ll1_analyzer.go

// Copyright (c) 2012-2022 The ANTLR Project. All rights reserved.
// Use of this file is governed by the BSD 3-clause license that
// can be found in the LICENSE.txt file in the project root.

package antlr

type LL1Analyzer struct {
	atn *ATN
}

func NewLL1Analyzer(atn *ATN) *LL1Analyzer {
	la := new(LL1Analyzer)
	la.atn = atn
	return la
}

const (
	// LL1AnalyzerHitPred is a special value added to the lookahead sets to indicate that we hit
	// a predicate during analysis if
	//
	//   seeThruPreds==false
	LL1AnalyzerHitPred = TokenInvalidType
)

// *
// Calculates the SLL(1) expected lookahead set for each outgoing transition
// of an {@link ATNState}. The returned array has one element for each
// outgoing transition in {@code s}. If the closure from transition
// <em>i</em> leads to a semantic predicate before Matching a symbol, the
// element at index <em>i</em> of the result will be {@code nil}.
//
// @param s the ATN state
// @return the expected symbols for each outgoing transition of {@code s}.
func (la *LL1Analyzer) getDecisionLookahead(s ATNState) []*IntervalSet {
	if s == nil {
		return nil
	}
	count := len(s.GetTransitions())
	look := make([]*IntervalSet, count)
	for alt := 0; alt < count; alt++ {

		look[alt] = NewIntervalSet()
		// TODO: This is one of the reasons that ATNConfigs are allocated and freed all the time - fix this tomorrow jim!
		lookBusy := NewJStore[*ATNConfig, Comparator[*ATNConfig]](aConfEqInst, ClosureBusyCollection, "LL1Analyzer.getDecisionLookahead for lookBusy")
		la.look1(s.GetTransitions()[alt].getTarget(), nil, BasePredictionContextEMPTY, look[alt], lookBusy, NewBitSet(), false, false)

		// Wipe out lookahead for la alternative if we found nothing,
		// or we had a predicate when we !seeThruPreds
		if look[alt].length() == 0 || look[alt].contains(LL1AnalyzerHitPred) {
			look[alt] = nil
		}
	}
	return look
}

// Look computes the set of tokens that can follow s in the [ATN] in the
// specified ctx.
//
// If ctx is nil and the end of the rule containing
// s is reached, [EPSILON] is added to the result set.
//
// If ctx is not nil and the end of the outermost rule is
// reached, [EOF] is added to the result set.
//
// Parameter s the ATN state, and stopState is the ATN state to stop at. This can be a
// [BlockEndState] to detect epsilon paths through a closure.
//
// Parameter ctx is the complete parser context, or nil if the context
// should be ignored
//
// The func returns the set of tokens that can follow s in the [ATN] in the
// specified ctx.
func (la *LL1Analyzer) Look(s, stopState ATNState, ctx RuleContext) *IntervalSet {
	r := NewIntervalSet()
	var lookContext *PredictionContext
	if ctx != nil {
		lookContext = predictionContextFromRuleContext(s.GetATN(), ctx)
	}
	la.look1(s, stopState, lookContext, r, NewJStore[*ATNConfig, Comparator[*ATNConfig]](aConfEqInst, ClosureBusyCollection, "LL1Analyzer.Look for la.look1()"),
		NewBitSet(), true, true)
	return r
}

//*
// Compute set of tokens that can follow {@code s} in the ATN in the
// specified {@code ctx}.
//
// <p>If {@code ctx} is {@code nil} and {@code stopState} or the end of the
// rule containing {@code s} is reached, {@link Token//EPSILON} is added to
// the result set. If {@code ctx} is not {@code nil} and {@code addEOF} is
// {@code true} and {@code stopState} or the end of the outermost rule is
// reached, {@link Token//EOF} is added to the result set.</p>
//
// @param s the ATN state.
// @param stopState the ATN state to stop at. This can be a
// {@link BlockEndState} to detect epsilon paths through a closure.
// @param ctx The outer context, or {@code nil} if the outer context should
// not be used.
// @param look The result lookahead set.
// @param lookBusy A set used for preventing epsilon closures in the ATN
// from causing a stack overflow. Outside code should pass
// {@code NewSet<ATNConfig>} for la argument.
// @param calledRuleStack A set used for preventing left recursion in the
// ATN from causing a stack overflow. Outside code should pass
// {@code NewBitSet()} for la argument.
// @param seeThruPreds {@code true} to true semantic predicates as
// implicitly {@code true} and "see through them", otherwise {@code false}
// to treat semantic predicates as opaque and add {@link //HitPred} to the
// result if one is encountered.
// @param addEOF Add {@link Token//EOF} to the result if the end of the
// outermost context is reached. This parameter has no effect if {@code ctx}
// is {@code nil}.

