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diff --git a/deps/v8/third_party/antlr4/runtime/Cpp/runtime/src/atn/PredictionMode.h b/deps/v8/third_party/antlr4/runtime/Cpp/runtime/src/atn/PredictionMode.h new file mode 100644 index 0000000000..042e4b19a0 --- /dev/null +++ b/deps/v8/third_party/antlr4/runtime/Cpp/runtime/src/atn/PredictionMode.h @@ -0,0 +1,442 @@ +/* Copyright (c) 2012-2017 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. + */ + +#pragma once + +#include "support/BitSet.h" + +namespace antlr4 { +namespace atn { + +/** + * This enumeration defines the prediction modes available in ANTLR 4 along with + * utility methods for analyzing configuration sets for conflicts and/or + * ambiguities. + */ +enum class PredictionMode { + /** + * The SLL(*) prediction mode. This prediction mode ignores the current + * parser context when making predictions. This is the fastest prediction + * mode, and provides correct results for many grammars. This prediction + * mode is more powerful than the prediction mode provided by ANTLR 3, but + * may result in syntax errors for grammar and input combinations which are + * not SLL. + * + * <p> + * When using this prediction mode, the parser will either return a correct + * parse tree (i.e. the same parse tree that would be returned with the + * {@link #LL} prediction mode), or it will report a syntax error. If a + * syntax error is encountered when using the {@link #SLL} prediction mode, + * it may be due to either an actual syntax error in the input or indicate + * that the particular combination of grammar and input requires the more + * powerful {@link #LL} prediction abilities to complete successfully.</p> + * + * <p> + * This prediction mode does not provide any guarantees for prediction + * behavior for syntactically-incorrect inputs.</p> + */ + SLL, + + /** + * The LL(*) prediction mode. This prediction mode allows the current parser + * context to be used for resolving SLL conflicts that occur during + * prediction. This is the fastest prediction mode that guarantees correct + * parse results for all combinations of grammars with syntactically correct + * inputs. + * + * <p> + * When using this prediction mode, the parser will make correct decisions + * for all syntactically-correct grammar and input combinations. However, in + * cases where the grammar is truly ambiguous this prediction mode might not + * report a precise answer for <em>exactly which</em> alternatives are + * ambiguous.</p> + * + * <p> + * This prediction mode does not provide any guarantees for prediction + * behavior for syntactically-incorrect inputs.</p> + */ + LL, + + /** + * The LL(*) prediction mode with exact ambiguity detection. In addition to + * the correctness guarantees provided by the {@link #LL} prediction mode, + * this prediction mode instructs the prediction algorithm to determine the + * complete and exact set of ambiguous alternatives for every ambiguous + * decision encountered while parsing. + * + * <p> + * This prediction mode may be used for diagnosing ambiguities during + * grammar development. Due to the performance overhead of calculating sets + * of ambiguous alternatives, this prediction mode should be avoided when + * the exact results are not necessary.</p> + * + * <p> + * This prediction mode does not provide any guarantees for prediction + * behavior for syntactically-incorrect inputs.</p> + */ + LL_EXACT_AMBIG_DETECTION +}; + +class ANTLR4CPP_PUBLIC PredictionModeClass { + public: + /** + * Computes the SLL prediction termination condition. + * + * <p> + * This method computes the SLL prediction termination condition for both of + * the following cases.