<fstream>: Importing as a header unit leads to error C2079: undefined class 'std::basic_ofstream<char,std::char_traits<char>>' #3112
Description
After updating to Visual Studio 17.4.0 Preview 2.0 using <fstream> as a header unit leads to compilation error.
Text.ixx
export module Test;
// Importing <filesystem> and/or <string> with <fstream> leads to compilation error.
// But importing <fstream> without <filsystem> and <string> or importing it first works.
import <filesystem>;
import <string>;
import <fstream>;
export class Test
{
std::ofstream stream;
};main.cpp
import Test;
int main()
{
Test t;
}Command-line test case
D:\test> cl /std:c++20 /EHsc /exportHeader /headerName:angle fstream string filesystem
Microsoft (R) C/C++ Optimizing Compiler Version 19.34.31823.3 for x64
Copyright (C) Microsoft Corporation. All rights reserved.
fstream
string
filesystem
D:\test> cl /c /std:c++20 /EHsc .\Test.ixx .\main.cpp /headerUnit:angle fstream=.\fstream.ifc /headerUnit:angle string=.\string.ifc /headerUnit:angle filesystem=.\filesystem.ifc
Microsoft (R) C/C++ Optimizing Compiler Version 19.34.31823.3 for x64
Copyright (C) Microsoft Corporation. All rights reserved.
Test.ixx
main.cpp
D:\test\Test.ixx(12): error C2079: 'Test::stream' uses undefined class 'std::basic_ofstream<char,std::char_traits<char>>'
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