rename evaluateDatabaseName function and header, add comments

dbms/include/DB/Interpreters/evaluateDatabaseName.h

@@ -1,42 +0,0 @@
-#pragma once
-
-#include <DB/Interpreters/Context.h>
-#include <DB/Interpreters/ExpressionAnalyzer.h>
-#include <DB/DataTypes/DataTypeString.h>
-#include <DB/Parsers/ASTIdentifier.h>
-#include <DB/Parsers/ASTLiteral.h>
-
-
-namespace DB
-{
-	namespace
-	{
-		ASTPtr makeIdentifier(const ASTPtr & expr, const Context & context)
-		{
-			/// for identifier just return its name
-			if (typeid_cast<const ASTIdentifier *>(expr.get()))
-				return expr;
-
-			/// for string literal return its value
-			if (const auto literal = typeid_cast<const ASTLiteral *>(expr.get()))
-				return new ASTIdentifier{{}, safeGet<const String &>(literal->value)};
-
-			/// otherwise evaluate expression and ensure it has string type
-			Block block{};
-			ExpressionAnalyzer{expr, context, { { "", new DataTypeString } }}.getActions(false)->execute(block);
-
-			const auto & column_name_type = block.getByName(expr->getColumnName());
-
-			if (!typeid_cast<const DataTypeString *>(column_name_type.type.get()))
-				throw Exception{""};
-
-			return new ASTIdentifier{{}, column_name_type.column->getDataAt(0).toString()};
-		}
-
-		String evaluateDatabaseName(ASTPtr & expr, const Context & context)
-		{
-			expr = makeIdentifier(expr, context);
-			return static_cast<ASTIdentifier *>(expr.get())->name;
-		}
-	}
-}

dbms/include/DB/Interpreters/reinterpretAsIdentifier.h

@@ -0,0 +1,50 @@
+#pragma once
+
+#include <DB/Interpreters/Context.h>
+#include <DB/Interpreters/ExpressionAnalyzer.h>
+#include <DB/DataTypes/DataTypeString.h>
+#include <DB/Parsers/ASTIdentifier.h>
+#include <DB/Parsers/ASTLiteral.h>
+
+
+namespace DB
+{
+	namespace
+	{
+		ASTPtr reinterpretAsIdentifierImpl(const ASTPtr & expr, const Context & context)
+		{
+			/// for string literal return its value
+			if (const auto literal = typeid_cast<const ASTLiteral *>(expr.get()))
+				return new ASTIdentifier{{}, safeGet<const String &>(literal->value)};
+
+			/// otherwise evaluate the expression
+			Block block{};
+			/** pass a dummy column name because ExpressioAnalyzer
+		     *  does not work with no columns so far. */
+			ExpressionAnalyzer{
+				expr, context,
+				{ { "", new DataTypeString } }
+			}.getActions(false)->execute(block);
+
+			const auto & column_name_type = block.getByName(expr->getColumnName());
+
+			/// ensure the result of evaluation has String type
+			if (!typeid_cast<const DataTypeString *>(column_name_type.type.get()))
+				throw Exception{"Expression must evaluate to a String"};
+
+			return new ASTIdentifier{{}, column_name_type.column->getDataAt(0).toString()};
+		}
+	}
+
+	/** \brief if `expr` is not already ASTIdentifier evaluates it
+	 *  and replaces by a new ASTIdentifier with the result of evaluation as its name.
+	 *  `expr` must evaluate to a String type */
+	inline ASTIdentifier & reinterpretAsIdentifier(ASTPtr & expr, const Context & context)
+	{
+		/// for identifier just return its name
+		if (!typeid_cast<const ASTIdentifier *>(expr.get()))
+			expr = reinterpretAsIdentifierImpl(expr, context);
+
+		return static_cast<ASTIdentifier &>(*expr);
+	}
+}

dbms/include/DB/TableFunctions/TableFunctionMerge.h

@@ -8,7 +8,7 @@
 #include <DB/Parsers/ASTIdentifier.h>
 #include <DB/Parsers/ASTLiteral.h>
 #include <DB/TableFunctions/ITableFunction.h>
-#include <DB/Interpreters/evaluateDatabaseName.h>
+#include <DB/Interpreters/reinterpretAsIdentifier.h>
 
 
 namespace DB
@@ -41,7 +41,7 @@ public:
 				" - name of source database and regexp for table names.",
 				ErrorCodes::NUMBER_OF_ARGUMENTS_DOESNT_MATCH);
 