</p> + * + * <ul> + * <li>The usual SLL+LL fallback upon SLL conflict</li> + * <li>Pure SLL without LL fallback</li> + * </ul> + * + * <p><strong>COMBINED SLL+LL PARSING</strong></p> + * + * <p>When LL-fallback is enabled upon SLL conflict, correct predictions are + * ensured regardless of how the termination condition is computed by this + * method. Due to the substantially higher cost of LL prediction, the + * prediction should only fall back to LL when the additional lookahead + * cannot lead to a unique SLL prediction.</p> + * + * <p>Assuming combined SLL+LL parsing, an SLL configuration set with only + * conflicting subsets should fall back to full LL, even if the + * configuration sets don't resolve to the same alternative (e.g. + * {@code {1,2}} and {@code {3,4}}. If there is at least one non-conflicting + * configuration, SLL could continue with the hopes that more lookahead will + * resolve via one of those non-conflicting configurations.</p> + * + * <p>Here's the prediction termination rule them: SLL (for SLL+LL parsing) + * stops when it sees only conflicting configuration subsets. In contrast, + * full LL keeps going when there is uncertainty.</p> + * + * <p><strong>HEURISTIC</strong></p> + * + * <p>As a heuristic, we stop prediction when we see any conflicting subset + * unless we see a state that only has one alternative associated with it. + * The single-alt-state thing lets prediction continue upon rules like + * (otherwise, it would admit defeat too soon):</p> + * + * <p>{@code [12|1|[], 6|2|[], 12|2|[]]. s : (ID | ID ID?) ';' ;}</p> + * + * <p>When the ATN simulation reaches the state before {@code ';'}, it has a + * DFA state that looks like: {@code [12|1|[], 6|2|[], 12|2|[]]}. Naturally + * {@code 12|1|[]} and {@code 12|2|[]} conflict, but we cannot stop + * processing this node because alternative to has another way to continue, + * via {@code [6|2|[]]}.</p> + * + * <p>It also let's us continue for this rule:</p> + * + * <p>{@code [1|1|[], 1|2|[], 8|3|[]] a : A | A | A B ;}</p> + * + * <p>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, don't declare the state done.</p> + * + * <p><strong>PURE SLL PARSING</strong></p> + * + * <p>To handle pure SLL parsing, all we have to do is make sure that we + * combine stack contexts for configurations that differ only by semantic + * predicate. From there, we can do the usual SLL termination heuristic.</p> + * + * <p><strong>PREDICATES IN SLL+LL PARSING</strong></p> + * + * <p>SLL decisions don't evaluate predicates until after they reach DFA stop + * states because they need to create the DFA cache that works in all + * semantic situations. In contrast, full LL evaluates predicates collected + * during start state computation so it can ignore predicates thereafter. + * This means that SLL termination detection can totally ignore semantic + * predicates.</p> + * + * <p>Implementation-wise, {@link ATNConfigSet} combines stack contexts but + * not semantic predicate contexts so we might see two configurations like the + * following.</p> + * + * <p>{@code (s, 1, x, {}), (s, 1, x', {p})}</p> + * + * <p>Before testing these configurations against others, we have to merge + * {@code x} and {@code x'} (without modifying the existing configurations). + * For example, we test {@code (x+x')==x''} when looking for conflicts in + * the following configurations.</p> + * + * <p>{@code (s, 1, x, {}), (s, 1, x', {p}), (s, 2, x'', {})}</p> + * + * <p>If the configuration set has predicates (as indicated by + * {@link ATNConfigSet#hasSemanticContext}), this algorithm makes a copy of + * the configurations to strip out all of the predicates so that a standard + * {@link ATNConfigSet} will merge everything ignoring predicates.