// All adds to dfa are done after we've created full D state
return addDFAEdge(dfa, previousD, t, D)
}
protected open fun predicateDFAState(dfaState: DFAState, decisionState: DecisionState) {
// We need to test all predicates, even in DFA states that
// uniquely predict alternative.
val nAlts = decisionState.numberOfTransitions
// Update DFA so reach becomes accept state with (predicate,alt)
// pairs if preds found for conflicting alts
val altsToCollectPredsFrom = getConflictingAltsOrUniqueAlt(dfaState.configs)
val altToPred = getPredsForAmbigAlts(altsToCollectPredsFrom, dfaState.configs, nAlts)
if (altToPred != null) {
dfaState.predicates = getPredicatePredictions(altsToCollectPredsFrom, altToPred)
dfaState.prediction = ATN.INVALID_ALT_NUMBER // Make sure we use preds
} else {
// There are preds in configs, but they might go away
// when OR'd together like {p}? || NONE == NONE.
// If neither alt has preds, resolve to min alt
dfaState.prediction = altsToCollectPredsFrom.nextSetBit(0)
}
}
// Comes back with reach.uniqueAlt set to a valid alt
@Suppress("LocalVariableName")
protected open fun execATNWithFullContext(
dfa: DFA,
D: DFAState, // How far we got in SLL DFA before failing over
s0: ATNConfigSet,
input: TokenStream,
startIndex: Int,
outerContext: ParserRuleContext,
): Int {
if (debug || trace_atn_sim) {
System.out.println("execATNWithFullContext $s0")
}
val fullCtx = true
var foundExactAmbig = false
var reach: ATNConfigSet?
var previous = s0
input.seek(startIndex)
var t = input.LA(1)
var predictedAlt: Int
while (true) {
reach = computeReachSet(previous, t, fullCtx)
if (reach == null) {
// If any configs in previous dipped into outer context, that
// means that input up to t actually finished entry rule
// at least for LL decision. Full LL doesn't dip into outer
// so don't need special case.
// We will get an error no matter what so delay until after
// decision; better error message. Also, no reachable target
// ATN states in SLL implies LL will also get nowhere.
// If conflict in states that dip out, choose min since we
// will get error no matter what.
val e = noViableAlt(input, outerContext, previous, startIndex)
input.seek(startIndex)
val alt = getSynValidOrSemInvalidAltThatFinishedDecisionEntryRule(previous, outerContext)
if (alt != ATN.INVALID_ALT_NUMBER) {
return alt
}
throw e
}
val altSubSets = PredictionMode.getConflictingAltSubsets(reach)
if (debug) {
System.out.println(
"LL altSubSets=$altSubSets" +
", predict=${PredictionMode.getUniqueAlt(altSubSets)}" +
", resolvesToJustOneViableAlt=${PredictionMode.resolvesToJustOneViableAlt(altSubSets)}"
)
}
reach.uniqueAlt = getUniqueAlt(reach)
// Unique prediction?
if (reach.uniqueAlt != ATN.INVALID_ALT_NUMBER) {
predictedAlt = reach.uniqueAlt
break
}
if (predictionMode != PredictionMode.LL_EXACT_AMBIG_DETECTION) {
predictedAlt = PredictionMode.resolvesToJustOneViableAlt(altSubSets)
if (predictedAlt != ATN.INVALID_ALT_NUMBER) {
break
}
} else {
// In exact ambiguity mode, we never try to terminate early.
// Just keeps scarfing until we know what the conflict is
if (PredictionMode.allSubsetsConflict(altSubSets) && PredictionMode.allSubsetsEqual(altSubSets)) {
foundExactAmbig = true
predictedAlt = PredictionMode.getSingleViableAlt(altSubSets)
break
}
// Else there are multiple non-conflicting subsets, or
// we're not sure what the ambiguity is yet.
// So, keep going.
}
previous = reach
if (t != IntStream.EOF) {
input.consume()
t = input.LA(1)
}
}
// If the configuration set uniquely predicts an alternative,
// without conflict, then we know that it's a full LL decision
// not SLL.
if (reach!!.uniqueAlt != ATN.INVALID_ALT_NUMBER) {
reportContextSensitivity(dfa, predictedAlt, reach, startIndex, input.index())
return predictedAlt
}
// We do not check predicates here because we have checked them
// on-the-fly when doing full context prediction.
// In non-exact ambiguity detection mode, we might actually be able to
// detect an exact ambiguity, but I'm not going to spend the cycles
// needed to check. We only emit ambiguity warnings in exact ambiguity
// mode.
//
// For example, we might know that we have conflicting configurations.
// But, that does not mean that there is no way forward without a
// conflict. It's possible to have non-conflicting alt subsets as in:
//
// LL altSubSets=[{1, 2}, {1, 2}, {1}, {1, 2}]
//
// from
//
// [(17,1,[5 $]), (13,1,[5 10 $]), (21,1,[5 10 $]), (11,1,[$]),
// (13,2,[5 10 $]), (21,2,[5 10 $]), (11,2,[$])]
//
// In this case, (17,1,[5 $]) indicates there is some next sequence that
// would resolve this without conflict to alternative 1. Any other viable
// next sequence, however, is associated with a conflict. We stop
// looking for input because no amount of further lookahead will alter
// the fact that we should predict alternative 1. We just can't say for
// sure that there is an ambiguity without looking further.
reportAmbiguity(
dfa = dfa,
D = D,
startIndex = startIndex,
stopIndex = input.index(),
exact = foundExactAmbig,
ambigAlts = reach.alts,
configs = reach,
)
return predictedAlt
}
protected open fun computeReachSet(closure: ATNConfigSet, t: Int, fullCtx: Boolean): ATNConfigSet? {
if (debug) {
System.out.println("in computeReachSet, starting closure: $closure")
}
if (mergeCache == null) {
mergeCache = DoubleKeyMap()
}
val intermediate = ATNConfigSet(fullCtx)
// Configurations already in a rule stop state indicate reaching the end
// of the decision rule (local context) or end of the start rule (full
// context). Once reached, these configurations are never updated by a
// closure operation, so they are handled separately for the performance
// advantage of having a smaller intermediate set when calling closure.
