Bug: Spurious IntelliSense errors with C++20 Modules #1610

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1. hoshiizumiya commented on Jul 23, 2026

   

   hoshiizumiya

   on Jul 23, 2026

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   I could say that it can not work at all in my module proj (C++23). VS xaml intellisense too. It's my feedback link https://developercommunity.visualstudio.com/t/XAML-IntelliSense-and-Hot-Reload-stop-wo/11117521

   
2. YexuanXiao commented on Jul 23, 2026

   

   Yexuan Xiao (YexuanXiao)

   on Jul 23, 2026

   Last edited by YexuanXiao

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   I believe this is indeed a bug in IntelliSense and the workaround is difficult to implement in C++/WinRT.
   I checked the output from IntelliSense, which is as follows:

   error: failed to load an
             IFC entity reference in module "winrt_base"
               from partition "expr.decl" element 1934 (file position 1113216,
                         relative position 30944)
             detected during:
               instantiation of type "winrt::impl::base_implements<D, I...>" at
                         line 8088
               instantiation of class "winrt::impl::promise_base<Derived,
                         AsyncInterface, TProgress> [with
                         Derived=std::coroutine_traits<winrt::Windows::Foundation:
                         :IAsyncOperation<winrt::hstring>>::promise_type,
                         AsyncInterface=winrt::Windows::Foundation::IAsyncOperatio
                         n<winrt::hstring>, TProgress=void]" at line 4110 of
                         module "winrt.Windows.Foundation"
   

   So it looks like this is caused by a bug in IntelliSense’s support for IFC.

   A limited workaround is to add the following at the top of your source files:

   #ifdef __INTELLISENSE__
   #include "winrt/base.h"
   #endif

   How to debug IntelliSense:

   In the project property pages under C/C++ / General, set Suppress Start Banner to No, or edit the .vcxproj file and add the property <SuppressStartupBanner>false</SuppressStartupBanner> to the ClCompile item. After that, building the project will print the cl command line that was used.
   Next, insert the /BE option right before the name of the source file you’re currently building (e.g., main.cpp), open a VS Command Prompt, cd to the .vcxproj directory, and run the modified command to see the actual output from the IntelliSense engine.

   For modules you have to do a full build of the project first to generate the IFC files, and then run the modified command. In addition, MSBuild currently seems to have a defect where it adds modules to the build command even if they aren’t used. I reported this issue on DevCom. For a C++/WinRT project this results in an extremely long command (around 48 KB), so you need to trim the command line by removing the irrelevant module references. The command I used is:

   cl /c /I"x64\Debug\Generated Files\\" /reference std=R:\ConsoleApplication1\ConsoleApplication1\x64\Debug\microsoft\STL\std.ixx.ifc /reference std.compat=R:\ConsoleApplication1\ConsoleApplication1\x64\Debug\microsoft\STL\std.compat.ixx.ifc /reference winrt.Windows.Foundation=R:\ConsoleApplication1\ConsoleApplication1\x64\Debug\winrt.Windows.Foundation.ixx.ifc /reference winrt_base=R:\ConsoleApplication1\ConsoleApplication1\x64\Debug\winrt_base.ixx.ifc /reference winrt_numerics=R:\ConsoleApplication1\ConsoleApplication1\x64\Debug\winrt_numerics.ixx.ifc /ZI /JMC /W4 /WX- /diagnostics:column /Od /D _DEBUG /D _CONSOLE /D WIN32_LEAN_AND_MEAN /D WINRT_LEAN_AND_MEAN /D _UNICODE /D UNICODE /Gm- /EHsc /RTC1 /MDd /GS /fp:precise /Zc:wchar_t /Zc:forScope /Zc:inline /std:c++20 /Fo"x64\Debug\\" /Fd"x64\Debug\vc145.pdb" /external:W4 /Gd /TP /FC /errorReport:prompt  /permissive- /bigobj /BE main.cpp
   
3. YexuanXiao commented on Jul 24, 2026

   

   Yexuan Xiao (YexuanXiao)

   on Jul 24, 2026

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   I just received some good news: the MSVC team is preparing to address the issue of IntelliSense's poor support for modules, and we can expect some improvement within this year.

   👍React with 👍4Reacted by rtanabe999, pjmlp, Makoto Sakaguchi and Victor Derks