func (la *LL1Analyzer) look2(_, stopState ATNState, ctx *PredictionContext, look *IntervalSet, lookBusy *JStore[*ATNConfig, Comparator[*ATNConfig]],
	calledRuleStack *BitSet, seeThruPreds, addEOF bool, i int) {

	returnState := la.atn.states[ctx.getReturnState(i)]
	la.look1(returnState, stopState, ctx.GetParent(i), look, lookBusy, calledRuleStack, seeThruPreds, addEOF)

}

func (la *LL1Analyzer) look1(s, stopState ATNState, ctx *PredictionContext, look *IntervalSet, lookBusy *JStore[*ATNConfig, Comparator[*ATNConfig]], calledRuleStack *BitSet, seeThruPreds, addEOF bool) {

	c := NewATNConfig6(s, 0, ctx)

	if lookBusy.Contains(c) {
		return
	}

	_, present := lookBusy.Put(c)
	if present {
		return

	}
	if s == stopState {
		if ctx == nil {
			look.addOne(TokenEpsilon)
			return
		} else if ctx.isEmpty() && addEOF {
			look.addOne(TokenEOF)
			return
		}
	}

	_, ok := s.(*RuleStopState)

	if ok {
		if ctx == nil {
			look.addOne(TokenEpsilon)
			return
		} else if ctx.isEmpty() && addEOF {
			look.addOne(TokenEOF)
			return
		}

		if ctx.pcType != PredictionContextEmpty {
			removed := calledRuleStack.contains(s.GetRuleIndex())
			defer func() {
				if removed {
					calledRuleStack.add(s.GetRuleIndex())
				}
			}()
			calledRuleStack.remove(s.GetRuleIndex())
			// run thru all possible stack tops in ctx
			for i := 0; i < ctx.length(); i++ {
				returnState := la.atn.states[ctx.getReturnState(i)]
				la.look2(returnState, stopState, ctx, look, lookBusy, calledRuleStack, seeThruPreds, addEOF, i)
			}
			return
		}
	}

	n := len(s.GetTransitions())

	for i := 0; i < n; i++ {
		t := s.GetTransitions()[i]

		if t1, ok := t.(*RuleTransition); ok {
			if calledRuleStack.contains(t1.getTarget().GetRuleIndex()) {
				continue
			}

			newContext := SingletonBasePredictionContextCreate(ctx, t1.followState.GetStateNumber())
			la.look3(stopState, newContext, look, lookBusy, calledRuleStack, seeThruPreds, addEOF, t1)
		} else if t2, ok := t.(AbstractPredicateTransition); ok {
			if seeThruPreds {
				la.look1(t2.getTarget(), stopState, ctx, look, lookBusy, calledRuleStack, seeThruPreds, addEOF)
			} else {
				look.addOne(LL1AnalyzerHitPred)
			}
		} else if t.getIsEpsilon() {
			la.look1(t.getTarget(), stopState, ctx, look, lookBusy, calledRuleStack, seeThruPreds, addEOF)
		} else if _, ok := t.(*WildcardTransition); ok {
			look.addRange(TokenMinUserTokenType, la.atn.maxTokenType)
		} else {
			set := t.getLabel()
			if set != nil {
				if _, ok := t.(*NotSetTransition); ok {
					set = set.complement(TokenMinUserTokenType, la.atn.maxTokenType)
				}
				look.addSet(set)
			}
		}
	}
}

func (la *LL1Analyzer) look3(stopState ATNState, ctx *PredictionContext, look *IntervalSet, lookBusy *JStore[*ATNConfig, Comparator[*ATNConfig]],
	calledRuleStack *BitSet, seeThruPreds, addEOF bool, t1 *RuleTransition) {

	newContext := SingletonBasePredictionContextCreate(ctx, t1.followState.GetStateNumber())

	defer func() {
		calledRuleStack.remove(t1.getTarget().GetRuleIndex())
	}()

	calledRuleStack.add(t1.getTarget().GetRuleIndex())
	la.look1(t1.getTarget(), stopState, newContext, look, lookBusy, calledRuleStack, seeThruPreds, addEOF)

}