//
// For full-context reach operations, separate handling is required to
// ensure that the alternative matching the longest overall sequence is
// chosen when multiple such configurations can match the input.
var skippedStopStates: MutableList? = null
// First figure out where we can reach on input t
for (c in closure) {
if (debug) {
System.out.println("testing ${getTokenName(t)} at $c")
}
if (c.state is RuleStopState) {
assert(c.context!!.isEmpty)
if (fullCtx || t == IntStream.EOF) {
if (skippedStopStates == null) {
skippedStopStates = ArrayList()
}
skippedStopStates.add(c)
}
continue
}
val n = c.state.numberOfTransitions
// For each transition
for (ti in 0..()
val treatEofAsEpsilon = t == Token.EOF
for (c in intermediate) {
closure(c, reach, closureBusy, false, fullCtx, treatEofAsEpsilon)
}
}
if (t == IntStream.EOF) {
// After consuming EOF no additional input is possible, so we are
// only interested in configurations which reached the end of the
// decision rule (local context) or end of the start rule (full
// context). Update reach to contain only these configurations. This
// handles both explicit EOF transitions in the grammar and implicit
// EOF transitions following the end of the decision or start rule.
//
// When reach==intermediate, no closure operation was performed. In
// this case, removeAllConfigsNotInRuleStopState needs to check for
// reachable rule stop states as well as configurations already in
// a rule stop state.
//
// This is handled before the configurations in skippedStopStates,
// because any configurations potentially added from that list are
// already guaranteed to meet this condition whether it's
// required.
reach = removeAllConfigsNotInRuleStopState(reach, reach === intermediate)
}
// If skippedStopStates is not null, then it contains at least one
// configuration. For full-context reach operations, these
// configurations reached the end of the start rule, in which case we
// only add them back to reach if no configuration during the current
// closure operation reached such a state. This ensures adaptivePredict
// chooses an alternative matching the longest overall sequence when
// multiple alternatives are viable.
if (skippedStopStates != null && (!fullCtx || !PredictionMode.hasConfigInRuleStopState(reach))) {
assert(skippedStopStates.isNotEmpty())
for (c in skippedStopStates) {
reach.add(c, mergeCache)
}
}
if (trace_atn_sim) {
System.out.println("computeReachSet $closure -> $reach")
}
return if (reach.isEmpty()) {
null
} else {
reach
}
}
/**
* Return a configuration set containing only the configurations from
* [configs] which are in a [RuleStopState].
*
* If all configurations in [configs] are already in a rule stop state, this
* method simply returns [configs].
*
* When [lookToEndOfRule] is `true`, this method uses
* [ATN.nextTokens] for each configuration in [configs] which is
* not already in a rule stop state to see if a rule stop state is reachable
* from the configuration via epsilon-only transitions.
*
* @param configs The configuration set to update
* @param lookToEndOfRule When `true`, this method checks for rule stop states
* reachable by epsilon-only transitions from each configuration in [configs]
* @return [configs] if all configurations in [configs] are in a
* rule stop state, otherwise return a new configuration set containing only
* the configurations from [configs] which are in a rule stop state
*/
protected open fun removeAllConfigsNotInRuleStopState(configs: ATNConfigSet, lookToEndOfRule: Boolean): ATNConfigSet {
if (PredictionMode.allConfigsInRuleStopStates(configs)) {
return configs
}
val result = ATNConfigSet(configs.fullCtx)
for (config in configs) {
if (config.state is RuleStopState) {
result.add(config, mergeCache)
continue
}
if (lookToEndOfRule && config.state.onlyHasEpsilonTransitions()) {
val nextTokens = atn.nextTokens(config.state)
if (nextTokens.contains(Token.EPSILON)) {
val endOfRuleState = atn.ruleToStopState!![config.state.ruleIndex]
result.add(ATNConfig(config, endOfRuleState!!), mergeCache)
}
}
}
return result
}
protected open fun computeStartState(p: ATNState, ctx: RuleContext, fullCtx: Boolean): ATNConfigSet {
// Always at least the implicit call to start rule
val initialContext = PredictionContext.fromRuleContext(atn, ctx)
val configs = ATNConfigSet(fullCtx)
if (trace_atn_sim) {
System.out.println("computeStartState from ATN state $p initialContext=${initialContext.toString(parser!!)}")
}
for (i in 0..()
closure(c, configs, closureBusy, true, fullCtx, false)
}
return configs
}
// parrt internal source brain dump that doesn't mess up
// external API spec.
// context-sensitive in that they can only be properly evaluated
// in the context of the proper prec argument. Without pruning,
// these predicates are normal predicates evaluated when we reach
// conflict state (or unique prediction). As we cannot evaluate
// these predicates out of context, the resulting conflict leads
// to full LL evaluation and nonlinear prediction which shows up
// very clearly with fairly large expressions.
//
// Example grammar:
//
// e : e '*' e
// | e '+' e
// | INT
// ;
//
// We convert that to the following:
//
// e[int prec]
// : INT
// ( {3>=prec}? '*' e[4]
// | {2>=prec}? '+' e[3]
// )*
// ;
//
// The (..)* loop has a decision for the inner block as well as
// an enter or exit decision, which is what concerns us here. At
// the 1st + of input 1+2+3, the loop entry sees both predicates
// and the loop exit also sees both predicates by falling off the
// edge of e. This is because we have no stack information with
// SLL and find the follow of e, which will hit the return states
// inside the loop after e[4] and e[3], which brings it back to
// the enter or exit decision. In this case, we know that we
// cannot evaluate those predicates because we have fallen off
// the edge of the stack and will in general not know which prec
// parameter is the right one to use in the predicate.