</p> + */ + static bool hasSLLConflictTerminatingPrediction(PredictionMode mode, + ATNConfigSet* configs); + + /// <summary> + /// Checks if any configuration in {@code configs} is in a + /// <seealso cref="RuleStopState"/>. Configurations meeting this condition + /// have reached the end of the decision rule (local context) or end of start + /// rule (full context). + /// </summary> + /// <param name="configs"> the configuration set to test </param> + /// <returns> {@code true} if any configuration in {@code configs} is in a + /// <seealso cref="RuleStopState"/>, otherwise {@code false} </returns> + static bool hasConfigInRuleStopState(ATNConfigSet* configs); + + /// <summary> + /// Checks if all configurations in {@code configs} are in a + /// <seealso cref="RuleStopState"/>. Configurations meeting this condition + /// have reached the end of the decision rule (local context) or end of start + /// rule (full context). + /// </summary> + /// <param name="configs"> the configuration set to test </param> + /// <returns> {@code true} if all configurations in {@code configs} are in a + /// <seealso cref="RuleStopState"/>, otherwise {@code false} </returns> + static bool allConfigsInRuleStopStates(ATNConfigSet* configs); + + /** + * Full LL prediction termination. + * + * <p>Can we stop looking ahead during ATN simulation or is there some + * uncertainty as to which alternative we will ultimately pick, after + * consuming more input? Even if there are partial conflicts, we might know + * that everything is going to resolve to the same minimum alternative. That + * means we can stop since no more lookahead will change that fact. On the + * other hand, there might be multiple conflicts that resolve to different + * minimums. That means we need more look ahead to decide which of those + * alternatives we should predict.</p> + * + * <p>The basic idea is to split the set of configurations {@code C}, into + * conflicting subsets {@code (s, _, ctx, _)} and singleton subsets with + * non-conflicting configurations. Two configurations conflict if they have + * identical {@link ATNConfig#state} and {@link ATNConfig#context} values + * but different {@link ATNConfig#alt} value, e.g. {@code (s, i, ctx, _)} + * and {@code (s, j, ctx, _)} for {@code i!=j}.</p> + * + * <p>Reduce these configuration subsets to the set of possible alternatives. + * You can compute the alternative subsets in one pass as follows:</p> + * + * <p>{@code A_s,ctx = {i | (s, i, ctx, _)}} for each configuration in + * {@code C} holding {@code s} and {@code ctx} fixed.</p> + * + * <p>Or in pseudo-code, for each configuration {@code c} in {@code C}:</p> + * + * <pre> + * map[c] U= c.{@link ATNConfig#alt alt} # map hash/equals uses s and x, not + * alt and not pred + * </pre> + * + * <p>The values in {@code map} are the set of {@code A_s,ctx} sets.</p> + * + * <p>If {@code |A_s,ctx|=1} then there is no conflict associated with + * {@code s} and {@code ctx}.</p> + * + * <p>Reduce the subsets to singletons by choosing a minimum of each subset. + * If the union of these alternative subsets is a singleton, then no amount of + * more lookahead will help us. We will always pick that alternative. If, + * however, there is more than one alternative, then we are uncertain which + * alternative to predict and must continue looking for resolution. We may + * or may not discover an ambiguity in the future, even if there are no + * conflicting subsets this round.</p> + * + * <p>The biggest sin is to terminate early because it means we've made a + * decision but were uncertain as to the eventual outcome. We haven't used + * enough lookahead. On the other hand, announcing a conflict too late is no + * big deal; you will still have the conflict. It's just inefficient. It + * might even look until the end of file.</p> + * + * <p>No special consideration for semantic predicates is required because + * predicates are evaluated on-the-fly for full LL prediction, ensuring that + * no configuration contains a semantic context during the termination + * check.</p> + * + * <p><strong>CONFLICTING CONFIGS</strong></p> + * + * <p>Two configurations {@code (s, i, x)} and {@code (s, j, x')}, conflict + * when {@code i!