fix: fix unclosed literal error for consecutive backslashes

Author: rayudu3745

google-cloud-spanner/src/main/java/com/google/cloud/spanner/connection/SpannerStatementParser.java

@@ -145,7 +145,7 @@ String removeCommentsAndTrimInternal(String sql) {
             startQuote = 0;
           }
         } else if (c == '\\') {
-          lastCharWasEscapeChar = true;
+          lastCharWasEscapeChar = !lastCharWasEscapeChar;
         } else {
           lastCharWasEscapeChar = false;
         }
@@ -294,7 +294,7 @@ protected boolean checkReturningClauseInternal(String rawSql) {
             startQuote = 0;
           }
         } else if (c == '\\') {
-          lastCharWasEscapeChar = true;
+          lastCharWasEscapeChar = !lastCharWasEscapeChar;
         } else {
           lastCharWasEscapeChar = false;
         }

google-cloud-spanner/src/test/java/com/google/cloud/spanner/connection/SpannerStatementParserTest.java

@@ -16,10 +16,13 @@
 
 package com.google.cloud.spanner.connection;
 
+import static com.google.cloud.spanner.ErrorCode.INVALID_ARGUMENT;
 import static com.google.cloud.spanner.connection.StatementParserTest.assertUnclosedLiteral;
 import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.fail;
 
 import com.google.cloud.spanner.Dialect;
+import com.google.cloud.spanner.SpannerException;
 import com.google.cloud.spanner.connection.StatementParserTest.CommentInjector;
 import org.junit.Test;
 import org.junit.runner.RunWith;
@@ -39,6 +42,35 @@ static String skip(String sql, int currentIndex) {
     return sql.substring(currentIndex, position);
   }
 
+  @Test
+  public void testRemoveCommentsAndTrim() {
+      AbstractStatementParser parser = AbstractStatementParser.getInstance(Dialect.GOOGLE_STANDARD_SQL);
+
+      // Statements that should parse correctly
+      String[] validStatements = new String[] {
+              "SELECT '\\\\'", // SELECT '\\' (escaped backslash, followed by quote)
+              "SELECT '\\''", // SELECT '\'' (escaped quote, followed by an actual closing quote)
+              "SELECT '\\\\\\\\'" // SELECT '\\\\' (two escaped backslashes)
+      };
+      for (String sql : validStatements) {
+          assertEquals(sql, parser.removeCommentsAndTrim(sql));
+      }
+
+      // Statements that contain an unclosed literal because the final quote is escaped
+      String[] invalidStatements = new String[] {
+              "SELECT '\\'" // SELECT '\' (escaped closing quote)
+      };
+
+      for (String sql : invalidStatements) {
+          try {
+              parser.removeCommentsAndTrim(sql);
+              fail("Expected SpannerException for unclosed literal: " + sql);
+          } catch (SpannerException e) {
+              assertEquals(INVALID_ARGUMENT, e.getErrorCode());
+          }
+      }
+  }
+
   @Test
   public void testSkip() {
     assertEquals("", skip(""));