lower the severity of CxxParseErrorLoggerVisitor from WARN to INFO

* I profiled our visitors (SonarOpenCommunity#1507) and came to the conclusion,
  that CxxParseErrorLoggerVisitor might require a terrible amount
  of time in order to analyze and to print out all the parsing errors

* The ordinary user should not be interested in the parsing process.
  He/she has no influence on that. Such information is important
  if parsing affects some internal checks or metrics. If user decides
  to submit a bug report, the full debug trace will include the
  parsing errors.

* In general I believe, that our trace is too verbose. So this
  change address this problem too.

cxx-squid/src/main/java/org/sonar/cxx/CxxAstScanner.java

@@ -229,7 +229,9 @@ public SourceCode createSourceCode(SourceCode parentSourceCode, AstNode astNode)
     builder.withSquidAstVisitor(new CxxFileVisitor<>(context));
 
     // log syntax errors
-    builder.withSquidAstVisitor(new CxxParseErrorLoggerVisitor<>(context));
+    if (CxxParseErrorLoggerVisitor.isLoggingEnabled()) {
+      builder.withSquidAstVisitor(new CxxParseErrorLoggerVisitor<>(context));
+    }
 
     /* External visitors (typically Check ones) */
     for (SquidAstVisitor<Grammar> visitor : visitors) {

cxx-squid/src/main/java/org/sonar/cxx/visitors/CxxParseErrorLoggerVisitor.java

@@ -26,6 +26,7 @@
 import com.sonar.sslr.api.TokenType;
 import java.util.List;
 import org.sonar.api.utils.log.Logger;
+import org.sonar.api.utils.log.LoggerLevel;
 import org.sonar.api.utils.log.Loggers;
 import org.sonar.cxx.api.CxxPunctuator;
 import org.sonar.cxx.parser.CxxGrammarImpl;
@@ -42,6 +43,15 @@ public CxxParseErrorLoggerVisitor(SquidAstVisitorContext<?> context) {
     this.context = context;
   }
 
+  /**
+   * This only thing this visitor does is to logs with INFO severity; Disable
+   * the entire visitor if logging level was set to the level > INFO
+   */
+  public static boolean isLoggingEnabled() {
+    final LoggerLevel level = LOG.getLevel();
+    return level == LoggerLevel.TRACE || level == LoggerLevel.DEBUG || level == LoggerLevel.INFO;
+  }
+
   @Override
   public void init() {
     subscribeTo(CxxGrammarImpl.recoveredDeclaration);
@@ -64,7 +74,7 @@ public void visitNode(AstNode node) {
       } else if (type.equals(CxxPunctuator.CURLBR_LEFT)) {
         // part with CURLBR_LEFT is typically an ignored declaration
         if (identifierLine != -1) {
-          LOG.warn("[{}:{}]: skip declaration: {}",
+          LOG.info("[{}:{}]: skip declaration: {}",
             context.getFile(), identifierLine, sb.toString());
           sb.setLength(0);
           identifierLine = -1;
@@ -79,7 +89,7 @@ public void visitNode(AstNode node) {
 
     if (identifierLine != -1 && sb.length() > 0) {
       // part without CURLBR_LEFT is typically a syntax error
-      LOG.warn("[{}:{}]:    syntax error: {}",
+      LOG.info("[{}:{}]:    syntax error: {}",
         context.getFile(), identifierLine, sb.toString());
     }
   }