fix: add GRACE and PERIOD to the nonReserved and automate testing

ksqldb-parser/src/main/antlr4/io/confluent/ksql/parser/SqlBase.g4

@@ -336,6 +336,7 @@ nonReserved
     | EMIT
     | CHANGES
     | ESCAPE
+    | GRACE | PERIOD
     ;
 
 EMIT: 'EMIT';

ksqldb-parser/src/main/java/io/confluent/ksql/parser/DefaultKsqlParser.java

@@ -15,6 +15,7 @@
 
 package io.confluent.ksql.parser;
 
+import com.google.common.annotations.VisibleForTesting;
 import io.confluent.ksql.metastore.TypeRegistry;
 import io.confluent.ksql.parser.SqlBaseParser.SingleStatementContext;
 import io.confluent.ksql.parser.exception.ParseFailedException;
@@ -37,7 +38,8 @@
 public class DefaultKsqlParser implements KsqlParser {
   // CHECKSTYLE_RULES.ON: ClassDataAbstractionCoupling
 
-  private static final BaseErrorListener ERROR_LISTENER = new BaseErrorListener() {
+  @VisibleForTesting
+  static final BaseErrorListener ERROR_LISTENER = new BaseErrorListener() {
     @Override
     public void syntaxError(
         final Recognizer<?, ?> recognizer,