//
// Because we have special information, that these are precedence
// predicates, we can resolve them without failing over to full
// LL despite their context-sensitive nature. We make an
// assumption that prec[-1] <= prec[0], meaning that the current
// precedence level is greater than or equal to the precedence
// level of recursive invocations above us in the stack. For
// example, if predicate {3>=prec}? is true of the current prec,
// then one option is to enter the loop to match it now. The
// other option is to exit the loop and the left recursive rule
// to match the current operator in rule invocation further up
// the stack. But, we know that all of those prec are lower or
// the same value, and so we can decide to enter the loop instead
// of matching it later. That means we can strip out the other
// configuration for the exit branch.
//
// So imagine we have (14,1,$,{2>=prec}?) and then
// (14,2,$-dipsIntoOuterContext,{2>=prec}?). The optimization
// allows us to collapse these two configurations. We know that
// if {2>=prec}? is true for the current prec parameter, it will
// also be true for any prec from an invoking e call, indicated
// by dipsIntoOuterContext. As the predicates are both true, we
// have the option to evaluate them early in the decision start
// state. We do this by stripping both predicates and choosing to
// enter the loop as it is consistent with the notion of operator
// precedence. It's also how the full LL conflict resolution
// would work.
//
// The solution requires a different DFA start state for each
// precedence level.
//
// The basic filter mechanism is to remove configurations of the
// form (p, 2, pi) if (p, 1, pi) exists for the same p and pi. In
// other words, for the same ATN state and predicate context,
// remove any configuration associated with an exit branch if
// there is a configuration associated with the enter branch.
//
// It's also the case that the filter evaluates precedence
// predicates and resolves conflicts according to precedence
// levels. For example, for input 1+2+3 at the first +, we see
// prediction filtering
//
// [(11,1,[$],{3>=prec}?), (14,1,[$],{2>=prec}?), (5,2,[$],up=1),
// (11,2,[$],up=1), (14,2,[$],up=1)],hasSemanticContext=true,dipsIntoOuterContext
//
// to
//
// [(11,1,[$]), (14,1,[$]), (5,2,[$],up=1)],dipsIntoOuterContext
//
// This filters because {3>=prec}? evals to true and collapses
// (11,1,[$],{3>=prec}?) and (11,2,[$],up=1) since early conflict
// resolution based upon rules of operator precedence fits with
// our usual match first alt upon conflict.
//
// We noticed a problem where a recursive call resets precedence
// to 0. Sam's fix: each config has flag indicating if it has
// returned from an expr[0] call. then just don't filter any
// config with that flag set. flag is carried along in
// closure(). So to avoid adding field, set bit just under sign
// bit of dipsIntoOuterContext (SUPPRESS_PRECEDENCE_FILTER).
// With the change you filter "unless (p, 2, pi) was reached
// after leaving the rule stop state of the LR rule containing
// state p, corresponding to a rule invocation with precedence
// level 0"
/**
* This method transforms the start state computed by
* [computeStartState] to the special start state used by a
* precedence DFA for a particular precedence value.
*
* The transformation process applies the following changes to
* the start state's configuration set.
*
* 1. Evaluate the precedence predicates for each configuration using
* [SemanticContext.evalPrecedence].
* 2. When [ATNConfig.isPrecedenceFilterSuppressed] is `false`,
* remove all configurations which predict an alternative greater than `1`,
* for which another configuration that predicts alternative `1` is in the
* same ATN state with the same prediction context. This transformation is
* valid for the following reasons:
*
* * The closure block cannot contain any epsilon transitions which bypass
* the body of the closure, so all states reachable via alternative `1` are
* part of the precedence alternatives of the transformed left-recursive
* rule
* * The "primary" portion of a left recursive rule cannot contain an
* epsilon transition, so the only way an alternative other than `1` can exist
* in a state that is also reachable via alternative `1` is by nesting calls
* to the left-recursive rule, with the outer calls not being at the
* preferred precedence level.
* The [ATNConfig.isPrecedenceFilterSuppressed] property marks ATN
* configurations which do not meet this condition, and therefore are not
* eligible for elimination during the filtering process.
*
* The prediction context must be considered by this filter to address
* situations like the following.
*
* ```
* grammar TA;
* prog: statement* EOF;
* statement: letterA | statement letterA 'b' ;
* letterA: 'a';
* ```
*
* If the above grammar, the ATN state immediately before the token
* reference `'a'` in `letterA` is reachable from the left edge
* of both the primary and closure blocks of the left-recursive rule
* `statement`. The prediction context associated with each of these
* configurations distinguishes between them, and prevents the alternative
* which stepped out to `prog` (and then back in to `statement`
* from being eliminated by the filter).
*
* @param configs The configuration set computed by
* [computeStartState] as the start state for the DFA
* @return The transformed configuration set representing the start state
* for a precedence DFA at a particular precedence level (determined by
* calling [Parser.precedence])
*/
public open fun applyPrecedenceFilter(configs: ATNConfigSet): ATNConfigSet {
val statesFromAlt1 = HashMap()
val configSet = ATNConfigSet(configs.fullCtx)
for (config in configs) {
// Handle alt 1 first
if (config.alt != 1) {
continue
}
val updatedContext = config.semanticContext.evalPrecedence(parser!!, _outerContext!!)
