New function currentUser() implemented

dbms/src/Functions/currentUser.cpp

@@ -0,0 +1,54 @@
+#include <Functions/IFunction.h>
+#include <Functions/FunctionFactory.h>
+#include <Interpreters/Context.h>
+#include <DataTypes/DataTypeString.h>
+
+
+namespace DB
+{
+
+class FunctionCurrentUser : public IFunction
+{
+    const String user_name;
+
+public:
+    static constexpr auto name = "currentUser";
+    static FunctionPtr create(const Context & context)
+    {
+        return std::make_shared<FunctionCurrentUser>(context.getClientInfo().current_user);
+    }
+
+    explicit FunctionCurrentUser(const String & user_name_) : user_name{user_name_}
+    {
+    }
+
+    String getName() const override
+    {
+        return name;
+    }
+    size_t getNumberOfArguments() const override
+    {
+        return 0;
+    }
+
+    DataTypePtr getReturnTypeImpl(const DataTypes & /*arguments*/) const override
+    {
+        return std::make_shared<DataTypeString>();
+    }
+
+    bool isDeterministic() const override { return false; }
+
+    void executeImpl(Block & block, const ColumnNumbers &, size_t result, size_t input_rows_count) override
+    {
+        block.getByPosition(result).column = DataTypeString().createColumnConst(input_rows_count, user_name);
+    }
+};
+
+
+void registerFunctionCurrentUser(FunctionFactory & factory)
+{
+    factory.registerFunction<FunctionCurrentUser>();
+    factory.registerAlias("user", FunctionCurrentUser::name, FunctionFactory::CaseSensitive);
+}
+
+}

dbms/src/Functions/registerFunctionsMiscellaneous.cpp

@@ -6,6 +6,7 @@ namespace DB
 class FunctionFactory;
 
 void registerFunctionCurrentDatabase(FunctionFactory &);
+void registerFunctionCurrentUser(FunctionFactory &);
 void registerFunctionHostName(FunctionFactory &);
 void registerFunctionVisibleWidth(FunctionFactory &);
 void registerFunctionToTypeName(FunctionFactory &);
@@ -56,6 +57,7 @@ void registerFunctionConvertCharset(FunctionFactory &);
 void registerFunctionsMiscellaneous(FunctionFactory & factory)
 {
     registerFunctionCurrentDatabase(factory);
+    registerFunctionCurrentUser(factory);
     registerFunctionHostName(factory);
     registerFunctionVisibleWidth(factory);
     registerFunctionToTypeName(factory);

dbms/tests/queries/0_stateless/00990_function_current_user.reference

@@ -0,0 +1,3 @@
+1
+1
+1

dbms/tests/queries/0_stateless/00990_function_current_user.sql

@@ -0,0 +1,4 @@
+-- since actual user name is unknown, have to perform just smoke tests
+select currentUser() IS NOT NULL;
+select length(currentUser()) > 0;
+select currentUser() = user();