Extend EXECABORT with "previous errors" redis#4084

Propagate errors in transaction on command queuing (e.g before actual EXEC).
Errors are added as suppressed exceptions when EXEC is processed.

https://redis.io/docs/latest/develop/interact/transactions/
-A command may fail to be queued, so there may be an error before EXEC is called. For instance the command may be syntactically wrong (wrong number of arguments, wrong command name, ...), or there may be some critical condition like an out of memory condition (if the server is configured to have a memory limit using the maxmemory directive).

 closes redis#4084

src/main/java/redis/clients/jedis/Transaction.java

@@ -169,11 +169,25 @@ public List<Object> exec() {
     try {
       // ignore QUEUED (or ERROR)
       // processPipelinedResponses(pipelinedResponses.size());
-      connection.getMany(1 + pipelinedResponses.size());
+      List<Object> queuedCmdResponses = connection.getMany(1 + pipelinedResponses.size());
+
 
       connection.sendCommand(EXEC);
 
-      List<Object> unformatted = connection.getObjectMultiBulkReply();
+      List<Object> unformatted;
+      try {
+        unformatted = connection.getObjectMultiBulkReply();
+      } catch (JedisDataException jce) {
+        // A command may fail to be queued, so there may be an error before EXEC is called
+        // In this case, the server will discard all commands in the transaction and return the EXECABORT error.
+        // Enhance the final error with suppressed errors.
+        queuedCmdResponses.stream()
+            .filter(o -> o instanceof Exception)
+            .map(o -> (Exception) o)
+            .forEach(jce::addSuppressed);
+        throw jce;
+      }
+
       if (unformatted == null) {
         pipelinedResponses.clear();
         return null;

src/test/java/redis/clients/jedis/TransactionV2Test.java

@@ -1,6 +1,8 @@
 package redis.clients.jedis;
 
+import static org.hamcrest.Matchers.containsString;
 import static org.junit.Assert.*;
+import static org.junit.Assert.assertTrue;
 import static redis.clients.jedis.Protocol.Command.INCR;
 import static redis.clients.jedis.Protocol.Command.GET;
 import static redis.clients.jedis.Protocol.Command.SET;
@@ -9,6 +11,8 @@
 import java.util.ArrayList;
 import java.util.List;
 import java.util.Set;
+
+import org.hamcrest.MatcherAssert;
 import org.junit.After;
 import org.junit.Before;
 import org.junit.Test;
@@ -213,6 +217,23 @@ public void transactionResponseWithError() {
     assertEquals("bar", r.get());
   }
 
+  @Test
+  public void transactionPropagatesErrorsBeforeExec() {
+    // A command may fail to be queued, so there may be an error before EXEC is called.
+    // For instance the command may be syntactically wrong (wrong number of arguments, wrong command name, ...)
+    CommandObject<String> invalidCommand =
+        new CommandObject<>(new CommandObjects().commandArguments(PipeliningTest.Foo.FOO), BuilderFactory.STRING);
+
+    Transaction t = new Transaction(conn);
+    t.appendCommand(invalidCommand);
+    t.set("foo","bar");
+    JedisDataException exception = assertThrows(JedisDataException.class, t::exec);
+    Throwable[] suppressed = exception.getSuppressed();
+    assertNotNull("Suppressed exceptions should not be null", suppressed);
+    assertTrue("There should be at least one suppressed exception", suppressed.length > 0);
+    MatcherAssert.assertThat(suppressed[0].getMessage(), containsString("ERR unknown command 'FOO'"));
+  }
+
   @Test
   public void testCloseable() {
     Transaction transaction = new Transaction(conn);