?: continue // The configuration was eliminated
statesFromAlt1[config.state.stateNumber] = config.context!!
if (updatedContext !== config.semanticContext) {
configSet.add(ATNConfig(config, updatedContext), mergeCache)
} else {
configSet.add(config, mergeCache)
}
}
for (config in configs) {
if (config.alt == 1) {
// Already handled
continue
}
if (!config.isPrecedenceFilterSuppressed) {
// In the future, this elimination step could be updated to also
// filter the prediction context for alternatives predicting alt>1
// (basically a graph subtraction algorithm).
val context = statesFromAlt1[config.state.stateNumber]
if (context != null && context == config.context) {
// Eliminated
continue
}
}
configSet.add(config, mergeCache)
}
return configSet
}
protected open fun getReachableTarget(trans: Transition, ttype: Int): ATNState? =
if (trans.matches(ttype, 0, atn.maxTokenType)) {
trans.target
} else {
null
}
public open fun getPredsForAmbigAlts(
ambigAlts: BitSet,
configs: ATNConfigSet,
nAlts: Int,
): Array? {
// REACH=[1|1|[]|0:0, 1|2|[]|0:1]
//
// altToPred starts as an array of all null contexts. The entry at index i
// corresponds to alternative i. altToPred[i] may have one of three values:
// 1. null: no ATNConfig c is found such that c.alt==i
// 2. SemanticContext.NONE: At least one ATNConfig c exists such that
// c.alt==i and c.semanticContext==SemanticContext.NONE. In other words,
// alt i has at least one unpredicated config.
// 3. Non-NONE Semantic Context: There exists at least one, and for all
// ATNConfig c such that c.alt==i, c.semanticContext!=SemanticContext.NONE.
//
// From this, it is clear that NONE||anything==NONE.
val altToPred = arrayOfNulls(nAlts + 1)
for (c in configs) {
if (ambigAlts.get(c.alt)) {
altToPred[c.alt] = SemanticContext.or(altToPred[c.alt], c.semanticContext)
}
}
var nPredAlts = 0
for (i in 1..nAlts) {
if (altToPred[i] == null) {
altToPred[i] = SemanticContext.Empty.Instance
} else if (altToPred[i] !== SemanticContext.Empty.Instance) {
nPredAlts++
}
}
// non-ambig alts are null in altToPred
if (nPredAlts == 0) {
if (debug) {
System.out.println("getPredsForAmbigAlts result null")
}
return null
}
if (debug) {
System.out.println("getPredsForAmbigAlts result ${altToPred.joinToString()}")
}
return altToPred
}
protected open fun getPredicatePredictions(
ambigAlts: BitSet?,
altToPred: Array,
): Array? {
val pairs = ArrayList()
var containsPredicate = false
for (i in 1.. 0) {
alt = getAltThatFinishedDecisionEntryRule(semInvalidConfigs)
if (alt != ATN.INVALID_ALT_NUMBER) {
// Syntactically viable path exists
return alt
}
}
return ATN.INVALID_ALT_NUMBER
}
protected open fun getAltThatFinishedDecisionEntryRule(configs: ATNConfigSet): Int {
val alts = IntervalSet()
for (c in configs) {
if (c.outerContextDepth > 0 || c.state is RuleStopState && c.context!!.hasEmptyPath()) {
alts.add(c.alt)
}
}
if (alts.size() == 0) {
return ATN.INVALID_ALT_NUMBER
}
return alts.minElement
}
/**
* Walk the list of configurations and split them according to
* those that have preds evaluating to true/false.
*
* If no pred, assume true pred and include in succeeded set.
* Returns a pair of sets.
*
* Create a new set so as not to alter the incoming parameter.
*
* Assumption: the input stream has been restored to the starting point
* prediction, which is where predicates need to evaluate.
*/
protected fun splitAccordingToSemanticValidity(
configs: ATNConfigSet,
outerContext: ParserRuleContext,
): Pair {
val succeeded = ATNConfigSet(configs.fullCtx)
val failed = ATNConfigSet(configs.fullCtx)
for (c in configs) {
if (c.semanticContext !== SemanticContext.Empty.Instance) {
val predicateEvaluationResult = evalSemanticContext(c.semanticContext, outerContext, c.alt, configs.fullCtx)
if (predicateEvaluationResult) {
succeeded.add(c)
} else {
failed.add(c)
}
} else {
succeeded.add(c)
}
}
return Pair(succeeded, failed)
}
/**
* Look through a list of predicate/alt pairs, returning alts for the
* pairs that win.
*
* A `NONE` predicate indicates an alt containing an
* unpredicated config which behaves as "always true".
*
* If [complete] is `false`, we stop at the first predicate that evaluates to `true`.
* This includes pairs with `null` predicates.
*/
public open fun evalSemanticContext(
predPredictions: Array,
outerContext: ParserRuleContext,
complete: Boolean,
): BitSet {
val predictions = BitSet()
for (pair in predPredictions) {
if (pair.pred === SemanticContext.Empty.Instance) {
predictions.set(pair.alt)
if (!complete) {
break
}
continue
}
val fullCtx = false // In dfa
val predicateEvaluationResult = evalSemanticContext(pair.pred, outerContext, pair.alt, fullCtx)
if (debug || dfa_debug) {
System.out.println("eval pred $pair=$predicateEvaluationResult")
}
if (predicateEvaluationResult) {
if (debug || dfa_debug) {
System.out.println("PREDICT ${pair.alt}")
}
predictions.set(pair.alt)
if (!complete) {
break
}
}
}
return predictions
}
/**
* Evaluate a semantic context within a specific parser context.
*
* This method might not be called for every semantic context evaluated
* during the prediction process. In particular, we currently do not
* evaluate the following, but it may change in the future:
*
* * Precedence predicates (represented by [SemanticContext.PrecedencePredicate])
* are not currently evaluated through this method
* * Operator predicates (represented by [SemanticContext.AND] and
* [SemanticContext.OR]) are evaluated as a single semantic
* context, rather than evaluating the operands individually.