=j} but {@code x=x'}. Because we merge all + * {@code (s, i, _)} configurations together, that means that there are at + * most {@code n} configurations associated with state {@code s} for + * {@code n} possible alternatives in the decision. The merged stacks + * complicate the comparison of configuration contexts {@code x} and + * {@code x'}. Sam checks to see if one is a subset of the other by calling + * merge and checking to see if the merged result is either {@code x} or + * {@code x'}. If the {@code x} associated with lowest alternative {@code i} + * is the superset, then {@code i} is the only possible prediction since the + * others resolve to {@code min(i)} as well. However, if {@code x} is + * associated with {@code j>i} then at least one stack configuration for + * {@code j} is not in conflict with alternative {@code i}. The algorithm + * should keep going, looking for more lookahead due to the uncertainty.</p> + * + * <p>For simplicity, I'm doing a equality check between {@code x} and + * {@code x'} that lets the algorithm continue to consume lookahead longer + * than necessary. The reason I like the equality is of course the + * simplicity but also because that is the test you need to detect the + * alternatives that are actually in conflict.</p> + * + * <p><strong>CONTINUE/STOP RULE</strong></p> + * + * <p>Continue if union of resolved alternative sets from non-conflicting and + * conflicting alternative subsets has more than one alternative. We are + * uncertain about which alternative to predict.</p> + * + * <p>The complete set of alternatives, {@code [i for (_,i,_)]}, tells us + * which alternatives are still in the running for the amount of input we've + * consumed at this point. The conflicting sets let us to strip away + * configurations that won't lead to more states because we resolve + * conflicts to the configuration with a minimum alternate for the + * conflicting set.</p> + * + * <p><strong>CASES</strong></p> + * + * <ul> + * + * <li>no conflicts and more than 1 alternative in set => continue</li> + * + * <li> {@code (s, 1, x)}, {@code (s, 2, x)}, {@code (s, 3, z)}, + * {@code (s', 1, y)}, {@code (s', 2, y)} yields non-conflicting set + * {@code {3}} U conflicting sets {@code min({1,2})} U {@code min({1,2})} = + * {@code {1,3}} => continue + * </li> + * + * <li>{@code (s, 1, x)}, {@code (s, 2, x)}, {@code (s', 1, y)}, + * {@code (s', 2, y)}, {@code (s'', 1, z)} yields non-conflicting set + * {@code {1}} U conflicting sets {@code min({1,2})} U {@code min({1,2})} = + * {@code {1}} => stop and predict 1</li> + * + * <li>{@code (s, 1, x)}, {@code (s, 2, x)}, {@code (s', 1, y)}, + * {@code (s', 2, y)} yields conflicting, reduced sets {@code {1}} U + * {@code {1}} = {@code {1}} => stop and predict 1, can announce + * ambiguity {@code {1,2}}</li> + * + * <li>{@code (s, 1, x)}, {@code (s, 2, x)}, {@code (s', 2, y)}, + * {@code (s', 3, y)} yields conflicting, reduced sets {@code {1}} U + * {@code {2}} = {@code {1,2}} => continue</li> + * + * <li>{@code (s, 1, x)}, {@code (s, 2, x)}, {@code (s', 3, y)}, + * {@code (s', 4, y)} yields conflicting, reduced sets {@code {1}} U + * {@code {3}} = {@code {1,3}} => continue</li> + * + * </ul> + * + * <p><strong>EXACT AMBIGUITY DETECTION</strong></p> + * + * <p>If all states report the same conflicting set of alternatives, then we + * know we have the exact ambiguity set.</p> + * + * <p><code>|A_<em>i</em>|>1</code> and + * <code>A_<em>i</em> = A_<em>j</em></code> for all <em>i</em>, + * <em>j</em>.</p> + * + * <p>In other words, we continue examining lookahead until all {@code A_i} + * have more than one alternative and all {@code A_i} are the same. If + * {@code A={{1,2}, {1,3}}}, then regular LL prediction would terminate + * because the resolved set is {@code {1}}. To determine what the real + * ambiguity is, we have to know whether the ambiguity is between one and + * two or one and three so we keep going. We can only stop prediction when + * we need exact ambiguity detection when the sets look like + * {@code A={{1,2}}} or {@code {{1,2},{1,2}}}, etc...