-		String source_database 		= evaluateDatabaseName(args[0], context);
+		String source_database 		= reinterpretAsIdentifier(args[0], context).name;
 		String table_name_regexp	= safeGet<const String &>(typeid_cast<ASTLiteral &>(*args[1]).value);
 
 		/// В InterpreterSelectQuery будет создан ExpressionAnalzyer, который при обработке запроса наткнется на этот Identifier.

dbms/include/DB/TableFunctions/TableFunctionRemote.h

@@ -4,7 +4,7 @@
 #include <DB/Storages/StorageDistributed.h>
 #include <DB/Parsers/ASTIdentifier.h>
 #include <DB/DataStreams/RemoteBlockInputStream.h>
-#include <DB/Interpreters/evaluateDatabaseName.h>
+#include <DB/Interpreters/reinterpretAsIdentifier.h>
 
 
 struct data;
@@ -44,7 +44,7 @@ public:
 			throw Exception(err, ErrorCodes::NUMBER_OF_ARGUMENTS_DOESNT_MATCH);
 
 		String descripton	 	= safeGet<const String &>(typeid_cast<ASTLiteral &>(*args[0]).value);
-		String remote_database 	= evaluateDatabaseName(args[1], context);
+		String remote_database 	= reinterpretAsIdentifier(args[1], context).name;
 		String remote_table 	= args.size() % 2 ? typeid_cast<ASTIdentifier &>(*args[2]).name : "";
 		String username = args.size() >= 4
 			? safeGet<const String &>(typeid_cast<ASTLiteral &>(*args[args.size() - 2]).value) : "default";

dbms/src/Storages/StorageFactory.cpp

@@ -6,7 +6,7 @@
 #include <DB/Parsers/ASTLiteral.h>
 
 #include <DB/Interpreters/Context.h>
-#include <DB/Interpreters/evaluateDatabaseName.h>
+#include <DB/Interpreters/reinterpretAsIdentifier.h>
 
 #include <DB/Storages/StorageLog.h>
 #include <DB/Storages/StorageTinyLog.h>
@@ -108,7 +108,7 @@ StoragePtr StorageFactory::get(
 			if (args.size() < 3 || args.size() > 4)
 				break;
 
-			String source_database = evaluateDatabaseName(args[0], local_context);
+			String source_database = reinterpretAsIdentifier(args[0], local_context).name;
 			String source_table_name_regexp = safeGet<const String &>(typeid_cast<ASTLiteral &>(*args[1]).value);
 			size_t chunks_to_merge = safeGet<UInt64>(typeid_cast<ASTLiteral &>(*args[2]).value);
 
@@ -156,7 +156,7 @@ StoragePtr StorageFactory::get(
 				" - name of source database and regexp for table names.",
 				ErrorCodes::NUMBER_OF_ARGUMENTS_DOESNT_MATCH);
 
-		String source_database 		= evaluateDatabaseName(args[0], local_context);
+		String source_database 		= reinterpretAsIdentifier(args[0], local_context).name;
 		String table_name_regexp	= safeGet<const String &>(typeid_cast<ASTLiteral &>(*args[1]).value);
 
 		return StorageMerge::create(table_name, columns, source_database, table_name_regexp, context);
@@ -182,7 +182,7 @@ StoragePtr StorageFactory::get(
 				ErrorCodes::NUMBER_OF_ARGUMENTS_DOESNT_MATCH);
 
 		String cluster_name 	= typeid_cast<ASTIdentifier &>(*args[0]).name;
-		String remote_database 	= evaluateDatabaseName(args[1], local_context);
+		String remote_database 	= reinterpretAsIdentifier(args[1], local_context).name;
 		String remote_table 	= typeid_cast<ASTIdentifier &>(*args[2]).name;
 
 		const auto & sharding_key = args.size() == 4 ? args[3] : nullptr;