fix: better error message on self-join (#4248)

Fixes: #4241

Self-joins are not yet supported. Previously they resulted in an confusing error message:

>  Invalid topology: Topic <something> has already been registered by another source.

They not result in:

> Can not join 'something' to 'something': self joins are not yet supported.

ksql-engine/src/main/java/io/confluent/ksql/analyzer/Analyzer.java

@@ -341,6 +341,14 @@ protected AstNode visitJoin(final Join node, final Void context) {
         throw new KsqlException("Only equality join criteria is supported.");
       }
 
+      if (left.getDataSource().getName().equals(right.getDataSource().getName())) {
+        throw new KsqlException(
+            "Can not join '" + left.getDataSource().getName().toString(FormatOptions.noEscape())
+                + "' to '" + right.getDataSource().getName().toString(FormatOptions.noEscape())
+                + "': self joins are not yet supported."
+        );
+      }
+
       final ColumnRef leftJoinField = getJoinFieldName(
           comparisonExpression,
           left.getAlias(),

ksql-engine/src/test/java/io/confluent/ksql/analyzer/AnalyzerFunctionalTest.java

@@ -106,7 +106,7 @@ public class AnalyzerFunctionalTest {
   public final ExpectedException expectedException = ExpectedException.none();
 
   @Mock
-  private SerdeOptionsSupplier serdeOptiponsSupplier;
+  private SerdeOptionsSupplier serdeOptionsSupplier;
   @Mock
   private Sink sink;
 
@@ -127,7 +127,7 @@ public void init() {
         jsonMetaStore,
         "",
         DEFAULT_SERDE_OPTIONS,
-        serdeOptiponsSupplier
+        serdeOptionsSupplier
     );
 
     when(sink.getName()).thenReturn(SourceName.of("TEST0"));
@@ -388,7 +388,7 @@ public void shouldFailIfExplicitNamespaceIsProvidedButEmpty() {
   public void shouldGetSerdeOptions() {
     // Given:
     final Set<SerdeOption> serdeOptions = ImmutableSet.of(SerdeOption.UNWRAP_SINGLE_VALUES);
-    when(serdeOptiponsSupplier.build(any(), any(), any(), any())).thenReturn(serdeOptions);
+    when(serdeOptionsSupplier.build(any(), any(), any(), any())).thenReturn(serdeOptions);
 
     givenSinkValueFormat(Format.AVRO);
     givenWrapSingleValues(true);
@@ -397,7 +397,7 @@ public void shouldGetSerdeOptions() {
     final Analysis result = analyzer.analyze(query, Optional.of(sink));
 
     // Then:
-    verify(serdeOptiponsSupplier).build(
+    verify(serdeOptionsSupplier).build(
         ImmutableList.of("COL0", "COL1").stream().map(ColumnName::of).collect(Collectors.toList()),
         Format.AVRO,
         Optional.of(true),
@@ -484,6 +484,26 @@ public void shouldNotIncludeMetaColumnsForSelectStartOnStaticQueries() {
     )));
   }
 
+  @Test
+  public void shouldThrowOnSelfJoin() {
+    // Given:
+    final CreateStreamAsSelect createStreamAsSelect = parseSingle(
+        "CREATE STREAM FOO AS "
+            + "SELECT * FROM test1 t1 JOIN test1 t2 ON t1.rowkey = t2.rowkey;"
+    );
+
+    final Query query = createStreamAsSelect.getQuery();
+
+    final Analyzer analyzer = new Analyzer(jsonMetaStore, "", DEFAULT_SERDE_OPTIONS);
+
+    // Expect:
+    expectedException.expect(KsqlException.class);
+    expectedException.expectMessage("Can not join 'TEST1' to 'TEST1': self joins are not yet supported.");
+
+    // When:
+    analyzer.analyze(query, Optional.of(createStreamAsSelect.getSink()));
+  }
+
   @SuppressWarnings("unchecked")
   private <T extends Statement> T parseSingle(final String simpleQuery) {
     return (T) Iterables.getOnlyElement(parse(simpleQuery, jsonMetaStore));

ksql-functional-tests/src/test/resources/query-validation-tests/joins.json

@@ -1922,6 +1922,17 @@
           {"name": "OUTPUT", "type": "stream", "schema": "ROWKEY STRING KEY, L_ROWKEY STRING, L1 INT, R1 INT"}
         ]
       }
+    },
+    {
+      "name": "self join",
+      "statements": [
+        "CREATE STREAM INPUT (ID bigint) WITH (kafka_topic='left_topic', value_format='JSON');",
+        "CREATE STREAM OUTPUT as SELECT * FROM INPUT s1 JOIN INPUT s2 WITHIN 1 HOUR ON s1.id = s2.id;"
+      ],
+      "expectedException": {
+        "type": "io.confluent.ksql.util.KsqlStatementException",
+        "message": "Can not join 'INPUT' to 'INPUT': self joins are not yet supported."
+      }
     }
   ]
 }