* Implementations which require evaluation results from individual
* predicates should override this method to explicitly handle evaluation of
* the operands within operator predicates.
*
* @param pred The semantic context to evaluate
* @param parserCallStack The parser context in which to evaluate the
* semantic context
* @param alt The alternative which is guarded by [pred]
* @param fullCtx `true` if the evaluation is occurring during LL
* prediction, otherwise `false` if the evaluation is occurring
* during SLL prediction
*
* @since 4.3
*/
protected open fun evalSemanticContext(
pred: SemanticContext,
parserCallStack: ParserRuleContext?,
alt: Int,
fullCtx: Boolean,
): Boolean =
pred.eval(parser!!, parserCallStack!!)
// TODO: If we are doing predicates, there is no point in pursuing
// closure operations if we reach a DFA state that uniquely predicts
// alternative. We will not be caching that DFA state and it is a
// waste to pursue the closure. Might have to advance when we do
// ambig detection thought :(
protected open fun closure(
config: ATNConfig,
configs: ATNConfigSet,
closureBusy: MutableSet,
collectPredicates: Boolean,
fullCtx: Boolean,
treatEofAsEpsilon: Boolean,
) {
val initialDepth = 0
closureCheckingStopState(
config = config,
configs = configs,
closureBusy = closureBusy,
collectPredicates = collectPredicates,
fullCtx = fullCtx,
depth = initialDepth,
treatEofAsEpsilon = treatEofAsEpsilon,
)
assert(!fullCtx || !configs.dipsIntoOuterContext)
}
protected open fun closureCheckingStopState(
config: ATNConfig,
configs: ATNConfigSet,
closureBusy: MutableSet,
collectPredicates: Boolean,
fullCtx: Boolean,
depth: Int,
treatEofAsEpsilon: Boolean,
) {
if (trace_atn_sim) {
System.out.println("closure(${config.toString(parser, true)})")
}
if (config.state is RuleStopState) {
// We hit rule end. If we have context info, use it
// run through all possible stack tops in ctx
if (!config.context!!.isEmpty) {
for (i in 0.. Int.MIN_VALUE)
closureCheckingStopState(
config = c,
configs = configs,
closureBusy = closureBusy,
collectPredicates = collectPredicates,
fullCtx = fullCtx,
depth = depth - 1,
treatEofAsEpsilon = treatEofAsEpsilon,
)
}
return
} else if (fullCtx) {
// Reached end of start rule
configs.add(config, mergeCache)
return
} else {
// Else if we have no context info, just chase follow links (if greedy)
if (debug) {
System.out.println("FALLING off rule ${getRuleName(config.state.ruleIndex)}")
}
}
}
closure_(
config = config,
configs = configs,
closureBusy = closureBusy,
collectPredicates = collectPredicates,
fullCtx = fullCtx,
depth = depth,
treatEofAsEpsilon = treatEofAsEpsilon,
)
}
/**
* Do the actual work of walking epsilon edges.
*/
@Suppress("FunctionName")
protected open fun closure_(
config: ATNConfig,
configs: ATNConfigSet,
closureBusy: MutableSet,
collectPredicates: Boolean,
fullCtx: Boolean,
depth: Int,
treatEofAsEpsilon: Boolean,
) {
val p = config.state
// Optimization
if (!p.onlyHasEpsilonTransitions()) {
configs.add(config, mergeCache)
// Make sure to not return here, because EOF transitions can act as
// both epsilon transitions and non-epsilon transitions.
}
for (i in 0.. 0.
if (_dfa != null && _dfa!!.isPrecedenceDfa) {
val outermostPrecedenceReturn = (t as EpsilonTransition).outermostPrecedenceReturn
if (outermostPrecedenceReturn == _dfa!!.atnStartState.ruleIndex) {
c.isPrecedenceFilterSuppressed = true
}
}
c.reachesIntoOuterContext++
if (!closureBusy.add(c)) {
// Avoid infinite recursion for right-recursive rules
continue
}
// TODO: can remove? only care when we add to set per middle of this method
configs.dipsIntoOuterContext = true
assert(newDepth > Int.MIN_VALUE)
newDepth--
if (debug) {
System.out.println("dips into outer ctx: $c")
}
} else {
if (!t.isEpsilon && !closureBusy.add(c)) {
// Avoid infinite recursion for EOF* and EOF+
continue
}
if (t is RuleTransition) {
// Latch when newDepth goes negative - once we step out of the entry context we can't return
if (newDepth >= 0) {
newDepth++
}
}
}
closureCheckingStopState(
config = c,
configs = configs,
closureBusy = closureBusy,
collectPredicates = continueCollecting,
fullCtx = fullCtx,
depth = newDepth,
treatEofAsEpsilon = treatEofAsEpsilon,
)
}
}
}
/**
* Implements first-edge (loop entry) elimination as an optimization
* during closure operations.
*
* See [antlr4#1398](https://github.com/antlr/antlr4/issues/1398).
*
* The optimization is to avoid adding the loop entry config when
* the exit path can only lead back to the same
* [StarLoopEntryState] after popping context at the rule end state
* (traversing only epsilon edges, so we're still in closure, in
* this same rule).
*
* We need to detect any state that can reach loop entry on
* epsilon w/o exiting rule. We don't have to look at `FOLLOW`
* links, just ensure that all stack tops for config refer to key
* states in `LR` rule.
*
* To verify we are in the right situation we must first check
* closure is at a [StarLoopEntryState] generated during `LR` removal.
* Then we check that each stack top of context is a return state
* from one of these cases:
*
* 1. 'not' expr, '(' type ')' expr. The return state points at loop entry state
* 2. expr op expr. The return state is the block end of internal block of `(...)*`
* 3. 'between' expr 'and' expr. The return state of 2nd expr reference.
