C++20 compiling modules with Visual Studio: doesn't compile or import ixx files - c++

Question

Visual Studio 2019 doesn't attempt to compile my .cxx or .ixx files. Here is my .cxx file:
export module greetings;
import std.core;
export std::string get_greeting_text()
{
return "Hello, World!";
}
and here is main:
import std.core;
import greetings;
int main()
{
std::cout << get_greeting_text() << '\n';
}
I do have these flags set: /std:c++latest, /experimental:module. Error messages are
C:\...\main.cpp(2,17):error C2230: could not find module 'greetings'
C:\...\main.cpp(6,2): error C3861: 'get_greeting_text': identifier not found
...but I don't see any line about trying to compile greetings.cxx, so that's got to be the problem. Changing it to .ixx has no effect. What's the fix?

Answer 1

Solution:
Add greeting.ixx to Header Files. (It won't work to add it to Source Files.)
Right-click properties on greeting.ixx, and
Set Item Type to C/C++ Compiler
Set Excluded from Build to No.
Save
Build
It seems a little flaky. Rebuild failed unless I did a Clean first.

Answer 2

Module declaration export module greetings; is not yet working on Visual studio 2019.
You may try to add the following compiler opinions for your greetings.cxx file:
/module:export /module:name greetings /module:wrapper greetings.h /module:output greetings.ifc -c greetings.cxx
Another solution, rename greetings.cxx to greetings.ixx. The .ixx extension is required for module interface files in Visual Studio.

Answer 3

In order to use a different file extension with MSVC so you can use intellisense in Visual Studio Code, there is actually a work-around.
With the cl.exe command, there is an '/interface' option. You can do like so:
In My cl.exe CommandFile:
/interface /Tp UI/ApplicationHost.cpp
/reference ApplicationHost=Build\Debug\ApplicationHost.ifc
UI/WorldEngine.cpp
/link /SUBSYSTEM:WINDOWS
Build/Debug/pch.obj
/Interface - Let's the compiler know there is an ifc module/header coming up.
/Tp - Forces the compiler to recognize it as a C++ file, useful if renaming to .cppm.
/reference - Tells the compiler where to get the dependency information for the following source code.