LibSQL: Fix handling of optional AS keywords

In some syntaxes, using the 'AS' keyword to define an alias is optional.
But if it does appear, an identifier better appear afterwards.

Userland/Libraries/LibSQL/Parser.cpp

@@ -822,11 +822,9 @@ NonnullRefPtr<ReturningClause> Parser::parse_returning_clause()
     do {
         auto expression = parse_expression();
 
-        consume_if(TokenType::As); // 'AS' is optional.
-
         String column_alias;
-        if (match(TokenType::Identifier))
-            column_alias = consume().value();
+        if (consume_if(TokenType::As) || match(TokenType::Identifier))
+            column_alias = consume(TokenType::Identifier).value();
 
         columns.append({ move(expression), move(column_alias) });
         if (!match(TokenType::Comma))
@@ -860,11 +858,10 @@ NonnullRefPtr<ResultColumn> Parser::parse_result_column()
     auto expression = table_name.is_null()
         ? parse_expression()
         : static_cast<NonnullRefPtr<Expression>>(*parse_column_name_expression(move(table_name), parsed_period));
-    consume_if(TokenType::As); // 'AS' is optional.
 
     String column_alias;
-    if (match(TokenType::Identifier))
-        column_alias = consume().value();
+    if (consume_if(TokenType::As) || match(TokenType::Identifier))
+        column_alias = consume(TokenType::Identifier).value();
 
     return create_ast_node<ResultColumn>(move(expression), move(column_alias));
 }
@@ -884,11 +881,9 @@ NonnullRefPtr<TableOrSubquery> Parser::parse_table_or_subquery()
             table_name = move(schema_or_table_name);
         }
 
-        consume_if(TokenType::As); // 'AS' is optional.
-
         String table_alias;
-        if (match(TokenType::Identifier))
-            table_alias = consume().value();
+        if (consume_if(TokenType::As) || match(TokenType::Identifier))
+            table_alias = consume(TokenType::Identifier).value();
 
         return create_ast_node<TableOrSubquery>(move(schema_name), move(table_name), move(table_alias));
     }

Userland/Libraries/LibSQL/Tests/TestSqlStatementParser.cpp

@@ -148,6 +148,8 @@ TEST_CASE(delete_)
     EXPECT(parse("DELETE FROM table WHERE 15").is_error());
     EXPECT(parse("DELETE FROM table WHERE 15 RETURNING").is_error());
     EXPECT(parse("DELETE FROM table WHERE 15 RETURNING *").is_error());
+    EXPECT(parse("DELETE FROM table WHERE 15 RETURNING column").is_error());
+    EXPECT(parse("DELETE FROM table WHERE 15 RETURNING column AS;").is_error());
     EXPECT(parse("DELETE FROM table WHERE (');").is_error());
     EXPECT(parse("WITH DELETE FROM table;").is_error());
     EXPECT(parse("WITH table DELETE FROM table;").is_error());
@@ -243,6 +245,7 @@ TEST_CASE(select)
     EXPECT(parse("SELECT *").is_error());
     EXPECT(parse("SELECT * FROM;").is_error());
     EXPECT(parse("SELECT table. FROM table;").is_error());
+    EXPECT(parse("SELECT column AS FROM table;").is_error());
     EXPECT(parse("SELECT * FROM (").is_error());
     EXPECT(parse("SELECT * FROM ()").is_error());
     EXPECT(parse("SELECT * FROM ();").is_error());
@@ -250,6 +253,7 @@ TEST_CASE(select)
     EXPECT(parse("SELECT * FROM (table1, )").is_error());
     EXPECT(parse("SELECT * FROM (table1, table2)").is_error());
     EXPECT(parse("SELECT * FROM table").is_error());
+    EXPECT(parse("SELECT * FROM table AS;").is_error());
     EXPECT(parse("SELECT * FROM table WHERE;").is_error());
     EXPECT(parse("SELECT * FROM table WHERE 1 ==1").is_error());
     EXPECT(parse("SELECT * FROM table GROUP;").is_error());