[ADQL] Fix incorrect ambiguous column name in subqueries

Fixes #158

ADQLLib/src/adql/db/DBChecker.java

@@ -1204,14 +1204,24 @@ protected void checkSubQueries(final ADQLQuery query, final Stack<CheckContext>
 		if (sHandler.getNbMatch() > 0) {
 
 			// Check each found sub-query:
-			for(ADQLObject result : sHandler) {
+			for(ADQLObject result : sHandler)
+			{
+				/* Create an empty context in order to use at first only the
+				 * local context (and if needed, we will look at the parent
+				 * contexts) ; see resolveColumn(final ADQLColumn column, final Stack<CheckContext> contextList): */
+				contextList.push(new CheckContext(null, null));
+
 				try {
-					check((ADQLQuery)result, contextList);
+					check((ADQLSet)result, contextList);
 				} catch(UnresolvedIdentifiersException uie) {
 					Iterator<ParseException> itPe = uie.getErrors();
 					while(itPe.hasNext())
 						errors.addException(itPe.next());
 				}
+				/* Forget about the pushed context: */
+				finally {
+					contextList.pop();
+				}
 			}
 		}
 	}

ADQLLib/test/adql/db/TestDBChecker.java

@@ -811,6 +811,28 @@ public void testTypesChecking() {
 		}
 	}
 
+	@Test
+	public void test_ShouldSucceed_WhenSubQueryUsesSameTableAsMainQuery() throws Exception {
+		// Given...
+		// ...this only table with 3 columns:
+		final ArrayList<DBTable> lstTables = new ArrayList<>(1);
+		final DefaultDBTable tableResource = new DefaultDBTable("resource");
+		tableResource.addColumn(new DefaultDBColumn("ivoid", tableResource));
+		tableResource.addColumn(new DefaultDBColumn("short_name", tableResource));
+		tableResource.addColumn(new DefaultDBColumn("res_description", tableResource));
+		lstTables.add(tableResource);
+		// ...and this parser:
+		final DBChecker dbChecker = new DBChecker(lstTables);
+		final ADQLParser parser = new ADQLParser();
+		parser.setQueryChecker(dbChecker);
+
+		// When parsing the query with a sub-query using the same table:
+		final ADQLSet query = parser.parseQuery("SELECT res_description FROM resource WHERE ivoid IN (SELECT ivoid FROM resource WHERE short_name = 'anything')");
+
+		// Then, the query should successfully pass:
+		assertNotNull(query);
+	}
+
 	private static class WrongUDFToto extends UDFToto {
 		public WrongUDFToto(final ADQLOperand[] params) throws Exception {
 			super(params);