</p> + */ + static size_t resolvesToJustOneViableAlt( + const std::vector<antlrcpp::BitSet>& altsets); + + /// <summary> + /// Determines if every alternative subset in {@code altsets} contains more + /// than one alternative. + /// </summary> + /// <param name="altsets"> a collection of alternative subsets </param> + /// <returns> {@code true} if every <seealso cref="BitSet"/> in {@code + /// altsets} has <seealso cref="BitSet#cardinality cardinality"/> > 1, + /// otherwise {@code false} </returns> + static bool allSubsetsConflict(const std::vector<antlrcpp::BitSet>& altsets); + + /// <summary> + /// Determines if any single alternative subset in {@code altsets} contains + /// exactly one alternative. + /// </summary> + /// <param name="altsets"> a collection of alternative subsets </param> + /// <returns> {@code true} if {@code altsets} contains a <seealso + /// cref="BitSet"/> with + /// <seealso cref="BitSet#cardinality cardinality"/> 1, otherwise {@code + /// false} + /// </returns> + static bool hasNonConflictingAltSet( + const std::vector<antlrcpp::BitSet>& altsets); + + /// <summary> + /// Determines if any single alternative subset in {@code altsets} contains + /// more than one alternative. + /// </summary> + /// <param name="altsets"> a collection of alternative subsets </param> + /// <returns> {@code true} if {@code altsets} contains a <seealso + /// cref="BitSet"/> with + /// <seealso cref="BitSet#cardinality cardinality"/> > 1, otherwise {@code + /// false} </returns> + static bool hasConflictingAltSet( + const std::vector<antlrcpp::BitSet>& altsets); + + /// <summary> + /// Determines if every alternative subset in {@code altsets} is equivalent. + /// </summary> + /// <param name="altsets"> a collection of alternative subsets </param> + /// <returns> {@code true} if every member of {@code altsets} is equal to the + /// others, otherwise {@code false} </returns> + static bool allSubsetsEqual(const std::vector<antlrcpp::BitSet>& altsets); + + /// <summary> + /// Returns the unique alternative predicted by all alternative subsets in + /// {@code altsets}. If no such alternative exists, this method returns + /// <seealso cref="ATN#INVALID_ALT_NUMBER"/>. + /// </summary> + /// <param name="altsets"> a collection of alternative subsets </param> + static size_t getUniqueAlt(const std::vector<antlrcpp::BitSet>& altsets); + + /// <summary> + /// Gets the complete set of represented alternatives for a collection of + /// alternative subsets. This method returns the union of each <seealso + /// cref="BitSet"/> + /// in {@code altsets}. + /// </summary> + /// <param name="altsets"> a collection of alternative subsets </param> + /// <returns> the set of represented alternatives in {@code altsets} + /// </returns> + static antlrcpp::BitSet getAlts(const std::vector<antlrcpp::BitSet>& altsets); + + /** Get union of all alts from configs. @since 4.5.1 */ + static antlrcpp::BitSet getAlts(ATNConfigSet* configs); + + /// <summary> + /// This function gets the conflicting alt subsets from a configuration set. + /// For each configuration {@code c} in {@code configs}: + /// + /// <pre> + /// map[c] U= c.<seealso cref="ATNConfig#alt alt"/> # map hash/equals uses s + /// and x, not alt and not pred + /// </pre> + /// </summary> + static std::vector<antlrcpp::BitSet> getConflictingAltSubsets( + ATNConfigSet* configs); + + /// <summary> + /// Get a map from state to alt subset from a configuration set. For each + /// configuration {@code c} in {@code configs}: + /// + /// <pre> + /// map[c.<seealso cref="ATNConfig#state state"/>] U= c.<seealso + /// cref="ATNConfig#alt alt"/> + /// </pre> + /// </summary> + static std::map<ATNState*, antlrcpp::BitSet> getStateToAltMap( + ATNConfigSet* configs); + + static bool hasStateAssociatedWithOneAlt(ATNConfigSet* configs); + + static size_t getSingleViableAlt( + const std::vector<antlrcpp::BitSet>& altsets); +}; + +} // namespace atn +} // namespace antlr4 |