ParserATNFactory.java 文件源码

@Override
public ATN createATN() {
    _createATN(g.rules.values());
    assert atn.maxTokenType == g.getMaxTokenType();
       addRuleFollowLinks();
    addEOFTransitionToStartRules();
    ATNOptimizer.optimize(g, atn);

    for (Triple<Rule, ATNState, ATNState> pair : preventEpsilonClosureBlocks) {
        LL1Analyzer analyzer = new LL1Analyzer(atn);
        if (analyzer.LOOK(pair.b, pair.c, null).contains(org.antlr.v4.runtime.Token.EPSILON)) {
            ErrorType errorType = pair.a instanceof LeftRecursiveRule ? ErrorType.EPSILON_LR_FOLLOW : ErrorType.EPSILON_CLOSURE;
            g.tool.errMgr.grammarError(errorType, g.fileName, ((GrammarAST)pair.a.ast.getChild(0)).getToken(), pair.a.name);
        }
    }

    optionalCheck:
    for (Triple<Rule, ATNState, ATNState> pair : preventEpsilonOptionalBlocks) {
        int bypassCount = 0;
        for (int i = 0; i < pair.b.getNumberOfTransitions(); i++) {
            ATNState startState = pair.b.transition(i).target;
            if (startState == pair.c) {
                bypassCount++;
                continue;
            }

            LL1Analyzer analyzer = new LL1Analyzer(atn);
            if (analyzer.LOOK(startState, pair.c, null).contains(org.antlr.v4.runtime.Token.EPSILON)) {
                g.tool.errMgr.grammarError(ErrorType.EPSILON_OPTIONAL, g.fileName, ((GrammarAST)pair.a.ast.getChild(0)).getToken(), pair.a.name);
                continue optionalCheck;
            }
        }

        if (bypassCount != 1) {
            throw new UnsupportedOperationException("Expected optional block with exactly 1 bypass alternative.");
        }
    }

    return atn;
}