* That state points at block end of internal block of (...)*
* 4. expr '?' expr ':' expr. The return state points at block end,
* which points at loop entry state
*
* If any is true for each stack top, then [closure] does not add a
* config to the current config set for `edge[0]`, the loop entry branch.
*
* Conditions fail if any context for the current config is:
*
* - empty (we'd fall out of expr to do a global `FOLLOW` which could
* even be to some weird spot in expr) or,
* - lies outside expr or,
* - lies within expr but at a state not the [BlockEndState]
* generated during LR removal
*
* Do we need to evaluate predicates ever in closure for this case?
*
* No. Predicates, including precedence predicates, are only
* evaluated when computing a DFA start state. I.e., only before
* the lookahead (but not parser) consumes a token.
*
* There are no epsilon edges allowed in `LR` rule alt blocks or in
* the "primary" part (`ID` here). If closure is in
* [StarLoopEntryState] any lookahead operation will have consumed a
* token as there are no epsilon-paths that lead to
* [StarLoopEntryState]. We do not have to evaluate predicates
* therefore if we are in the generated [StarLoopEntryState] of an `LR`
* rule. Note that when making a prediction starting at that
* decision point, decision `d=2`, compute-start-state performs
* closure starting at `edges[0]`, `edges[1]` emanating from
* [StarLoopEntryState]. That means it is not performing closure on
* [StarLoopEntryState] during compute-start-state.
*
* How do we know this always gives same prediction answer?
*
* Without predicates, loop entry and exit paths are ambiguous
* upon remaining input `+b` (in, say, `a+b`). Either paths lead to
* valid parses. Closure can lead to consuming `+` immediately or by
* falling out of this call to expr back into expr and loop back
* again to [StarLoopEntryState] to match `+b`. In this special case,
* we choose the more efficient path, which is to take the bypass
* path.
*
* The lookahead language has not changed because closure chooses
* one path over the other. Both paths lead to consuming the same
* remaining input during a lookahead operation. If the next token
* is an operator, lookahead will enter the choice block with
* operators. If it is not, lookahead will exit expr. Same as if
* closure had chosen to enter the choice block immediately.
*
* Closure is examining one config (some loopentrystate, some alt,
* context) which means it is considering exactly one alt. Closure
* always copies the same alt to any derived configs.
*
* How do we know this optimization doesn't mess up precedence in
* our parse trees?
*
* Looking through expr from left edge of stat only has to confirm
* that an input, say, `a+b+c`, begins with any valid interpretation
* of an expression. The precedence actually doesn't matter when
* making a decision in stat seeing through expr. It is only when
* parsing rule expr that we must use the precedence to get the
* right interpretation and, hence, parse tree.
*
* @since 4.6
*/
protected open fun canDropLoopEntryEdgeInLeftRecursiveRule(config: ATNConfig): Boolean {
if (TURN_OFF_LR_LOOP_ENTRY_BRANCH_OPT) {
return false
}
val p = config.state
// First check to see if we are in StarLoopEntryState generated during
// left-recursion elimination. For efficiency, also check if
// the context has an empty stack case. If so, it would mean
// global FOLLOW, so we can't perform optimization
if (
p.stateType != ATNState.STAR_LOOP_ENTRY ||
!(p as StarLoopEntryState).isPrecedenceDecision || // Are we the special loop entry/exit state?
config.context!!.isEmpty || // If SLL wildcard
config.context!!.hasEmptyPath()
) {
return false
}
// Require all return states to return back to the same rule
// that p is in.
val numCtxs = config.context!!.size()
// For each stack context
for (i in 0..= 0) {
return parser.ruleNames[index]
}
return ""
}
protected open fun getEpsilonTarget(
config: ATNConfig,
t: Transition,
collectPredicates: Boolean,
inContext: Boolean,
fullCtx: Boolean,
treatEofAsEpsilon: Boolean,
): ATNConfig? {
when (t.serializationType) {
Transition.RULE -> {
return ruleTransition(config, t as RuleTransition)
}
Transition.PRECEDENCE -> {
return precedenceTransition(
config,
t as PrecedencePredicateTransition,
collectPredicates,
inContext,
fullCtx,
)
}
Transition.PREDICATE -> {
return predTransition(
config, t as PredicateTransition,
collectPredicates,
inContext,
fullCtx,
)
}
Transition.ACTION -> {
return actionTransition(config, t as ActionTransition)
}
Transition.EPSILON -> {
return ATNConfig(config, t.target)
}
Transition.ATOM,
Transition.RANGE,
Transition.SET -> {
// EOF transitions act like epsilon transitions after the first EOF
// transition is traversed
if (treatEofAsEpsilon) {
if (t.matches(Token.EOF, 0, 1)) {
return ATNConfig(config, t.target)
}
}
return null
}
else -> return null
}
}
protected open fun actionTransition(config: ATNConfig, t: ActionTransition): ATNConfig {
if (debug) {
System.out.println("ACTION edge ${t.ruleIndex}:${t.actionIndex}")
}
return ATNConfig(config, t.target)
}
public open fun precedenceTransition(
config: ATNConfig,
pt: PrecedencePredicateTransition,
collectPredicates: Boolean,
inContext: Boolean,
fullCtx: Boolean,
): ATNConfig? {
if (debug) {
System.out.println("PRED (collectPredicates=$collectPredicates) ${pt.precedence}>=_p, ctx dependent=true")
if (parser != null) {
System.out.println("context surrounding pred is ${parser.getRuleInvocationStack()}")
}
}
var c: ATNConfig? = null
if (collectPredicates && inContext) {
if (fullCtx) {
// In full context mode, we can evaluate predicates on-the-fly
// during closure, which dramatically reduces the size of
// the config sets. It also obviates the need to test predicates
// later during conflict resolution.
val currentPosition = _input!!.index()
_input!!.seek(_startIndex)
val predSucceeds = evalSemanticContext(pt.predicate, _outerContext, config.alt, fullCtx)
_input!!.seek(currentPosition)
if (predSucceeds) {
// No pred context
c = ATNConfig(config, pt.target)
}
} else {
val newSemCtx = SemanticContext.and(config.semanticContext, pt.predicate)
c = ATNConfig(config, pt.target, newSemCtx!!)