ksqldb-parser/src/test/java/io/confluent/ksql/parser/ReservedWordMetaTest.java

@@ -0,0 +1,125 @@
+/*
+ * Copyright 2020 Confluent Inc.
+ *
+ * Licensed under the Confluent Community License (the "License"; you may not use
+ * this file except in compliance with the License. You may obtain a copy of the
+ * License at
+ *
+ * http://www.confluent.io/confluent-community-license
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+ * WARRANTIES OF ANY KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations under the License.
+ */
+
+package io.confluent.ksql.parser;
+
+import com.google.common.collect.ImmutableSet;
+import java.util.Set;
+import java.util.stream.Collectors;
+import org.antlr.v4.runtime.CharStreams;
+import org.antlr.v4.runtime.CommonTokenStream;
+import org.antlr.v4.runtime.Vocabulary;
+import org.antlr.v4.runtime.atn.PredictionMode;
+import org.apache.commons.lang3.text.WordUtils;
+import org.hamcrest.Matchers;
+import org.junit.Assert;
+import org.junit.Ignore;
+import org.junit.Test;
+import static org.hamcrest.MatcherAssert.assertThat;
+
+
+/**
+ * This test ensures that we don't accidentally add words to our grammar
+ * without adding them to our "nonReserved" list. This is necessary because
+ * adding words to our grammar is backwards incompatible if anyone has issued
+ * a query in the past that used on of those words.
+ */
+public class ReservedWordMetaTest {
+
+  private static final String[] RESERVED = new String[]{"SELECT", "FROM", "AS",
+      "ALL", "DISTINCT", "WHERE", "WITHIN", "WINDOW", "GROUP", "BY", "HAVING",
+      "LIMIT", "AT", "OR", "AND", "IN", "NOT", "EXISTS", "BETWEEN", "LIKE", "IS",
+      "NULL", "TRUE", "FALSE", "MILLISECOND", "YEARS", "MONTHS", "DAYS", "HOURS",
+      "MINUTES", "SECONDS", "MILLISECONDS", "TUMBLING", "HOPPING", "SIZE", "ADVANCE",
+      "RETENTION", "CASE", "WHEN", "THEN", "ELSE", "END", "JOIN", "FULL", "OUTER",
+      "INNER", "LEFT", "RIGHT", "ON", "WITH", "VALUES", "CREATE", "TABLE", "TOPIC",
+      "STREAM", "STREAMS", "INSERT", "DELETE", "INTO", "DESCRIBE", "EXTENDED",
+      "PRINT", "CAST", "LIST", "TOPICS", "QUERY", "QUERIES", "TERMINATE", "LOAD",
+      "DROP", "TO", "RENAME", "SAMPLE", "EXPORT", "CATALOG", "PROPERTIES",
+      "BEGINNING", "UNSET", "RUN", "SCRIPT", "DECIMAL", "CONNECTOR", "CONNECTORS",
+      "NAMESPACE", "MATERIALIZED", "VIEW", "EQ", "NEQ", "LT", "LTE", "GT", "GTE",
+      "PLUS", "MINUS", "ASTERISK", "SLASH", "PERCENT", "CONCAT", "ASSIGN",
+      "STRUCT_FIELD_REF", "STRING", "INTEGER_VALUE", "DECIMAL_VALUE",
+      "FLOATING_POINT_VALUE", "IDENTIFIER", "DIGIT_IDENTIFIER", "QUOTED_IDENTIFIER",
+      "BACKQUOTED_IDENTIFIER", "TIME_WITH_TIME_ZONE", "TIMESTAMP_WITH_TIME_ZONE",
+      "SIMPLE_COMMENT", "BRACKETED_COMMENT", "WS", "UNRECOGNIZED"};
+  private static final Set<String> RESERVED_SET = ImmutableSet.copyOf(RESERVED);
+
+  /**
+   * Enable this test to re-generate the grammar that is intentionally
+   * part of the reserved words.
+   */
+  @Test
+  @Ignore
+  public void generateExcludedWords() {
+    final Vocabulary vocabulary = SqlBaseParser.VOCABULARY;
+    final int tokens = vocabulary.getMaxTokenType();
+    final ImmutableSet.Builder<String> builder = ImmutableSet.builder();
+
+    for (int i = 0; i < tokens; i++) {
+      final String symbolicName = vocabulary.getSymbolicName(i);
+      if (symbolicName != null) {
+        try {
+          buildParser(symbolicName).nonReserved();
+        } catch (final ParsingException e) {
+          // word is reserved (not in nonReserved)
+          builder.add(symbolicName);
+        }
+      }
+    }
+
+    final ImmutableSet<String> reserved = builder.build();
+    System.out.println(WordUtils.wrap("private static final String[] RESERVED = new String[]{"
+        + reserved
+        .stream()
+        .map(s -> '"' + s + '"')
+        .collect(Collectors.joining(", ")) + "};", 80, "\n\t\t", false));
+  }
+
+  @Test
+  public void shouldAddWordToNonReserved() {
+    final Vocabulary vocabulary = SqlBaseParser.VOCABULARY;
+    final int tokens = vocabulary.getMaxTokenType();
+
+    for (int i = 0; i < tokens; i++) {
+      final String symbolicName = vocabulary.getSymbolicName(i);
+      if (symbolicName != null) {
+        try {
+          buildParser(symbolicName).nonReserved();
+        } catch (final ParsingException e) {
+          assertThat(
+              String.format("Detected new word ('%s') in the vocabulary that is reserved. "
+                  + "This is a breaking change!! If this is intentional, then add it to "
+                  + "the RESERVED set in this test, otherwise please add it to the nonReserved "
+                  + "parser rule.", symbolicName), symbolicName, Matchers.isIn(RESERVED_SET));
+        }
+      }
+    }
+  }
+
+  private static SqlBaseParser buildParser(final String symbolicName) {
+    final SqlBaseLexer lexer = new SqlBaseLexer(
+        new CaseInsensitiveStream(CharStreams.fromString(symbolicName)));
+
+    final CommonTokenStream tokenStream = new CommonTokenStream(lexer);
+    final SqlBaseParser parser = new SqlBaseParser(tokenStream);
+    parser.removeErrorListeners();
+    parser.addErrorListener(DefaultKsqlParser.ERROR_LISTENER);
+    parser.getInterpreter().setPredictionMode(PredictionMode.LL);
+
+    return parser;
+  }
+
+}