fix: fix unclosed literal error for consecutive backslashes (#4387)

Author: rayudu3745

java-spanner/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;
         }

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

@@ -16,10 +16,16 @@
 
 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.assertFalse;
+import static org.junit.Assert.assertTrue;
+import static org.junit.Assert.fail;
 
 import com.google.cloud.spanner.Dialect;
+import com.google.cloud.spanner.SpannerException;
+import com.google.cloud.spanner.Statement;
 import com.google.cloud.spanner.connection.StatementParserTest.CommentInjector;
 import org.junit.Test;
 import org.junit.runner.RunWith;
@@ -39,6 +45,55 @@ 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 testReturningClauseWithBackslashes() {
+    AbstractStatementParser parser =
+        AbstractStatementParser.getInstance(Dialect.GOOGLE_STANDARD_SQL);
+
+    // Valid returning clause, double backslash in string literal should be handled
+    // correctly.
+    String sqlWithReturning = "INSERT INTO my_table (value) VALUES ('foo \\\\ bar') THEN RETURN id";
+    assertTrue(parser.parse(Statement.of(sqlWithReturning)).hasReturningClause());
+
+    // No returning clause, `then return` is inside a string literal with a double
+    // backslash.
+    String sqlWithoutReturning = "INSERT INTO my_table (value) VALUES ('then \\\\ return')";
+    assertFalse(parser.parse(Statement.of(sqlWithoutReturning)).hasReturningClause());
+  }
+
   @Test
   public void testSkip() {
     assertEquals("", skip(""));