}
} else {
c = ATNConfig(config, pt.target)
}
if (debug) {
System.out.println("config from pred transition=${c}")
}
return c
}
protected open fun predTransition(
config: ATNConfig,
pt: PredicateTransition,
collectPredicates: Boolean,
inContext: Boolean,
fullCtx: Boolean,
): ATNConfig? {
if (debug) {
System.out.println(
"PRED (collectPredicates=$collectPredicates)" +
" ${pt.ruleIndex}:${pt.predIndex}" +
", ctx dependent=${pt.isCtxDependent}"
)
if (parser != null) {
System.out.println("context surrounding pred is ${parser.getRuleInvocationStack()}")
}
}
var c: ATNConfig? = null
if (collectPredicates && (!pt.isCtxDependent || pt.isCtxDependent && inContext)) {
if (fullCtx) {
// In full context mode, we can evaluate predicates on-the-fly
// during closure, which dramatically reduces the size of
// the config sets. It also obviates the need to test predicates
// later during conflict resolution.
val currentPosition = _input!!.index()
_input!!.seek(_startIndex)
val predSucceeds = evalSemanticContext(pt.predicate, _outerContext, config.alt, fullCtx)
_input!!.seek(currentPosition)
if (predSucceeds) {
// No pred context
c = ATNConfig(config, pt.target)
}
} else {
val newSemCtx = SemanticContext.and(config.semanticContext, pt.predicate)
c = ATNConfig(config, pt.target, newSemCtx!!)
}
} else {
c = ATNConfig(config, pt.target)
}
if (debug) {
System.out.println("config from pred transition=${c}")
}
return c
}
protected open fun ruleTransition(config: ATNConfig, t: RuleTransition): ATNConfig {
if (debug) {
System.out.println("CALL rule ${getRuleName(t.target.ruleIndex)}, ctx=${config.context}")
}
val returnState = t.followState
val newContext = SingletonPredictionContext.create(config.context, returnState.stateNumber)
return ATNConfig(config, t.target, newContext)
}
/**
* Gets a [BitSet] containing the alternatives in [configs]
* which are part of one or more conflicting alternative subsets.
*
* @param configs The [ATNConfigSet] to analyze
* @return The alternatives in [configs] which are part of one or more
* conflicting alternative subsets. If [configs] does not contain any
* conflicting subsets, this method returns an empty [BitSet]
*/
protected open fun getConflictingAlts(configs: ATNConfigSet): BitSet {
val altSets = PredictionMode.getConflictingAltSubsets(configs)
return PredictionMode.getAlts(altSets)
}
/**
* Sam pointed out a problem with the previous definition, v3, of
* ambiguous states. If we have another state associated with conflicting
* alternatives, we should keep going. For example, the following grammar:
*
* ```
* s : (ID | ID ID?) ';' ;
* ```
*
* When the ATN simulation reaches the state before `';'`, it has a DFA
* state that looks like: `[12|1|[], 6|2|[], 12|2|[]]`.
*
* Naturally `12|1|[]` and `12|2|[]` conflict, but we cannot stop processing
* this node because alternative to has another way to continue, via `[6|2|[]]`.
*
* The key is that we have a single state that has config's only associated
* with a single alternative, `2`, and crucially the state transitions
* among the configurations are all non-epsilon transitions. That means
* we don't consider any conflicts that include alternative `2`. So, we
* ignore the conflict between alts `1` and `2`. We ignore a set of
* conflicting alts when there is an intersection with an alternative
* associated with a single alt state in the state-config-list map.
*
* It's also the case that we might have two conflicting configurations but
* also a 3rd non-conflicting configuration for a different alternative:
* `[1|1|[], 1|2|[], 8|3|[]]`. This can come about from grammar:
*
* ```
* a : A | A | A B ;
* ```
*
* After matching input `A`, we reach the stop state for rule `A`, state `1`.
* State `8` is the state right before `B`. Clearly alternatives `1` and `2`
* conflict and no amount of further lookahead will separate the two.
* However, alternative `3` will be able to continue, and so we do not
* stop working on this state. In the previous example, we're concerned
* with states associated with the conflicting alternatives. Here alt
* `3` is not associated with the conflicting configs, but since we can continue
* looking for input reasonably, I don't declare the state done. We
* ignore a set of conflicting alts when we have an alternative
* that we still need to pursue.
*/
protected open fun getConflictingAltsOrUniqueAlt(configs: ATNConfigSet): BitSet {
val conflictingAlts: BitSet
if (configs.uniqueAlt != ATN.INVALID_ALT_NUMBER) {
conflictingAlts = BitSet()
conflictingAlts.set(configs.uniqueAlt)
} else {
conflictingAlts = configs.conflictingAlts!!
}
return conflictingAlts
}
public open fun getTokenName(t: Int): String {
if (t == Token.EOF) {
return "EOF"
}
val vocabulary = parser?.vocabulary ?: VocabularyImpl.EMPTY_VOCABULARY
val displayName = vocabulary.getDisplayName(t)
if (displayName == t.toString()) {
return displayName
}
return "$displayName<$t>"
}
public open fun getLookaheadName(input: TokenStream): String =
getTokenName(input.LA(1))
/**
* Used for debugging in [adaptivePredict] around [execATN] but I cut
* it out for clarity now that alg. works well. We can leave this
* "dead" code for a bit.
