From 297cfb4857836295f25cdb783d6b6afe78d7e017 Mon Sep 17 00:00:00 2001
From: Alexey Milovidov <milovidov@yandex-team.ru>
Date: Thu, 28 Jan 2021 06:34:44 +0300
Subject: [PATCH] Less parser depth

---
 src/Parsers/ParserDataType.cpp | 34 +++++++++++++++++++++-------------
 1 file changed, 21 insertions(+), 13 deletions(-)

diff --git a/src/Parsers/ParserDataType.cpp b/src/Parsers/ParserDataType.cpp
index 0148f2f3bb9..3d3f393a300 100644
--- a/src/Parsers/ParserDataType.cpp
+++ b/src/Parsers/ParserDataType.cpp
@@ -14,21 +14,29 @@ namespace
 {
 
 /// Wrapper to allow mixed lists of nested and normal types.
-class ParserNestedTableOrExpression : public IParserBase
+/// Parameters are either:
+/// - Nested table elements;
+/// - Enum element in form of 'a' = 1;
+/// - literal;
+/// - another data type (or identifier)
+class ParserDataTypeArgument : public IParserBase
 {
-    private:
-        const char * getName() const override { return "data type or expression"; }
-        bool parseImpl(Pos & pos, ASTPtr & node, Expected & expected) override
-        {
-            ParserNestedTable parser1;
+private:
+    const char * getName() const override { return "data type argument"; }
+    bool parseImpl(Pos & pos, ASTPtr & node, Expected & expected) override
+    {
+        ParserNestedTable nested_parser;
+        ParserDataType data_type_parser;
+        ParserLiteral literal_parser;
 
-            if (parser1.parse(pos, node, expected))
-                return true;
+        const char * operators[] = {"=", "equals", nullptr};
+        ParserLeftAssociativeBinaryOperatorList enum_parser(operators, std::make_unique<ParserLiteral>());
 
-            ParserExpression parser2;
-
-            return parser2.parse(pos, node, expected);
-        }
+        return nested_parser.parse(pos, node, expected)
+            || enum_parser.parse(pos, node, expected)
+            || literal_parser.parse(pos, node, expected)
+            || data_type_parser.parse(pos, node, expected);
+    }
 };
 
 }
@@ -104,7 +112,7 @@ bool ParserDataType::parseImpl(Pos & pos, ASTPtr & node, Expected & expected)
     ++pos;
 
     /// Parse optional parameters
-    ParserList args_parser(std::make_unique<ParserNestedTableOrExpression>(), std::make_unique<ParserToken>(TokenType::Comma));
+    ParserList args_parser(std::make_unique<ParserDataTypeArgument>(), std::make_unique<ParserToken>(TokenType::Comma));
     ASTPtr expr_list_args;
 
     if (!args_parser.parse(pos, expr_list_args, expected))