*/
public open fun dumpDeadEndConfigs(ex: NoViableAltException) {
System.err.println("dead end configs: ")
for (c in ex.deadEndConfigs!!) {
var trans = "no edges"
if (c.state.numberOfTransitions > 0) {
val t = c.state.transition(0)
if (t is AtomTransition) {
trans = "Atom ${getTokenName(t.label)}"
} else if (t is SetTransition) {
val not = t is NotSetTransition
trans = "${if (not) "~" else ""}Set ${t.set}"
}
}
System.err.println("${c.toString(parser, true)}:$trans")
}
}
protected open fun noViableAlt(
input: TokenStream,
outerContext: ParserRuleContext,
configs: ATNConfigSet,
startIndex: Int,
): NoViableAltException =
NoViableAltException(
recognizer = parser!!,
input = input,
startToken = input[startIndex],
offendingToken = input.LT(1),
deadEndConfigs = configs,
ctx = outerContext,
)
/**
* Add an edge to the DFA, if possible.
*
* This method calls [addDFAState] to ensure the [to] state is present
* in the DFA. If [from] is `null`, or if [t] is outside the
* range of edges that can be represented in the DFA tables, this method
* returns without adding the edge to the DFA.
*
* If [to] is `null`, this method returns `null`.
* Otherwise, this method returns the [DFAState] returned by
* calling [addDFAState] for the [to] state.
*
* @param dfa The DFA
* @param from The source state for the edge
* @param t The input symbol
* @param to The target state for the edge
* @return If [to] is `null` this method returns `null`,
* otherwise this method returns the result of calling
* [addDFAState] on [to]
*/
protected fun addDFAEdge(dfa: DFA, from: DFAState?, t: Int, to: DFAState?): DFAState? {
if (debug) {
System.out.println("EDGE $from -> $to upon ${getTokenName(t)}")
}
if (to == null) {
return null
}
// Used existing if possible not incoming
val tto = addDFAState(dfa, to)
if (from == null || t < -1 || t > atn.maxTokenType) {
return tto
}
synchronized(from) {
if (from.edges == null) {
from.edges = arrayOfNulls(atn.maxTokenType + 1 + 1)
}
// Connect
from.edges!![t + 1] = tto
}
if (debug) {
System.out.println("DFA=\n${dfa.toString(parser?.vocabulary ?: VocabularyImpl.EMPTY_VOCABULARY)}")
}
return tto
}
/**
* Add state [D] to the DFA if it is not already present, and return
* the actual instance stored in the DFA.
*
* If a state equivalent to [D] is already in the DFA,
* the existing state is returned. Otherwise, this
* method returns [D] after adding it to the DFA.
*
* If [D] is [ATNSimulator.ERROR], this method returns [ATNSimulator.ERROR]
* and does not change the DFA.
*
* @param dfa The DFA
* @param D The DFA state to add
* @return The state stored in the DFA. This will be either the existing
* state if [D] is already in the DFA, or [D] itself if the
* state was not already present
*/
@Suppress("LocalVariableName")
protected open fun addDFAState(dfa: DFA, D: DFAState): DFAState {
if (D === ERROR) {
return D
}
synchronized(dfa.states) {
val existing = dfa.states[D]
if (existing != null) {
if (trace_atn_sim) {
System.out.println("addDFAState $D exists")
}
return existing
}
D.stateNumber = dfa.states.size
if (!D.configs.isReadonly) {
D.configs.optimizeConfigs(this)
D.configs.isReadonly = true
}
if (trace_atn_sim) {
System.out.println("addDFAState new $D")
}
dfa.states[D] = D
return D
}
}
protected open fun reportAttemptingFullContext(
dfa: DFA,
conflictingAlts: BitSet,
configs: ATNConfigSet,
startIndex: Int,
stopIndex: Int,
) {
if (debug || retry_debug) {
val interval = Interval.of(startIndex, stopIndex)
System.out.println(
"reportAttemptingFullContext" +
" decision=${dfa.decision}:$configs" +
", input=${parser?.tokenStream?.getText(interval)}"
)
}
parser?.errorListenerDispatch?.reportAttemptingFullContext(
recognizer = parser,
dfa = dfa,
startIndex = startIndex,
stopIndex = stopIndex,
conflictingAlts = conflictingAlts,
configs = configs,
)
}
protected open fun reportContextSensitivity(
dfa: DFA,
prediction: Int,
configs: ATNConfigSet,
startIndex: Int,
stopIndex: Int,
) {
if (debug || retry_debug) {
val interval = Interval.of(startIndex, stopIndex)
System.out.println(
"reportContextSensitivity" +
" decision=${dfa.decision}:$configs" +
", input=${parser?.tokenStream?.getText(interval)}"
)
}
parser?.errorListenerDispatch?.reportContextSensitivity(
recognizer = parser,
dfa = dfa,
startIndex = startIndex,
stopIndex = stopIndex,
prediction = prediction,
configs = configs,
)
}
/**
* If context-sensitive parsing, we know it's ambiguity not conflict.
*/
@Suppress("LocalVariableName")
protected open fun reportAmbiguity(
dfa: DFA,
D: DFAState, // The DFA state from execATN() that had SLL conflicts
startIndex: Int, stopIndex: Int,
exact: Boolean,
ambigAlts: BitSet,
configs: ATNConfigSet, // Configs that LL not SLL considered conflicting
) {
if (debug || retry_debug) {
val interval = Interval.of(startIndex, stopIndex)
System.out.println("reportAmbiguity $ambigAlts:$configs, input=${parser?.tokenStream?.getText(interval)}")
}
parser?.errorListenerDispatch?.reportAmbiguity(
recognizer = parser,
dfa = dfa,
startIndex = startIndex,
stopIndex = stopIndex,
exact = exact,
ambigAlts = ambigAlts,
configs = configs,
)
}
}
